Bacteria Lectures PDF

Monday 10/21 - Gram Positive Bacteria - Part 1 Less begin: Alright, The genus Staphylococcus (a.k.a. "Staphylococci") includes the bacteria Staphylococcus aureus and Staphylococcus epidermidis. Important: Staphylococci are part of the microbiota in many individuals, but they can also cause various d...

Monday 10/21 - Gram Positive Bacteria - Part 1 Less begin: Alright, The genus Staphylococcus (a.k.a. "Staphylococci") includes the bacteria Staphylococcus aureus and Staphylococcus epidermidis. Important: Staphylococci are part of the microbiota in many individuals, but they can also cause various diseases. The acronym FOREST helps to remember these diseases: Food poisoning, Osteomyelitis, Respiratory infection, Endocarditis, Skin infection, and Toxic shock syndrome caused by toxic shock syndrome toxin (TSST-1). People at risk for serious staph infections include those in the community with uncovered or draining wounds or those who use injection drugs. In hospitals, risk factors include the presence of medical devices in the body, such as IV lines. In other healthcare facilities, risk is heightened for individuals undergoing outpatient surgeries, procedures like dialysis, or extended nursing home stays." Important: the genus Staphylococcus consists of Gram-positive cocci, typically arranged in clusters. These bacteria are catalase positive, some are non-spore-forming (like S. epidermidis) and coagulase- negative (like S. epidermidis), and non-motile. As facultative anaerobes, they can thrive in various temperature and salt conditions. Most Staphylococci possess a polysaccharide capsule that inhibits phagocytosis, and some strains of Staphylococcus like Staphylococcus epidermidis (coagulase-negative) can also form biofilms, which help them attach to tissues and surfaces like catheters and prosthetics. Important: Staphylococcus (a.k.a staphylococci) are a component of the microbiota in many individuals, but they can cause acute, locally destructive, and purulent lesions, often producing exotoxins. If an infection spreads to organs, it may lead to bacteremia and systemic disease. This lecture focuses on two key species: Staphylococcus aureus is coagulase-positive and Staphylococcus epidermidis is coagulase- negative. Important: Staphylococcus aureus is a typical representative of the Staphylococcus genus, staphylococcus aureus is gram-positive, catalase positive, coagulase positive, pore-forming and in terms of culture stain characteristics. Staphylococcus aureus forms white or yellowish colonies, exhibiting beta- hemolysis. Epidemiology and transmission of S. aureus Important: Staphylococcus aureus is ubiquitous (found everywhere) in the environment, with its primary habitat being mammalian body surfaces, including the skin and upper respiratory tract (especially the anterior nares). It is a component of the normal microbiota in most individuals, with 10–30% of the population being carriers. The primary source of infection is endogenous, meaning it usually arises from an individual's own microbiota. 1. Disease occurs when S. aureus gains access to deeper tissues, and 2. The risk of infection is heightened if the strain possesses specific virulence factors. Not every Staphylococcus aureus strain has all of the virulent factors that will be mentioned, and not all strains or species of Staphylococcus produce all of the toxins. Genes for these virulence factors are spread via horizontal gene transfer mechanisms, and the disease-causing potential of any particular strain of S. aureus varies depending on which virulence genes it may have. S. aureus virulence FACTORS. Important: Staphylococcus aureus can produce several toxins, important: including cytotoxins (such as α-toxin), which damage cells, and exfoliative toxins (ET), which can cause systemic diseases like staphylococcal scalded skin syndrome (SSSS) and bullous impetigo. Important: It also produces superantigen toxins, such as Toxic Shock Syndrome Toxin-1 (TSST-1), which can lead to toxic shock syndrome, a serious systemic disease by activating non-specific adaptive immune system “overresponse” that presents with symptoms such as hypotension, fever, rash, vomiting and diarrhea. Additionally, some S. aureus strains produce enterotoxins, which are associated with food poisoning (Toxin -mediated disease without infection of the host). Important: Food poisoning: this condition is classified as an intoxication rather than a true infection. The disease occurs when pre-formed toxins produced by Staphylococcus aureus contaminate a food product and are ingested. “cut” For the bacteria to proliferate and produce toxins, the food must be kept at room temperature for some time. More than 50% of food contamination cases are linked to asymptomatic carriers. The mean incubation time for symptoms to appear is 4 hours, with symptoms including vomiting, cramps, and diarrhea, typically resolving within 24 hours. Important: the toxin is heat stable, meaning that reheating contaminated food will not destroy the toxin. Important: Alpha (α) toxin is a protein exotoxin (pore-forming) produced by most disease-causing strains of Staphylococcus aureus. It binds to cell membranes, aggregates, and forms pores that are 1–2 nm in size. “cut” 1. disrupting the balance of ions such as K+, Na+, and Ca++, along with other small molecules. This disruption causes osmotic swelling and lysis of the affected cell. 2. Alpha toxin can target various cell types, including red blood cells (RBCs), leukocytes, and platelets. 3. It is considered an important mediator of tissue damage in local soft tissue infections. Very important: Staphylococcus aureus toxins that cause systemic diseases include 1. Exfoliatin toxin (ET), which acts as an enzyme that cleaves cell-cell adhesion molecules, leading to staphylococcal scalded skin syndrome (SSS), a systemic illness, or bullous impetigo, which presents with localized skin symptoms (baby skin). 