Recovery of multi-drug resistant, multiple antibiotic resistance genes-carrying non-typhoidal Salmonella from antibiotic-free and conventional chicken meat: A comparative study in Delhi, India

Food-associated Salmonella spp. are regularly implicated in diarrhoeal illnesses. Emergence of antibiotic resistance (AR) among Salmonella enterica (S. enterica) has become a global healthcare problem, necessitating an AR risk assessment along the food-chain network. Considering the growing trend of selling alternatively labelled meat products in low- and middle-income countries like India, a comprehensive evaluation of AR in non-typhoidal Salmonella (NTS) isolates associated with antibiotic-free (AF) labelled chicken meat was carried out. Additionally, the resistance profile of AF chicken meat-derived microbes was compared to the conventional (CL) chicken meat-derived ones. Results highlighted high degree of resistance in AF-derived NTS isolates to tetracycline (87.0 %), nalidixic-acid (53.0 %) and ampicillin (41.0 %), and moderate degree of resistance to imipenem (28.0 %), co-trimoxazole (27.0 %), cefazolin (23.0 %) and ciprofloxacin (15 %). Horizontally-transmissible AR genes (ARGs), such as, tetA (77.0 %), qnrS (53.0 %), ampC (41.0 %), sul3, (21.0 %) etc. were also prevalent among screened isolates. Overall, 74.0 % of S. enterica were multi-drug resistant (MDR) and 45.0 % harboured ≥ 3 ARGs. There was no difference in resistance profile and multiple antibiotic resistance (MAR) index of isolates derived from AF and CL chicken meat (two-way ANOVA, unpaired t-test, respectively; p < 0.05). Correlation analysis showed a positive relationship between various AR phenotypes and ARGs that provide the corresponding resistance (p < 0.05). This means that the prevalence of positively correlating ARGs could be used to predict physical resistance. Our study illustrates that choosing AF chicken meat in markets of Delhi may not effectively minimise the exposure of resistant NTS to consumers. Observations also recommend a systematic AR risk assessment of foodstuffs across the region for a more informed assistance to the authorities in distributing relevant labels to food products.