Mucoid and nonmucoid Burkholderia cepacia complex bacteria in cystic fibrosis infections

Abstract

Rationale: infection with Burkholderia cepacia complex (BCC) bacteria in cystic fibrosis (CF) is associated with an unpredictable rate of pulmonary decline. Some BCC, but not others, elaborate copious mucoid exopolysaccharide, endowing them with a gross mucoid phenotype, the clinical significance of which has not been described.

Objectives: to determine whether there was a correlation between bacterial mucoid phenotype, as assessed in a semiquantitative manner from plate culture, and severity of disease as assessed by the rate of decline in lung function.

Methods: we performed a retrospective clinical review of 100 patients with CF attending the Vancouver clinics between 1981 and 2007 and analyzed the rate of lung function decline (% predicted FEV(1)).

Measurements and main results: patients infected exclusively with nonmucoid BCC had a more rapid decline in lung function (annual FEV(1) change, -8.51 ± 2.41%) than those infected with mucoid bacteria (-3.01 ± 1.09%; P < 0.05). Linear mixed-effects data modeling revealed a statistically significant inverse association between semiquantitative mucoid exopolysaccharide production and rate of decline of lung function. In vitro incubation of BCC with ceftazidime and ciprofloxacin but not meropenem caused conversion of BCC from mucoid to nonmucoid.

Conclusions: our data suggest an inverse correlation between the quantity of mucoid exopolysaccharide production by BCC bacteria and rate of decline in CF lung function. Certain antibiotics may induce a change in bacterial morphology that enhances their virulence. A simple in vitro test of bacterial mucoidy may be useful in predicting the rate of decline of respiratory function in CF.