Detection of Multiple Drug Resistance and Complex Class I Integrons in Salmonella in Fresh Food
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Abstract:
Salmonella isolates from fresh food were subjected to resistant phenotype testing using the disk diffusion method, serotyping via slide agglutination, and sequence type analysis via the multilocus sequence typing (MLST) method. Class I integrons, ISCR1, and their gene cassettes in multidrug-resistant Salmonella were analyzed via PCR and sequence alignment. A total of 32 multidrug-resistant strains were detected, and the multidrug resistance rate among all strains was 48.48%. The multidrug-resistant strains were divided into 11 serotypes, with S. Thompson (21.88%) and S. Agona (18.75%) being the dominant serotypes. Using the MLST method, the multidrug-resistant strains were divided into 15 sequence types (STs), with the dominant STs being ST26 (21.88%) and ST13 (12.50%). Among the multidrug-resistant strains, the detection rate of class I integrons was 43.75% (14/32), with drug resistance gene cassettes amplified in five isolates (5/14, detection rate: 35.71%); the detection rate of ISCR1 was 34.38%, (11/32), with drug resistance gene cassettes amplified in four isolates (4/11, detection rate: 36.36%). Both genetic elements (complex class I integron and ISCR1) were present in nine strains (9/32, detection rate: 28.13%). The majority of detected gene cassettes contained one or two drug resistance genes, which correlated well with the resistant phenotypes. Through sequence comparison using BLAST, it was found that the resistance gene cassette of the class I integron in Strain No. 28 was homologous to the Nsa217 plasmid of Salmonella and the KP15-2-53 plasmid of Klebsiella pneumoniae. Our results indicate that the drug resistance of Salmonella in fresh food products is relatively strong, and that multidrug resistance in Salmonella is related to the complex class I integrons harbored by the strains.