2. Toxic Shock Syndrome Toxin (TSST-1) which is a superantigen that induces an intense, non- specific activation of the adaptive immune system, resulting in a severe "overresponse." This toxin can cause serious systemic symptoms, including hypotension, fever, rash, vomiting, and diarrhea. Very important: Staphylococcus aureus possesses anti-phagocytic virulence factors that help it evade the immune system: 1. Capsule: The capsule protects S. aureus by inhibiting phagocytosis. 2. Protein A: Found on the surface of S. aureus, Protein A binds to the Fc portion of IgG antibodies "backwards." This unusual binding prevents antibodies from functioning correctly, thus inhibiting phagocytosis and allowing the bacteria to evade immune detection. “Cut” Tissue invasion factors of Staphylococcus aureus include: 1. Enzymes that promote invasion and spread: o Hyaluronidase: Breaks down connective tissues.  o Fibrinolysin: Breaks down blood clots, aiding in invasion and spread. o Catalase: Neutralizes components of the phagolysosome. o Coagulase: Promotes blood clotting, which can contribute to abscess formation and local infection, helping to protect bacteria from phagocytic cells. 2. Important: Fibronectin-binding proteins (FnBP): These proteins aid in adherence by binding to mucosal cells. “cut” Staphylococcus aureus can cause a variety of infections and diseases, including local skin infections such as superficial abscesses (folliculitis), deeper abscesses (boils, carbuncles, furuncles), and impetigo. It can also lead to deep local body infections, such as in joints, as well as endocarditis (heart and heart valve), septicemia/bacteremia, possible UTIs, and pneumonia. Important: Toxin-mediated Systemic diseases caused by toxins released from S. aureus include 1. Toxic shock syndrome caused by S. aureus strains that produce toxic shock syndrome toxin-1 (TSST-1). TSST-1 is a superantigen. 2. Scalded skin syndrome (baby skin) is caused by systemically circulating exfoliatin (ET) which is an exotoxin that breaks down cell-cell junctions. ETs are serine proteases with high substance specificity, which selectively recognize and hydrolyze desmosomal (cell-cell junctions) protein in the skin. “cut” You also get this disease, through the use of tampons (menstruation), surgery and nasal packing after surgery. Local, cutaneous infections caused by Staphylococcus aureus, the acronym FiFC helps to remember. They include (F) folliculitis, similar to impetigo but occurring in a hair follicle; (I) impetigo, a localized infection with pus-filled vesicles (f) furuncles (boils), which are large, painful, pus-filled nodules; and (c) carbuncles, which are coalesced furuncles that invade subcutaneous tissue and may cause systemic symptoms such as fever. Many of these infections can resolve without treatment, but extensive lesions may require surgical drainage and antibiotics. Important: (i) impetigo caused by Staphylococcus aureus presents as honeycomb crusts on the skin, commonly found around the nose and mouth. This infection is most common in infants and young children. Transmission occurs through autoinfection and direct contact, including spread via fomites. Impetigo primarily affects the superficial layers of the epidermis. “cut” Diagnosis is usually clinical, but a skin swab for culture may be conducted if the infection is widespread or there is concern. Treatment typically involves cleansing the area, covering it with a dressing to prevent spread, and applying topical antibiotics. (f) Folliculitis is characterized by inflammation of hair follicles, often appearing as pustules, while (f) furuncles and (c) carbuncles are deep-seated boils with pus-filled centers. Less important: Systemic and deep tissue infections caused by S. aureus can occur without specific toxins. Bacteremia is the first stage in the spread of bacteria from a focal infection to the blood. Endocarditis refers to an infection of the endothelial lining of the heart, which, if untreated, can have a mortality rate near 50%.  Pneumonia can lead to abscess formation in the lungs, with higher risk in young and elderly patients. o The disease can result from hematogenous spread (bacteremia) or from the aspiration of pathogens. Osteomyelitis involves the destruction of bone tissue and results from either hematogenous spread or trauma that introduces S. aureus. Septic arthritis presents as a painful joint condition with pus in the joint space. Diagnosis and treatment of Staphylococcus aureus infections Diagnosis is typically straightforward through overnight culture of patient samples and Gram stain. Culture-based tests for metabolism, hemolysis, and catalase activity can also aid in identification. Rapid tests that identify cell surface proteins are additionally available. Treatment involves antibiotics, with specifics depending on the antibiotic sensitivity testing of the infecting strain. There are significant concerns regarding antibiotic resistance, including the prevalence of MRSA (methicillin-resistant Staphylococcus aureus). Important: Less than 10% of S. aureus strains today remain sensitive to penicillin – penicillin resistance due to Beta-lactamase enzymes produced by the bacteria. Important: Transpeptidase enzyme is used for cross-link peptidoglycan. Important: Staph aureus is gram-positive, catalase positive, coagulase positive and beta-hemolytic. Next bacteria: Ready! Important: Additional potential pathogens from the genus Staphylococcus (a.k.a staphylococci) include Staphylococcus epidermidis. Unlike Staphylococcus aureus, S. epidermidisa, 1. DOES NOT produce coagulase (it's classified as coagulase-negative Staphylococcus, or CoNS). 