Occurrence, drug resistance, and virulence genes of Salmonella isolated from chicken and eggs

Salmonella is considered one of the most important foodborne pathogens and is commonly associated with the consumption of eggs, chicken meat, chicken intestines and other animal products. Multidrug resistant (MDR) Salmonella strains are highly adaptive and have been responsible for several foodborne disease outbreaks. We investigated the genetic relatedness, antibiotic resistance and virulence genes of 160 strains which were recovered from 920 samples. The samples were collected from the chicken intestines and eggs in their environment in the wet markets and chicken farm in Jiang Su province of China. Of the total 920 samples analysed, 160 (17.4%) were positive for Salmonella. 61 (61/440) strains were detected in egg samples and 99 (99/480) strains detected in chicken intestine samples. The detection rates of Salmonella were different in different months and at different sampling sites. The resistance of 160 Salmonella strains to 16 antibiotics was detected by the agar disk diffusion method. The isolates from chicken intestines and eggs were more resistant to sulfamethoxazole (SMZ), ceftriaxone (CRO), nalidixic acid (NAL), cefazolin (CFZ), and amoxicillin (AMX). In addition, the strains isolated from eggs were relatively resistant to gentamicin (GEN) and kanamycin (KAN), while the strains isolated from chicken intestines were relatively resistant to ciprofloxacin (CIP) and tetracycline (TET). Salmonella strains isolated from eggs were mostly resistant to 2-5 antibiotics, and eight strains were resistant to six or more antibiotics. Salmonella strains isolated from eggs were mostly resistant to 2-5 antibiotics, and eight strains were resistant to six or more antibiotics. Salmonella isolates from chicken intestines were resistant to 3-7 antibiotics, nine strains were resistant to eight or more antibiotics, and only one strain were resistant to 10 antibiotics. Thirty-four strains of multi-drug-resistant Salmonella were tested for 15 kinds of drug resistance genes and 33 virulence genes by Polymerase Chain Reaction (PCR) amplification. Of these, 10 strains had seven or more drug resistance genes and six of them were found to have more than 20 virulence genes. Finally, 10 strains of highly resistant and pathogenic Salmonella were screened out.