Presence of metal-resistance and antibiotic-resistance genes in Salmonella spp. isolated from broiler chicken farms in Vinh Long province, Vietnam

Salmonella can carry multiple antibiotic-resistant and metalresistant genes and transmit these genes among strains worldwide. This study examined seventy-five Salmonella isolates from small-scale chicken farms (chicken feces, bedding, feed, wild animals) in Vinh Long province for the presence and relation of antibiotic and metal-resistance genes in these strains. The single PCR method was applied to detect seven antibiotic-resistance genes (blaampC, blaTEM, dfrA1, tetA, strA, sul2, mcr1) and four metal-resistance genes (pcoR, czcD, cnrA, silE). The results indicated that those Salmonella isolates harbored several patterns of antibiotic-resistance genes. Genes blaampC and tetA were the most prevalent (48.00%), while genes mcr1 and dfrA were the most minor (1.33%). Of those Salmonella isolates, 92.00% harbored one to five antibiotic-resistance genes, and the blaampC + strA pattern was frequently obtained (12.00%). Moreover, 30.67% of Salmonella isolates showed multidrug resistance to three or four antibiotic categories. Among metal-resistance genes, gene pcoR encoding for copper resistance was the most predominant (53.33%), and gene cnrA encoding for cobalt-nickel resistance was the lowest (5.33%). There were diverse patterns of metalresistance genes, and one Salmonella isolate carried four examined genes (1.33%). Furthermore, these Salmonella isolates had several combined patterns of metal-resistance and antibiotic-resistance genes. Among them, pcoR, czcD, and silE genes had a significant coefficient relation to the examined antibiotic-resistance genes. It indicated the correlation between metal resistance and antibiotic resistance genes and revealed the potential risk of increasing antibiotic resistance in Salmonella isolates in chicken farms in Vinh Long province.