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Streptococcus suis in retail markets: how prevalent is it in raw pork?
Pui-Yi Cheung1, Kin Land Lo, To To Cheung
1Food and Water Laboratory, Public Health Laboratory Services Branch, Department of Health, Hong Kong. pycheung@dh.gov.hk
Abstract:
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.
Insights
A new MPN-PCR method effectively detected Streptococcus suis in raw pork, revealing higher levels in supermarket meats during summer. This method aids in controlling human infections from contaminated pork.
Area of Science:
- Food Microbiology
- Molecular Biology
- Public Health
Background:
- Streptococcus suis is a pathogen found in pork, posing a risk to human health.
- Traditional culture methods struggle to detect low concentrations of S. suis in raw meat.
- Accurate enumeration of S. suis is crucial for food safety and infection control.
Purpose of the Study:
- To enumerate Streptococcus suis in raw pork using a novel MPN-PCR method.
- To compare S. suis prevalence and concentration across different retail environments and seasons.
- To evaluate the efficacy of MPN-PCR for detecting S. suis in raw pork.
Main Methods:
- Combined Most Probable Number (MPN) technique with PCR targeting a species-specific 16S rRNA gene sequence.
- Analyzed 78 raw pork lean meat samples from supermarkets and a wet market.
- Enumerated S. suis concentrations ranging from <3 to 4600 MPN/g and total bacterial counts (TBC).
Main Results:
- S. suis was detected in nearly all tested raw pork samples.
- Pork from a specific supermarket in summer showed significantly higher S. suis concentrations.
- A positive correlation was found between S. suis concentration and total bacterial count.
Conclusions:
- The MPN-PCR method is highly effective for detecting S. suis in raw pork, even at low levels.
- Raw pork from local markets can harbor S. suis, with variations based on retail location and season.
- This method offers improved detection for effective control of human S. suis infections linked to pork consumption or handling.
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