What do Staphylococcus and
Micrococcus have in common? - ANSWERS• Location: widespread in nature and on
human skin, although Micrococcus is more
transient
• Catalase Reaction: Strongly Positive
• Appearance on Gram Stain: Gram Positive
Cocci, nonmotile
Pathogenicity - ANSWERSMi...
Micrococcus have in common? - ANSWERS• Location: widespread in nature and on
human skin, although Micrococcus is more
transient
• Catalase Reaction: Strongly Positive
• Appearance on Gram Stain: Gram Positive
Cocci, nonmotile
Pathogenicity - ANSWERSMicrococcus is a harmless saprophyte; Staph is opportunistic, especially if skin
is penetrated
Oxygen Requirements - ANSWERSMicrococcus is a strict aerobe (it is also oxidase positive); Staph
species are facultative anaerobes
Arrangement - ANSWERSMicrococcus makes tetrads more often than Staph; both also make clusters
Resistance to Salt - ANSWERSStaph is a halophile, Micrococcus less so
Micrococcus vs Staphylococcus - ANSWERS* Since they are both commonly isolated from clinical
specimens, it is important to be able to differentiate whether the isolate is a harmless bystander or a
potential cause of infection.
* Remember Koch's Postulates? Isolating
something from a clinical specimen does
NOT prove it is the cause of the disease.
, Two Species of Staph Associated with Human Disease - ANSWERS• Staphylococcus aureus -the more
virulent
• Staphylococcus epidermidis - usually harmless unless inserted through skin via a catheter, surgical
procedure or needle
Exotoxins - Categories - ANSWERS- Neurotoxins work on neurons
- Enterotoxins work on the enteric tract; Gl symptoms
- Cytotoxins destroy cells, entire tissues
Optional Toxins Present in Staph aureus - ANSWERS• Cytolytic toxins that act against WBCs
• Exfoliative toxins dissolve desmosomes which lock epithelial cells together, causing skin cells to
separate and slough off
• TSS Toxin: causes toxic shock
• Enterotoxins: 5 proteins, A through E, which stimulate intense intestinal spasms, vomiting, nausea and
diarrhea.
S. aureus Food Intoxication - ANSWERS• NOT food poisoning - bacteria may be dead, but toxin is left
behind
• High-protein, creamy foods contaminated with skin flora, then kept at RT for several hours
• Re-heating food will not break down toxin: stable at boiling temps. for 30 minutes
• Food has no off taste or smell
• Rapid symptoms -within 4 hours
• Rapid resolution, once toxin is expelled
What Determines Pathogenicity in Staph? - ANSWERS• Coagulase is an enzyme bound to the outer
surface and secreted into environment
• Coagulase causes blood to clot by activating the conversion of fibrinogen to fibrin
• Fibrin clots hide the bacteria from phagocytic cells
• ONLY Staphylococcus aureus produces
coagulase!
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