Adhesivity оf standard and biofilm cultures of toxigenic Corynebacterium diphtheriaе strains

Background: Adhesion and ability to form a  biofilm are considered among the leading pathogenicity factors of Corynebacterium diphtheriaе, responsible for bacterial carriage. It is exactly bacterial carriage that ensures the circulation of diphtheria pathogen strains in the inter-epidemic periods. Aim: To assess and compare adhesivity of standard and biofilm cultures of toxigenic C. diphtheriae strains. Materials and methods: We studied standard and biofilm (120  and 720  hour) cultures of C.  diphtheriae strains. Their ability to form a  biofilm was tested according to P. Watnick (2000). Adhesivity was assessed in the pharyngeal epithelial carcinoma Hep-2 cell culture with various time exposures (2, 8, and 18  hours). The amounts of C. diphtheriae adhered to Нер-2 cells were measured by culturing the swabs in the 20% serum agar with subsequent calculation of mean numbers of colony-forming units (CFU) per 1  mL. Results: All standard and biofilm cultures of the studied toxigenic strains of C. diphtheriae had adhesive properties of various degrees. The highest adhesivity was found in a  circulating strain C.  diphtheriae gravis tox+ (from 0.26 ± 0.01 to 203.3 ± 3.3 CFU/mL), which differed from the same parameters in other strains studied (from 0.03 ± 0.003 to 0.20 ± 0.01  CFU/mL). The lowest adhesivity after a 2-hour exposure was found both in the standard and biofilm cultures of C.  diphtheriae gravis tox+ 6765, whereas after the exposure of 8 and 18  hours, the lowest adhesion properties were demonstrated by C.  diphtheriae gravis with a “silent” tox gene and C. diphtheriae mitis tox+ 269. All cultures of toxigenic C. diphtheriae strains showed a  statistically significant increase in their adhesivity (р ≤ 0.05) by 8 and 18  hour of cultivation. Conclusion: Circulating C.  diphtheriae gravis tox+ strain demonstrated the highest adhesivity among all toxigenic strains of the diphtheria pathogens studied.