Rational approach towards improving the predictive effectiveness of official antimicrobial challenge tests

ABSTRACT

Comparative resistance of naturally occurring strains of Pseudomonas aeruginosa and E. coli and type cultures of the same species to the preservatives was assessed. Some of the factors affecting their responses were also examined. The results indicated that minimum bactericidal concentration value [MBC] of E. coli ATCC 8739 and Pseudomonas aeruginosa ATCC 9027 were much lower than those of the environmental strains. This suggested that type culture organisms should be cultivated in conditions relevant to actual environmental in the pharmaceutical and cosmetic production field where they are subjected to starvation and many other stresses. The comparison between the usual pharmacopoeial cultivation method and multinutrient starved in different dilutions of trypticase soy agar showed that starved organisms had much higher D-values. The D-values of starved organisms increased with increasing of TSB dilution up to 10[-3]. Most air conditioned area in production field are adjusted at 20-25°C. Growth of starved organisms at 23°C showed highest homogeneous antimicrobial response curve. Thus this study suggested usage of multinutrient starved organisms. The results showed that the starved type culture strains were more aggressive than strains isolated from contaminated batches of the above products or from their water for preparation. While the nutrient amended ATCC type strains showed the least aggressiveness ability. The significance of these findings may alter the present concept of preservation testing systems as well as routine control procedures in cosmetic and pharmaceutical preparations