Heterogeneity of Cytolethal Distending Toxin Sequence Types of Campylobacter Jejuni and Correlation to Invasion/cytotoxicity Potential: The First Molecular Survey from Iran

The aim of this study was to evaluate the cytotoxicity and attachment/invasion potential of thermophilic Campylobacter isolates regarding their cdt sequence types and virulence-associated gene content. A total of 33 Campylobacter spp. were identified from 750 stool samples isolated from patients characterized with diarrhea. The prevalence rates of flaA, ciaB, and pldA genes among the isolates were 97, 100, and 15%, respectively. The iam gene was found in 100% of the C. coli isolates while it was not detected in C. jejuni isolates. Four PCR primer pairs jointly amplifying the entire cdt genes array and sequence analysis revealed variations dispersed along the sequence array. The isolates attachment to HeLa cells ranged from 89 ± 2-100%, and the range of invasions was also from 0 to 11 ± 0.04%. The cytotoxicity value was between 2 and 32 in cdt isolates with no significant correlation to any of the cdt sequence types. Moreover, the cdt encoding strains had increased invasion to HeLa cells, and all of the related patients presented much higher white and red blood cell shedding in stool specimens (P-value≤ 0.001). No significant difference was observed between cdt and cdt isolates in their attachment rate to HeLa cells. About 48% of all the Iranian Campylobacter population lacked a complete set of cdt genes array, suggesting low invasion and cytotoxicity potential of the isolates which are heterogeneous in their cdt genes and virulence.