| Abstract |
Cystic fibrosis (CF) predisposes patients to bacterial colonization and
infection of the lower airways. Several species belonging to the genus
Burkholderia are potential CF-related pathogens, but microbiological
identification may be complicated. This situation is not in the least due
to the poorly defined taxonomic status of these bacteria, and further
validation of the available diagnostic assays is required. A total of 114
geographically diverse bacterial isolates, previously identified in
reference laboratories as Burkholderia cepacia (n = 51), B. gladioli (n =
14), Ralstonia pickettii (n = 6), B. multivorans (n = 2), Stenotrophomonas
maltophilia (n = 3), and Pseudomonas aeruginosa (n = 11), were collected
from environmental, clinical, and reference sources. In addition, 27
clinical isolates putatively identified as Burkholderia spp. were
recovered from the sputum of Dutch CF patients. All isolates were used to
evaluate the accuracy of two selective growth media, four systems for
biochemical identification (API 20NE, Vitek GNI, Vitek NFC, and
MicroScan), and three different PCR-based assays. The PCR assays amplify
different parts of the ribosomal DNA operon, either alone or in
combination with cleavage by various restriction enzymes (PCR-restriction
fragment length polymorphism [RFLP] analysis). The best system for the
biochemical identification of B. cepacia appeared to be the API 20NE test.
None of the biochemical assays successfully grouped the B. gladioli
strains. The PCR-RFLP method appeared to be the optimal method for
accurate nucleic acid-mediated identification of the different
Burkholderia spp. With this method, B. gladioli was also reliably
classified in a separate group. For the laboratory diagnosis of B.
cepacia, we recommend parallel cultures on blood agar medium and selective
agar plates. Further identification of colonies with a Burkholderia
phenotype should be performed with the API 20NE test. For final
confirmation of species identities, PCR amplification of the small-subunit
rRNA gene followed by RFLP analysis with various enzymes is recommended. |