Development of a Multilocus Sequence Typing System for Medically Relevant Bipolaris Species

Abstract

Multilocus sequence typing (MLST) is the gold standard genotyping technique for many microorganisms. This classification approach satisfies the requirements for a high-resolution, standardized, and archivable taxonomic system. Here, we describe the development of a novel MLST system to assist with the investigation of an unusual cluster of surgical site infections caused by Bipolaris spp. in postoperative cardiothoracic surgery (POCS) patients during January 2008 to December 2013 in the southeastern United States. We also used the same MLST system to perform a retrospective analysis on isolates from a 2012 Bipolaris endophthalmitis outbreak caused by a contaminated product. This MLST system showed high intraspecies discriminatory power for Bipolaris spicifera, B. hawaiiensis, and B. australiensis. Based on the relatedness of the isolates, the MLST data supported the hypothesis that infections in the POCS cluster were from different environmental sources while confirming that the endophthalmitis outbreak resulted from a point source, which was a contaminated medication.

FIG 1

Dendrogram showing the discrimination of B. australiensis, B. hawaiiensis, and B. spicifera isolates inferred from ITS sequence data. The dendrogram was constructed with the neighbor-joining method using CLUSTALW alignment and rooted at B. ellisii. The genetic distance and topology reliability were calculated using the Tamura-Nei model and 1,000 bootstrap replicates, respectively. †Type strain from CBS.

FIG 2

Dendrogram showing discrimination of B. australiensis, B. hawaiiensis, and B. spicifera isolates by the RPB2 sequence, which was constructed with the neighbor-joining method and rooted at B. ellisii. The genetic distance and topology reliability were calculated using the Tamura-Nei model and 1,000 bootstrap replicates, respectively. †Type strain from CBS.

FIG 3

Dendrogram inferring the relatedness of 59 Bipolaris isolates using MLST. The dendrogram was constructed with the neighbor-joining method and rooted at B. ellisii. The genetic distance and topology reliability were calculated using the Tamura-Nei model and 1,000 bootstrap replicates, respectively. *Isolate from the POCS investigation; †type strain from CBS; #isolate from the endophthalmitis outbreak.