Abstract
We performed multilocus sequence typing of 64 North American Streptococcus suis serotype 2 porcine isolates. Strains were sequence type (ST) 28 (51%), ST25 (44%), and ST1 (5%). We identified nonrandom associations between STs and expression of the virulence markers suilysin (SLY), muramidase-relased protein (MRP), and extracellular factor (EF). Expression of pili encoded by the srtF and srtG pilus clusters was also nonrandomly associated with STs. ST1 strains were SLY+ EF+ MRP+ srtF pilus+ srtG pilus-. ST25 strains were SLY- EF- MRP- srtF pilus- srtG pilus+, and most ST28 strains were SLY- MRP+ EF- srtF pilus+ srtG pilus+. ST28 isolates proved essentially nonvirulent in a mouse infection model; ST25 strains showed moderate virulence and ST1 isolates were highly virulent. ST1 is responsible for a high proportion of S. suis disease in humans worldwide. Its presence in North America indicates that potential zoonotic S. suis outbreaks in this continent cannot be disregarded.
Highlights
Streptococcus suis causes meningitis and septicemia in pigs and is a zoonotic agent [1]
SLY, muramidase-relased protein (MRP), and extracellular factor (EF) are virulence markers that have been used in elaborated genotypic and phenotypic schemes to try to predict the virulence of a given S. suis strain [1,19]
ST28 strains were essentially nonvirulent for mice, ST25 strains were of intermediate virulence and able to induce severe disease
Summary
Streptococcus suis causes meningitis and septicemia in pigs and is a zoonotic agent [1]. Most cases of animal and human S. suis infection have been caused by serotype 2 strains [5]. The percentage of S. suis serotype 2 strains recovered from diseased pigs and the number of cases of human disease is lower in North America than in other parts of the world [6,7]. Most strains isolated from human patients in Japan were ST1 [9], whereas those causing the human outbreaks in People’s Republic of China were ST7, included in the ST1 complex [10,11]. Takamatsu et al showed that 80% of the isolates recovered from blood or cerebrospinal fluid of humans in Thailand belonged to STs grouped in the ST27 complex [12]. We used MLST to genotype a relatively large collection of US and Canadian S. suis serotype 2 strains
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