A comparative genomic analysis of small-colony variant and wild-type Burkholderia pseudomallei in a patient with bacterial liver abscess

Abstract

ObjectiveTo understand the genotypic variations of Burkholderia pseudomallei (B. pseudomallei) small-colony variant (SCV). MethodsA pair of isogenic wild-type (WT) and SCV B. pseudomallei strains (CX1-1 and CX2-1, respectively) were isolated from a patient with a bacterial liver abscess. They were further identified by multilocus sequence typing (MLST) analysis. To compare their growth speed, the time to detection for the two strains was assessed by BacT/Alert 3D. Antibiotic susceptibility tests were performed by disc diffusion method and Etest assay according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. The whole genomes of the two strains were sequenced. A comparative genome analysis was performed to determine the genotypic variations of the CX2-1 strain. ResultsThe CX1-1 and CX2-1 strains were both identified as ST70 by MLST. The CX2-1 grew more slowly than the WT strain CX1-1 and was more resistant to imipenem, meropenem, doxycycline, trimethoprim-sulfamethoxazole, and ceftazidime. The comparative genome analysis revealed 38 variations in 30 genes associated with metabolism, drug resistance and virulence. The mutated genes encoded some cell membrane proteins, membrane transporters and synthetases, including: LolB, HisP, PchF, putative polyketide synthetases, probable non-ribosomal peptide synthetases, putative TonB-dependent outer-membrane receptor protein, and putative type III secretion protein. ConclusionsThe reduced growth speed and increased drug resistance of B. pseudomallei SCV strain may be related to those variations in the genome. This provides some clues to their association between the morphotypic and phenotypic characteristics of colony variants, and the potential association of its colony morphotypes with metabolism, antibiotic resistance and virulence.