Detection of Fluoroquinolone and other Multi-drug Resistance Determinants in Multi-drug Resistant Non -Typhoidal Salmonella Isolated from Swine

Abstract

Background: Non-typhoidal Salmonella (NTS) is a significant pathogen that causes foodborne diseases in both humans and gastrointestinal illness in animals. The emergence of Multidrug Resistance among these strains is a public health concern.

Aim: The aim of this study was to determine the antibiotic and heavy metal resistance genes in Multi-drug resistant (MDR), Non-Typhoidal Salmonella of swine origin.

Methodology:  In order to detect the determinants of multidrug and fluoroquinolone resistance, we tested for QRDR, Class I integrons and heavy metal tolerance genes in Salmonella isolates of swine originating from Kenya and Ethiopia. 121 Salmonella isolates collected from swine farms in Nairobi, (n=86) and Ethiopia (n=35) were characterized. Antibimicrobial susceptibility tests were done in all isolates against 12 antibiotics. Serogrouping PCR and DNA sequencing was performed for further identification. Minimum Inhibitory Concentration (MIC) of zinc-chloride and copper-sulfate was also done.

Results: 50 (41.3%) of the isolates showed fluoroquinolone resistance. Sequencing for quinolone resistance determining region (QRDR) showed point mutation in gyrA gene at positions Ser83 and Asp87. 87 (71.9%) isolates showed sulfamethoxazole resistance; 10 carried Class I integrons with predominant size being 1.5kb. Some of the integrons carried aadA2, aadA7 and dhfr7 gene cassettes. The isolates subjected to zinc and copper MIC determination, 98% (N=84) were susceptible. Zinc (czcD) and copper genes (pcoA) were not detected.

Conclusion:  Fluoroquinolone resistance predominated the MDR NTS isolates and therefore swine were potential reservoir of antimicrobial-resistant NTS posing a risk in food production chain. Even though all Salmonella serovars, antimicrobial resistance was not correlated with heavy metal tolerance, NTS pose a public health hazard in humans by contact as well.

Keyword: Multidrug resistant Non-typhoidal Salmonella , Fluoroquinolone resistance, Heavy metals, Swine