blaCTX-M-15-carrying Escherichia coli and Salmonella isolates from livestock and food in Germany

The characterization of CTX-M-15 beta-lactamase-producing Escherichia coli and Salmonella isolates originating mainly from German livestock and food. E. coli (526, mainly commensals) and Salmonella (151) non-human isolates resistant to third-generation cephalosporins, originating from routine and monitoring submissions (2003-12) to the Federal Institute for Risk Assessment and different national targeted studies (2011-12), were examined for the presence of bla(CTX-M-15) genes by PCR amplification/sequencing. Additional resistance and virulence genes were screened by DNA microarray and PCR amplification. E. coli isolates with bla(CTX-M-15) were characterized by phylogenetic grouping, PFGE and multilocus sequence typing (MLST). The bla(CTX-M-15) plasmids were analysed by replicon typing, plasmid MLST, S1 nuclease PFGE and Southern blot hybridization experiments. Twenty-one E. coli (livestock, food and a toy; 4.0%) and two Salmonella (horse and swine; 1.3%) isolates were CTX-M-15 producers. E. coli isolates were mainly ascribed to three clonal lineages of sequence types ST678 (German outbreak with enteroaggregative Shiga-toxin-producing E. coli O104:H4; salmon, cucumber and a toy), ST410 (poultry, swine and cattle farms) and ST167/617 (swine farms and turkey meat). The bla(CTX-M-15) genes were located on IncI1 and multireplicon IncF plasmids or on the chromosome of E. coli ST410 isolates. The prevalence of CTX-M-15-producing isolates from non-human sources in Germany is still low. The bla(CTX-M-15) gene is, however, present in multidrug-resistant E. coli clones with pathogenic potential in livestock and food. The maintenance of the bla(CTX-M-15) gene due to chromosomal carriage is noteworthy. The possibility of an exchange of CTX-M-15-producing isolates or plasmids between livestock and humans (in both directions) deserves continuous surveillance.