Gram Positive bacteria.docx

**Gram-positive bacteria** - Staphylococcus - cocci - Streptococcus - cocci - Enterococcus - cocci - Listeria monocytogenes - coccobacilli - Clostridium -- bacilli Bacteria Firmicutes Bacilli Bacillales Staphylococcaceae **Staphylococcus** - Non-motile - Non-spore former...

**Gram-positive bacteria** - Staphylococcus - cocci - Streptococcus - cocci - Enterococcus - cocci - Listeria monocytogenes - coccobacilli - Clostridium -- bacilli Bacteria Firmicutes Bacilli Bacillales Staphylococcaceae **Staphylococcus** - Non-motile - Non-spore former - Facultative anaerobe - Ferments glucose anaerobically - Produce enzyme catalase and coagulase only S. aureus form coagulase **Virulence** The extent to which you cause a disease **Pathogenicity** - Surface factors - Capsule - Not on every Staph. - Surface protein A - Peptidoglycan & teichoic acids - Structure of gram +ve cell wall - Extracellular enzymes Things that go outside of the cell, secreted - Coagulase - Destroys the coagulation factor in blood = preventing the clots - S. aureus -- it won't tell if it's pathogenic or not - A toxin is what makes it highly virulent strain - Lipase - Break down lipids/fats - Staphylokinase/fibrinolysin - Break down fibrin = preventing the clots - Hyaluronidase - Break down Hyaluronic acid to use it as a nutrient source - Nuclease - Break down nucleic acids (DNA, RNA) Something that is not normally, particularly virulent but be in an immunocompromised person = opportunistic or pathobiont - Haemolysins - Forms pores in erythrocytes (RBCs), releasing hemoglobin and iron. - Effects: Provides iron for bacterial metabolism. - Leucocidin Killing white blood cells -- More associated with S.aureus - Exotoxin - Degradation of cytoplasm - Lysis of human polymorphonuclear cells (PMN) = neutrophils - Exfoliants/Epidermolytic toxins Killing skin cells -- More associated with S. epidermidis - ETA & ETB - Cause lysis of intercellular attachment between cells Might have exfoliants or Epidermolytic toxins in S. aureus that is infecting the skin BUT if it's one that's in the GI tract causing toxic shock, the problem is going to be more associated with toxic shock syndrome toxins or different exotoxins that some Staph. can have. - Enterotoxins - Increase intestinal peristalsis - Toxic shock syndrome toxin 1 - TSST-2 - Capillary leakage - Rash, high fever shock type - Can be life-threatening, fatal very quickly - Case: Super max tampons where you wouldn't have to change the tampons for two days - People started dying of shock - It was BECAUSE it was a nice environment for S.aureus to grow =\> toxic shock - Shock induced by exotoxins rather than induced by endotoxins (more like sepsis) +-----------------------------------+-----------------------------------+ | S. epidermidis | S. saprophyticus | +===================================+===================================+ | - Adhesin so that it can stick | - ESS-like substance Not ESS | | onto the cell | | | | - Urease use urea so happy in | | - Extracellular slime substance | bladder | | (ESS) allow It to make a | | | biofilm | - Surface-associated protein | | | (SSP) help it to adhere | | - Haemolysin break down haeme | | | | - Haemagglutinin break down | | - Lipase | haeme | | | | | - Protease | | +-----------------------------------+-----------------------------------+ **Antibiotic Resistance in Staphylococcus aureus** Mechanisms of Resistance \- Beta-lactamase Production: Enzyme that breaks down beta-lactam antibiotics. \- mecA Gene: Encodes altered PBPs (penicillin-binding proteins) that beta-lactam antibiotics cannot bind to. Bacteria Firmicutes Bacilli Lactobacillales Streptococcaceae **Streptococcus** +-----------------------+-----------------------+-----------------------+ | Gram-positive | Capsulated | Non-motile | | | | | | - generally | - True for some | | | Spherical; ovoid | species | | | to lancet-shaped, | | | | cocci | - Made of | | | | polysaccharide | | | - Singly; in pairs | | | | or chain rather | | | | than clusters | | | +-----------------------+-----------------------+-----------------------+ - Non-spore former - Facultative anaerobe - Homo fermentative - Glucose fermentation = lactic acid, with no gas formation - Catalase & oxidase negative **Virulence Factors** - Capsule - Surface protein - Haemolysins - 2 types: - Streptolysin O (SLO) - Streptolysin S (SLS) - Toxins - enzymes Streptococcus pyogenes - Beta haemolytic - Bacitracin sensitive (A disc) Streptococcus agalactiae - Beta haemolytic - Catalase -ve - Hippurate +ve - Bacitracin resistant - CAMP +ve Streptococcus pneumoniae - Alpha haemolytic - Optochin sensitive (P disc) - Bile