Comparison of solid-phase cytometry and the plate count method for the evaluation of the survival of bacteria in pharmaceutical oils.

OBJECTIVE

To compare the survival of four bacterial strains (Escherichia coli, Proteus mirabilis, Staphylococcus aureus, Pseudomonas aeruginosa) in pharmaceutical oils, including jojoba oil/tea tree oil, carbol oil, jojoba oil and sesame oil.

RESULTS

Oils were spiked with the test bacteria in a concentration of 10(4) CFU ml(-1). Bacteria were extracted from oils with phosphate-buffered saline containing 0.5% Tween 20. Aliquots of the pooled water layers were analysed by solid-phase cytometry and plate counting. Plate counts dropped to zero for all test strains exposed for 24 h to three of the four oils. In contrast, significant numbers of viable cells were still detected by SPC, except in the jojoba oil/tea tree oil mixture and partly in sesame oil.

CONCLUSIONS

Exposure of bacteria for 24 h to the two oils containing an antimicrobial led to a loss of their culturability but not necessarily of their viability. The antibacterial activity of the jojoba oil/tea tree oil mixture supersedes that of carbol oil.

CONCLUSIONS

These in vitro data suggest that the jojoba oil/tea tree oil mixture more than carbol oil inhibits bacterial proliferation when used for intermittent self-catherization.