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Gram positive cocci
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Gram Positive Cocci
GPC Identification
Lab Stuff
Staphylococcus species
Gram positive cocci
in clusters
Staphylococcus
Transmission
- person to person
- direct contact
- fomites
Virtually all colonized
Catalase Testing
Positive:
- Staphylococcus
Catalase
Negative:
- Streptococcus
- Enterococcus
Coagulase Testing
Organism mixed with plasma
Slide Test: detection of bound coagulase
aka "Clumping factor"
Negative:
- Staphylococcus epidermidis
- Staphylococcus hominis
- Staphylococcus haemolyticus
- and more!
Coagulase
-
+
Positive: S. aureus, S. intermedius
Tube Test: detection of free coagulase
Positive: S. aureus, S. lugdunensis
-
+
S. aureus
Staphylococcus aureus
2nd most common cause of hospital acquired infections (HAI)
Magill et al., NEJM, 2014
Staphylococcus
aureus
+
Laboratory Features
Coagulase
Catalase
Mannitol Salt Agar
S. aureus
Normal flora in 30% of humans
-Carrier are at a higher risk for infections and are presumed to be important source for transmission
- Nares, groin, axilla, ears
Features
Virulence Factors
Protein A
Binds Fc component of IgG; inhibits complement activation and phagocytosis
Enterotoxins
Fast acting, heat stable
Exotoxins
Exfoliatins, toxic shock syndrome toxin (TSST-1)
Virulence
Factors
Clumping Factor, coagulase, hyaluronidase
Enhance invasion and survival in tissue
Leucocidin (PVL)
Mediates destruction of phagocytes
Alpha, beta, gamma and delta toxins
Act on host cell membranes
and mediate cell destruction
Staphylococcus aureus
Osteomyelitis: Bone pain, fever, lytic bone lesions on imaging (cytolysins, coagulase)
Endocarditis: acute, right sided; most common cause (cytolytic toxins)
Clinical Associations
Gastroenteritis: 2-6 hour onset; self-limiting- toxin ingested preformed in food (enterotoxins)
Pneumonia: nosocomial, acute, rapid onset, ventilator, CF... (coagulase, cytolysins)
Bacteremia
Septic arthritis: monoarticular joint pain; inflammation (coagulase, cytolysins)
Skin and Soft Tissue Infections
Clinical Associations: SSTI
Impetigo
Erythematous papules to bullous
Coagulase, exfoliatins
Impetigo
Toxic Shock Syndrome
Desquamating rash, fever, hypotension,
multiorgan failure
May develop in otherwise healthy individuals
TSST-1
Toxic Shock Syndrome
Folliculitis
Folliculitis --> deeper infections -->
furuncles (boils) --> carbuncles
Folliculitis
Scalded Skin Syndrome
diffuse epidermal peeling
coagulase, exfoliatin
Scalded Skin Syndrome
Treatment
Treatment
Gastroenteritis- self limiting (no treatment)
Nafcillin/oxacillin: drugs of choice
Mupirocin- topical treatment; decolonization
Vancomycin or ceftaroline- MRSA
Methicillin Resistant S. aureus (MRSA)
Resistance
MRSA
important cause of serious nosocomial and community acquired infections
MRSA
mecA gene --> alterations of penicillin binding protein
resistant to beta-lactam drugs
exception: ceftaroline
Vancomycin resistant S. aureus
vanA gene --> same gene that confers vancomycin resistance in Enterococcus
First reported in 2002
14 VRSA isolates in US between 2002-2015
8 cases in Michigan and 4 in Delaware
Very rare finding
VRSA
J Clin Invest. 2003;111(9):1265-1273.
