Model studies on a membrane filtration method for the enumeration of coagulase-positive staphylococci in swimming-pool water using rabbit plasma-bovine fibrinogen agar.

The recovery of Staphylococcus aureus from swimming-pool water by membrane filtration was studied in model experiments. On the nonselective medium tryptone soya agar (TSA) there was no difference in counts of noninjured S. aureus with all membrane filters tested and with pour plates. Chlorine-injured S. aureus was enumerated most efficiently on TSA by Gelman Tuffryn HT-450 and Sartorius SM 13806 filters. Tuffryn filters were also most productive when used in combination with the selective medium rabbit plasma - bovine fibrinogen agar (RPFA). Other filters, particularly Gelman GN-6 and Millipore HAWP, when used on RPFA were shown to have a synergistic inhibitory effect on both noninjured and chlorine-injured S. aureus. This effect was not found on Baird-Parker agar. Using Tuffryn filters, counts on RPFA were equal to those on TSA for noninjured S. aureus and 0.1-2.0 log units less for chlorine-injured S. aureus. Despite this, the possibility for reading the in situ coagulase reaction for individual colonies on RPFA is considered such an advantage of this medium that its general use for enumeration of S. aureus in swimming pools is recommended. Further studies should be carried out to allow better resuscitation.