Week 11 Part One Gram Positive Bacteria 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...

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. 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, non-spore-forming, 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 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 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, 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. 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. Exfoliative toxin, which acts as an enzyme to cleave cell-cell adhesion molecules, leading to staphylococcal scalded skin syndrome (SSSS), a systemic illness, or bullous impetigo, which presents with localized skin symptoms. 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: results of infection with S. aureus that produce TSST-1 toxin. TSST-1 is a superantigen. 2. scalded skin syndrome: systemically circulating exfoliatin (ET) exotoxin 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. Good luck, good luck and the end.