2. DONES NOT produce alpha-toxin 3. DOES NOT produce exfoliatin 4. Is non-spore forming. 5. DOES NOT produce superantigen toxins. However, S. epidermidis possesses adhesins and has the ability to form biofilms. It is a normal commensal of the skin and a component of the microbiota, being most abundant in the axillae, head, and nares, though it can also be found in other areas of the skin. 6. Important Staphylococcus epidermidis is rarely the cause of significant disease in general settings but is best considered an opportunistic pathogen, primarily causing disease in sick, immunocompromised, and/or hospitalized patients. Thus, is identified as a chief cause of hospital-acquired infections of central lines and catheters. Important: Infections and diseases that can be caused by Staphylococcus epidermidis include 1. Urinary tract infections 2. Frequently implicated in hospital-acquired infections such as a. Infections of intravenous catheters, central lines, and surgical wound infections.  3. Additionally, S. epidermidis is associated with infections involving implanted devices, such as artificial heart valves or joint replacements. The end good luck: Proceed to the second half of the lecture. Monday 10/21 - Gram Positive Bacteria - Part 1 New group of bacteria. Ok, let’s begin. Important: The genus Streptococcus consists of three species: 1. Streptococcus pyogenes (Group A Streptococcus also known as GAS are beta-hemolysis) 2. Streptococcus agalactiae (Group B Streptococcus also known as GBS are beta-hemolysis), and 3. Streptococcus pneumoniae (alpha-hemolysis). Beta-hemolysis on blood agar indicates complete lysis of red blood cells, whereas alpha-hemolysis indicates incomplete lysis. All three species are gram-positive cocci that grow in pairs or chains and are catalase and coagulase-negative, which helps distinguish them from Staphylococci. As facultative anaerobes, many species of Streptococcus exhibit hemolysis on blood agar. They are classified based on their hemolytic properties and grouped according to the carbohydrate antigens found in their cell wall structure. “Cut” What are Lancefield groups? 1. Lancefield groups are classification system based on carbohydrate antigens found on the bacterial cell walls of Gram-positive, catalase-negative bacteria, particularly like streptococci. 2. This system was developed in the early 20th century by Rebecca Lancefield, who used serological typing to categorize various species of Streptococcus. 3. While the use of Lancefield groups is less common today due to advances in DNA typing and other identification methods, the terminology is still widely recognized and used in clinical microbiology. Streptococcus pyogenes (known as Group A Streptococcus also known as GAS which are beta-hemolysis). Important: Streptococcus pyogenes (Group A Streptococcus, GAS) is Gram-positive, catalase- negative, coagulase-negative, has hair-like pili (and exhibits beta-hemolysis on blood agar. It may have a capsule, which contributes to its virulence. Its virulence is influenced by its ability to avoid phagocytosis, adhere to tissues and cells, and produce various toxins and enzymes. This bacterium can cause a wide variety of infections, both local and systemic. The exotoxins produced by S. pyogenes, including streptolysin O and streptolysin S, are responsible for the observed beta- hemolysis on blood agar. Important: M protein is a key component of Streptococcus pyogenes (Group A Streptococcus - GAS) that is embedded in the peptidoglycan cell wall and anchored in cytoplasmic membrane. There are over 100 known antigenic variants of M protein, which serve as the basis for subtyping S. pyogenes into various serotypes (strain based on antigens). M protein functions as an adhesin, facilitating the adhesion of the bacteria to host tissues. Virulence and pathogenesis of GAS Important: Numerous adherence factors are critical for initiating disease in Streptococcus pyogenes (Group A Streptococcus). These include 1. pili and several different adhesins, such as M protein and protein F. The expression of these adherence proteins is variable and can change based on environmental conditions. 2. S. pyogenes (GAS) is known to be invasive, although the specifics of its invasiveness are poorly understood. Following invasion, various factors, including peptidases that inactivate complement components, play important roles in the bacteria's ability to evade the immune response. 3. Additionally, some strains of S. pyogenes possess a capsule, which is antiphagocytic. The antigenic variation of M protein is also considered a mechanism for evading phagocytosis. Important: Extracellular toxins and enzymes of S. pyogenes (GAS) include. Streptolysin O which is a pore forming toxin which lyses RBC, WBC, tissue cells and platelets. Streptolysin S is another pore forming exotoxin which lyses RBC causing hemolysis. About 10% of GAS produce exotoxins that act as superantigens such as 1. Erythrogenic toxin which causes scarlet fever. 2. Streptococcal pyogenic exotoxin (which causes streptococcal toxic shock syndrome) All of these extracellular toxins and enzyme of S. pyogenes (GAS) have similar effects of fever, T and B cell activation and proliferation. most of the symptoms are due to cytokine release and Produce enzymes such as hyaluronidase, nucleases, peptidases that break down complement components, help invade tissues. Important: Although S. aureus tends to be localized, GAS tend to spread diffusely, as shown - may be due to hyaluronidase (a spreading factor) or resistance to phagocytosis. Streptococcus pyogenes (Group A strep) – GAS infections. The acronym NICE will help remember. GAS infections include 1. (N) Necrotizing fasciitis: A rare but life-threatening infection that can cause tissue death in skin, wound and epithelial surface. 