Survival and growth of Enterobacter sakazakii on produce, conditions affecting biofilm formation, and its sensitivity to sanitizers
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Survival and growth of Enterobacter sakazakii on produce and conditions affecting its attachment and biofilm formation were investigated. Sensitivity of the pathogen to sanitizers and disinfectants was determined. E. sakazakii grew on fresh-cut produce and in unpasteurized fruit and vegetable juice stored at 12 and 25°C, and survived at least 5 days but did not grow at 4°C. Populations significantly decreased on whole produce stored at 4, 12, and 25°C. Retention of viability was enhanced at refrigerator temperatures. Treatment of apples, tomatoes, and lettuce ®with chlorine, chlorine dioxide, and Tsunami 200, a peroxyacetic acid sanitizer, caused significant reductions in populations of E. sakazakii, although the extent of lethality depended on the type of produce, sanitizer concentration, and treatment time. Attachment of E. sakazakii to enteral feeding tubes and stainless steel was enhanced at 25°C compared to 12°C. The pathogen formed biofilm on enteral feeding tubes and stainless steel at 25°C when immersed in infant formula broth but not in tryptic soy broth or lettuce juice broth; biofilm was not formed at 12°C. When the surface of stainless steel was spot inoculated with infant formula or water containing E. sakazakii, dried, and exposed to a relative humidity of 43% at 4, 25, and 37°C, the pathogen survived for at least 60 days. Survival was enhanced at 4°C, compared to 25 and 37°C, and when formula rather than water was used as a carrier. The efficacy of sanitizers in killing E. sakazakii in dried inoculum and in biofilm on the surface of stainless steel varied, depending on the composition of the carrier used to suspend cells before drying, type of sanitizer, and treatment time. The overall order of resistance of E. sakazakii to disinfectants routinely used in hospitals, day-care centers, and food service kitchens was planktonic cells < cells spot inoculated and dried on stainless steel < cells in biofilms on stainless steel. This study provides information useful in assessing the potential of produce to serve as a vehicle for E. sakazakii infections, understanding attachment and biofilm formation on abiotic surfaces, and evaluating the effectiveness of sanitizers and disinfectants for its elimination.