LAB EX 32

what is the common cause of nosocomial infections in immunocompromised patients? how about urinary tract infection?

S. epidermidis S. saprophyticus

what characteristics can be used to differentiate staphylococcus from streptococcus? Explain how you would test for this characteristic

Staphylococcus aureus - gram positive - coccus shaped - facultative anaerobe (presence/absence of oxygen), halotolerant (high salt), acidotolerant -resistant to drying, high pH, and high tempt Since staphylococcus is halotolerant and acidotolerant, we can use mannitol salt agar. The high salt content inhibits most bacteria other than staphylococcus. Fermentation of mannitol by S. aureus and S. saprophyticus produces acid, lowering the pH of the media and causing the phenol red indicator to turn from red to yellow.

differential media

allow all microbes to grow but each will take on different visual appearance

why is a high salt media used during the initial isolation of staphylococci?

because the high salt content inhibits most bacteria growth other than staphylococcus.

how was streptococcus initially eliminated from your three cultures?

by using selective media to isolate staphylococcus from a complex mixture and then using a variety of differential tests to determine the species of an isolate by using blood agar and mannitol salt agar

m-staphylococcus broth

contain sodium chloride or salt making it highly selective for staphylococci

selective media

contain substance that inhibits the growth of most bacteria allowing only one type to grow

what is the function of NaCl and phenol red?

inhibits most bacteria growth other than staphylococcus To detect color change from red to yellow caused by fermentation of mannitol by S. aureus and S. saprophyticus

would m-staphylococcus broth be an appropriate choice for isolation of bacteria other than staphylococcus from a complex mixture?

no because the high salt content in the broth inhibits most bacteria growth other than staphylococcus no because the salt in the broth makes it highly selective for staphylococcus

blood agar

sheep's blood this differential media allows to detect hemolysis or the lysing of red blood cells by bacterial toxins. S. aureus produces alpha toxins that causes red blood cells of a bacterial colony to lyse.

methicillin resistant S. aures (MRSA)

strain of bacterium that is resistant to beta lactam anitbiotic methicillin as well as to other antibiotics of the same class

mannitol salt agar

this media is both selective and differential containing NaCl, mannitol, and phenol red indicator. The high salt content inhibits most bacteria other than staphylococcus. Fermentation of mannitol by S. aureus and S. saprophyticus produces acid, lowering the pH of the media and causing the phenol red indicator to turn from red to yellow. staphylococcus epidermidis doesnt ferment mannitol and causes no color change.