Plasmid-Mediated Quinolone Resistance (PMQR) in Two Clinical Strains of Serovar Corvallis.

Non-typhoid serovars of are one of the main causes of bacterial food-borne infections worldwide. For the treatment of severe cases of salmonellosis in adults, fluoroquinolones are amongst the drugs of choice. They are categorized by the World Health Organization (WHO) as "critically important with highest priority in human medicine". In the present study, two clinical serovar Corvallis isolates (HUA 5/18 and HUA 6/18) from a Spanish hospital, selected on the basis of fluoroquinolone resistance, were characterized. The MICs of ciprofloxacin, determined by E-test, were 0.5 and 0.75 µg/mL for HUA 5/18 and HUA 6/18, respectively, and both were also resistant to pefloxacin but susceptible to nalidixic acid. Whole genome sequencing (WGS) of the isolates was performed with Illumina platform, and different bioinformatics tools were used for sequence analysis. The two isolates belonged to ST1541, and had the Thr57Ser substitution in the ParC protein which is also found in ciprofloxacin susceptible isolates. However, they harbored identical ColE plasmids of 10 kb carrying the gene. In these plasmids, the gene was flanked by defective versions of IS-like and IS-like insertion sequences. HUA 5/18 and HUA 6/18 were also phenotypically resistant to streptomycin, sulfonamides and tetracycline, with the responsible genes: , , and (A) genes, being located on a IncQ1 plasmid. ColE plasmids with the gene are widely spread among multiple serovars of from different samples and countries. These mobilizable plasmids are playing an important role in the worldwide spread of . Thus, their detection in hospitals is a cause of concern which deserves further attention.