Evaluation of Non-Pathogenic Surrogate Bacteria As Process Validation Indicators for Salmonella Enterica
Iowa State University, Department of Animal Science
Texas A&M University, Department of Animal Science
S. E. Niebuhr, A. Laury, G. R. Acuff, and J. S. Dickson
To compare the responses of several non-pathogenic Escherichia coli surrogate bacteria strains to the response of a mixed culture of Salmonella to various meat processes to determine which, if any, of the non-pathogenic surrogates could be used for process validation for the reduction of Salmonella on meat.
Pre-rigor lean and adipose beef carcass tissue was artificially inoculated individually with stationary phase cultures of the five non-pathogenic E. coli cultures or a mixture of five Salmonella strains in a fecal inoculum. Each tissue sample was processed with the following microbial interventions: 90° C water; 90° C water followed by 55° C 2% lactic acid; 90° C water followed by 20° C 2% lactic acid; 20° C water followed by 20° C 2% lactic acid; 20° C water followed by 20° C 20ppm chlorine; 20° C water followed by 20° C 10% trisodium phosphate. The log10 reductions of the E. coli isolates were generally not statistically different from the Salmonellae inoculum within a specific treatment.
Similar inoculation experiments were conducted with ground beef stored at either 4° C or -20° C. When compared to the Salmonella inoculum, at least three of the five E. coli strains survived in a manner which was not statistically different from the Salmonellae. The E. coli strains and the Salmonellae 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) that the Salmonella mixed culture. Potentially several of the non-pathogenic E. coli strains may be used either individually or collectively for specific process validation indicators for Salmonella.
This study demonstrates that some of the non-pathogenic surrogate E. coli, either individually or collectively, have the potential to be used to validate meat processes for the reduction of Salmonella. These cultures may allow a small or very small processing establishment to internally validate their own processes for Salmonella reduction. Potentially, by being able to do this in-house in lieu of paying for an outside lab to conduct tests may make it cost effective and thus could be of particular value to small and very small plants. This research could decrease their operating cost while helping them to ensure food safety and public health protection. However, plants will need to validate that their methodology achieves these parameters.
The full report on this research can be found on the Fiscal Year 2005 table under the column Food Safety Technologies - Additional Information.