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

Abstract

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°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°C and strain FRIK 816-3 exposed to cleaner 7 at 23°C had significantly higher D 55°C (decimal reduction time, minutes at 55°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°C showed significantly higher D 55°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°C were not cross-protected against subsequent exposure to sanitizers containing quaternary ammonium compounds or sodium hypochlorite, or to cetylpyridinium chloride and benzalkonium chloride.

Functional Heterogeneity of RpoS in Stress Tolerance of Enterohemorrhagic Escherichia coli Strains

“…There are conflicting reports in the literature on the involvement of RpoS in alkali tolerance of E. coli (45,46). We observed that with prior exposure to alkaline pH (i.e., growth in either LB or LB-MOPS), cells induce rpoS-independent mechanisms which seem to play a major role in protecting cells from alkali shock.…”

Inactivation of Escherichia coli O157:H7 in biofilm on stainless steel by treatment with an alkaline cleaner and a bacteriophage

“…Biofilms may protect cells through a combination of mechanisms, including diffusional resistance of the EPS matrix, chemical and enzymatic inactivation of sanitizers and disinfectants, physiological changes in cells, and the induction of stress responses in cells (Gilbert et al 2002). Strong alkaline cleaners containing hypochlorite have been shown to be effective in killing planktonic cells of E. coli O157:H7 (Sharma and Beuchat 2003) but little is known about the ability of alkaline cleaners to inactivate E. coli O157:H7 in biofilms.…”

Effectiveness of Disinfectants in Killing Enterobacter sakazakii in Suspension, Dried on the Surface of Stainless Steel, and in a Biofilm

“…The microbicidal activity of commercial surface cleaners and disinfectants is largely based on quaternary ammonium compounds, phenolic compounds, organic acids, alcohols, chlorine, and iodophors. Various commercial hard-surface cleaners and disinfectants have been evaluated for their efficacy in killing bacteria capable of causing food-borne infections (15,45,49,53). During infant formula preparation and feeding, reconstituted formula containing E. sakazakii may contaminate abiotic surfaces.…”