Within-Host Evolution of Burkholderia pseudomallei in Four Cases of Acute Melioidosis

Abstract

Little is currently known about bacterial pathogen evolution and adaptation within the host during acute infection. Previous studies of Burkholderia pseudomallei, the etiologic agent of melioidosis, have shown that this opportunistic pathogen mutates rapidly both in vitro and in vivo at tandemly repeated loci, making this organism a relevant model for studying short-term evolution. In the current study, B. pseudomallei isolates cultured from multiple body sites from four Thai patients with disseminated melioidosis were subjected to fine-scale genotyping using multilocus variable-number tandem repeat analysis (MLVA). In order to understand and model the in vivo variable-number tandem repeat (VNTR) mutational process, we characterized the patterns and rates of mutations in vitro through parallel serial passage experiments of B. pseudomallei. Despite the short period of infection, substantial divergence from the putative founder genotype was observed in all four melioidosis cases. This study presents a paradigm for examining bacterial evolution over the short timescale of an acute infection. Further studies are required to determine whether the mutational process leads to phenotypic alterations that impact upon bacterial fitness in vivo. Our findings have important implications for future sampling strategies, since colonies in a single clinical sample may be genetically heterogeneous, and organisms in a culture taken late in the infective process may have undergone considerable genetic change compared with the founder inoculum.

Tracing Melioidosis Back to the Source: Using Whole-Genome Sequencing To Investigate an Outbreak Originating from a Contaminated Domestic Water Supply

“…Given that the clinical isolate from P811 was the only instance of MLVA-4 type 402, it is possible that this MLVA variant arose as either a consequence of within-host evolution or via laboratory passage. This finding was not surprising given that MLVA loci are known to evolve rapidly, and multiple mutations have been documented in acute B. pseudomallei infections (11,23). However, despite the MLVA differences of P741 and P811, no remarkable features were noted between the clinical presentation of these two cases, consistent with the intergenic nature of these MLVA loci, which are not expected to impart a selective advantage to the bacterium or to cause more severe disease (10,24).…”

Melioidosis as a Consequence of Sporting Activity

“…15 MSHR2078 and MSHR2080 strains from the patient were identical at all four MLVA loci to MSHR2188 retrieved from soil at the location of the abrasion incident. In contrast, the three ST36 environmental isolates from different locations of the same field contained 1-3 MLVA locus mismatches when compared with MSHRs 2078, 2080 and 2188.…”

Burkholderia pseudomallei: Challenges for the Clinical Microbiology Laboratory

“…These relatively large chromosomes encode several putative virulence factors, including quorum sensing, type III secretion systems, and the capsular polysaccharide (13). The chromosomes are thought to be highly dynamic, evidenced by the presence of several recently acquired mobile genetic elements in the chromosome (6,12) and the extensive genetic diversification observed over time in a single patient (14,15). The portion of the genome with high variability between strains may contribute to virulence and antibiotic resistance (16).…”