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Flashcards in Gram (+) Cocci Deck (28):

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)