Clinical Bacteriology Lab Chapter 14 PDF

​ Food poisoning ( B, A, D ) ​ TSS (B, C sometimes G, l) CHAPTER 14: STAPHYLOCOCCI ​ Enterotoxin B has been linked to staphylococcal...

​ Food poisoning ( B, A, D ) ​ TSS (B, C sometimes G, l) CHAPTER 14: STAPHYLOCOCCI ​ Enterotoxin B has been linked to staphylococcal pseudomembranous enterocolitis. STAPHYLOCOCCI TOXIC SHOCK SYNDROME TOXIN-1 ​ Catalase - Positive ​ Previously referred to as enterotoxin F ​ Gram-positive cocci singly, in pairs, and in clusters. ​ Causes the majority of cases of menstruating-associated TSS ​ Greek term staphle = “ bunches of grapes “ ​ Staphylococci are members of the family Staphylococcaceae. EXFOLIATIVE TOXIN ​ Nonmotile, non–spore-forming, and aerobic or facultatively ​ Epidermolytic toxin anaerobic. ​ Exfoliative toxin A and exfoliative toxin B ​ 18 to 24 hours of incubation are medium sized (4 to 8 mm) and ​ Staphylococcal SSS = cause the epidermal layer of the skin to appear cream-colored, white or rarely light gold, and slough off, sometimes referred to as Ritter disease. “buttery-looking.” ​ RITTER DISEASE is most common in newborns and infants, with most cases reported in children younger than 5 years. MICROCOCCI ​ Bullous impetigo. ​ Catalase-producing, coagulase-negative, gram-positive cocci found in the environment and as members of the indigenous skin CYTOLYTIC TOXINS microbiota. ​ These hemolysins and leukocidins are cytolytic toxins with ​ Micrococci have a tendency to produce a yellow pigment properties different from the properties of previously described toxins. COAGULASE ​ S. aureus produces four hemolysins: alpha, beta, gamma, and ​ Positive test = clot formed in a tube containing plasma, due to delta. staphylocoagulase ​ a-Hemolysin = lyses erythrocytes, can damage platelets ​ The staphylocoagulase - producing (coagulase positive ) macrophage: and cause severe tissue damage. staphylococci are; ​ B-Hemolysin = (sphingomyelinase C) acts on sphingomyelin in -​ S. aureus the plasma membrane of erythrocytes. "hot-cold" lysin. -​ S. intermedius ​ δ-Hemolysin, although found in a higher percentage of S. -​ S. pseudintermedius aureus strains and some CoNS, is considered less toxic to cells. -​ S. hyicus ​ γ-Hemolysin is found only in association with Panton-Valentine -​ S. delphini ​ leukocidin (PVL). -​ S. lutrae ​ PVL is an exotoxin lethal to polymorphonuclear leukocytes. -​ S. agnetis -​ And some strains of S. schleiferi PROTEIN A -​ S. lugdunensis and S. schleiferi can be occasionally ​ Bind the Fc portion of immunoglobulin G (IgG) mistaken for coagulase-positive staphylococci ​ Binding IgG in this manner can block phagocytosis and negate because of the presence of clumping factor. the protective effects of IgG. -​ CLUMPING FACTOR - causes bacterial cells to agglutinate in plasma and basis of a test known as the Staphylococcus epidermidis -​ slide coagulase test. ​ Is considered normal skin biota but is a common source of hospital-acquired infections and often a contaminant in improperly collected blood cultures specimens. ​ Prosthetic valve endocarditis - most commonly cause caused S. epidermidis] Staphylococcus saprophyticus ​ Associated with UTIs in young women ​ Second most common cause after E. coli Staphylococcus lugdunensis ​ Can cause both community-associated and hospital-acquired infections \ ​ More virulent than other is known to contain the gene mecA, which encodes oxacillin resistance Staphylococcus aureus ​ Most clinically significant species ​ Various cutaneous infections and purulent abscesses ​ Skin and soft tissue infections it can be SUPERFICIAL = Impetigo, cellulitis ​ Cutaneous infections can progress to deeper abscesses = Carbuncles ​ Endocarditis ​ Toxin - induced diseases = food poisoning ​ Scalded skin syndrome ( SSS ) ​ Toxic shock syndrome ( TSS ) ANTIMICROBIAL SUSCEPTIBILITY ENTEROTOXINS ​ Testing of CoNS depends on source and determination if the ​ Heat - stable exotoxins that cause symptoms, including diarrhea isolate is a contaminant or a likely pathogen. and vomiting. ​ Antimicrobial susceptibility testing of S. saprophyticus from urine ​ Groups A through E and G through J. not required ​ Stable at 100° C for 30 minutes, ​ Serious infections with S. aureus and S. lugdunensis require ​ Reheating contaminated food does not prevent disease. susceptibility testing. METHICILLIN - RESISTANT STAPHYLOCOCCI ​ Isolates that are resistant to nafcillin or oxacillin ​ Vancomycin remains the treatment of choice for MRSA & MRSE ​ The latest CLSI M100 document recommends cefoxitin be used to detect methicillin resistance. ​ An oxacillin-salt agar plate can be used to screen for MRSA in clinical samples. ​ Oxacillin resistance is due to the gene mecA ​ mecA codes for an altered penicillin-binding ​ protein (PBP) called PBP2a, also designated PBP2ʹ ​ The “gold standard” for MRSA detection is the detection of the mecA gene by using molecular nucleic acid probes or PCR amplification. VANCOMYCIN-RESISTANT STAPHYLOCOCCI ​ Vancomycin is the drug of choice and sometimes the only drug available for serious staphylococcal infections MACROLIDE RESISTANCE ​ Modified double disk diffusion test ( D-zone test )