Virulence and genotypic characterization of Listeria monocytogenes isolated from vegetable and soil samples

Abstract

Background: Listeria monocytogenes, a foodborne pathogen is ubiquitous to different environments including the agroecosystem. The organism poses serious public health problem. Therefore, an attempt has been made to gain further insight to their antibiotic susceptibility, serotypes and the virulence genes.

Results: Out of the 10 vegetables selected, 6 (brinjal, cauliflower, dolichos-bean, tomato, chappan-kaddu and chilli), 20 isolates (10%) tested positive for L. monocytogenes. The prevalence of the pathogen in the respective rhizosphere soil samples was 5%. Noticeably, L. monocytogenes was absent from only cabbage, broccoli, palak and cowpea, and also the respective rhizospheric soils. The 30 isolates + ve for pathogenicity, belonged to serogroup 4b, 4d or 4e, and all were positive for inlA, inlC, inlJ, plcA, prfA, actA, hlyA and iap gene except one (VC3) among the vegetable isolates that lacked the plcA gene. ERIC- and REP-PCR collectively revealed that isolates from vegetables and their respective rhizospheric soils had distinct PCR fingerprints.

Conclusions: The study demonstrates the prevalence of pathogenic L. monocytogenes in the selected agricultural farm samples. The increase in the number of strains resistant to ciprofloxacin and/or cefoxitin seems to pose serious public health consequences.

Figure 1

DNA fingerprints generated by ERIC-PCR amplification from vegetable and soil isolates of L. monocytogenes . The dendrogram was generated using the Bionumerics Fingerprint Analyst Software (Applied Maths), and data clustered by the unweighted pair group method with arithmetic means. Similarity of the ERIC-PCR fingerprint profiles was calculated using the average simple-match similarity matrix and the default cluster settings of 0.00% optimization and 1.00% band position tolerance were used.

Figure 2

DNA fingerprints generated by REP-PCR amplification from vegetable and soil isolates of L. monocytogenes . The dendrogram was constructed using the Bionumerics Fingerprint Analyst Software (Applied Maths) as described in the legend of Figure 1.