Inactivation of Escherichia coli O157:H7 in biofilm on stainless steel by treatment with an alkaline cleaner and a bacteriophage.
OBJECTIVE
To determine the effectiveness of an alkaline cleaner used in food-processing plants and a lytic bacteriophage specific for Escherichia coli O157:H7 in killing wild type and rpoS-deficient cells of the pathogen in a biofilm.


RESULTS
Wild type and rpoS-deficient cells were attached to stainless steel coupons (c. 7-8 log CFU per coupon) on which biofilms were developed during incubation at 22 degrees C for 96 h in M9 minimal salts media (MSM) with one transfer to fresh medium. Coupons were treated with 100 and 25% working concentrations of a commercial alkaline cleaner (pH 11.9, with 100 microg ml(-1) free chlorine) used in the food industry, chlorine solutions (50 and 100 microg ml(-1) free chlorine), or sterile deionized water (control) at 4 degrees C for 1 and 3 min. Treatment with 100% alkaline cleaners reduced populations by 5-6 log CFU per coupon, a significant (P < or = 0.05) reduction compared with treatment with water. Initial populations (2.6 log CFU per coupon) of attached cells of both strains were reduced by 1.2 log CFU per coupon when treated with bacteriophage KH1 (7.7 log PFU ml(-1)) for up to 4 days at 4 degrees C. Biofilms containing low populations (2.7-2.8 log CFU per coupon) of wild type and rpoS-deficient cells that had developed for 24 h at 22 degrees C were not decreased by more than 1 log CFU per coupon when treated with KH1 (7.5 log PFU ml(-1)) at 4 degrees C.


CONCLUSIONS
Higher numbers of cells of E. coli O157:H7 in biofilms are killed by treatment with an alkaline cleaner than with hypochlorite alone, possibly through a synergistic mechanism of alkaline pH and hypochlorite. Populations of cells attached on coupons were reduced by treating with bacteriophage but cells enmeshed in biofilms were protected.


CONCLUSIONS
The alkaline pH, in combination with hypochlorite, in a commercial cleaner is responsible for killing E. coli O157:H7 in biofilms. Treatment with bacteriophage KH1 reduces populations of cells attached to coupon surfaces but not cells in biofilms.
Sharma
M
M
Center for Food Safety and Department of Food Science and Technology, University of Georgia, 1109 Experiment Street, Griffin, GA 30223-1797, USA.
Ryu
J-H
JH
Beuchat
L R
LR
D000468:Alkalies / Q000737:chemistry*; D001426:Bacterial Proteins / Q000235:genetics; D001435:Bacteriophages; D018441:Biofilms / Q000187:drug effects; D002713:Chlorine / Q000494:pharmacology; D015169:Colony Count, Microbial; D003470:Culture Media; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics; D005516:Food Microbiology; D005798:Genes, Bacterial; D006997:Hypochlorous Acid / Q000494:pharmacology; D016877:Oxidants / Q000494:pharmacology; D010933:Plankton / Q000187:drug effects; D012808:Sigma Factor / Q000235:genetics; D013193:Stainless Steel
D000468:Alkalies; D001426:Bacterial Proteins; D003470:Culture Media; D029968:Escherichia coli Proteins; D016877:Oxidants; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; D013193:Stainless Steel; D002713:Chlorine; D006997:Hypochlorous Acid