Staphylococcus (Characteristics)
- Gram positive, cocci, non motile
- Pairs; short chains; clusters
- Facultative anaerobes; diversity
Staphyle:
Coccus:
Staphyle: bunch of grapes
Coccus: a grain or berry
Indigenous Bacteria
Establish residence on surface tissue or alimentary tract; especially the anterior nares
Staphylococci are part of the ______ ______
Natural flora
There are >__ species of Staphylococcus
20
Coagulase
A biochemical test that differentiates S. aureus from other Staph - contributes to the clotting of plasma
Coagulase converts ______ to ______
Fibrinogen to Fibrin
How do we differentiate Staphylococcus and Streptococcus (both gram positive)
Catalase produced by staphylococcus under aerobic conditions
Multiple _______ ______ assist establishing a staphylococcus infection
extracellular factors
Protein A
Unique to S. Aureus
- Major protein component of cell wall that is covalently bound to peptidoglycan
IgG effects on Protein A
- With IgG molecules bound in the “wrong” orientation (om relation to normal antibody function), the IgG disrupts opsonization and phagocytosis of bacteria
Toxins produced by S. aureus (4)
1) Hemolysins
2) Leukotoxins
3) Enterotoxins (superantigens) - toxic shock syndrome
4) Exfoliative toxins
Hemolysins
Red blood cell membrane damaging proteins
- Contribute to pathogenicity by producing tissue damage after the establishment of a focus infection
Leukotoxin
A two protein toxin, attacks polymorphonuclear leukocytes and macrophage
Enterotoxins
Large family of Staphylococcus toxins, superantigens
Enterotoxins
Function:
Source:
Symptoms:
Function: Cause diarrhea and emesis
Source: S. aureus contaminated foods
Symptoms: Within 2-6 hours of ingestion
- Cramping, nausea, vomiting, diarrhea
Enterotoxins are _____-stable
heat
TSST
Toxic shock syndrome toxin
Enterotoxins and TSST bind directly to ______ and ______ independent of antigen
MHC class II; TCR
Enterotoxins and TSST: method of toxicity
Massive cytokine production yields systemic toxicity of host/ Suppression of the adaptive immune response
Exfoliative toxin
2 forms ETA/ETB - proteases
Stimulate lysis of the intercellular attachment between cells of the epidermis
Staphylococcus Epidemiology
Staphylococcus are a normal component of human indigenous flora and are carried asymptomatically at several body sites, especially anterior nares
Staphylococcus Transmission
Direct contact by the hands is the most important route of transmission
Staphylococcus Infection
- Typically localized
- Intact skin major barrier to infection
- Skin primary sites of infection
Appearances of Staphylococcus infectio``````n
Folliculitis Boil Impetigo Scalded skin syndrome Pneumonia
Treatment of S. Aureus infections
- Adequate drainage of wound
- Removal of foreign objects
- Antibiotic Therapy
- Methicillin
- Vancomycin
Methicillin Resistant S. Aureus (MRSA)
MR of SA is due to the selection of SA with mutations within the Penicillin Binding Proteins that have low affinity for penicillin
PBP
Penicillin Binding Proteins
Vancomycin Resistance
- SA strain resistant to intermediate, but clinically significant levels of vancomycin VIrSA
- Typically in MRSA - patients with prolonged vancomycin therapy, up to 18 wks, selects for VIrSA
- VIrSA resistance due to changes in cell wall
MICs for Vancomycin
SA vancomycin - susceptible: 0.5 - 2µg/ml
SA vancomycin - intermediate (VIrSA): 4-8 µg/ml
SA vancomycin - resistant (VRSA): >16 µg/ml
HA-MRSA vs. CA-MRSA
HA-MRSA infection is easily contracted in hospital settings
CA-MRSA infection spreads through those living in close contact, such as military barracks, dormitories and gyms
S. Epidermis
Low virulence
- Hospital acquired - contamination of surgical site binds to plastics
- Treatment, problem multi-drug resistant use antibiogram
S. Saprophyticus
Urinary tract infections selectively binds to cells of the urinary tract
- Does not posses any virulence factors found in SA
