**3.4** *Yersinia*

*Yersinia pseudotuberculosis* is the enteropathogen that causes gastrointestinal illnesses in people. Antibiotics that target gram-negative bacteria are typically effective against this species. However, the resistance to *Yersinia* is becoming more widespread. Three multi-drug-resistant (MDR) strains of *Y. pseudotuberculosis* were recovered from the environment in Russia and patients in France [31]. The resistance genes in *Yersinia* include *tetD*, *tetA bla*TEM-1B, *dfrA14*, *drfA1, sul2* and *catA2,* etc., which are related to the tetracycline, minocycline, ticarcillin, amoxicillin and Trimethoprim resistance (**Table 1**).

The genetic diversity of *Yersinia pestis* is still mainly studied by typing. There have been many studies on the genetic diversity of *Yersinia*. Xu et al. [32] screened 102 *Y. pestis* isolates from Qinghai and 16 genotypes were identified by CRISPR (Clustered Regularly Interspaced Short Palindromic Repeat).

*Yersinia* is considered to be the pathogen of human intestinal diseases, and its molecular epidemiology is the focus of current research. The presence of a 70-kb virulence plasmid was required for the pathogenicity of *Y. pseudotuberculosis*, which was necessary for virulence. According to Fukushima [33], *Y. pseudotuberculosis* could produce a novel super antigenic toxin by chromosomal encoding, known as YPMa, YPMb or YPMc. It could also produce a pathogenicity island termed as HPI (highpathogenicity island) or R-HPI (a right-hand part of the HPI with truncation in its left-hand part). All of these can contribute to its pathogenicity.
