Transcript Pathology Resident Microbiology Lecture Series

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
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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
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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
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Staphylococcus: General Characteristics
 Nonmotile
 Non–spore-forming
 Nonencapsulated
 Catalase-producing
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Genus Staphylococcus
 Approximately 33 species
 14 to 17 species associated with humans
 Several veterinary pathogens
 Species initially differentiated by the coagulase test
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Coagulase-Positive Staphylococci
 S. aureus
Human pathogen
 S. intermedius
 S. hyicus
 S. delphini
 S. schleiferi
Animal-associated
species
Veterinary
pathogens
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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
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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
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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
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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
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Virulence Factors: Extracellular Enzymes
 Hyaluronidase: connective tissue
 Staphylokinase: fibrinolysin
 Coagulase: virulence marker
 Lipase: allows colonization
 Penicillinase: confers resistance
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Staphylococcus aureus: Clinical Infections
 Skin and wound
 Impetigo
 Furuncles
 Carbuncles
 Boils
 Surgical wound infections
 Food poisoning
 Scalded skin syndrome
Bullous impetigo
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Staphylococcus aureus: Clinical Infections
 Toxic shock syndrome
 Other infections
 Respiratory (less often)
 Bacteremia
 Osteomyelitis
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Coagulase-Negative Staphylococci
 Habitat: skin and mucous membranes
 Approximately 33 species
 Common human isolates
 S. epidermidis
 S. saprophyticus
 S. haemolyticus
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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
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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
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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
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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
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Laboratory Diagnosis:
Direct Smear Examination
Microscopic Examination
 Gram-positive cocci
Insert Figure 10-1
 pairs and clusters
 Numerous polymorphonuclear cells
(PMNs)
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Laboratory Diagnosis:
Cultural Characteristics
 Colony morphology
 Smooth, butyrous, white to
yellow, creamy
 S. aureus may produce
hemolysis on blood agar
S. aureus
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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
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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)
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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
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Identification Tests: Coagulase Test
Tube test detects the
extracellular enzyme
“free coagulase”
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Novobiocin Susceptibility Test
 Test to differentiate coagulasenegative staphylococci from
S.saprophyticus from urine samples
 S. saprophyticus is resistant (top)
 Other CNS are susceptible
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Schematic Diagram for Identifying Staphylococcal
Species
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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
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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
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