Recovery and identification of staphylococci from water using a modified lipovitellenin salt mannitol medium
Jacoby, Lawrence H.
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A modified lipovitellenin salt mannitol medium incorporating 0.005% sodium azide (5mLSM) was used to selectively recover staphylococci from water. The pH and agar volumes of the medium were adjusted to evaluate these effects on recovery. A pH of 6.6 prior to autoclaving was found to be necessary in order to achieve optimum selectivity. At that pH, 5mLSM successfully eliminated more than 90% of the Gram-positive rods and 99% of yeasts present in environmental samples. Catalase-positive, Gram-positive cocci recovered on membrane filters were selected for further testing. Lysostaphin susceptibility, a modified glucose oxidation-fermentation test and growth in thioglycollate medium were used to differentiate staphylococci from micrococci. The modified Hugh-Leifson test for glucose oxidation-fermentation was most accurate in resolving the staphylococci, as 91% of these isolates were positive for this test. The lysostaphin susceptibility test correctly discerned 95% of the non-staphylococci that were recovered. A modified version of the Kloos and Schleifer (KEY) Scheme was subsequently employed to speciate the staphylococci. S. epidermidis was the most frequently isolated species, and members of that species group were dominant among identified isolates in six of seven sampling categories.