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Gram Positive Cocci


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Name the three gram positive cocci
Staphylococcus, Streptococcus, enterococcus
What laboratory test is used to identify gram positive cocci?
Catalase test
Gram Positive will break down H2O2 to water and hydrogen
Name catalase positive cocci.
Name catalase negative cocci.
Streptococcus and entercoccus
What gram positive cocci give positive test in coagulase test aka coagulate-positive staphylococci?
Staphylococcus aureus
What test negative in coagulase test aka coagulate-negative staphylococci?
Staphylococcus epidermitis, staphylococcus saphrophyticus
What is the effect of novobiocin antibiotic on S. aureus, S. epidermitis, and S. saphrophyticus?
S.Aureus and S.Epidermitis - sensitive to the drug
S.saphrophyticus - resistant
Where are the sources of S.Aureus?
- Found in human like the external nares, skin, perineum, oropharynx, feces
- Ppl to ppl contact: hand contact, aerosol
- fomites
What are some of the associated infection caused by S.Aureus?
- Impetigo, furuncles/boils, carbuncles, folliculitis, bacteremia and endocarditis, osteomyelitis, septic arthritis, pneumonia and empyema
What are some of the toxin-mediated disease caused by S.Aureus?
- Bullous impetigo, scalded skin syndrome, TSS, Food poisoning
What cause staphylococal food poisoning?
Enterotoxins - will not be inactivated even when food is heated
Name the virulence factors for S.Aureus?
Capsules: inhibit phagocytosis, facilitate adherence
Peptidoglycan: Endotoxin like activity and attract leukocytes
Teichoic acid: involved in complement activation, facilitate adherence
Protein A: bind to Fc on IgG reducing phagocytes binding. inhibit complement activation
Catalase:break down H2O2 so neutrophil can't attack due to O2 radical
Coagulase: clots plasma, bacterias hide in there and WBC can't penetrate clot
Enzymes that help spread of bacteria. and Cytotoxinx
What are some of the enzymes that promote bacterial spread?
Fibrinolysin, Hyaluronidase, Lipase, Nucleases
What are the virulence factors for S.epidermis?
- ability to bind to foreign materials
- biofilm production
What are the clinical manifestations of s.epidermis?
- Endocarditis
- Infections of shunts and catheters
- Infections of prosthetic joints
Name 3 medically important streptococci?
s.pyogenes, s.agalactiae, s.pneumonia
How is streptococci classified?
1. Serologic properties using Lancefield grouping
2. Hemolytic patterns: complete (beta), incomplete (alpha), no (gamma) hemolysis
3. biochemical properties
What group of Serologic grouping do Streptococcus pyogenes and agalactiae belong to respectively?
Pyogene - Lancefield Group A
Agalactiae - Lancefield Group B
(note: pneumonia is not in any group)
Main disease caused by strep.pyogenese
Scarlet fever, pharyngitis, necrotizing fasciitis, rheumatic fever, acute glomerulonephritis
Main disease caused by strep.agalactiae
- neonatal meningitis, neonatal sepsis, leading cause of infectious death in newborn
What antibiotic is Strep.pneumonia sensitive to?
(Note: Lyses when put in bile)
Strep. pneumonia causes what disease>
- pneumonia, otitis media, sinusitis, meningitis
Enterococci example
E. Faecium, E. Faecalis
Characteristis of enterococci
- low virulence, normally commensal, caused serious disease in hospitalized patients, can become resistant to antibiotic

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