2. (I) Impetigo: Similar to S. aureus impetigo, but often with more extensive lesions which infect in skin, wound and epithelial surface. 3. (C) Cellulitis: A diffuse, spreading skin infection with redness, swelling, and pain.  4. (E) Erysipelas: A rapidly spreading, red, tender skin infection with sharp borders. Pyoderma means pus in skin. GAS can also cause skin infections and toxic shock syndrome. Additionally, Pharyngitis caused by Streptococcus pyogenes (Group A Streptococcus, GAS) is commonly referred to as “strep throat” and is the most frequent cause of pharyngitis in children (GAS pharyngitis is usually self-limited). The infection primarily affects the upper respiratory tract (URT) and is transmitted from person to person through respiratory droplets. Symptoms include an acute sore throat, malaise, fever, and headache. Examination may reveal redness and swelling of the tonsils, uvula, and soft palate, along with possible yellow-white exudate. Lymphadenopathy may also be present. Diagnosis is typically made through a laboratory culture of a throat swab or by detecting specific bacterial antigens using point-of-care tests. However, culture methods are more sensitive, and any negative in- office tests should be confirmed by culture. Treatment usually involves antibiotics to eliminate the infection (useful for all GAS infections). Important: Potential sequelae of strep throat include late complications such as acute rheumatic fever (ARF), which can develop several weeks after the initial infection, typically peaking in individuals aged 5 to 15 years. ARF is characterized as an inflammatory disease, with fever being a key symptom. Genetic susceptibility may contribute to the disease, and molecular mimicry is believed to play a significant role in initiating tissue injury. Important: ARF is a systemic autoimmune disorder and is recognized as a leading cause of acquired heart disease in both adults and children in many parts of the world. The manifestations of ARF can be categorized as follows: 1. Cardiac: Symptoms may include chest pain, shortness of breath, and tachycardia. 2. Neurological: Patients may experience fatigue and uncontrollable body movements. 3. Dermatological: A rash may also be present. Important: Immunity to Group A Streptococcus (GAS) infection is primarily mediated by 1. Antibodies against M protein, which provides protection against reinfection. However, this protection is type-specific, as there are over 100 different M protein types, and immunity is not cross-reactive among these types. 2. Mucosal IgA may play a role in protecting against adherence of the bacteria to host tissues, while serum IgG may help protect against bacterial invasion. 3. Other aspects of immunity to GAS are still under investigation. 4. Currently, there is no vaccine available to prevent GAS infections. Next bacteria: Streptococcus agalactiae also known as Group B strep (GBS) Important: Streptococcus agalactiae – group B strep (GBS) is gram-positive, beta-hemolytic (produces Beta hemolysin which is a pore-forming toxin), has polysaccharide capsule (variety of different antigenic types) which is major virulence factor) and has pili and various surface proteins – adherence factors. Streptococcus agalactiae – group B strep (GBS) causes sepsis and meningitis in newborns 1. GBS can colonize the lower gastrointestinal tract as part of the normal microbiota, often without causing symptoms. 2. “Cut” It can also be found on the skin and in the genital tract. Infection is typically acquired during birth (intrapartum), with approximately 10–40% of women having GBS present in their vaginal microbiota. 3. Additionally, infection may occur in utero through amniotic fluid. Infants are infected in about 1– 2% of cases involving affected mothers, with the risk being higher for premature infants. This highlights the importance of monitoring and managing GBS colonization in pregnant women to reduce the risk of serious infections in newborns. GBS in Infants ▪ In the United States, GBS bacteria are a leading cause of meningitis and bloodstream infections in a newborn’s first three months of life. ▪ Average rate about 1/5000 births (2020), disparities exist with rate higher in African American individuals ▪ Disease onset in first days of life although there are some cases of “late onset”(1 – 3 months old) ▪ Poor feeding, lethargy, jaundice, hypotension, respiratory distress – non specific ▪ Can progress to pneumonia and meningitis ▪ Mortality even with treatment is about 10% In Adults ▪ Maternal infection possible, also some skin and soft tissue infections in other settings ▪ Urinary tract infection, endometritis, wound infection Diagnosis, prevention, and treatment of Group B Streptococcus (GBS) in neonates involve several key strategies: 1. Diagnosis is achieved through the culture of blood or other fluids to identify the presence of GBS. The American College of Obstetricians and Gynecologists recommend screening all pregnant women in the U.S. late in pregnancy (weeks 35 – 37), that they do a swab, a vaginal and rectal swab, send it for culture and those who’re positive are treated with IV antibiotics during labor o protect the newborn. 2. Colonization of the vagina in pregnant women can be evaluated prior to delivery; however, the elimination of the carrier state has not been proven feasible. 