A modified medium for the recovery of Staphylococcus from water

Various contemporary methods available for recovering staphylococci from water were evaluated as to quantitative recovery and degree of selectivity. Each of the methods tested was found to be somewhat inadequate for the selective isolation of staphylococci from water in this area. A modified medium is being proposed which incorporates 0.005% sodium azide into a mannitol salt agar base. This medium when used with a membrane filter procedure and incubated at 32 degrees C for 48 h recovers 85% of Staphylococcus aureus, 88% of Staphylococcus epidermidis, and 100% of Staphylococcus saprophyticus present. Environmental testing in this area indicates that this modified procedure will recover only Gram-positive, catalase-positive cocci. Ninety percent of these cocci are Staphylococcus as ascertained by the lysostaphin susceptibility test.