Characterization of Listeria monocytogenes isolated from Ganges water, human clinical and milk samples at Varanasi, India

Listeria monocytogenes isolated from Ganges water, human clinical and milk samples were characterized by antibiotic susceptibility, serotype identification, detection of virulence genes and ERIC- and REP-PCR fingerprint analyses. All isolates were uniformly resistant to ampicillin, except two isolates, and showed variable resistance to gentamicin, cotrimoxazole, ofloxacin, rifampicin and tetracycline. Of the 20 isolates found positive for pathogens, seven (four human and three water isolates) belong to serogroups 4b, 4d and 4e; six (one human and five water isolates) belong to serogroups 1/2c and 3c; four milk isolates belong to serogroups 1/2b and 3b; and three milk isolates belong to serogroups 1/2a and 3a. Two water isolates, all human isolates, except one (Pb1) lacking inlJ gene, and three milk isolates possess inlA, inlC, plcA, prfA, actA, hlyA and iap genes. The remaining water and milk isolates showed variable presence of inlJ, plcA, prfA, and iap genes. ERIC- and REP-PCR based analyses collectively indicated that isolates of human clinical samples belong to identical or similar clone and isolates of water and milk samples belong to different clones. Overall study demonstrates the prevalence of pathogenic L. monocytogenes species in the environmental and clinical samples. Most of the isolates were resistant to commonly used antibiotics.

- Listeria monocytogenes isolates, irrespective of source of isolation, were uniformly resistant to ampicillin.
- Isolates from human and water belong to 4b, 4d, 4e or 1/2c, 3c serogroups and milk isolates to 1/2b, 3b or 1/2a, 3a.
- All human isolates, except one isolate (Pb1) lacking inlJ gene, possess inlA, inlC, plcA, prfA, actA, hlyA and iap genes.
- Water and milk isolates showed variable presence of inlA, inlC, inlJ and hlyA, plcA, prfA, actA and iap genes.
- Human and water isolates showing distinct fingerprint profiles, had ability to invade and can cause infection.