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Staphylococci Case Study A 19-year-old woman complained of fever, flank pain, dysuria, urgency to urinate, and blood-tinged urine A urinalysis revealed many white blood cells and white blood cell casts A urine culture grew 45,000 CFU/ml of white nonhemolytic colonies on blood agar; no growth appeared on MacConkey’s agar The organism was catalase-positive and slide-and-tube–coagulase negative It produced no zone of inhibition in the presence of a novobiocin disc W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Points to Consider What clinical manifestation does the patient present? How would you characterize this group of organisms? What factors contribute to the virulence of this group of organisms? What other factors would you consider to determine the clinical significance of this group of organisms? Other points to consider W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Staphylococcus: General Characteristics Gram-positive spherical cells (0.51.5 mm) in singles, pairs, and clusters Appear as “bunches of grapes” Gram-stained smear of staphylococci from colony Scanning electron micrograph of staphylococci W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Staphylococcus: General Characteristics Nonmotile Non–spore-forming Nonencapsulated Catalase-producing W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Genus Staphylococcus Approximately 33 species 14 to 17 species associated with humans Several veterinary pathogens Species initially differentiated by the coagulase test W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Coagulase-Positive Staphylococci S. aureus Human pathogen S. intermedius S. hyicus S. delphini S. schleiferi Animal-associated species Veterinary pathogens W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Coagulase-Negative Staphylococci S. epidermidis S. saprophyticus S. haemolyticus S. lugdunensis S. kloosii S. saccharolyticus S. simulans S. capitis S. caprae S. sciuri S. hominis S. schlieferi S. cohnii S. xylosus W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Clinically Significant Staphylococci: Staphytoccus aureus Habitat: anterior nares (carriers) Primary pathogen of the genus Produce superficial to systemic infections Mode of transmission: traumatic introduction Predisposing conditions Chronic infections Indwelling devices Skin injuries Immune response defects W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Virulence Factors: Extracellular Enzymes Hemolysins: hemolyze RBCs Alpha: platelets/WBCs/tissue Beta (hot/cold): sphingomyelin of RBCs Gamma: host cell membranes Delta: less lethal Leukocidin (Panton-Valentine): kill PMNs Enterotoxins A/D: food poisoning F: TSSAT B: pseudomembranous enterocolitis W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Virulence Factors: Extracellular Enzymes Exfoliatin Epidermolytic toxin Phage group II staphylococci SSS or Ritters Disease TSST-1: Toxic shock syndrome toxin-1 Multisystem disease High fever Hypotension Shock W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Virulence Factors: Extracellular Enzymes Hyaluronidase: connective tissue Staphylokinase: fibrinolysin Coagulase: virulence marker Lipase: allows colonization Penicillinase: confers resistance W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Staphylococcus aureus: Clinical Infections Skin and wound Impetigo Furuncles Carbuncles Boils Surgical wound infections Food poisoning Scalded skin syndrome Bullous impetigo W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Staphylococcus aureus: Clinical Infections Toxic shock syndrome Other infections Respiratory (less often) Bacteremia Osteomyelitis W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Coagulase-Negative Staphylococci Habitat: skin and mucous membranes Approximately 33 species Common human isolates S. epidermidis S. saprophyticus S. haemolyticus W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Coagulase-Negative Staphylococci: Staphylococcus epidermidis Habitat: skin and mucous membranes Cell wall: glycerol-teichoic acids Virulence factor: “slime” Mode of transmission: implantation of medical devices such as catheters, shunts, and prosthetic devices Infections are acquired nosocomially Serious infections among immunosuppressed patients may occur W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Coagulase-Negative Staphylococci: Staphylococcus saprophyticus Habitat: skin and mucosal membranes of the genitourinary tract Common cause of urinary tract infections in young, sexually active females When present in urine cultures, may be found in low numbers, but significant W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Other Gram-Positive Cocci Habitat: skin and mucous membranes Rarely implicated in infections S. haemolyticus associated with wound infections, bacteremia, and endocarditis S. lugdunensis and S. schleiferi are also found to be opportunists W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Laboratory Diagnosis: Specimen Collection and Handling Samples must be taken from the actual site of infection Prevent delay in transport of collected material from infected sites Transport in appropriate collection device that would prevent drying and minimize growth of contaminating organisms W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Laboratory Diagnosis: Direct Smear Examination Microscopic Examination Gram-positive cocci Insert Figure 10-1 pairs and clusters Numerous polymorphonuclear cells (PMNs) W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Laboratory Diagnosis: Cultural Characteristics Colony morphology Smooth, butyrous, white to yellow, creamy S. aureus may produce hemolysis on blood agar S. aureus W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Laboratory Diagnosis: Cultural Characteristics Coagulase-negative staphylococci Smooth, creamy, white Small-to medium- sized, usually non-hemolytic S. saprophyticus Smooth, creamy, may produce a yellow pigment W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Identification Tests: Catalase Principle: tests for enzyme catalase 2 H2O 2 2 H2O + O2 Drop H2O2 onto smear Bubbling = POS (Most bacteria, O2 generated) No bubbling = NEG (Streptococci and other lactic acid bacteria, no O2 generated) W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Identification Tests: Coagulase Test Detects enzyme coagulase Cell-bound “clumping factor” Extracellular enzyme “free coagulase” Two methods Slide test Tube test Slide coagulase test detects clumping factor W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Identification Tests: Coagulase Test Tube test detects the extracellular enzyme “free coagulase” W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Novobiocin Susceptibility Test Test to differentiate coagulasenegative staphylococci from S.saprophyticus from urine samples S. saprophyticus is resistant (top) Other CNS are susceptible W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Schematic Diagram for Identifying Staphylococcal Species W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Antimicrobial Susceptibility For non–beta-lactamase producing S. aureus (methicillinsusceptible) Penicillinase-resistant synthetic penicillins (methicillin, nafcillin, oxacillin, dicloxacillin) For methicillin -resistant S. aureus (MRSA) and methicillinresistant S. epidermidis (MRSE) Vancomycin combined with rifampin or gentamicin Emergence of vancomycin resistance W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company. Points to Remember General characteristics of staphylococcal species Infections produced by pathogenic species Microscopic and colony morphology Tests used to identify these species Emergence of resistant strains W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company.