, 1990). Mutations in the ompR gene have also been shown to decrease the pathogenicity of Salmonella enterica serovar Typhimurium (Dorman et al., 1989; Lee et al., 2000). Moreover, it has been demonstrated that S. enterica with mutations in the ompR gene is unable to infect murine cells or induce the apoptosis of macrophages in vitro (Lindgren et al., 1996). The OmpR protein of Y. enterocolitica is known to be involved in the adaptation of this

bacterium to multiple environmental stresses, and in survival and replication within macrophages (Dorrell et al., 1998; Brzostek et al., 2003). OmpR was identified in Y. enterocolitica and Yersinia pseudotuberculosis as the response regulator for osmolarity-regulated Yop proteins (Brzostek et al., 2003; Flamez et buy Torin 1 al., 2008). A recent study has demonstrated that OmpR negatively regulates invasin gene (inv) expression in Y. enterocolitica (Brzostek et al., 2007). Lastly, it has been shown that OmpR plays a role in coordinating the motility of Y. enterocolitica and Y. pseudotuberculosis by positive regulation of the transcription of the flhDC operon coding for FlhDC, the master VX-765 supplier activator of the flagellar regulon

(Hu et al., 2009; Raczkowska et al., 2011). In contrast, OmpR has been reported to play a negative role in the regulation of flhDC expression in E. coli (Shin & Park, 1995). Based on the available data, we propose a model for EnvZ/OmpR-dependent regulation of the synthesis of flagella, invasin, porins and the secretion of Yop proteins in Y. enterocolitica Ye9 (Fig. 1). It appears that motility and invasion, the two major factors involved in the early stages of Y. enterocolitica Florfenicol pathogenesis, might be regulated in an opposing manner by OmpR in response to some environmental stimuli. In an attempt to reveal the physiological meaning of the inverse regulation of inv and the flhDC operon, we analyzed the effect of OmpR regulatory function on the ability of Y. enterocolitica to adhere to and invade human epithelial HEp-2 cells and to

form biofilms. The strains and plasmids used in this study are listed in Table 1. Escherichia coli strain S17-1 λpir (Simon et al., 1983) was used as the donor in conjugation with Y. enterocolitica Ye9N. Yersinia enterocolitica strains were cultivated in minimal medium A (MMA) or Luria–Bertani broth (LB) medium at 25 °C (Miller, 1972). Escherichia coli strains were grown in LB medium with aeration at 37 °C. Where appropriate, antibiotics were added to media at the following concentrations: chloramphenicol (25 μg mL−1), nalidixic acid, (20 μg mL−1), kanamycin (50 μg mL−1) and tetracycline (12.5 μg mL−1). DNA manipulations, such as restriction digestion, ligation, transformation and conjugation, were performed using standard protocols (Sambrook et al., 1989). Plasmid and chromosomal DNA were purified using Invitrogen kits. DNA fragments were amplified by PCR using Taq DNA polymerase (Invitrogen) and oligonucleotide primers.