Homology searches revealed that the plasmid (designated pMK100) found in S. Infantis (S20) exhibited 100% homology with

qnrB19-carrying plasmids including pSGI15, a see more small ColE plasmid identified recently in S. enterica serovar Typhimurium isolated in Germany (Hammerl et al., 2010), and a qnrB19-containing plasmid pPAB19 from an S. Infantis clinical isolate recovered in Argentina (GenBank accession number GQ412195). The plasmid purified from isolate S75 (designated pMK101) was found to be 97% similar to these latter plasmids. The dissimilarity noted was mapped to an insertion located between nucleotide positions 896 and 957. Remarkably, the latter DNA sequence was identical to one found in a pBC633 from a K. pneumoniae strain KN633 (accession number EU176012), a urinary isolate from Colombia displaying carbapenem resistance and reported in 2005. This plasmid of approximately 15.5 kb carried a blaKPC−2 gene encoding a class A carbapenemase (Villegas et

al., 2006). The additional JQ1 DNA sequence contained in the plasmid from the isolate S75 was located between the qnrB19 gene and orf2, and was found to be homologous with a region of pBC633. Furthermore, nucleotide sequence similarity was observed in the region upstream of the inserted fragment, possibly facilitating the incorporation of the new DNA fragment. The fact that pBC633 was found only in Colombia indicates that the homology found here may not be coincidental. It is interesting to speculate that pMK101 (the plasmid from isolate S75) is chimeric and may have emerged as a result of a recombination event that led to the horizontal acquisition of a fragment from another plasmid containing blaKPC−2. The process is likely to have occurred in a bacterium simultaneously hosting BCKDHA a plasmid similar to or identical to pBC633, as well as a small ColE-like plasmid such as pMK100. While blaKPC−2 genes are frequent in K. pneumoniae and only sporadic in other Enterobacteriaceae, there are insufficient data to conclude what species was the primary host of the new plasmid structure (Villegas et al., 2006; Pournaras et al., 2009). In addition, it is noteworthy

that pBC633 containing a blaKPC−2 gene was found on a transposon Tn4401 with multiple insertion sequence (IS) elements that have likely contributed to its emergence (Naas et al., 2008). Of particular concern is the possibility of the emergence of chimeric plasmids carrying both qnr genes and blaKPC−2 that could compromise the clinical value of fluoroquinolones and virtually all β-lactams. In view of this, monitoring of phenotypic resistance as well as associated mechanisms and mobility is essential. Furthermore, the occurrence of both blaKPC−2 and qnr in Colombia and their associated plasmids is likely to be under-reported as a result of poor surveillance as well as diagnostic challenges associated with the low-level resistance conferred (Villegas et al., 2006).