Yersinia

definition

Yersinia (family Yersiniaceae) is a genus of Gram-negative, facultative anaerobic, non-spore-forming bacilli. The primary food safety hazards within this genus, as recognized by regulatory bodies (Codex Alimentarius, EFSA, and US FDA), are the enteropathogenic species Yersinia enterocolitica and Yersinia pseudotuberculosis. These species are the main causative agents of yersiniosis, a zoonotic infectious disease. Though yersiniosis cases are mostly sporadic, significant outbreaks have been documented in the USA, Canada, Japan, and Europe.

Yersinia is uniquely characterized by its psychrotrophic nature, retaining the ability to proliferate at refrigeration temperatures (0°C to 4°C), which poses a significant risk in cold-chain-dependent food systems. Specifically, Y. enterocolitica can grow at temperatures ranging from 0°C to 45°C (optimum 25°C to 32°C), and Y. pseudotuberculosis can grow from 0°C to 43°C (optimum 25°C to 28°C). Additionally, Y. enterocolitica can produce a thermostable toxin under cooling conditions (4–8°C). Both species are capable of growing at pH values between approximately 4.0 and 10.0, with an optimum pH of around 7.6.

Pathogenicity is largely determined by the presence of the pYV virulence plasmid and chromosomal markers (e.g., ail, yst genes). Y. enterocolitica is classified into six biotypes. Biotypes 1B, 2, 3, 4, and 5 are considered pathogenic to humans, while Biotype 1A is generally regarded as environmental/non-pathogenic. Only specific combinations of biotypes and serotypes are associated with infections in both humans and animals, with the most frequently reported bioserotype in the EU being 4/O:3, followed by 2/O:9. Non-pathogenic bioserotypes, which lack the virulence plasmid and other genes crucial for pathogenesis, are widespread and are the most common types isolated from food and the environment. In contrast to Y. enterocolitica, all strains of Y. pseudotuberculosis are uniformly classified as pathogenic due to the ubiquitous presence of the virulence plasmid and virulence genes. Y. pseudotuberculosis is categorised into 15 O-serotypes: serotype I is by far the most commonly associated with human and animal infections, followed by serotype III. The regulatory definitions are harmonized around the One Health perspective, recognizing the zoonotic transmission route primarily from porcine reservoirs (BT4/O:3) and, increasingly, ruminant and environmental sources.

Y. enterocolitica and Y. pseudotuberculosis strains are typically susceptible to most antimicrobials used to treat humans and animals. However, there is an increasing prevalence of multidrug-resistant Y. enterocolitica strains, particularly in food and the environment, which poses a growing risk to both human and animal health. Additionally, Y. enterocolitica exhibits intrinsic resistance to certain antibiotics, including β-lactams. [1]