Prevalence of virulence and antimicrobial resistance genes in Salmonella spp. isolated from commercial chickens and human clinical isolates from South Africa and Brazil

Abstract

Salmonellosis is a significant public health concern around the world. The injudicious use of antimicrobial agents in poultry production for treatment, growth promotion and prophylaxis has resulted in the emergence of drug resistant strains of Salmonella. The current study was conducted to investigate the prevalence of virulence and antimicrobial resistance genes from Salmonella isolated from South African and Brazilian broiler chickens as well as human clinical isolates. Out of a total of 200 chicken samples that were collected from South Africa 102 (51%) tested positive for Salmonella using the InvA gene. Of the overall 146 Salmonella positive samples that were screened for the iroB gene most of them were confirmed to be Salmonella enterica with the following prevalence rates: 85% of human clinical samples, 68.6% of South African chicken isolates and 70.8% of Brazilian chicken samples. All Salmonella isolates obtained were subjected to antimicrobial susceptibility testing with 10 antibiotics. Salmonella isolates from South African chickens exhibited resistance to almost all antimicrobial agents used, such as tetracycline (93%), trimethoprim-sulfamthoxazole (84%), trimethoprim (78.4%), kanamycin (74%), gentamicin (48%), ampicillin (47%), amoxicillin (31%), chloramphenicol (31%), erythromycin (18%) and streptomycin (12%). All samples were further subjected to PCR in order to screen some common antimicrobial and virulence genes of interest namely spiC, pipD, misL, orfL, pse-1, tet A, tet B, ant (3")-la, sul 1 and sul. All Salmonella positive isolates exhibited resistance to at least one antimicrobial agent; however, antimicrobial resistance patterns demonstrated that multiple drug resistance was prevalent. The findings provide evidence that broiler chickens are colonised by pathogenic Salmonella harbouring antimicrobial resistance genes. Therefore, it is evident that there is a need for prudent use of antimicrobial agents in poultry production systems in order to mitigate the proliferation of multiple drug resistance across species.

Keywords: Salmonella; antimicrobial resistance; chicken; human; susceptibility; virulence gene..

FIGURE 1

Detection of the 284 bp invA gene amplicon from eight representative Salmonella isolates by agarose gel electrophoresis.

FIGURE 2

Detection of the 606 bp iroB gene amplicon from nine representative Salmonella isolates by agarose gel electrophoresis.

FIGURE 3

Detection of the 309 bp spiC gene amplicon from eight representative Salmonella isolates by agarose gel electrophoresis.

FIGURE 4

Detection of the 550 bp misL gene amplicon from seven representative Salmonella isolates by agarose gel electrophoresis.

FIGURE 5

Detection of the 350 bp orfL gene amplicon from nine representative Salmonella isolates by agarose gel electrophoresis.

FIGURE 6

Detection of the 400 bp pipD gene amplicon from nine representative Salmonella isolates by agarose gel electrophoresis.

FIGURE 7

Detection of the 412 bp pse-1 gene amplicon from eight representative Salmonella isolates by agarose gel electrophoresis.

FIGURE 8

Detection of the 526 bp ant (3”)-la gene amplicon from eight representative Salmonella isolates by agarose gel electrophoresis.

FIGURE 9

Detection of the 210 bp tet A gene amplicon from seven representative Salmonella isolates by agarose gel electrophoresis.

FIGURE 10

Detection of the 659 bp tet B gene amplicon from four representative Salmonella isolates by agarose gel electrophoresis.

FIGURE 11

Detection of the 350 bp sul 1 gene amplicon from seven representative Salmonella isolates by agarose gel electrophoresis.

FIGURE 12

Detection of the 720 bp sul 2 gene amplicon from eight representative Salmonella isolates by agarose gel electrophoresis.