3. To prevent transmission to the newborn, treatment of the mother with antibiotics during labor (administered several hours before delivery) has been shown to significantly reduce the risk of infection in the infant. There are ongoing efforts to develop a vaccine against GBS.  4. For treatment of GBS infections in neonates, antibiotics are administered, with the choice depending on the antibiotic sensitivity of the strain, as there are significant levels of antibiotic resistance observed in Streptococcus species. Despite treatment, there is a notable rate of neurologic sequelae associated with GBS infections in neonates. Next bacteria Streptococcus pneumoniae (alpha-hemolysis) Streptococcus pneumoniae is a gram positive, catalase-negative, coagulase-negative and alpha- hemolytic (presenting a greenish zone and incomplete hemolysis (partial hemolysis) in culture and blood agar causing the reduction of red blood cell hemoglobin to methemoglobin). S. pneumoniae causes meningitis and otitis media (“ear infection”) in young children, and about 5% - 40% of healthy individuals are asymptomatic carriers of S. pneumoniae in their nasopharynx. The most severe disease occurs in the very young (under 2 years old) and elderly populations (immunocompromised individuals, those with HIV, emphysema and diabetes etc.). Infection is typically spread through respiratory transmission, making it a common cause of community-acquired pneumonia. Major virulence factors include: 1. The production of pneumolysin, an exotoxin that degrades hemoglobin, 2. A capsule, which is a key factor in its pathogenicity. Non-capsulated S. pneumoniae do not cause disease and are part of the normal microbiota. 3. In Gram-stained sputum from patients with pneumococcal pneumonia, S. pneumoniae appears as oval diplococci, often with a clear halo around each pair, a result of the capsule that does not pick up the Gram stain. Very important: Pneumococcal pneumonia – major virulence factors include: 1. Bacterial Capsule: Plays a crucial role in virulence due to its anti-phagocytic properties. The capsule prevents phagocytosis, and strains of Streptococcus pneumoniae without a capsule DO NOT cause disease. 2. Production of Pneumolysin (PLY) which is an exotoxin protein that is toxic to pulmonary endothelial cells, damages cilia, and suppresses immune function. These effects collectively enhance the ability of Streptococcus pneumoniae to cause disease in the lungs. Clinical Manifestations – Potential Diseases Caused by Streptococcus pneumoniae. The acronym POMBAS will help to remember. (p) Pneumonia (O) Otitis media – common in young children (M) Meningitis (B) Bacteremia – can occur alone or in combination with pneumonia (A) and (S) Sinusitis Symptoms of Pneumonia: Symptoms of pneumonia caused by Streptococcus pneumoniae include fever, chills, chest pain, shortness of breath, cough, and pleuritic consolidation. The severity and mortality of the disease increase significantly in elderly populations. Pneumonia is often accompanied by bacteremia. Immunity and Prevention: Immunity is typically provided by antibodies to capsule antigens, but there are many serotypes of S. pneumoniae, and the bacteria can undergo antigenic variation, making complete immunity challenging. Vaccines are available (subunit vaccine which are conjugate polysaccharide vaccine); however, they do not offer complete protection due to the large number of capsule antigenic types and the potential for antigenic variation. Diagnosis: Diagnosis is confirmed by culturing appropriate specimens. Treatment: Treatment involves the use of antimicrobials, such as penicillins, although resistance to these antibiotics is a significant concern. We ARE DONE WITH COCCUS Bacteria, next will we be discussing Bacilli– ROD like bacteria. Ready. Gram positive bacilli Listeria monocytogenes & Clostridium perfringens Listeria monocytogenes Listeria monocytogenes is a gram-positive, rod-shaped (bacillus) bacterium that is beta- hemolytic, catalase-positive, and capable of intracellular growth. It infects both humans and animals and can also grow at low temperatures, including those in refrigerators. Additionally, it is motile, exhibiting tumbling motility by light microscopy, and has several flagella. It is found widely in the environment, including soil, groundwater, and the intestinal tracts of animals. Listeria monocytogenes is a facultative intracellular pathogen that grows inside eukaryotic cells. It has two major virulence factors: 1. Internalin, which consists of surface proteins involved in invasion, and 2. Listeriolysin O (LLO), an exotoxin. Listeria monocytogenes causes the disease Listeriosis. Epidemiology: Listeria monocytogenes Listeria monocytogenes has several primary reservoirs and sources, including soil, water, animal intestines, feces, raw foods, and decaying matter, making it fairly ubiquitous in the environment. It colonizes the gut of 5–10% of the human population. Most adult infections likely result from oral ingestion and penetration of the intestinal mucosa. Additionally, Listeria monocytogenes can survive exposure to proteolytic enzymes, stomach acid, and bile salts. Risk groups for more severe disease include: PENI (P) for Pregnant women (E) for Elderly individuals (N) for Neonates (I) for Immunocompromised populations (transplant, AIDS etc.). Clearing Listeria monocytogenes infection requires cellular immune responses, as antibodies alone are insufficient. Listeria monocytogenes major virulence factors L. monocytogenes possesses several major virulence factors that enable it to survive and infect host cells effectively. It can withstand passage through the stomach, surviving exposure to digestive enzymes and acidic pH, and then attaches to cells in the intestinal lining (enterocytes). Two key virulence factors contribute to its pathogenicity: Internalin A and Listeriolysin O (LLO). 1. Internalin A allows Listeria to attach to epithelial E-cadherin receptors, while other internalins help the bacterium recognize receptors on a wide range of host cells. Internalin A is crucial for Listeria monocytogenes’ ability to invade host cells. 