Yersinia Testing

The genus Yersinia is a group of gram-negative, coccobacilli, and facultative anaerobic bacteria. Some species of Yersinia are pathogenic in humans especially Y. enterocolitica.

Figure 1. Electron micrograph of Yersinia and related contaminated foods

Yersinia infection is mostly caused by eating raw or undercooked pork products that is contaminated with Y. enterocolitica bacteria or through contact with people who have prepared a pork product and do not adequately clean their hands. The main reservoirs for the pathogenic Yersinia strains are pigs and other animals such as rabbits, cattle, sheep, and horses can also carry Yersinia that cause human illness. It also has been found in environmental sources such as water and soil. Yersinia can be transferred through the food supply chain by cross-contamination during food handling. The geographical distribution of Y. enterocolitica is diverse. Occasionally people can get infected after drinking untreated water or contaminated milk. Yersinia grows well at low temperatures and survive in frozen foods for extended periods. Because it can grow easily under refrigeration conditions for extended periods, Yersinia is an increasing food safety concern for food industry. Appropriate sanitation and proper sterilization techniques by food handlers are important control steps to reduce the contamination of Yersinia. Yersinia is sensitive to heat and can be destroyed with proper cooking step to safe temperatures.

The symptoms of Yersinia infection (Yersiniosis) is dependent on the age of the person infected. Young children under five years old have more risk with Yersinia infection than adults and the infection is more common in the winter. For children, common gastrointestinal symptoms include abdominal pain, diarrhea, and fever. The predominant symptoms in adults are right-sided abdominal pain and fever.

Currently there are no food safety criterions that have been established for Yersinia. Generally, Y. enterocolitica should be absent in 25 g of ready-to-eat foods. The infectious dose of Y. enterocolitica is approximately greater than 106 CFU/g to cause people sick. Prevalence in the United Sates is limited and the majority of Yersinia infections were seen in Northern Europe and Japan.

Yersinia Testing of Food at Alfa Chemistry

The standard methods (EN/ISO, FDA BAM and AOAC) that have been widely used to isolation and identify Yersinia are culture-based methods using general microbiological testing supplies. Initial enrichment step is usually recommended for isolating Yersinia from food, water, and environmental samples. Y. enterocolitica can grow on most of regular laboratory culture medium and grows more slowly than other normal GI flora Enterobacteriaceae. MacConkey agar and CIN agar are generally used to incubate the culture. Selective mediums are used to incubate Yersinia for appropriate time. Suspect colonies on MacConkey agar are flat, colorless, or pale pink. Growth and identification specifically as Y. enterocolitica are considered as a positive result. Most results should be available within 48-72 hours. The confirmation test is then performed using biochemical identification technique.

Alfa Chemistry offer accurate and validated testing platforms for the quantification and confirmation of Yersinia in various food samples to meet customers' needs. We also have experience working on different standards and regulations.

Platform: Plate counting technique

Limit of detection: 10 CFU/g

Sample type: Solid and liquid food samples

Sample size: 25 g