ICAAC edition:40th location:Toronto date:17-20 September 2000
BACKGROUND: The adhesin Choline-binding protein A (CbpA) represents a potential protective antigen operative at the site of colonization. CbpA deficient pneumococci fail to colonize the infant rat nasopharynx. We have used an in vitro model of the human nasopharynx to study the adherence of CbpA deficient pneumococci.METHODS: Human nasal epithelial cells in a confluent culture on collagen-coated membranes (0.6 cm) and expressing differentiated characteristics, were inoculated with 100 micro-L of a 10 CFU/mL pneumococcal suspension. Strains D39 (type 2) and D39 CbpA- were from J. Paton, strains R6 (unencapsulated) and R6 CbpA- from E. Tuomanen. Adherent and non-adherent bacteria were quantified after 24 h incubation. The Transepithelial Electrical Resistance (TEER) of the cell-layer was followed for 48 h post-inoculation.RESULTS: Both the amount of adherent and the total amount of bacteria were lower for the CbpA-mutants compared to their parent strains. Adherence expressed as a percentage of control (parent strain) was 33.5% +/- 2.1% for D39 CbpA- and 12.3% +/- 4.0% for R6 CbpA-. The total amount of bacteria expressed as a percentage of control was 30.5% +/- 3.5% for D39 CbpA- and 23.1% +/- 8.7% for R6 CbpA-. There was no difference in the evolution of the TEER between the parent strains and their mutants. The decrease of the TEER (disruption of epithelial integrity) started much earlier with R6 (after 7 h incubation) than with D39 (after 27 h incubation). After 48 h incubation, the TEER had dropped by > 85% for all strains, but the viability of the epithelial cells was still > 90%. Conclusion: Both survival and adherence of CbpA- pneumococci to epithelial cells were reduced in our in vitro model of the human nasopharynx.