Antimicrobial susceptibility and plasmid analysis of Campylobacter jejuni isolated from diarrhoeal patients and healthy chickens in northern India.

Seventy-five strains of Campylobacter jejuni isolated from humans with diarrhoea (45 strains) and healthy chickens (30 strains) were tested for their susceptibility to different antimicrobial agents: ampicillin, tetracycline, erythromycin, gentamicin, kanamycin, furazolidine and quinolones (nalidixic acid, norfloxacin, ciprofloxacin). The frequencies of resistance to ampicillin and tetracycline were 16 and 9.3% respectively. Two strains (2.7%) exhibited resistance to quinolones as mentioned. One strain (1.3%) was resistant to erythromycin, and both ampicillin plus tetracycline. One strain (1.3%) exhibited resistance to multi-drugs (ampicillin, tetracycline and erythromycin). Resistance to ampicillin was higher in human strain (22.2%) compared to chickens (6.7%). On the contrary, the frequency of resistance to tetracycline was higher in chicken strains (13.3%) than in human (6.7%). All the ampicillin-resistant strains produced beta-lactamase. None of the ampicillin, erythromycin and quinolone-resistant strains contained any plasmid but all the tetracycline-resistant strains contained 23 kilobase (kb) plasmid which could be transferred to an ampicillin-resistant C. jejuni strain. This study thus shows that ampicillin and tetracycline resistance in C. jejuni are common in northern India. Ampicillin resistance is chromosomally determined but tetracycline resistance is mediated through 23 kb plasmid.