Influence of antibiotic-resistance and exudate on peroxyacetic acid tolerance in O157 and non-O157 Shiga toxin producing E. coli

Shiga toxin producing Escherichia coli (STEC) continues to cause foodborne outbreaks associated with beef and beef products despite consistent use of antimicrobial interventions. In this study, the influence of antibiotic resistance (ABR) in E. coli O157:H7 H1730, O157:H7 43,895, O121:H19 and O26:H11 on tolerance to peroxy-acetic acid (PAA) was evaluated. Further, bactericidal concentrations of PAA in the presence of nutrient rich media (Tryptic Soy Broth, TSB and beef exudates) and nutrient deficient media (Sterile Deionized Water, SDW and Phosphate Buffered Saline, PBS) were evaluated for all bacterial strains. Antibiotic resistance to ampicillin (amp C), or ampicillin and streptomycin (amp P strep C) was generated in each bacterial strain through incre-mental exposure to the antibiotics or by plasmid transformation (n = 12 total strains). The mean bactericidal concentrations of PAA were higher (p <= 0.05) in nutrient rich media (205.55 +/- 31.11 in beef exudate and 195.83 +/- 25.00 ppm in TSB) than in nutrient deficient media (57.91 +/- 11.97 ppm in SDW and 56.66 +/- 9.56 ppm in PBS). Strain O157: H7 ampP strepC was the most tolerant to PAA (p <= 0.05). At 200 ppm in nutrient rich media and 60 ppm in nutrient deficient media, all bacterial strains declined in population to below the limit of detection. Analysis of the beef exudates indicated the presence of diverse amino acids that have been associated with acid tolerance. The results from this study indicate that beef exudates could contribute to acid tolerance and suggest that some STEC bacterial strains with certain ABR profiles might be more tolerant to PAA.