Gram Positive Flashcards
Toxins of Gram-positive organisms
Exotoxin
Toxins of Gram-negative organisms
Endotoxin
Virulence factor of S.aureus responsible for Toxic shock syndrome
Pyrogenic exotoxin C
- are called superantigens they bind to MHC class II mediating T-cell response.
Main virulence factor of S.aureus
Coagulase
VF of S.aureus responsible for resistance to beta-lactams
Beta-lactamase/Penicillinase
Toxic to WBC’s, responsible for causing MRSA/ORSA
Panton valentine leukocidine (PVL)
Enterotoxin
causes food poisoning
VF responsible for Scalded Skin syndrome/ Ritter’s disease caused by S.aureus infection
Exfoliative toxin
The initial presumptive identification for all gram (+) cocci
Gram staining
Characteristics in gram stain:
Staphylococcus
Streptococcus
Micrococcus
Staph: pinhead- cocci in clusters
Strep: pinpoint- cocci in chains
Micro: cocci in tetrads
produces a “yellow-pigmented” beta-hemolytic colonies in 5% BAP
S. aureus
aureus= “golden”
True/False:
I. S. aureus is capable of fermenting mannitol
II. It grows in high salt concentrations
Both are TRUE
S. aureus produces “yellow-halo” in mannitol salt agar which contains:
(✓) ferments mannitol
(✓) 10% salt conc.
(✓) phenol red
Media used to enhance pigmentation of staphylococcus
Loeffler’s serum slant
Characteristics in Loeffler’s serum slant:
S. aureus
S. citreus
S. albus
C. diptheriae
SA: golden yellow
SC: lemon yellow
SAL: porcelain white “albino”
CD: metachromatic granules
Reagent used in catalase test for Staphylococci
3% H2O2
15% - Anaerobe
30$- N. gonorrheae & Mycobacterium
Positive result for Modified Oxidase test
Blue color within 2 minutes
A selective and differential media for the identification of MRSA
Chrom Agar
MRSA: mauve colored colonies
the gene responsible for the resistance of S.aureus to beta-lactams
*methicilin
* nafcillin
* oxacillin
mecA gene
- which encodes for PBP 2a
gold standard for MRSA detection
PCR
how to differentiate S.haemolyticus
and S.aureus
Coagulase
- both are beta-hemolytic but S.haemolyticus is coagulase (-)
Commonly associated with the implantation of medical devices or prosthetic heart valves
S.epidermidis
S. aureus vs CONS
Coagulase tets
Staphylococcus & Micrococcus vs Streptococcus
Catalase test
Test used to differentiate S. aureus and S. intermedius
VP test
- S.aureus: PYR (-) & VP (+)
*is capable of producing acetoin
S. intermedius: PYR (+) & VP (-)
DOC for MRSA
Vancomycin
S. epidermidis vs S. saphrophyticus
Novobiocin test
S. epidermidis: (S)
S. saphrophyticus: (R)
Most common cause of UTI among sexually active young females
S. saphrophyticus
Causes pyelonephritis and cystitis in those with “indwelling catheter”
S. saphrophyticus
Flesh eating bacteria
S.pyogenes
major Vf of Group A streptococcus which mimics heart antigen
M protein
Group A streptococcus VF which causes scarlet fever
Streptococcal pyrogenic exotoxin (SPEs)
Strawberry tongue is a classical manifestation of ______ which is caused by _______
Scarlet fever – Group A strep/ S.pyogenes
Smells like “butterscotch” on Chocolate agar (CA)
Viridans group
Skin tests:
S. pyogenes
S.pneumoniae
C. diptheriae
SP: Dicks test
SPN: Francis test
CD: Shick test
Smith and Brown classification is based on
hemolytic pattern
Most common cause of newborn meningitis
S.agalactiae
Group B- baby (common in newborn)
pneumonia in 0-2 month old px.
Media that contains antimicrobials which suppresses growth of other organisms that normally in vaginal flora
Todd-Hewitt broth
Reagent used in Hippurate hydrolysis test
Reagent: Ninhydrin
(+): Purple color
- for S. agalactiae
Organisms that tests (+) for PYR hydrolysis
S.pyogenes & enterococcus
Diseases that may be caused by S.pyogenes
-Strep throat
- Scarlet fever/ Scarlatina
- Rheumatic fever
- Strep TSS
- Erysipelas
- NF/ Galloping gangrene
Gas gangrene
Galloping gangrene
Gas: C. perfringens
galloping: S. pyogenes
Inverted pine tree
Inverted Christmas tree
Test tube brush appearance
Pine: B. anthracis
Christmas: L.monocytogenes
Test tube: E. rhusiopathiae
Anthrax:
most common- least severe
most severe- least common
most common- least severe: Cutaneous
most severe- least common: Intestinal
BB contaminants
S. epidermidis
B. cereus
Characteristics of Bacillus spp.
Lecithinase (+)
Produce acid from GSM
Causes eye infection associated w/ trauma
Causes eye infection associated w/ HEROIN addict
EI in trauma: B.cereus
EI in heroin: B.subtillis
Agent of Bioterrorism
B. anthracis
Source of bacitracin
B. subtillis
