Q-282. Bacterial Resistance within Endoscope Washer Disinfectors and their Survival Mechanisms

D. J. H. Martin1, G. McDonnell2, S. P. Denyer1, J-Y. Maillard1;
1Cardiff Univ., Cardiff, UNITED KINGDOM, 2Steris Ltd, Basingstoke, UNITED KINGDOM.

Background Persistent bacterial strains were isolated from washer-disinfectors used for the reprocessing of flexible endoscopes. The efficacy of high-level oxidising disinfectants (chlorine dioxide-, peracetic acid- and hydrogen peroxide-based) against these persistent bacteria and their resistance mechanisms that allow for survival following exposure were studied. Methods The effects of various oxidising agents on isolate survival were tested using a standard carrier test method. Isolates that showed unexpected resistance to in-use contact times and concentrations were studied to understand their mechanisms of survival and resistance. These investigations included scanning and transmission electron microscopy (EM), Q-PCR investigating possible resistance genes expression, and penetration studies, looking particularly at the role of the extracellular polysaccharide matrix (EPS) of the resistant isolates. Results Two bacterial isolates (Bacillus subtilis and Micrococcus luteus) were shown to have high resistance to chlorine dioxide. The vegetative B. subtilis isolate showed resistance to chlorine dioxide at a higher than recommended in use concentration and cross-resistance with other oxidizing agents. EM investigation highlighted significant structural differences between isolates and control strains that may account for the resistance phenotype. The B. subtilis isolate was prone to clumping and the associated large quantity of EPS was likely to be interfering with the oxidizing agent activity. The M. luteus isolate demonstrated different resistance mechanism(s). Genes for catalase and superoxide dismutase were present in B. subtilis; these genes are currently under investigation with Q-PCR to establish whether upregulation occurs following biocide exposure. Conclusions This study demonstrated that bacteria can survive high-level disinfection. In this study, two chlorine-dioxide resistant isolates were identified. The mechanism(s) of resistance appeared to be different, highlighting the propensity and diversity in the ability of bacteria to adapt to adverse environmental conditions.