General features of Staphylococci

• staphylos = grapes, from the Greek

• nonmotile

• non-spore forming

• Gram+ cocci in clusters

cell wall of gram-positive bacteria

• thick, heavily-crosslinked cell wall with peptidoglycan and lipotechoic acid

• techoic acids link cell wall to the cytoplasmic membrane

• there also exist a variety of surface anchoring proteins

• generally, much thicker than Gram- cell wall; complement can lyse Gram-negative bacteria but not Gram-positive bacteria

catalase test—add hydrogen peroxide

• to distinguish Staph from Strep, drop a bit of hydrogen peroxide on the organism

• Staphylococcus has catalase, which will convert H₂O₂ to H₂O and O₂, leading to bubbling from oxygen

• Streptococcus is catalase-negative and no bubbling is seen

catalase confers resistance to oxidative burst

• catalase effectively neutralizes H₂O₂, conferring upon the bacteria a resistance to oxidative burst

coagulase test

• interested in distinguishing primary pathogen among the Staph cocci (i.e., S. aureus) from the low-virulence, nosocomial infections of S. epidermidis and S. saprophyticus

• S. aureus is the major human pathogen because it exhibits coagulase. in the test, S. aureus clots the human serum

mannitol-salt agar plate

• S. epi. is able to metabolize the mannitol, and this allows us to distinguish it

Category: Microbiology Notes