Sensitivity of Escherichia coli O157:H7 to Commercially Available Alkaline Cleaners and Subsequent Resistance to Heat and Sanitizers

The effects of seven commercially available alkaline cleaners used in the food processing industry, 0.025 M NaOH, and 0.025 M KOH on viability of wild-type (EDL 933) and rpoS-deficient (FRIK 816-3) strains of Escherichia coli O157:H7 in logarithmic and stationary phases of growth were determined. Cells were treated at 4 or 23 degrees C for 2, 10, or 30 min. Cleaners 2, 4, 6, and 7, which contained hypochlorite and <11% NaOH and/or KOH (pH 11.2 to 11.7), killed significantly higher numbers of cells than treatment with cleaner 3, containing sodium metasilicate (pH 11.4) and <10% KOH, and cleaner 5, containing ethylene glycol monobutyl ether (pH 10.4). There were no differences in the sensitivities of logarithmic and stationary-phase cells to the alkaline cleaners. Treatment with KOH or NaOH (pH 12.2) was not as effective as four out of seven commercial cleaners in killing E. coli O157:H7, indicating that chlorine and other cleaner components have bactericidal activity at high pH. Stationary-phase cells of strain EDL 933 that had been exposed to cleaner 7 at 4 or 23 degrees C and strain FRIK 816-3 exposed to cleaner 7 at 23 degrees C had significantly higher D(55 degrees C) (decimal reduction time, minutes at 55 degrees C) values than control cells or cells exposed to cleaner 5, indicating that exposure to cleaner 7 confers cross-protection to heat. Cells of EDL 933 treated with cleaner 7 at 12 degrees C showed significantly higher D(55 degrees C) values than cells of FRIK 816-3, indicating that rpoS may play a role in cross-protection. Stationary-phase cells treated with cleaner 5 or cleaner 7 at 4 or 12 degrees C were not cross-protected against subsequent exposure to sanitizers containing quaternary ammonium compounds or sodium hypochlorite, or to cetylpyridinium chloride and benzalkonium chloride.