soluble = bile sensitive Enterococcus - Alpha or gamma haemolysis - Opportunistic pathogen - Catalase -ve - Extreme conditions -- sodium chloride, pH, temperature - Resistant to bile salt Bacteria Firmicutes Bacilli Bacillales Listeriaceae **Listeria** - L. monocytogenes **General characteristics** - Gram-positive coccobacilli - motile at room temperature 25 - Non-spore former - Facultatively anaerobic, **facultative intracellular organisms** can live in both inside or outside the cell - Oxidase - ve , catalase and aesculin + ve - Grow optimally at 35o C to 37o C, but growth also occurs at 4oC fridge - **Usually β-haemolytic** Unwashed lettuce, deli meats, pregnant--vulnerable **Virulence factors** - Listeriolysin O (LLO) -- inhibits macrophage-mediated antigen processing block the antigen presenting process = no signaling that there is an infection - Actin-assembly-inducing protein (ActA) the whole journey within the cell (moving from cell-cell) is done by recruiting actin -- -filaments within a cell that gives eukaryotic cells their structure - the ActA allows the bacteria to gather up all of the actin fibres and use them to move from the cell to the next cell - Phospholipases C (PLCs) - Zinc metalloproteinase (Mpl) degrade proteins but requires zinc (metal) as a co-factor - Internalin A (InlA) - Internalin B (InlB) - Endotoxins-like material the components of cell walls **Cell cycle of *Listeria monocytogenes*** 1. **Engulfment and Entry:** L. monocytogenes is a pathogenic bacterium that can enter host cells through "phagocytosis," where the host cell engulfs the bacterium. 2. **Endosomal/Lysosomal Fusion Escape:** Once inside the host cell, *L. monocytogenes* is initially contained within a membrane-bound vesicle, endosome. Normally, endosomes fuse with lysosomes, which contain digestive enzymes that break down and destroy the engulfed bacteria. However, *L. monocytogenes* has evolved mechanisms to escape from the endosome before it fuses with the lysosome, avoiding destruction. 3. **Recruitment of Actin:** After escaping into the host cell cytoplasm, *L. monocytogenes* begins to recruit and polymerise host cell actin. Actin is a structural protein that forms part of the cell's cytoskeleton. The bacterium uses this actin to propel itself through the host cell cytoplasm. 4. **Intracellular Movement and Spread:** a. Option 1 -- The bacterium can remain inside the host cell, where it continues to grow and divide. b. Alternatively, *L. monocytogenes* can use the polymerised actin to form actin comet tails, which allow it to move within the host cell. This motility enables the bacterium to push against the host cell membrane and eventually protrude into neighbouring cells. The bacterium can then enter adjacent cells, continuing the infection cycle without having to exit into the extracellular environment, thereby evading the host's immune system. **Pathogenesis** \- Foodborne; common sources include contaminated unpasteurised dairy products and cold deli meats. **Cellular Invasion** 1\. Attachment: Uses internalins to attach to host cell receptors like E-cadherin on goblet cells in the intestinal mucosa. 2\. Internalisation: Invades host cells via endocytosis, forming an internalisation vacuole. 3\. Escape from Vacuole: Releases listeriolysin O and phospholipases to degrade the vacuolar membrane. 4\. Intracellular Replication: Multiplies by binary fission in the host cell cytoplasm. 5\. Cell-to-Cell Spread: Propels to adjacent cells using actin-based motility, forming double-membrane vacuoles and repeating the invasion process. **Clinical significance** - Listeriosis Can look like gastroenteritis - Meningitis infection of CNS -- spinal fluid and the brain - Septicaemia sepsis -- too much toxins in the blood - Encephalitis another type of CNS infection **Populations at Risk** \- Immunocompromised Individuals: Neonates, elderly, pregnant individuals, adults with conditions like diabetes, malignancy, or HIV infection. **Diagnosis** \- Culture Samples: Depends on symptoms: \- Stool culture for gastroenteritis. \- Blood culture for bacteremia. \- Cerebrospinal fluid (CSF) culture for meningitis. \- Amniotic fluid culture for trans-placental infection. \- Imaging Studies: Ultrasound or CT scan to identify liver abscesses. **Treatment** \- Gastrointestinal Listeriosis: Supportive care (hydration, rest). \- Disseminated Listeriosis: Intravenous ampicillin combined with gentamicin. \- Alternatives: Meropenem for those with contraindications to ampicillin (e.g., pregnant individuals, those allergic to ampicillin). Bacteria Firmicutes Clostridia Eubacteriales Clostridiaceae **Clostridium** 