Session 7 & 8: Staphylococci and Streptococci

what are the two species of Gram-positive cocci in this lab session?

Streptococcus

Enterococcus

what are some characteristics of Streptococcus and Enterococcus?

gram (+)

catalase (-)

in pairs or chains

oxidase (-)

most are facultative anaerobes (few are strict anaerobes)

most are homofermentative

what does it mean to be homofermentative?

(for Strep. species)

most medically significant streptococci are this

sole product of glucose fermentation is lactic acid

what makes up the cell wall of Streptococci?

composed of peptidoglycan

(carbohydrates, teichoic acids, lipoproteins, and surface proteins antigens are embedded in the peptidoglycan)

how are Streptococci classified?

classified serologically based on cell surface carbohydrate antigens → Lancefield grouping system

what Streptococci species detects cell wall polysaccharide antigens?

(Lancefield grouping)

Group A, B, C, F, and G streptococci

(ex. S. pyogenes (A), S. agalactiae (B))

what Streptococci species detects cell wall lipoteichoic acid antigens?

(Lancefield grouping)

ex. Group D streptococci and Enterococcus sp.

what Streptococci species is unable to detect Lancefield cell wall antigens?

(Lancefield grouping)

ex. Viridans group Streptococci

what is an example of Group A streptococci?

S. pyogenes

what is an example of Group B streptococci?

S. agalactiae

what is an example of Streptococcus-like (formerly Group D)?

E. faecalis

what is an example of Pneumococci?

S. pneumoniae

what is an example of Viridans Group streptococci?

S. mitis

S. oralis

S. salivarius

S. sanguis

S. mutans

what is an example of Group C streptococci?

S. equisimilis

S. zooepidemicus

S. equi

what makes inoculation of streptococci unique compared to other species in lab?

when inoculating SBA (Sheep Blood Agar)

complete normal streaking technique and then stab holes at each quadrant with unflamed loop

purpose → to see enhanced hemolysis in microaerobic environments (streptococcal hemolysins)

what is coagulase?

protein capable of converting fibrinogen into fibrin → results in formation of visible clot

present in two forms: bound and free

what happens to coagulase in vivo (tested in an organism)?

coagulase functions to produce a fibrin barrier at the site of staphylococcal infection

what does tube test for coagulase test for?

tests for free and bound coagulase

(if a suspension of coagulase-producing organism is added to tube containing plasma → clots forms)

what does slide test for coagulase test for?

tests for bound coagulase