Plasmid profile and role in virulence of salmonella enterica serovars isolated from food animals and humans in Lagos Nigeria

ABSTRACT

Infections caused by non-typhoidal Salmonella (NTS) are common around the world, with high morbidity and mortality rates recorded annually. Salmonella serovars harbor plasmids of various sizes which may play roles in antibiotic resistance and virulence. The aim of this study was to profile and determine the role of plasmids in ciprofloxacin resistance and virulence of Salmonella serovars. Using alkaline lysis method 25 NTS serovars from food animals and humans were assayed for plasmids. Isolates ability to resist healthy human serum, bind congo red, produce hemolysin and susceptibility to ciprofloxacin before and after plasmid curing were evaluated. Mobility of plasmids was determined by conjugation. Fifteen (60%) of the 25 Salmonella serovars harbored plasmids with sizes ranging from 0.4 to 38.4 kb. S. Budapest serovars harbored 5–9 plasmids, while S. Essen and S. Mura had six plasmids each. S. Chomedey and a S. Budapest serovar were sensitive to ciprofloxacin after plasmid curing while other serovars remained resistant to ciprofloxacin after plasmid curing. All Salmonella isolates had the ability to withstand human serum before and after plasmid curing, however, some serovars lost their ability to bind congo red after plasmid curing. All Salmonella isolates that initially displayed hemolysin activity retained their ability after curing. Thirteen (86.7%) of the 15 serovars that harbored plasmids conjugatively transferred their plasmids to E. coli K-12 (DH5α). Having Salmonella serovars that harbor transferrable plasmids in the food chain can drive antibiotic resistance and enhanced virulence of otherwise less virulence strains.

KEYWORDS:

• Plasmid
• serovar
• salmonella
• virulence
• ciprofloxacin
• conjugation

Acknowledgments

We thank Dr. Ayorinde James of the Department of Biochemistry, College of Medicine University of Lagos for providing us with the recipient E. coli K-12 (DH5α) for this work.

Disclosure statement

No potential conflict of interest was reported by the authors.

Ethical approval

Ethical approval for this research was obtained from the Human Research and Ethical Committee (HREC) of the Lagos University Teaching Hospital with code number ADM/DCST/HREC/APP/1118 and Nigerian Institute of Medical Research – Institutional Review Board, with project number IRB/12/180.