176 species **General Characteristics** - Gram-positive may appear Gram-negative in older cultures - Straight or curved rods may appear singly, in pairs, or in chains - Spore former -- Endospores so it looks like a gram -ve rod with gram +ve cocci in it - Motile -- peritrichous flagella; except *C. ramosum, C. innocuum* - Non-encapsulated -- except *C. perfringens* - Obligate anaerobes strict anaerobes Some *Clostridium* like *C. difficile* will die, or sporulate and the spores will survive. Some are oxygen tolerant, like C. perfringens -- won't die but not going to grow. - Catalase -- ve - Saccharolytic can break down sugars and eat sugars, Harmless saprophytes -- some are pathogens - Proteolytic breakdown proteins **Virulence factors:** Exotoxins -- varied among species *C. perfringens* -- Type A, B, C, D, E the main types of toxins *C. difficile* -- 2 exotoxins (Toxin A & B) = Antibiotic-associated diarrhoea (AAD) mostly hospital-acquired, can have community-acquired, associated with older people in nursing homes, recently taking antibiotics =\> perfused watery diarrhea that can be acute or progress into the long term chronic diarrhea that can be so severe that people waste away and die over a longer period of time -- dying over months from diarrhea. Not like cholera -- die in a few days. \- can cause pseudomembranous colitis -- inflammation of the colon -- a sever inflammation of the inner lining of the large intestine.\ *C. tetani* -- flagellar antigens (10 types), all of the antigens associated with flagella somatic; spore antigens; haemolysin haemolytic; tetanolysin; lyse the cells tetanus toxin (tetanospasmin) lead to the spasming tetanus two tetanus-causing toxins\ *C. botulinum* -- botulinum toxin (neurotoxin) well-studied **Clinical significance** *C. perfringens* - Wound and soft tissue infections - Simple wound contamination - Cellulitis deeper tissues - Clostridial myonecrosis (gas gangrene) can cause GI issues as well *C. tetani* - Tetanus *C. difficile* - Enteric pathogens - Antibiotic-associate diarrhoea (AAD) - Antibiotic-associated colitis (AAC) - **Pseudomembranous colitis (PMC)** *C. botulinum* - Botulism ***Clostridium botulinum*** **Habitat** \- Natural Environment: Found in deep, compact soil with low oxygen levels. **Toxin Production** \- Botulinum Toxin: Causes botulism and comes in eight distinct types (A, B, C, D, E, F, G, H), varying in toxicity. (neurotoxin) **Pathogenesis** \- Contamination: Spores can contaminate food during preparation processes that block out air, like canning and sausage making. \- Gas Production: Bacteria metabolise sugars into short-chain fatty acids, creating gas (mainly carbon dioxide and hydrogen) that causes cans to bulge. **Mechanism of Action** 1\. Ingestion: Consumption of contaminated food introduces botulinum toxin into the body. 2\. Binding to Nerves: Toxin binds to nerves that use acetylcholine for muscle control. 3\. Endocytosis: Neuron takes in the toxin via endocytosis, forming a vesicle in the cytoplasm. 4\. Activation and Action: Toxin activates, exits the vesicle, and cleaves SNARE proteins. 5\. Inhibition of Neurotransmitter Release: Without SNARE proteins, acetylcholine is not released, preventing muscle contraction and leading to flaccid paralysis. **Clinical Manifestations** \- Early Symptoms: Affects muscles controlled by cranial nerves (facial muscles, eye movements, chewing, swallowing). \- Autonomic Nervous System Effects: Can cause dry mouth, postural hypotension, nausea, vomiting, and constipation. \- Progression: May lead to descending paralysis and potentially lethal flaccid paralysis if respiratory muscles are involved. \- Symptoms: Double vision, drooping eyelids, inability to make facial expressions, difficulty swallowing. **Diagnosis** \- Serum Analysis: Detection of botulinum toxin in the bloodstream. \- Culture: Growing Clostridium botulinum in culture is difficult due to its anaerobic nature. **Uses of Botulinum Toxin** \- Medical Applications: Types A and B are less toxic and used in treating various conditions: \- Neuromuscular Conditions: Relax rigid muscles. \- Hyperhidrosis: Reduce excessive sweating. \- Achalasia: Treat esophageal spasm. \- Cervical Dystonia: Reduce involuntary muscle spasticity. \- Cosmetic Surgery: Used as Botox to smooth out wrinkles for a few months. ***Clostridium perfringens*** **Growth and Laboratory Identification** \- Optimum Temperature: Have one of the fastest growth rates of any bacterium under optimal conditions. \- Gram-positive, appearing purple and rod-shaped (bacilli) under the microscope. **Foodborne Illness** \- Common Cause: Often called the \"cafeteria