Virulence characteristics of five new Campylobacter jejuni chicken isolates

Abstract

Campylobacter enteritis has emerged as one of the most common forms of human diarrheal illness. In this study we have investigated the virulence potential of five new C. jejuni chicken isolates (RO14, RO19, RO24, RO29 and RO37) originated from private households in the rural regions of Banat and Transylvania in Romania. Following isolation and in vitro virulence assay, on HCT-8 cells, our results show that all the C. jejuni chicken isolates overcome the virulence abilities of the highly virulent strain C. jejuni 81-176. Motility, an important virulence factor was significantly improved in all the new chicken isolates. The ability to survive to the antimicrobial activity of the human serum, to resist to the violent attack of bile acids and to survive in the presence of synthetic antibiotics was increased in all the chicken isolates. However, these were statistically significant only for isolates RO29 and RO37. In conclusion our study shows, based on invasiveness and motility, and also on the data provided by the serum and bile resistance experiments that all the new chicken isolates are able to infect human cells, in vitro, and could potentially represent a health hazard for humans.

Figure 1

Increased adhesion and invasion for all chicken isolates. (A) adhesion to HCT-8 cells, (B) invasion of HCT-8 cells of C. jejuni 81-176 and C. jejuni chicken isolates RO14, RO19, RO24, RO29 and RO37. Statistical significance (Student’s t test) relative to the level of C. jejuni 81-176 strain is indicated. The experiments were done in triplicate and on three separate occasions. The error bars represent standard deviations for six separate wells.

Figure 2

Motility of C. jejuni chicken isolates in 0.4% motility agar. Motility of C. jejuni chicken isolates RO14, RO19, RO24, RO29 and RO37 by comparison with the highly virulent strain C. jejuni 81-176. Size of the motility halo after 48 h at 37°C. Results are the mean of three separate experiments. Statistical significance (Student’s t test) relative to the level of C. jejuni 81-176 strain is indicated.

Figure 3

Serum resistance. Serum resistance of C. jejuni chicken isolates RO14, RO19, RO24, RO29 and RO37 by comparison to C. jejuni 81-176. The survival rate is defined as the number of C. jejuni colonies isolated following exposure to human serum divided by the number of colonies surviving in heat-inactivated serum, expressed as a percentage. The experiment was performed in triplicate. The error bars represent standard deviations. Statistical significance was assessed with Student’s t test.

Figure 4

Bile resistance. The ability of C. jejuni chicken isolates (RO14, RO19, RO24, RO29, RO37) and C. jejuni 81-176 to survive to bile salts in Mueller Hinton medium was studied. Following agar growth bacteria were transferred into 50 mL of medium containing 0.5% bile salts. Samples were removed after 24 h and diluted prior plating. The surviving cells were counted after 42 h incubation. The experiments were done in triplicates and Student t test was used for statistical significance.