Development of a multilocus sequence typing scheme for Streptococcus gallolyticus

Abstract

Streptococcus gallolyticus is often found as a member of the normal gut microflora in various animals. However, it has been reported to cause mastitis in cattle, septicaemia in pigeons, and meningitis, septicaemia and endocarditis in humans. However, little is known about the epidemiology and crucial virulence factors of S. gallolyticus. To help address these issues, we developed a multilocus sequence typing (MLST) scheme for S. gallolyticus. Seven housekeeping gene fragments were sequenced from each of 58 S. gallolyticus isolates collected from diverse origins and sources. The MLST scheme had good discriminatory ability. The 63 strains, including the 5 whole genome sequenced strains examined, resolved into 57 sequence types (STs), with 52 STs represented by only a single strain. With respect to the identification of S. gallolyticus subspecies (i.e. S. gallolyticus subsp. gallolyticus, S. gallolyticus subsp. pasteurianus and S. gallolyticus subsp. macedonicus), the results of biochemical tests and DNA-DNA hybridization were in high concordance with those of the MLST scheme. The MLST scheme developed in this study may be a useful tool capable of replacing the conventional methods used for S. gallolyticus subspecies identification. The results of this study suggest that the biology and virulence of two pathogenic S. gallolyticus subspecies (i.e. S. gallolyticus subsp. gallolyticus and S. gallolyticus subsp. pasteurianus) are very different. The MLST scheme offers researchers a valuable typing tool that will promote further investigation of the epidemiology of S. gallolyticus.

Development and Application of a Multilocus Sequence Typing Scheme for Streptococcus gallolyticus subsp. gallolyticus

“…gallolyticus isolates. A d N /d S ratio of Ͻ1 was also calculated by Shibata et al (17). The number of alleles in the subspecies-specific MLST scheme varies from 14 (glgB) to 22 (p20), which distinguishes more than 3.6 ϫ 10 8 STs.…”

“…However, in contrast to our work, the publication of Shibata et al supports no SID calculations. Therefore, the description of the divergent structure is based only on the calculated number of STs (17).…”

“…The clusters presented also contain S. gallolyticus subsp. gallolyticus isolates from animals or humans, as well as from both animals and humans (17).…”

“…Recombination events were tested by using Sawyer's run test in the MLST scheme for all three subspecies, whereby two genes with evidence of recombination (rpoC, parC) were identified (17). However, this test is less sensitive for detecting recombination (39).…”

“…There was no indication of pathogenic groups within the clusters of S. gallolyticus subsp. gallolyticus (17). To explore the zoonotic potential and characterize the epidemiology of S. gallolyticus subsp.…”