2. Listeriolysin O (LLO) is a pore-forming exotoxin activated by the acidic environment within the phagolysosome. This toxin enables Listeria to survive and replicate within macrophages, promoting immune evasion and persistence within host cells. Pathogenesis at Cellular Level – Immune Escape Strategy Listeria monocytogenes enters intestinal cells through a "zipper" mechanism that stimulates phagocytosis. It produces an exotoxin, Listeriolysin O (LLO), which allows it to "escape" from the phagolysosome. Once inside the cell, Listeria assembles actin fibers that enable it to move through the host cell and into adjacent cells directly: This actin-based motility allows the bacterium to spread from cell to cell without exposure to the extracellular environment, facilitating immune evasion. When Listeria infects macrophages in the intestinal lining, it can spread to other areas of the body, promoting further dissemination of the infection. Human innate and adaptive immune response are activated and control infection in most cases Listeria monocytogenes causes the disease Listeriosis. Remember – Listeria can grow at refrigerator temperatures! Listeriosis: Most cases of listeriosis are associated with consumption of dairy products, poultry, and undercooked processed meats. Raw (unpasteurized) milk and milk products are a risk for listeria contamination. “cut” Listeria monocytogenes can contaminate foods and continue to grow during refrigeration. Foods with a small initial bacterial load can become heavily contaminated if stored for prolonged periods at low temperatures. In healthy adults, listeriosis often presents as a mild or subclinical intestinal illness, causing acute self-limited gastroenteritis with symptoms such as diarrhea, fever, nausea, and headache. The incubation period is typically 1 day, with symptoms lasting about 2 days. Important: However, in high- risk patients, listeriosis can disseminate and cause invasive disease, “cut” leading to conditions such as sepsis and meningitis. Although meningitis is rare in healthy adults, it should be considered in immunocompromised individuals, organ transplant patients, and during pregnancy, as these groups are at higher risk for severe complications. Listeriosis in fetus and neonate 1. Listeria monocytogenes infection can be acquired transplacentally, usually during the third trimester, or during birth (intrapartum) and shortly afterward. In utero infection can lead to stillbirth, miscarriage, or premature birth, which is classified as "early onset" listeriosis. 2. Perinatal infection can result in meningitis with septicemia, referred to as "late onset" listeriosis. When diagnosing neonatal listeriosis, it is important to exclude other central nervous system diseases, such as Group B Streptococcus (GBS). 3. To prevent listeriosis, pregnant women should avoid foods that may be contaminated with Listeria monocytogenes. This includes soft cheeses (which may be unpasteurized) and other unpasteurized dairy products. Processed meats, such as hot  dogs, cold cuts, and deli meats, should be avoided unless they are well cooked before consumption. Other foods to avoid include meat spreads and smoked fish. Diagnosis and Control: Listeria monocytogenes Important: Listeria monocytogenes can be diagnosed by culture, with a motility test conducted if it is grown in liquid media as an initial identification method. “cut” Rapid diagnostic tests, including ELISA, immunofluorescence, and DNA analysis, are also available. Treatment with antibiotics is recommended if needed, as Listeria is a gram-positive bacterium. General prevention strategies include pasteurization of milk and dairy products and careful cooking. Special precautions should be taken by individuals at high risk, such as those who are pregnant or immunocompromised. NEXT BACTERIA, READY. Clostridium perfringens: Wound infections, gastroenteritis Clostridium perfringens is a large, Gram-positive bacillus, beta-hemolytic and an obligate anaerobe that produces exotoxin alpha-toxin (that breakdown the lipids of cell membranes). It has a ubiquitous environmental distribution, commonly found in soil, sewage, food, feces, and the normal intestinal microbiota of humans and animals. This bacterium produces spores (remember that), which are resistant to heat, desiccation, and disinfectants, allowing it to survive in harsh conditions. Clostridium perfringens can produce numerous exotoxins and is medically significant in causing two primary conditions: 1. Gas gangrene, which is a necrotizing soft tissue infection: Clostridium perfringens is the most common clostridia involved in soft tissue and wound infections, particularly myonecrosis, also known as gas gangrene. Predisposing factors for gas gangrene include surgical incisions, compound fractures, diabetic ulcers, septic abortions, puncture wounds, and gunshot wounds, with a high association in war zones due to trauma. The infection presents a sudden onset of severe pain at the site of trauma. Systemic symptoms can include tachycardia and fever, leading to shock and multiorgan failure. AND 2. Food poisoning which is an enterotoxin-mediated. Oxygen is very toxic to Clostridium perfringens, and it is not highly invasive. Clostridium perfringens is a large gram-positive spore-forming bacillus that is anaerobic bacteria, meaning they are doing fermentation, and fermentation produces lots of CO2. Thus, when a patient has a Gangrenous wound, one of the symptoms and a well known diagnosis is the development of little gas pockets deep in the wound. So, when you palpate it, you get what is called “repetitions” meaning it feels like bubble wraps. This is