Molecular Epidemiology, Virulence Potential and Source Tracking by Source Specific Markers of Campylobacter jejuni

Abstract

Globally Campylobacter jejuni, major cause of bacterial human gastroenteritis, is frequently isolated from poultry, cattle and waste water. The goal of this research was to assess (1) the isolation frequency of C. jejuni from diverse sources, (2) antibiotic resistance profiling, (3) source attribution and distribution in clusters, (4) occurrence of newly identified Type VI secretion system (T6SS). Samples were collected from Islamabad, Karachi, Lahore, Peshawar and Gilgit. Overall 1305 samples were collected from different sources, then confirmed by morphology, biochemical tests and PCR. Antibiotic susceptibility was determined by disc diffusion method according to CLSI 2010. Beta lactamase producing strains were identified by Nitrocefin method. C. jejuni isolates were grouped into clusters by two triplex predictive PCRs. Multiplex PCR based on T6SS conserved genes was employed to screen Pakistani C. jejuni isolates and their gene expression was determined by RT-PCR. C. jejuni strains were isolated from 13.6 % clinical, 46.47 % poultry, 21.40 % cattle and 22.06 % wastewater samples. Highest resistance rates were observed among poultry and wastewater isolates. Highest resistance was observed for nalidixic acid, erythromycin and ceftriaxone. Most sensitive antibiotics were found to be chloramphenicol and spectinomycin. Beta lactamase producing strains were detected in 35 % clinical, 57 % poultry, 39 % cattle and 32 % wastewater isolates. Group clustering showed majority of the isolates were in C4/C6 and C7/C8 groups while none were assigned to C1/C2/C3 cluster. Results of identification of T6SS in C. jejuni isolates revealed 4.64 % of all the isolates were positive for T6SS. Gene expression analysis demonstrated down-regulation of T6SS in acidic environment. Our results showed a high isolation frequency of multidrug resistant C. jejuni isolates in different sources. Source tracking PCR revealed majority of clinical isolates were tracked to nonlivestock sources. Surveillance strategies should be intended to lessen the burden of C. jejuni infections by limiting transmission from livestock as well as non-livestock sources. Our findings regarding T6SS highlight the need to establish the role of the T6SS in environmental survival or virulence.