Gram (+) Cocci Flashcards
Catalase positive, coagulase positive, beta hemolytic, ferments mannitol, yellow colonies
Staphylococcus aureus
Catalase positive, coagulase negative, gamma hemolytic, novobiocin sensitive
Staphylococcus epidermidis
Catalase positive, coagulase negative, gamma hemolytic, novobiocin resistant
Staphylococcus saphrophyticus
Catalase negative, coagulase negative, beta hemolytic, bacitracin sensitive, PYR+
Streptococcus pyogenes (Group A)
Catalase negative, coagulase negative, beta hemolytic, bacitracin resistant, CAMP+
Streptococcus agalactiae (Group B)
Catalase negative, coagulase negative, alpha hemolytic, optochin sensitive
Streptococcus pneumoniae
Catalase negative, coagulase negative, alpha hemolytic, optochin resistant
Streptococcus viridans
Catalase negative, coagulase negative, alpha/beta/gamma hemolytic, PYR+, esculin agar
Enterococcus (Group D Streptococcus)
Catalase positive, gamma hemolytic, associated with endocarditis in IV drug users or catheter infections
Staphylococcus epidermidis
Catalase positive, gamma hemolytic, associated with UTIs in sexually active females
Staphylococcus saprophyticus
What are the virulence factors of S. aureus?
- TSST-1 toxin - superantigen that overactivates immune system
- Enterotoxin - fast acting and heat stabile
- Exfolatin - skin exfoliating
- Protein A binds Fc of IgG, inhibiting phagocytosis
- coagulase - keeps infection local
- cytolytic alpha toxin forms pores
Patient presents with fever, hypotension, sunburn like rash on palms and soles that progresses to multiorgan failure and death
Toxic shock syndrome - vignette will hopefully mention something about recent menses or packed wounds
What color is the sputum in S. aureus pneumonia?
Salmon colored
Most common cause of osteomyelitis in previously healthy patient?
S. aureus
What is the best way to differentiate between Staphylococcus and Streptococcus?
Catalase test. Gram stain is insufficient to tell the difference (even though Staph is clusters and Strep is chains) because the chains can group together to look like clusters.
Skin infection with honey crusted lesions
Impetigo - could be S. aureus or S. pyogenes (Group A). Differentiate with catalase test.
What is the most common cause of adult meningitis, otitis media/sinusitis in children, and community acquired pneumonia?
Streptococcus pneumoniae
What is the major virulence factor of S. pneumoniae? Name some VFs.
- major is polysaccharide capsule (test with Quellung or latex particle agglutination and asplenia predisposes to infection)
- IgA protease
- teichoic acid
- Pneumolysin O: a hemolysin/cytolysin that damages respiratory epithelium
Has an antiphagocytic M protein that differentiates strains - M12 is associated with acute glomerulonephritis
Streptococcus pyogenes (Group A)
These factors make Streptococcus pyogenes good at spreading
Streptokinase, Streptococcal DNAse, Hyaluronidase, Exotoxins A-C (phage coded superantigen and causes fever/rash)
Leading cause of neonatal meningitis
Streptococcus agalactiae (Group B)
Abrupt onset of sore throat, fever, malaise and headache followed by a blanchable “sandpaper” rash and strawberry tongue with nausea and vomiting
Pharyngitis then scarlet fever, caused by Streptococcus pyogenes (Group A)
Two sequelae of Group A Strep infections and their mechanisms
1) Rheumatic fever - Abs to heart tissue 2 weeks post pharyngitis, Type II HSN
2) Acute glomerulonephritis - M12, immune complexes on glomeruli with pulmonary edema, hypertension, smoky urine, Type III HSN
Antibodies to streptolysin O titer > 200
Rheumatic fever (Group A Strep)
Pathogenesis factors of Streptococcus agalactiae (Group B)
capsule, beta hemolysin, CAMP factor
Treatment of pregnant mother that tests positive for Group B Strep
prophylactic ampicillin, clindamycin, or erythromycin during delivery
Virulence factors of Viridans streptococci (S. mutans, S. sanguinis)
Dextran biofilm! Mediates adherence to tooth enamel or damaged heart valve, causing dental caries or infective endocarditis
Catheter-associated UTI with G+ cocci in chains, resistant to treatment even after vancomycin
VRE - Vancomycin resistant Enterococcus faecium/faecalis (terminal D-ala-D-ala replaced with D-ala-D-lac)
