Staphylococci Chapter 14

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Staphylococci Chapter 14
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Staphylococci Chapter 14

• Family Micrococcaceae
• Genus
• Staphylococcus
• Micrococcus

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Staphylococcus General Characteristics

• Gram-positive spherical cells (0.5-1.5 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
• Nonspore-forming
• Nonencapsulated
• Catalase-producing
• Oxidase negative
• Glucose fermenters
• Primarily aerobic, some facultatively anaerobic

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Genus Staphylococcus

• Approximately 33 species
• 14 to 17 species associated with humans, mainly
  on skin and mucous membranes
• Several veterinary pathogens
• Staphylococcus divided into coagulase-positive
  and coagulase-negative categories with the
  coagulase test

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Genus Staphylococcus

• Bacitracin resistant
• Grow on agar that contains peptone
• Inhibited by media that has high bile salt
  concentration
• Some are ß-hemolytic
• Colony morphology buttery looking, cream or
  white colored

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Coagulase-Positive Staphylococci

• S. aureus
• S. intermedius
• S. hyicus
• S. delphini
• S. schleiferi

Human pathogens
Veterinary pathogens
Animal-associated species
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Coagulase-Negative Staphylococci

• Coagulase negative
• Found as normal flora
• In clinical environment, seeing an increase due
  to prosthetic devices, catheters and
  immunocompromised
• Abbreviated CNS or CoNS

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Coagulase-Negative Staphylococci

• S. capitis
• S. caprae
• S. sciuri
• S. hominis
• S. schlieferi
• S. cohnii
• S. xylosus

• S. epidermidis
• S. saprophyticus
• S. haemolyticus
• S. lugdunensis
• S. kloosii
• S. saccharolyticus
• S. simulans

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Clinically Significant Staphylococci
Staphylococcus aureus

• Habitat anterior nares (carriers)
• Colonization axilla, vagina, pharynx
• Primary pathogen of the genus
• Produce superficial to systemic infections
• Mode of transmission traumatic introduction,
  direct contact with infected person, inanimate
  objects
• Predisposing conditions
• Chronic infections
• Indwelling devices
• Skin injuries
• Immune response defects

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Staphylococci Chapter 14

• Infection will elaborate inflammatory response
  with GPC accumulating as pus
• Pus mix of active and inactive neutrophils,
  bacterial cells and extravascular fluid

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Virulence Factors Extracellular Enzymes

• Enterotoxins heat stable _at_ 100o C for 30 minutes
• A through D food poisoning (i.e potato salad,
  custard foods)
• F TSSAT
• B pseudomembranous enterocolitis, occurs when
  normal flora are altered in bowel

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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

• Cytolytic Toxins
• Alpha- hemolysin lyses rbcs, damages plts,
  causes severe tissue damage
• ß- hemolysin acts on sphingomyelin in the plasma
  membrane of rbcs, exhibited in CAMP test to id
  Group B strep
• Gamma
• Delta only found with Panton-Valentine
  leukocidin, PVL is lethal to PMNs

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Virulence Factors Extracellular Enzymes

• Hyaluronidase Hydrolyzes hyaluronic acid in
  connective tissue allowing spread of infection
• Staphylokinase fibrinolysin which allows spread
  of infection
• Coagulase virulence marker
• Lipase allows colonization

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Virulence Factors Extracellular Enzymes

• Penicillinase confers resistance
• DNase degrades DNA
• Beta-lactamase
• Protein A in cell wall, it binds to Fc part of
  IgG to block phagocytosis

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Staphylococcus aureus Clinical Infections

• Skin and wound
• Impetigo
• Furuncles/Boils (Infection of hair follicles
  usually in areas that sweat)
• Carbuncles (clusters of boils)
• Surgical wound infections
• Food poisoning source is infected food handler

Bullous impetigo
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Staphylococcus aureus Clinical Infections

• Scalded skin syndrome Ritters disease
• Extensive exfoliative dermatitis
• Young children and newborns

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Staphylococcus aureus Clinical Infections

• Toxic shock syndrome
• Other infections
• Respiratory (less often)
• pneumonia
• Bacteremia
• Osteomyelitis/arthritis
• Endocarditis
• Pseudomembranous enterocolitis

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Coagulase-Negative Staphylococci

• Habitat skin and mucous membranes
• Common human isolates
• S. epidermidis
• S. saprophyticus
• S. haemolyticus

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Coagulase-Negative Staphylococci Staphylococcus
epidermidis

• Virulence factor slime Helps to prevent
  phagocytosis
• 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

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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
• pairs and clusters
• Numerous polymorphonuclear cells (PMNs)

Insert Figure 10-1
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Laboratory Diagnosis Cultural Characteristics

• Colony morphology
• Smooth, butyrous, white to yellow, creamy
• Grow well _at_ 18-24 hours
• 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 H2O2 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 converts fibrinogen
  to fibrin which precipitates on cell causing
  agglutination
• Extracellular enzyme free coagulase
• Two methods
• Slide test screens for clumping factor
• Tube test

Slide coagulase test detects clumping factor
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Identification Tests Coagulase Test
Tube test detects the extracellular enzyme free
coagulase or staphylocoagulase by causing a
clot to form when bacterial cells are incubated
with plasma
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Novobiocin Susceptibility Test

• Test to differentiate coagulase-negative
  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 nonbeta-lactamase producing S. aureus
  (methicillin-susceptible)
• Penicillinase-resistant synthetic penicillins
  (methicillin, nafcillin, oxacillin,
  dicloxacillin)
• Beta-lactamase producers break down the
  beta-lactam ring of penicillin so it inactivates
  antibiotic before it acts on bacterial cells

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Antimicrobial Susceptibility

• For methicillin -resistant S. aureus (MRSA) and
  methicillin-resistant S. epidermidis (MRSE)
• Vancomycin combined with rifampin or gentamicin
• Increased in hospital acquired infections
• Must adhere to strict infection control practices
• To detect methicillin resistance, use oxacillin.
  Resistance is due to gene mecA which codes for
  new penicillin binding protein (PBP)
• Gold standard for testing for MRSA is nucleic
  acid probe or PCR
• Emergence of vancomycin resistance (VRSA)
• Use screening agar and confirm

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Antimicrobial Susceptibility

• Macrolide Resistance
• Clindamycin sensitivity often requested by
  physician to treat Staph skin infection.
  Referred to as D test
• Clindamycin resistance is often inducible meaning
  it only is detectable when bacteria are also
  exposed to erythromycin