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

Abstract

Aims: 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. Methods and 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°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 11AE9, with 100 lg ml )1 free chlorine) used in the food industry, chlorine solutions (50 and 100 lg ml )1 free chlorine), or sterile deionized water (control) at 4°C for 1 and 3 min. Treatment with 100% alkaline cleaners reduced populations by 5-6 log CFU per coupon, a significant (P £ 0AE05) reduction compared with treatment with water. Initial populations (2AE6 log CFU per coupon) of attached cells of both strains were reduced by 1AE2 log CFU per coupon when treated with bacteriophage KH1 (7AE7 log PFU ml )1 ) for up to 4 days at 4°C. Biofilms containing low populations (2AE7-2AE8 log CFU per coupon) of wild type and rpoS-deficient cells that had developed for 24 h at 22°C were not decreased by more than 1 log CFU per coupon when treated with KH1 (7AE5 log PFU ml )1 ) at 4°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. Significance and Impact of the Study: 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.

Bacteriophage-Mediated Dispersal of Campylobacter jejuni Biofilms

“…Clearly a formal mathematical model, based on morerefined data, will need to be developed to properly understand the kinetic properties of the system. Bacteriophages have been shown to diffuse through the biofilms of other bacteria (6), and it has also been reported that biofilm formation does not provide additional protection against bacteriophage attack (43). Our data support these observations, since campylobacters within the biofilm are subject to bacteriophage-mediated lysis.…”

“…Moreover, engineered bacteriophage enzymes have been employed to disperse biofilms by breaking down components of the extracellular polymeric matrix (30). However, when stainless-steel-adherent Escherichia coli O157:H7 cells were treated with bacteriophages, there was a reduction in the viability of the exposed adhered cells but not in the cells within the biofilm itself (43).…”

Bacteriophages Reduce Experimental Contamination of Hard Surfaces, Tomato, Spinach, Broccoli, and Ground Beef by Escherichia coli O157:H7

“…Bacteriophages have been used to decontaminate bacterially contaminated hospital rooms in the Soviet Union (A. Meiphariani, personal communication). However, with the exception of one recent study (35) that examined the value of using an E. coli O157:H7-specific bacteriophage to kill wild-type and rpoS-deficient cells of E. coli O157:H7 attached to coupons, rigorous scientific data demonstrating the efficacy of phage treatment for reducing E. coli O157:H7 contamination of inanimate hard surfaces is not readily available. The results of our studies support the idea that E. coli O157:H7-specific lytic bacteriophages significantly reduce contamination of inanimate hard surfaces by E. coli O157:H7, even when the bacteria are surrounded by dried organic matter.…”

“…More recently, O'Flynn et al (33) observed that a mixture of three E. coli O157:H7-specific phages eliminated E. coli O157:H7 from the surfaces of seven of nine specimens of sliced, experimentally contaminated beef. Also, E. coli O157:H7-specific phages were effective in reducing the concentrations of E. coli O157:H7 (i) in the gastrointestinal tracts of mice (40) and ruminants (36) and (ii) on stainless steel coupons (35). The goal of the studies described in this communication was to determine whether treatment with E. coli O157:H7-specific phages significantly reduces the number of viable E. coli O157:H7 cells on experimentally contaminated (i) inanimate surfaces that mimic those of various types of building materials and (ii) foods with various textures.…”

Evaluation of the efficacy of commercial sanitizers against adhered and planktonic cells of Listeria monocytogenes and Salmonella spp.

“…However, the formation of a biofilm starts with the attachment of bacteria to the surface. Sharma, Ryu and Beuchat (2005) found differences in sensibility to disinfectants of Escherichia coli O157:H7 attached to stainless steel or embedded in a biofilm. Sagripanti and Bonifacino (2000) showed that the increased resistance of attached Pseudomonas aeruginosa to treatment with disinfectants precedes biofilm formation.…”