germ\" due to frequent outbreaks in food prepared in large quantities and kept warm for prolonged periods. \- Contamination: Spores can contaminate food left out for a while, which then colonizes the gut upon ingestion. \- Toxin Production: Produces Clostridium perfringens enterotoxin (CPE) within 24 hours of colonisation, targeting and destroying tight junctions in intestinal epithelial cells. \- Heat Sensitivity: CPE is heat-labile and can be inactivated by cooking at 72°C or above. **Symptoms of Foodborne Illness** \- Common Symptoms: Abdominal cramping, watery diarrhea, and vomiting. \- Symptoms typically improve within a day without the need for antibiotics; hydration is the primary treatment. **Wound Infections** \- Introduction to Wounds: Can infect wounds made by dirty, sharp objects in contact with soil (e.g., gardening or farming injuries). \- Myonecrosis: Causes clostridial myonecrosis (gas gangrene) via Clostridium perfringens alpha-toxin (CPAT), leading to rapid and massive destruction of muscle and soft tissues. \- Symptoms: Extreme pain, swelling, thin watery pus, blood-filled bullae, and crepitus (crackling sound of gas in tissue). **Pathogenesis and Symptoms of Myonecrosis** *C. perfringens* -- Type A, B, C, D, E the main types of toxins \- Cell Death: Causes necrosis (uncontrolled cell death), which is different from apoptosis (programmed cell death). \- Progression: Rapidly progresses to fever, tachycardia, hypotension, shock, and potentially death within hours if untreated. **Diagnosis** \- Early Diagnosis: Difficult due to similarity to cellulitis; diagnosis usually based on severity and rapid spread of infection. \- Confirmation: Anaerobic tissue culture can confirm diagnosis but takes too long for urgent cases. **Treatment** \- Surgical Intervention: Prompt and complete surgical excision of necrotic tissue, potentially including amputation. \- Supportive Care: Management of fluids and hemodynamic status. \- Antibiotics: High-dose penicillin B or clindamycin, with the possible addition of broad-spectrum antibiotics for co-infections. ***\ *** ***Clostridium difficile*** **Growth and Laboratory Identification** \- Gram Stain: Gram-positive, appearing purple and rod-shaped (bacilli) under the microscope. **Colonisation and Infection** \- Fecal-Oral Route: Typically acquired through ingestion of bacteria from fecal matter, often via unwashed hands. \- Asymptomatic Carriers: About 5% of the population carry C. difficile without symptoms due to competition with normal gut flora. \- Disturbance of Gut Flora: Antibiotic use, chemotherapy, and prolonged elemental diets can disrupt normal flora, allowing C. difficile overgrowth. **Pathogenic Mechanism** \- Toxin Production: Main pathogenic mechanism involves producing toxins. \- Toxin A (TCDA): A potent enterotoxin that destroys the cytoskeleton of intestinal cells, causing apoptosis and breakdown of tight junctions. \- Toxin B (TCDB): A cytotoxin that enters cells, including neutrophils, causing apoptosis and contributing to inflammation. *C. difficile* -- 2 exotoxins (Toxin A & B) = Antibiotic-associated diarrhoea (AAD) mostly hospital-acquired, can have community-acquired, associated with older people in nursing homes, recently taking antibiotics =\> perfused watery diarrhea that can be acute or progress into the long term chronic diarrhea that can be so severe that people waste away and die over a longer period of time -- dying over months from diarrhea. Not like cholera -- die in a few days. \- can cause pseudomembranous colitis -- inflammation of the colon -- a sever inflammation of the inner lining of the large intestine. **Symptoms and Complications** \- Common Symptoms: Diarrhea (with or without mucus and blood), abdominal pain, and high fever. \- Severe Complications: Can lead to toxic megacolon, intestinal rupture, septic shock, and death if untreated. **Diagnosis** \- Stool Testing: Presence of C. difficile toxins detected by enzyme-linked immunosorbent assay (ELISA). \- Colonoscopy/Sigmoidoscopy: Used to visualize pseudomembranes in the colon. **Treatment** \- Discontinuation of Offending Antibiotics: Important to stop antibiotics that caused the overgrowth. \- Targeted Antibiotics: Metronidazole for mild to moderate cases; vancomycin for severe cases, both taken orally. \- Oral Rehydration Therapy: To manage diarrhea. \- Avoiding Antidiarrheal Medications: Medications like loperamide can worsen the disease. \- Fecal Transplant: For recurrent or prolonged infections to restore normal flora. \- Probiotics: Use of organisms like Lactobacillus and Saccharomyces boulardii to prevent and treat pseudomembranous colitis.