Radiation sensitivity and inactivation of antibiotic-resistant Salmonella spp. in fresh chicken legs

In the Philippines, a total of 21,000 typhoid cases with 40 deaths caused by Salmonella typhi were reported in 2016. Previous studies have shown that multi-drug resistant Salmonella (MDRS) exists in fresh chicken meat purchased from retail stalls and supermarkets. MDRS has become a global health concern because of its resistance to treatment with the usual battery of antibiotics. Some studies show that gamma irradiation can eliminate antibiotic-resistant bacteria in food. This study was aimed at determining the radiation sensitivity and inactivation of antibiotic-resistant Salmonella spp. in fresh chicken legs. In phase one, four strains of freshly prepared Salmonella spp. were identified for resistance/susceptibility using disk diffusion method and minimum inhibitory concentration (MIC) with a different spectrum of Ampicillin (AMP), Chloramphenicol (CHL), Gentamicin (GN), Tetracycline (TET) Sulfamethoxazole/Trimethoprim (STX), based on the breakpoints established by CLSI (Clinical and Laboratory Standards Institute). Results showed that the S. enterica ser. Enteritidis 1963, S. enterica ser. Typhi 1768 and S. enterica ser. Typhimurium 1741were resistant to AMP and GN, while S. enterica ser. Typhimurium ATCC 14028 was resistant to GN. In phase two, the freshly prepared pure strains of antibioticresistant Salmonella spp. were grown in tryptic soy broth (TSB) for 24 h, centrifuged, and cell pellets were resuspended in phosphate buffer saline (PBS) and adjusted at 0.5 McFarland (1.0 x 108 CFU per mL). One ml of Salmonella spp. was inoculated into fresh chicken meat then irradiated at different doses of control (0, 0.2, 0.4, 0.6, 0.8 1.0, and 2.0 kGy) at the Gamma Irradiation Facility of the Philippine Nuclear Research Institute. The D10values, for the four strains of Salmonella, ranged from 0.14 to 0.19 kGy. This indicates that low dose radiation can induce a 1-log reduction of Salmonella spp. in fresh chicken legs and at 2 kGy doses, effectively eliminate the Salmonella spp. by 6 logs cycle. The four strains of Salmonella were mostly resistant to AMP and GN. Therefore, S. enterica serovar Enteritidis 1963, S. enterica serovar Typhi 1768, and S. enterica serovar Typhimurium 1741 exhibited multi-drug resistance. Gamma radiation can be used as a feasible technique to inactivate the presence of Salmonella spp. including the antibiotic-resistant Salmonella in fresh chicken meat.