Microbiology: To Know and be Known

We started out making working slants for our unknown. Next we isolated our unknowns on PEA, MSA and EMB. My #30 made the same flourescent yellow halo on MSA as the control Staph. aureus did. It also would show similare growth and fermentation patterns when compared to Staph. aureus as a control. In this way I was lucky, since most of the other unknowns did not use a control that was the same microbe. Our controls where usually S. aureus, Bacillus subtilis, E. coli, Psuedomonas aerugenosa or Proteus vulgaris. Still from the MSA experiment onward I was pretty sure I was dealing with S. aureus and it soon became my favorite microbe. It's a very common microbe that lives as normal flora on the skin and nasal passages. It can become a pathogen if there is a break in the skin and the microbe enteres the sterile tissue below. Infact I saw a show about a girl who obtained a S. aureus infection in her brain due to a head injury. There is a highly virulent strain called MRSA S. aures. MRSA stands for Methicillin Resistant Staph. Aureus. My lab partner was shown to have this after we did nasal swabs and isolted our own microbes. She was put on some heavy antibiotics to clear herself of carriage. I hope I didn't pick up this hand me down from her. Staph aureus is a non-spore forming cocci that forms irregulare groups or clumps. The name Satphylococcus Aureus in in Greek literally means golden clusters of grapes. When isolated on media it almost always produces a golden colored growth. It is non-motile and a facultative aerobe which means it prefers aerobic conditions but will also grow, though not as well, in anaerobic conditions. Staph. aureus is Catalase positive and Oxidase negative. It test positive for Gelatinase, DNase and Lypase but does not posses the enzyme amylase. Staph. aureus tolerates NaCl and ferments mannitol. It also tolerates phenyl ethyl alcohol and Eosin-methyline blue. It is Urease negative and MR+ and VP +/-. The IMViC test for Staph. aureus will be completely negative and ferments Sucrose, Lactose or Glucose. My unknown also had similare growth patterns to the S. aureus control when comparing resistance and susceptability to Iodine, Alcohol, H2O2 and Lysol. Just like Staph. aureus it was Susceptable to H2O2, Lysol and Iodine but resistant to Alcohol. This wasn't surprising since S. aureus will grow on Phenyl Ethyl Alcohol agar.