The method described here may be useful for identifying the sourc

The method described here may be useful for identifying the source of S. suis infection and monitoring its spread. S. suis, an important zoonotic agent worldwide which has often been linked with occupational exposure to pigs or porcine products, may cause arthritis, endocarditis, meningitis, pneumonia, and septicemia (1–3). Thirty-three serotypes based on the capsular antigens have been described, serotype 2 being the most prevalent in humans and animals (1, 4). The originally named S. suis serotype 32 and 34 were recently identified

to be Streptococcus orisratti (5). Since the first human case was reported in 1968, about 550 cases have occurred worldwide through to June 2005 (1, 6–9). During July 2005, a sudden outbreak of 215 human cases occurred in Sichuan Province, China (9, 10). Sixty-one of the 215 patients (28%), all previously click here healthy farmers, presented with an unusual streptococcal toxic shock-like syndrome with a high mortality (62%) (8–10). Because such an explosive outbreak and such rapid deaths of patients had not previously been observed, DNA Damage inhibitor strong interest concerning the emergence of a possible mutant with increased virulence was provoked within the scientific community (1, 3, 8). Using MLST, ST7 S. suis was identifed as the causative pathogen for the Sichuan outbreak (1, 8, 9, 11). A phylogenetic tree of S. suis constructed using concatenated Sitaxentan sequences

from seven housekeeping genes used in the MLST analysis showed that ST7 had been derived from ST1 by a single nucleotide change in the housekeeping gene thyA (9, 11). S. suis ST7 was first found in Hong Kong in 1996 (1, 11, 12); caused a small outbreak in Jiangsu Province in 1998; and was responsible for the large 2005 Sichuan outbreak. It has been suggested that ST7 S. suis has greater virulence than ST1

because data show that ST7 can stimulate a larger amount of pro-inflammatory cytokines in both patients and experimental animals (8, 13). To date, S. suis ST7 strain has not been isolated in any country other than China. The PFGE method is recognized as the best method for comparing genetic relatedness among isolates from various origins, having greater discriminatory power than other methods (14). Our previous study showed that SmaI digested chromosomal DNA of all 100 outbreak-associated ST7 isolates had an identical PFGE pattern. This observation meant that the ST7 strains were indistinguishable using the PFGE method (9); therefore, a more sensitive method was required to discriminate between ST7 strains. Here, we report a novel MLVA method that may be useful for subtyping ST7 and other sequence types of S. suis serotype 2 strains. A total of 166 S. suis serotype 2 isolates, including 154 from China and 12 from other countries (UK, France, Canada and the Netherlands), were used in this study (Table 1).

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