Identification of antimicrobial susceptibility of foodborne Salmonella and related plasmid

Abstract:

[Objective] We tested the antimicrobial susceptibility of 390 Salmonella isolates. We also studied the relationship between plasmids in some multidrug resistant Salmonella isolates and the antibiotic resistance profile of their hosts, as well as conjugation test of some multidrug resistant Salmonellas. [Methods] Salmonella strains were isolated by using selective cultures, putative Salmonella was confirmed by PCR. Antimicrobial susceptibility was tested according to the National Committee for Clinical Laboratory Standards. Plasmid of some representative multidrug resistant strains was isolated by using QIAGEN Plasmid Mini Kit and digested with HindⅢ. The plasmid profiles were acquired by gel electrophoresis and analyzed by DPS. The conjugation test was done to illustrate the function of plasmid during the antibiotic resistance transfer. [Results] Of the Salmonella isolates, 58.2% were resistant to tetracycline, followed by resistance to streptomycin (42.8%), kanamycin (39%), ampicillin (38.2%), cefoxitin (27.2%), chloramphenicol (26.9%), gentamicin (21%), ceftriaxone (19%), amoxicillin-clavulanic (18.2%), trimethoprim-sulfamethoxazole (17.9%), ceftiofur (14.6%) and nalidixic acid (12.3%). There was no strict corresponding relationship between antibiotic resistance profile of the host Salmonella and its plasmid profile. The conjugation frequency of the plasmid was from 2.4×10-4 to 5.6×10-1. [Conclusion] Antimicrobial resistance is common in foodborne Salmonella, direct relativity does not exist between the homology of plasmids and their hosts’ antibiotic resistance phenotype, antibiotic resistant genes in the plasmid can transfer from donor to the recipient in interspecies and intraspecies with high frequency accompanying conjugation.