Comparison of Vogel-Johnson and Baird-Parker media for membrane filtration recovery of staphylococci in swimming pool water.

Previous studies have indicated that the coagulase-positive Staphylococcus (Staphylococcus aureus) has potential as a useful indicator of the infection hazard associated with the use of swimming pools and other recreational waters. However, before this indicator system can be used effectively, a recovery system that is sufficiently selective, accurate, and reliable for the enumeration of S. aureus must be developed. In this study, Vogel-Johnson (VJ) and Baird-Parker (BP) agars were compared for efficacy in the primary isolation and recovery of S. aureus from swimming pool water. For equal sample volumes of pool water containing adequate free chlorine residual, VJ agar was found to be more selective for staphylococcal species and less inhibitory to general cell growth than was BP agar. However, neither medium was found to be sufficiently differential to permit the accurate identification of S. aureus. In contrast, water samples obtained from a swimming pool containing very low levels of chlorine (none of which was in the free form) showed abundant growth of staphylococci on both test media, with both VJ and BP agars showing increased sensitivity for the detection of S. aureus. Thus, VJ and BP agars show increased sensitivity for the detection of coagulase-positive staphylococci from unchlorinated versus chlorinated waters.