P-029. Comparison of Resistance to Heat, Ultra High Pressure and Antibiotics among Salmonella Serovars

J. J. Perry, A. E. Yousef;
The Ohio State Univ., Columbus, OH.

Concern regarding the health threat posed by antibiotic-resistant bacteria has risen greatly in recent years. This risk is intimately tied to the food industry due to the widespread use of antibiotics on food animals and the transmission of pathogens from food to humans. Because genes conferring antibiotic resistance are often encoded on mobile DNA elements, the possibility exists for acquisition of resistance in nearly any species, including processing-resistant pathogenic strains. In this study, eighteen Salmonella enterica serovars, including ten Salmonella Enteritidis egg isolates, were tested for tolerance to heat (57°C for < 60 minutes), and ultra high pressure (400 and 500 MPa for one minute). Isolates were also tested for susceptibility to four antibiotics (AMP, CHL, KAN and TET) via the dilution plating method. No significant differences in thermal tolerance (p < 0.05) were observed among isolates. At 400 MPa, Salmonella Anatum and Salmonella Muechen were significantly less resistant to pressure than Salmonella Kentucky and Salmonella Enteritidis ODA 99-30581-13. At 500 MPa, Salmonella Muechen was significantly more sensitive than Salmonella Enteritidis ODA 99-30581-36 and Salmonella Kentucky. Serovars were classified as susceptible, intermediate or resistant to antibiotics according to criteria published by the Clinical and Laboratory Standards Institute (2005). Three strains of Salmonella Typhimurium as well as one each of Salmonella Seftenberg and Salmonella Heidelberg displayed resistance to TET, CHL, and AMP. Salmonella Kentucky also displayed resistance to AMP and intermediate resistance to KAN. All Salmonella Enteritidis strains were susceptible to the antibiotics tested, while all Salmonella Typhimurium strains were resistant to three of four drugs, suggesting a marked difference in acquired resistance between the two serovars. Studies offer conflicting evidence regarding correlations among resistance to different stresses. These data do not prove the association among Salmonella resistances, but demonstrate strong strain variability in response to processing and antibiotic treatment.