Differential persistence among genomovars of the Burkholderia cepacia complex in a murine model of pulmonary infection

Abstract

Cystic fibrosis patients infected with strains from different genomovars of the Burkholderia cepacia complex can experience diverse clinical outcomes. To identify genomovar-specific determinants that might be responsible for these differences, we developed a pulmonary model of infection in BALB/c mice. Mice were rendered leukopenic by administration of cyclophosphamide prior to intranasal challenge with 1.6 x 10(4) bacteria. Five of six genomovar II strains persisted at stable numbers in the lungs until day 16 with minimal toxicity, whereas zero of seven genomovar III strains persisted but resulted in variable toxicity. We have developed a chronic pulmonary model of B. cepacia infection which reveals differences among genomovars in terms of clinical infection outcome.

FIG. 1.

Effect of CPA treatment and bacterial infection on animal health over time. PBS-treated and CPA-treated mice were challenged with ≈1.6 × 10⁴ B. cepacia genomovar III strain C6433 or B. multivorans strain C1576. Animals were monitored daily for the duration of the experiment and assessed on a three-point system for ill health. Unhealthy animals (light bars) and healthy animals (dark bars) are shown for each day. The total number of animals studied decreased over time as animals were removed for analysis. Asterisks denote days on which animals were euthanatized due to extreme systemic illness. Arrows denote administration of either CPA or PBS.

FIG. 2.

Effect of CPA treatment on pulmonary bacterial load after infection with five BCC strains. CPA-treated (closed symbols) and PBS-treated (open symbols) BALB/c mice were intranasally challenged with ≈1.6 × 10⁴ CFU. Quantitative bacteriology of the lung was assessed at 0 (3 h), 4, and 16 days. Values for the C1394-infected CPA group were identical to those for the PBS-treated group. Data are the mean and standard error of the mean from six animals at each time point.

FIG. 3.

Effect of CPA treatment on animal health over time. PBS-treated and CPA-treated mice were challenged with gHBSS only. Animals were monitored daily for the duration of the experiment and assessed on a three-point system for ill health. Unhealthy animals (light bars) and healthy animals (dark bars) are shown at each day. The total number of animals studied decreased over time as animals were removed for analysis. Arrows denote administration of either CPA or PBS.