Streptococcus suis in retail markets: how prevalent is it in raw pork?

Streptococcus suis present in raw pork meats sold in local retail markets was enumerated by Most Probable Number (MPN)-PCR method. This method combined the conventional MPN technique with a specifically designed PCR assay based on the amplification of a 294-bp S. suis species-specific 16S rRNA gene sequence. A total of 78 raw pork lean meat samples purchased at two different supermarkets (Site A and B) and a wet market (Site C) were tested. Results indicated that S. suis could be detected from the enriched MPN tubes of all, except one, sample homogenates. The concentration of S. suis ranged from <3 to 4600 MPN/g of pork meat, with a total bacterial count (TBC) varying from 3.6 log to 7.4 log CFU/g. Statistical analyses indicated that pork meats purchased from the supermarket at Site B in summer contained significantly higher concentration of S. suis organisms than those from other retailers in any season. A significant correlation existed between log S. suis concentration and log TBC of the samples. This study revealed that raw pork meats available in local supermarkets or wet markets could contain S. suis at concentrations that were usually difficult to detect with traditional culture method. Field application of this method may contribute to a measurable evaluation, and thus the effective control, of human S. suis infection due to raw pork or pig carcass handling.