Basics of Bacteriology and Medically Important Gram-Positive Bacteria PDF

Basics of bacteriology and medically important Gram-positive bacteria microbial pathogenesis and infection routes of transmission direct direct contact droplets - relatively large, short-range aerosols, cannot be suspended in air indirect airborne - droplet nucle...

Basics of bacteriology and medically important Gram-positive bacteria microbial pathogenesis and infection routes of transmission direct direct contact droplets - relatively large, short-range aerosols, cannot be suspended in air indirect airborne - droplet nuclei degree of pathogenicity relevant in context of interaction w susceptibe host characteristics low infective dose - amount req to produce disease high attack rate high case fatality rate some can be virulent for everyone but some are pathogenic to people w abnormalities in immune conditiosn or predisposition virulence factors fac microbial attachment, invasion, multiplication and evade host defence mech host microbe interaction outcome will dep on characteristic of host and pathogen abnormal host -> commensal bact can even cause infection bacterial cell structure cytoplasm nucleoid region (DNA) plasmids ribosomes cytoplasmic membrane contains bilipid layer but no cholesterol cell wall outside cell wall capsule surface appendages - pili, fimbriae, flagella can have endospores peptidoglycan (cell wall) most important component of cell wall repeating units of NAM, NAG connected by transpeptide bridges (covalent) gram positive - thick peptidoglycan layer gram negative - thin ' ' outer membrane of gram negative bacteria  only present in gram negative Lipid, polysaccharide, lipoproteins, lipopolysaccharide. Reduces permeability to antibiotics. also has endotoxins that can cause damage (e.g septic shock) bacterial emdospores (geam psotive) metabolically inert Survival advantages: Resistant to heat, chemicals, radiation. Environmental persistence, e.g., Bacillus anthracis, Clostridium tetani, Clostridioides difficile. Clinical relevance: Contamination of food, e.g., Bacillus cereus, Clostridium perfringens, Clostridium botulinum. Disinfection and sterilisation processes.  Infection control implications, e.g., Clostridioides difficile bacterial - basic classification gram stain (positive/negative) staining properties oxygen requirement strictly aerobic facultatively anaerobic strictly anaerobic microaerophilic (some O2 5%, some CO2) morphology medically important gram positive cocci staphylococci microbiology gram positive in clusters 0.5-1.5 um diameter FA salt tolerance (7-10% NaCl) fermentation of mannitol creates yellow pigment catalase reaction classification coagulase - formation of bacterial clumps bound/clumping factor -> slide coagulase test binds to fibrinogen fibrin deposited on surface fo S.aureus hinders phagocytosis extracellular staphylocoagulase -> tube coagulase test - activates prothrombin initiating clot formation in plasma  S.aureus is coagulase positive coagulase negative staphylococci s.epidermidis Part of the normal human microbiota, typically the skin microbiota (commensal / normal flora). Adheres to prosthetic devices, e.g., implants, catheters. Causes prosthesis-associated infections. s.saprophyticus cause acute cystitis n young women only (urinary tract infection) staphylococcus aureus golden yellow colones produces staphyloxanthin (yellow) protects s.aureus from toxic oxygen radicals virulence factors attachment teichoic acid evasion of host defence protein A - inhibit phagocytosis of bacteria (opsonophagocytosi), induces B cell death catalase coagulase invasion and toxins  invasion - Protease, hyaluronidase, lipase, DNase to allow bacteria entry toxins Haemolysins. alpha hemolysin damage erythryocytes, lymphocytes and mponocutes, making pore in cell causing content to leak out Epidermolytic toxins → staphylococcal scalded skin syndrome. Toxic shock syndrome toxin → staphylococcal toxic shock syndrome. Enterotoxins → food poisoning. Panton-Valentine leucocidin → dermonecrosis. epidimiology diseases pyogenic (pus formation) skin and soft tissue infection Folliculitis: inflamed hair follicles. Furuncles: skin abscesses involving the hair follicles and surrounding tissue. Carbuncles: coalescing clusters of furuncles, deeper suppuration and scarring skin surface breached so bacteria can enter deeper tissue  toxin mediated antibiotics Streptococci microbiology characteristics gram positive cocci in chains or pairs 0.5-1/2 um dia FA, some req CO2 species encapsulated catalse negative non spore forimng identification alpha - green beta - complete clearing of agar presence of clumping or not medically important gram-positive bacilli listeria monocytogenes short non spore forming gram pos bacili grow in wide range of temp (-1.5-45ºC) majority fo cases r foodborne also mother baby transmission disease assoc Severe foetal and neonatal infections. Invasive listeriosis in older adults (>60 years) and immunocompromised patients Acute febrile gastroenteritis corynebacterium spp gram positive pleomorphic bacili, palisaing or angular arrangement in V or L forms w club shaped swelling or beaded appearances  C.striatum - commensal fo skin and mucous membrane, opportunitisc pathogen C.diphtheriae - causative agent of diphtheira greyish memrbane Diphtheria toxin. Manifestations: Respiratory. Cutaneous. Myocarditis. Neuropathy antitoxin may be needed bacillus spp  gram positive bacilli, boxcar shaped usually single endospore B;antrhacis - causes anthrax B.cereus - ubiquitous in env, causes food poisoning ,invasive infection assoc w indewlling catheters nocardia spp thin, delicate gram pos bacili w beaded/branching app  partially acid-fast causes suppurative granulomatous inflammation - pulmonary - cerebral - osteoarticular (bones n joints) - cutaneous (skin) - disseminated clostridium spp anaerobic gram pos bacili, spore forming C. perfringens: produces various toxins. Skin and soft tissue infection, e.g., clostridial myonecrosis/gas gangrene Intra-abdominal/pelvic sepsis. Food poisoning. C. botulinum: produces botulinum toxins. => Botulism. C. tetani: produces tetanus toxin/tetanospasmin. => Tetanus. Clostridioides difficile: produces toxins A and B. => C. difficile infection (CDI). (diahrrea in patiengts that have taken antibiotics)