Survival of Staphylococcus aureus in oral administration liquid medicaments and influence of count medium on survival.

ABSTRACT

The survival of Staphylococcus aureus was studied in 30 oral administration liquid medicaments (15 syrups and 15 solutions) to determine the effectiveness of the preservatives, the influence of the culture medium used in the enumeration of the surviving microorganisms, and the loss of the enzyme coagulase, phosphatase, DNase (deoxyribonuclease), and thermonuclease. Samples were inoculated with 6.3-6.5 x 10(5) viable cells per milliliter and were stored at room temperature for 60 days. Aliquots were taken for analysis at 0, 15, 22, 30, and 60 days after samples were inoculated. The enumeration of S. aureus was made by most probable number method (MPN) with six liquid culture media triptone soy (TS), TS with 10% NaCl (TSS), TS and TSS with 0.2% catalase, Mannitol salt, and Tellurite-mannitol-glycine. The survival of S. aureus was lower in solutions than in syrups, decreased with the storage time, and depended on the culture medium utilized in the enumeration. Nonselective media were more sensitive than selective ones; that is, a better percentage of recovery was achieved with TS and the catalase medium. The preservative was effective in 93.3% of the samples. Coagulase was the most stable enzyme and phosphatase, DNase, and thermonuclease disappeared during the storage period.