Approaches to measure the fitness of Burkholderia cepacia complex isolates.

Members of the Burkholderia cepacia complex (Bcc) are highly resistant to many antibacterial agents and infection can be difficult to eradicate. A coordinated approach has been used to measure the fitness of Bcc bacteria isolated from cystic fibrosis (CF) patients with chronic Bcc infection using methods relevant to Bcc growth and survival conditions. Significant differences in growth rate were observed among isolates; slower growth rates were associated with isolates that exhibited higher MICs and were resistant to more antimicrobial classes. The nucleotide sequences of the quinolone resistance-determining region of gyrA in the isolates were determined and the ciprofloxacin MIC correlated with amino acid substitutions at codons 83 and 87. Biologically relevant methods for fitness measurement were developed and could be applied to investigate larger numbers of clinical isolates. These methods were determination of planktonic growth rate, biofilm formation, survival in water and survival during drying. We also describe a method to determine mutation rate in Bcc bacteria. Unlike in Pseudomonas aeruginosa where hypermutability has been detected in strains isolated from CF patients, we were unable to demonstrate hypermutability in this panel of Burkholderia cenocepacia and Burkholderia multivorans isolates.