Contamination of Streptococcus suis and S. suis Serotype 2 in Raw Pork and Edible Pig Organs: A Public Health Concern in Chiang Mai, Thailand

Abstract

Streptococcus suis is one of the most important zoonotic pathogens causing serious diseases in both pigs and humans, especially serotype 2. In northern Thailand, there is a notable prevalence of S. suis infection in humans and transmission has occurred mainly through the consumption of raw pork products. Despite the continued practice of consuming raw pork in this region, limited data exist regarding S. suis contamination in such products. Therefore, this study aimed to assess the prevalence of S. suis and S. suis serotype 2 in retail raw pork meat and edible pig organs sold in Chiang Mai city, Thailand. A total of 200 samples, comprising raw pork meat and edible pig organs, were collected from nine fresh markets in Chiang Mai city between May and July 2023. Samples were prepared and cultured in Todd-Hewitt broth. Bacterial DNA was extracted and tested for any serotypes of S. suis and serotype 2 using loop-mediated isothermal amplification (LAMP) techniques. The study revealed contaminations of S. suis and serotype 2 at rates of 84% and 34%, respectively, with a higher prevalence observed in pig organs compared to raw pork. Both S. suis and serotype 2 were detected across all nine fresh markets investigated. The prevalence of S. suis remained consistently high throughout the study period, whereas serotype 2 showed peaks in May and July. These high rates of contamination indicate that people who consume or work in close contact with raw pork or edible pig organs are at a high risk of S. suis infection. Urgent implementation and maintenance of food safety campaigns and public health interventions are crucial for disease prevention and control.

Keywords: Streptococcus suis; Streptococcus suis serotype 2; Thailand; foodborne pathogens; raw pork meat.

Figure 1

Locations of the sites. The black stars on the map indicate locations of the 9 fresh markets (Market A–I) in Chiang Mai city.

Figure 2

LAMP results for Streptococcus suis and Streptococcus suis serotype 2 detection in the first 11 representative raw pork samples. Lanes 1–11 represent the raw pork samples. (a) Results from LAMP-SS targeting S. suis, three samples were positive (lanes 1, 2, and 5) and two samples were negative (lanes 3 and 4). (b) Results from LAMP-SS2 targeting S. suis serotype 2, three samples were positive (lanes 6, 9, and 10) and three samples were negative (lanes 7, 8, and 11). DNA extracted from S. suis serotype 2 was used as positive control in both LAMP-SS and LAMP-SS2. The pattern of the LAMP products on gel electrophoresis corresponded with color change in the reaction tube. The maker (M) was a 1 kb DNA ladder. PC, positive control; NTC, no-template control.

Figure 3

Prevalence of S. suis and S. suis serotype 2 contamination based on sample type. * indicates a statistically significant result (p < 0.05).

Figure 4

Pie charts represent the prevalences of S. suis (a) and S. suis serotype 2 (b) contamination among 9 fresh markets located in Chiang Mai city, Thailand. Black area in the pie chart represents the percent of positive samples. The black stars on the map indicate locations of the 9 fresh markets (Market A–I) in Chiang Mai city.

Figure 5

The prevalence rates of S. suis and S. suis serotype 2 contamination in raw pork/edible pig organs collected from 9 fresh markets according to the month of sample collection. * indicates a statistically significant result (p < 0.05).