REGULATION OF MULTIDRUG RESISTANCE IN S AUREUS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We have completed the investigation of the response of "golden staph" (S. aureus) to ethanol (Eth). Eth is the active antimicrobial present in the numerous disinfectant hand gels which are often utlized often to reduce the spread of Staphylococcus aureus throughout hospital environments. Our finding support the efficacy of these hand gels by demonstrating that under laboratory conditions, S. aureus cannot become resistant to the ethanol concentrations in hand gels. The highest Eth inhibitory concentration uncovered among 106 clinical S. aureus strains was only 15% and Eth reduced susceptibility (EthRS) mutants step-selected to 15% Eth after ~3 months demonstrated only 1% Eth resistance increases, both levels well below the ethanol levels of hand gels (~60%). The Eth stimulon of two unrelated strains revealed dramatically increased heat shock gene transcription (e.g. clpB, groES, and groEL). Two hundred and fifty nine altered genes were shared between the Eth stimulon and the amino acid starvation stimulon. In support of this finding we found that the addition of certain single amino acids (e.g. arg, lys and leu) to Eth susceptibility broth, led to increased resistance to Eth in all strains investigated. From these findings we were able to conlcude that the Eth susceptibility variability among the strains and the creation of EthRS mutants demonstrates that genetic alteration(s) contribute to the expression of Eth susceptibility levels. Eth static and cidal activity may be due to amino acid starvation, as well as membrane and protein denaturation.