a clinical indicator of Clostridium perfringens presence. Important: Clostridium perfringens Alpha Toxin (major virulence factor)– Systemic Effects Important: The alpha toxin produced by Clostridium perfringens is present in all strains of this bacterium and plays a key role in the pathogenesis of wound infections, specifically gas gangrene. This toxin is an enzyme that breaks down lipids in cell membranes, leading to cell death. It is responsible for the toxemia typically observed during gas gangrene and has lethal, dermonecrotic (killing cells), and hemolytic properties. Effects of Alpha Toxin of Clostridium perfringens Increases vascular permeability of blood vessels. Causes massive hemolysis, bleeding, tissue destruction, and myocardial dysfunction. Lyses erythrocytes, leukocytes, platelets, and endothelial cells. Pathology: C. perfringens Clostridium perfringens is not highly invasive on its own; it requires damaged or dead tissue and anaerobic conditions to thrive. Under these conditions, the bacteria's spores germinate, leading to vegetative growth and the release of exotoxins and other virulence factors. The fermentation of muscle carbohydrates results in the formation of gas (CO₂), which causes further tissue destruction. This extensive local tissue damage is exacerbated by the production of enzymes like hyaluronidase, collagenase, and other proteinases. The infection can rapidly progress, spreading through a contaminated wound within 1–3 days. It produces "crepitation," or pockets of CO₂ gas, in the subcutaneous tissue and muscle, which is often accompanied by a foul smell. Systemic symptoms include fever, hemolysis, and toxemia, and the condition can progress to profound shock and death, primarily due to the effects of the exotoxins. The treatment and prevention of gas gangrene caused by Clostridium perfringens involve several steps. 1. Immediate and thorough cleansing of dirty wounds, deep wounds, compound fractures, and infected incisions is essential to prevent infection. 2. Surgical removal of necrotic tissue, known as debridement, is often necessary and may involve resection or even amputation of the affected limb to control the spread of the bacteria. 3. “cut” Antibiotic therapy, typically with drugs like Metronidazole and some cephalosporins, is effective, as C. perfringens is largely susceptible to these antibiotics.  4. Important: Hyperbaric oxygen therapy may also be employed, as the high-pressure oxygen inhibits anaerobic bacterial growth and aids tissue recovery. Currently, no vaccines are available for gas gangrene. “cut” Clostridial food poisoning, caused by Clostridium perfringens, leads to a relatively mild intestinal illness and is notably the second most common form of food poisoning worldwide, with over a million cases each year in the U.S., according to CDC estimates. The illness is not to be confused with botulism, as it involves a different mechanism and symptoms. Important: C. perfringens produces an enterotoxin (CPE), which is an enteric exotoxin that accumulates at the onset of spore formation and is released into the extracellular environment. This toxin binds to the small intestine epithelium, disrupting ion transport and membrane permeability. The effects on epithelial cells result in symptoms such as acute abdominal pain (cramps), watery diarrhea, and nausea, though vomiting and fever are typically absent. Important: This enterotoxin is heat labile (sensitive to heat), meaning it can be destroyed by heating. C. perfringens spores can survive in improperly cooked foods. “CPE” is clostridium perfringens enterotoxin which is produced by the clostridium perfringens once its in the gut. Food cooked in large batches and held at unsafe temperatures are often involved in outbreaks. So, cook food well to avoid this by keeping food above 140 and below 40 Fahrenheit. THE END. Now we will discuss the last genus of the Gram-positive bacteria. Mycobacteria The genus Mycobacteria which are gram-positive consists of mycobacterium tuberculosis ( causes the disease tuberculosis) and mycobacterium leprae (causes the disease leprosy). Mycobacteria are classified as gram-positive due to their thick peptidoglycan cell wall, but they are difficult to visualize using traditional gram staining techniques. Instead, they require an acid- fast staining method due to their unique cell wall structure. Important: These rod-shaped (bacilli) bacteria are stained with a red dye called carbolfuchsin, which their cell walls retain even after acid washing, giving them the designation “acid-fast.” Several species within this genus cause diseases in humans, with the most significant being Mycobacterium tuberculosis, which causes tuberculosis, and Mycobacterium leprae, which causes leprosy. An acid-fast stained image of M. tuberculosis from sputum highlights their characteristic staining pattern. Mycobacteria have an unusual cell wall structure that contains 1. Mycolic acids, which are long-chain fatty acids, and 2. lipoarabinomannan (LAM). These mycolic acids are responsible for the acid-fast staining pattern characteristic of mycobacteria, as they allow the cell wall to retain stains even after acid washing. The high lipid content of the cell wall gives it a "waxy" texture, which contributes to the bacteria's resilience. With over 120 known species, many mycobacteria infect animals, and some are also capable of infecting humans. Due to their thick peptidoglycan layer and lack of an outer membrane, mycobacteria are classified as gram-positive, even though they do not show up well with traditional gram staining. Mycobacterium tuberculosis cause the disease: Tuberculosis Tuberculosis (TB) is a disease that has been known since ancient times and was historically referred to as "consumption." It became an epidemic in the Western world during the industrial revolution in the 18th and 19th centuries. Despite advancements in medical treatment, TB continues to cause high morbidity and mortality rates, particularly in developing countries. It is estimated that between one-quarter to one-third of the world’s population is infected with Mycobacterium tuberculosis (they do not have active symptoms). Drug resistance poses a significant challenge to TB control, complicating treatment efforts. According to the World Health Organization (WHO), in 2018, there were 1.5 million deaths and 10 million new cases of TB globally. Important: Tuberculosis has the highest mortality rate of any infectious disease! Mycobacterium tuberculosis is highly resistant to environmental conditions, able to withstand drying, various disinfectants, acids, and alkalis, largely due to the mycolic acids in its cell wall. Important: Mycobacterium tuberculosis is sensitive to heat and UV light, which can effectively kill the bacterium. Very important: M. tuberculosis is slow-growing in culture, often requiring weeks to yield results. Thus, culture is not a good diagnostic approach for Mycobacterium tuberculosis. It displays the typical acid-fast staining pattern, with a cell wall that contains mycolic acids and lipoarabinomannan (LAM). An extract of proteins and polysaccharides from the cell wall of M. tuberculosis, known as tuberculin or purified protein derivative (PPD), is used in diagnostic tests. Very important: A key characteristic of M. tuberculosis is its nature as a gram-positive, rod-like facultative intracellular pathogen, usually residing within macrophages in the human host. Notably, it does not produce exotoxins, capsules, or adhesins. 1. Mycobacterium tuberculosis does not produce exotoxins, does not have a capsule, and it does not have adhesions. Its mechanism for phylogenesis is the fact that it grows inside macrophages. It is also stable in the environment, and resistant to things like drying and disinfectants. Epidemiology 1. Humans are the only known reservoir for human disease, with transmission occurring through respiratory aerosols in person-to-person contact. 2. Although some animals can be infected with M. tuberculosis, they do not appear to transmit the infection back to humans. The highest-risk populations include 1. Unhoused individuals, those with drug and alcohol misuse issues, individuals in prisons, and people living with HIV or other conditions that compromise the immune system. Additionally, some related mycobacteria, such as M. bovis, can infect animals and may occasionally cause rare diseases in humans. 2. In the US origin of birth is a significant risk factor for latent or active disease (due to different rates of TB in various parts of the world). TB – THE DISAESE 1. Primary tuberculosis is the initial infection, which may or may not produce symptoms. Individuals with symptoms of primary TB infection are potentially infectious to others. In active tuberculosis the granuloma grows and eventually releases M. tuberculosis into bronchioles – disease can disseminate. 2. Latent Tuberculosis Infection (LTBI), the disease enters a "dormant" phase, showing no symptoms, which is considered a state of clinical latency. 3. Reactivation tuberculosis occurs when the latent infection reactivates, leading to active disease. Immune response to M. tuberculosis : “CUT” Adaptive immune response (led by CD4 T cells – TH1) is induced production of cytokines such as IFN-g which “activate” macrophages – allows macrophages to kill the bacteria which are inside them  Activation of CD8 T cells to kill infected macrophages Also initiates a destructive type of adaptive response called a delayed type hypersensitivity response (DTH) – this can cause immunopathology Granuloma formation – especially in lung Important: Granuloma area of inflammation which are aggregate or “cluster” of immune cells (adaptive and innate) that surround infected macrophages. T-cell response is important for this pathogen. Granulomas form in the lung can be seen on x-ray (an in structure that forms in the lung). ▪ People infected with M. tuberculosis present with symptoms which are often non-specific such as Malaise, Weight loss, Cough (possibly hemoptysis), Night sweats, Fever and chills. You diagnose M. tuberculosis with a very common skin test called Mantoux skin test, chest x-ray and PCR. M. tuberculosis can also infect other cells of the body, and it is not transmitted by shared eating utensils, surfaces or touch (handshake). Mycobacterium leprae: Disease: Leprosy Mycobacterium leprae, an acid-fast staining bacillus classified as gram-positive, cannot be cultured on artificial media and is instead grown in mice or armadillos for research purposes. Most animals clear the bacteria without developing disease, with the armadillo being the only suitable model animal for studying M. leprae. This bacterium grows very slowly, with a long doubling time, and in human hosts, it multiplies within tissue cells, including macrophages, epithelial cells, and nerve cells. Leprosy, caused by Mycobacterium leprae, presents in two major forms: "tuberculoid (body fights off)" and "lepromatous (weaker immune response)," with some patients exhibiting intermediate manifestations between these two types. Tuberculoid leprosy (also known as paucibacillary): Intense granulomatous response – lots of CD4 T cells - active cellular immune response, very few bacteria in skin lesions and Strong immune response causes nerve destruction/damage (anesthetic macules with hypopigmentation). Lepromatous leprosy (multibacillary) patients present almost unrestrained multiplication of bacteria in macrophages and skin lesions. No cellular immune response.