Evaluation of Nonpathogenic Surrogate Bacteria as Process Validation Indicators for Salmonella enterica for Selected Antimicrobial Treatments, Cold Storage, and Fermentation in Meat

Abstract

Prerigor lean and adipose beef carcass tissues were artificially inoculated individually with stationary-phase cultures of five nonpathogenic Escherichia coli cultures that had been previously identified as surrogates for E. coli O157:H7 or a mixture of five Salmonella strains in a fecal inoculum. Each tissue sample was processed with microbial interventions comparable with those used in the meat industry. The log reductions of the E. coli isolates were generally not statistically different from the salmonellae inoculum within a specific treatment. Inoculation experiments were also conducted with ground beef stored at either 4 or -20 degrees C. When compared with the Salmonella inoculum, at least three of the five E. coli strains survived in a manner that was not statistically different from the salmonellae. The E. coli strains and the Salmonella mixed culture were also inoculated into summer sausage batter, and the population enumerated both before and after fermentation. Four of the E. coli strains showed a lower population reduction (higher survival) than the Salmonella mixed culture. The five nonpathogenic E. coli strains may be used as individually or collectively for specific process validation indicators for Salmonella.

Reduction of Surrogates for Escherichia coli O157:H7 and Salmonella during the Production of Nonintact Beef Products by Chemical Antimicrobial Interventions

“…Mutants of these isolates were selected based on resistance to 100 mg/liter rifampin by incubating and growing the microorganisms in the presence of this antibiotic and then selecting for isolates with stable resistance (Rif*) using previously published procedures (17,41). Previous research (4,22,24) has revealed that these isolates have lactic acid and thermal tolerances similar to those of E. coli 0157:H7 and five serovars of Salmonella enterica subsp. enterica.…”

Antimicrobial Efficacy of a Lactic Acid and Citric Acid Blend against Shiga Toxin-Producing Escherichia coli, Salmonella, and Nonpathogenic Escherichia coli Biotype I on Inoculated Prerigor Beef Carcass Surface Tissue

“…Four inoculum mixtures were used in the laboratory study: (i) a 5-strain mixture of rifampin-resistant E. coli O157:H7 (Table 1), (ii) a 12strain mixture of rifampin-resistant non-O157 STEC (two strains each of serogroups O26, O45, O103, O111, O121, and O145; Table 1), (iii) a 6-strain mixture of Salmonella (Table 1), and (iv) a 5-strain mixture of rifampin-resistant nonpathogenic E. coli biotype I (ATCC BAA-1427, ATCC BAA-1428, ATCC BAA-1429, ATCC BAA-1430, and ATCC BAA-1431 (21,25,27)) that could serve as surrogates for E. coli O157:H7, non-O157 STEC, and Salmonella spp. Spontaneous rifampin-resistant mutants of the E. coli O157:H7, non-O157 STEC, and nonpathogenic E. coli strains were used for selection and differentiation of the inocula from natural meat-associated microbial populations.…”

“…Using pathogen testing or natural meat microflora to verify process control may be difficult due to the low number of bacterial cells naturally present on products (2). The use of high levels of nonpathogenic surrogate microorganisms that mimic the behavior of specific pathogens may be a helpful mechanism to validate efficacy of a food safety intervention in a commercial beef harvest facility and to provide evidence that a system is working properly (2,11,18,21,22,25,27). One antimicrobial that is composed of a combination of lactic acid and citric acid has not been adequately researched to provide validating evidence to beef processing facilities in regard to its effectiveness against pathogens.…”

Radiofrequency pasteurization of inoculated ground beef homogenate

“…All isolates were obtained from cattle and known to exhibit characteristics relatively similar to E. coli O157:H7 (Niebuhr, Laury, Acuff and Dickson, 2008;Marshall, Niebuhr, Acuff, Lucia and Dickson, 2005).…”