Environmental testing of improved lipovitellenin salt mannitol agar for the isolation of Staphylococcus aureus from water
Van Hoeck, Kathlyn L.
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The presence of staphylococci in water is of concern due to their potential pathogenicity and the ease with which this organism finds its way into the water supply. Their value as indicators of contact water quality has been recognized for some time; however, a suitable method for recovering and isolating the organism from water has been a major reason for its lack of use. Lipovitellenin salt mannitol agar containing 0.005% sodium azide and 0.4% lithium chloride, also known as m5LSM4, was tested against Trypticase soy agar for its ability to recover environmentally stressed Staphylococcus aureus. A suspension of 5L_ aureus was put into a McFeters chamber and suspended in a four-liter beaker of river water on a magnetic mixer for 48 hours. Although only 11% of the original population survived the exposure period, the m5LSM4 recovered an average of 92% of the organisms that remained viable. Two broths were tested for their ability to allow stressed S_j_ aureus to repair any injury incurred during the 48 hours of exposure to environmental water. The percent recovery of organisms on m5LSM4 before incubation in Trypticase soy broth was 85% or greater. Organisms incubated during a four-hour repair period showed little improvement in this recovery. When grown in Bacto-m- Staphylococcus broth, recovery was very erratic over the same period. These results indicate that incubation in broth before inoculation is not necessary with this medium and may even prove deleterious, depending on the broth that is chosen. Catalase added to the surface of the plates did little to improve recovery. The medium was poured with and without egg yolk to determine its effect on recovery. After 48 hours of environmental contact, there was 17% recovery of the organism on the medium without egg yolk, compared to 90% recovery on the medium with egg yolk. Therefore, it appears that egg yolk is a major protective factor in the isolation of Staphylococcus aureus from the environment.