High-level fluoroquinolone resistant Salmonella enterica serovar Kentucky ST198 epidemic clone with IncA/C conjugative plasmid carrying blaCTX-M-25 gene

• Further characteristics of S. Kentucky epidemic clone ST198 is provided.
• S. Kentucky-specific high-level quinolone resistance mechanism is identified.
• Sequence of a conjugative plasmid of IncA/C family is revealed.
• The plasmid bears blaCTX-M-25 and an integron with a novel cassettes array.

Multidrug resistant Salmonella Kentucky strains have been isolated from turkeys in Poland since 2009. Multiple mutations within chromosomal genes gyrA and parC were responsible for high-level ciprofloxacin resistance. One of the isolates was extended spectrum β-lactamase- (ESBL) positive: the strain 1643/2010 carried a conjugative 167,779 bps plasmid of IncA/C family. The sequence analysis revealed that it carried a blaCTX-M-25 gene and an integron with another β-lactamase encoding gene—blaOXA-21. This is the first known report of a CTX-M-25 encoding gene both in Poland and in Salmonella Kentucky world-wide, as well as in the IncA/C plasmid. Analysis of the integron showed a novel arrangement of gene cassettes—aacA4, aacC-A1 and blaOXA-21 where the latter might result from an intergeneric gene transfer. The study confirmed Salmonella Kentucky population isolated in Poland belongs to global epidemics of high level fluoroquinolone resistant clone ST198 that can carry rare β-lactamase genes.