Culture media (1): Mannitol salt agar media

Microstudy/Dr Ahmed Talaat Medical microbiology قناة متخصصه لشرح مادة الميكروبيولوجي والمناعة لجميع طلبة الكليات العملية Culture media (1) : Mannitol Salt Agar Mannitol salt agar or MSA is a commonly used selective and differential growth medium in microbiology. It encourages the growth of staphylococci while inhibiting the growth of others It contains a high concentration (about 7.5–10%) of salt (NaCl) which is inhibitory to most bacteria - making MSA selective against most Gram-negative and selective for some Gram-positive bacteria (Staphylococcus, and Enterococcus) that tolerate high salt concentrations. It is also a differential medium for mannitol-fermenting staphylococci, containing mannitol and the indicator phenol red, a pH indicator for detecting acid produced by mannitol-fermenting staphylococci. Staphylococcus aureus produces yellow colonies with yellow zones, whereas other coagulase-negative staphylococci produce red colonies with no colour change to the medium