Improved selectivity for Staphylococcus from water utilizing lipovitellenin salt mannitol agar as a base medium

Bibliography: pages [88]-94.The presence of staphylococci in public water systems is cause for concern because of the potential pathogenicity of the organism. Recovery of staphylococci from water for enumeration and identification has been recognized as a reasonable means for evaluating contact water quality in terms of human contamination. The currently utilized media, however, have been criticized for inadequate recovery of organisms and lack of selectivity for staphylococci. Previous work using lipovitellenin salt mannitol agar with 0.005% sodium azide (M5LSM) has been shown to successfully recover 85% of the Staphylococcus aureus present when using membrane filtration and incubating at 32°C for 48 hours. This methodology suppresses the growth of bacilli and yeast, allowing only the Gram-positive cocci to grow. In this study, it was found that the recovery of staphylococci is markedly affected by the stage of growth of the organisms, temperature, and suspending fluid. Greater than 99% recovery of staphylococci on this medium was attained when log phase organisms suspended in 1% peptone water held at 2°C were tested. Addition of 0.3 to 0.5% lithium chloride completely suppressed the growth of Staphylococcus faecalis without affecting the percentage recovery of the staphylococci when the organisms are in log phase, making the medium selective for staphylococci. Environmental testing found 88% of the organisms recovered on M5LSM with 0.4% lithium chloride (M5LSM4) to be catalase positive, Gram-positive cocci, further differentiated to 68% Staphylococcus spp. and 20% Micrococcus spp. Eight percent of the remaining organisms were Gram-positive rods, 2% Staphylococcus spp., 1% Gram-negative rods, and 1% yeast. The few streptococci recovered on the M5LSM4 were found to represent only 1.1% of the streptococci actually present in the sample. This shows greater than 98% suppression of the environmental streptococci using this medium.M.S. (Master of Science