S. epidermidis
Lab Features:
Coagulase negative
White colonies
Non-hemolytic
Novobiocin S
Staphylococcus epidermidis
Clinical Features:
Normal skin flora
Frequent contaminant (blood cultures)
Prosthetic device infections, catheter associated infections
Endocarditis (IV drug users)
S. saprophyticus
"Honeymoon Cystitis"
Lab Features:
Coagulase negative
White colonies
Non-hemolytic
Novobiocin R
Staphylococcus saprophyticus
Clinical Features:
Uncomplicated UTI in young women
2nd most common cause (E. coli is 1st)
Streptococci
Streptococcus
Gram-positive cocci in chains (or pairs)
Catalase negative
Beta-Hemolytic Streptococci
Lancefield Antigen
Beta- hemolytic Streptococci
Group A Strep: Streptococcus pyogenes
Group B Strep: Streptococcus agalactiae
Streptococcus pyogenes
Lab Features:
Large zone of hemolysis
Bacitracin S
PYR +
CAMP -
Group A Strep
Clinical Features:
Reservoir: skin, mucous membranes
Diseases:
pyogenic
toxigenic
immunologic
pharyngitis
cellulitis
erysipelas
impetigo
"Honey-crusted lesions"
Pyogenic
scarlet fever
toxic shock like syndrome
necrotizing fasciitis
Toxigenic
rheumatic fever
occurs after pharyngitis
glomerulonephritis
occurs after pharyngitis, skin infection
Immunologic
Testing Methodology
GAS
Assays
Rapid Antigen Tests
58-96% sensitivity
Throat culture is the gold standard
Inexpensive, rapid
More sensitive in children than adults
Not recommended in adults
** Negative rapid tests must be confirmed by culture for children and adolescents
Molecular tests rapidly replacing Ag tests: increased sensitivity
S. agalactiae
Weakly beta-hemolytic
Bacitracin R
PYR -
CAMP +
Group B Strep
Group B Strep
Colonizes GU/GI tract in 10-35% of women
Transmitted to infants at birth (50-75%)
Neonatal meningitis
Early and late onset
Pneumonia, sepsis
Clinical Features
Prenatal Screening
Pregnant women (35-37 weeks) screened for GBS colonization
Culture +: receive prophylaxis
VGS
Lab Features:
alpha hemolytic
Optochin R
Viridans Group Streptococci
Clinical Features:
Normal flora of oropharynx
S. mutans, S. mitis: dental caries
S. mitis, S. sanguis: endocarditis (following dental work)
S. gallolyticus: assc with colon cancer
S. anginosus: abscess (brain and liver)
VSG vs
S. pneumo
S. pneumoniae
Streptococcus pneumoniae
Laboratory Features
Optochin R
Laboratory
Bile solubile
Diseases
Clinical
Normal upper respiratory tract flora
Spread via respiratory droplets
Otitis Media, Sinusitis
Children
Meningitis
Most common cause of adult meningitis
Pneumonia
Blood tinged/rusty colored sputum
Treatment
S. pyogenes and S. agalactiace are universally susceptible to penicillin and other betaβ-lactam antibiotics
In penicillin allergic patients, clindamycin is the drug of choice
S. pneumoniae has reduced susceptibility to penicillin (10-25%)
Viridans Group Streptococci have variable susceptibility to many drug classes, so susceptibility testing is recommended
Enterococcus
Enterococcus
Normal flora in GI/GU tract
UTI
Biliary tract infections
Endocarditis following GI/GU procedures
Enterococci
Gram + cocci, pairs and chains
alpha or gamma hemolysis
Catalase -
PYR +
Group D Lancefield Ag
Hydrolizes esculin in 40% bile and 6.5% NaCl
Laboratory
Identification
E. faecalis
"less"
80-90% of Enterococci isolates from human clinical specimens
Ampicillin S
E. faecalis
E. faecium
"mean"
Ampicillin Resistant
More likely to be VRE --> Vancomycin resistant Enterococcus
vanA gene (plasmid associated)
Important nosocomial infection
E. faecium
Identification of Gram + Cocci
Identification Algorithm
Identification of Betaβ-Hemolytic Streptococci
Beta-Strep
Catalase positive GPC
Anaerobic GPC
Aerobic GPC
Commensals of human oral, upper respiratory and GI tracts, female GU system and skin
Opportunistic infections
Mild skin abscesses to severe disease including
brain abscess, bacteremia, endocarditis, septic abortion
Micrococcus spp.
Frequent contaminant, skin flora
Catalase +
Aerococcus urinae
Catalase -
UTI
Some Other GPC Friends
Anaerococcus spp.
Atopobium spp.
Finegoldia magna
Micomonas micros
Peptococcus spp.
Peptoniphilus spp.
Peptostreptococcus anaerobius
Staphylococcus saccharolyticus
Staphylococcus aureus subsp. anaerobius