M029: THE POSSIBLE ROLE OF DORMANCY IN CYSTIC FIBROSIS LUNG
INFECTIONS WITH PSEUDOMONAS AERUGINOSA AND BURKHOLDERIA
CEPACIA
M. Desai*, B. Baretto, S. Ballestero, P.H. Weller*, M.R.W.
Brown, and J.R.W. Govan** (Dept of Pharmaceutical and Biological
Sciences, Aston University, Birmingham, U. K., *Birmingham Children's
Hospital, Birmingham, U.K. and **Dept of Medical Microbiology,
University of Edinburgh, U.K.).
Pseudomonas aeruginosa (P.a.) and possibly Burkholderia cepacia (B.c.) grow in biofilms in chronic infections in the cystic fibrosis (CF) iron restricted lung. These are physiologically heterogeneous cultures, including nutrient stressed, slow growing, possibly dormant cells. We have studied the conditions required for prolonged survival of B.c. which dies quickly after growth on agar, but both clinical and non clinical strains were shown to survive longer on iron-depleted agar than on nutritionally complete agar. There was also prolonged survival on charcoal supplemented agar. When grown in suspension, all strains survived longer under conditions of iron-depletion (-Fe). Longitudinal study of ageing planktonic B.c. NCTC 10661 cultures (-Fe) has shown a gradual decrease in cell size, using photon correlation spectroscopy. In addition, these cells became increasingly resistant to Ceftazidime and suggested the possibility of dormancy. Agar colony storage-survival also increased at temperatures of 30 C and 37 C compared to 4 C and in conditions of high humidity. When P.a. ATCC 6750 (-Fe) was stored in suspension at 37 C, a drop in viable count of 2 log-cycles occurred over 85 days. The total count of cells remained relatively constant. However, when stored at 4 C, the viable counts dropped more markedly. Resuscitation by a temperature upshift to 37 C, resulted in a viable count approaching the original count, suggesting a possible dormant state. P.a. was also grown on polycarbonate membranes on the surface of iron-depleted agar. The growth curve of these biofilms was shown to represent that of a batch culture with a 2 hour doubling-time and expressed iron-regulated outer membrane proteins. Cell size decreased with age of biofilm. This provides a useful simple model for the further study of P.a. and possibly B.C.