Multilocus sequence typing of Australian Streptococcus suis type 2 by MALDI-TOF mass spectrometry analysis of PCR amplicons

Streptococcus suis serotype 2 is a ubiquitous pathogen of swine and is known to cause severe disease in humans. Multilocus sequence typing (MLST) is ideal for characterising this organism because it permits isolates to be compared on a national and international scale. A novel approach to MIST using matrix-assisted laser desorption ionisation-time of flight mass spectrometry (MS-MLST) provides a more rapid alternative to dideoxy sequencing. This study used MS-MLST to define the multilocus sequence types (STs) present among a collection of Australian S. suis type 2, and thus, delivered a basis for comparison of Australian isolates with international strains already well characterised for virulence attributes. A collection of 45 isolates recovered from infected humans (n = 3) and diseased pigs (n = 42) was genotyped using MS-MLST and conventional MIST. Both methods were 100% concordant in their classification of sequence types (STs), although MS-MIST permitted much quicker analysis of sequence data. The collection contained ST25 (n = 31), ST1 (n = 10), ST28 (n = 3) and ST369 (n = 1). These results are consistent with the population structure of S. suis type 2 observed in diseased pigs and humans in Canada and the United Kingdom. MS-MIST may have utility for studying the population structure and epidemiology of S. suis in countries where the diversity of S. suis is greater and human disease is more common.