Retrospective Analysis of Bacterial Cultures Sampled in German Chicken-
Fattening Farms During the Years 2011–2012 Revealed Additional VIM-1
Carbapenemase-Producing Escherichia coli and a Serologically Rough Salmonella
enterica Serovar Infantis
Carbapenems are last-resort antibiotics used in human medicine. The increased
detection of carbapenem-resistant Enterobacteriaceae (CRE) is therefore
worrying. In 2011 we reported the first livestock-associated VIM-1-producing
Salmonella (S.) enterica serovar Infantis (R3) isolate from dust, sampled in a
German chicken fattening farm. Due to this observation we retrospectively
investigated more than 536 stored bacterial cultures, isolated from 45 chicken
fattening farms during the years 2011 and 2012. After a non-selective
overnight incubation, the bacteria were transferred to selective media.
Escherichia (E.) coli and Salmonella growing on these media were further
investigated, including antibiotic susceptibility testing, carbapenemase gene
screening and whole genome sequencing (WGS). In total, four CRE were found in
three out of 45 investigated farms: Besides R3, one additional Salmonella
(G-336-1a) as well as two E. coli isolates (G-336-2, G-268-2). All but G-268-2
harbored the blaVIM-1 gene. Salmonella isolates R3 and G-336-1 were closely
related although derived from two different farms. All three blaVIM-1-encoding
isolates possessed identical plasmids and the blaVIM-1- containing transposon
showed mobility at least in vitro. In isolate G-268-2, the AmpC beta-lactamase
gene blaCMY-2 but no known carbapenemase gene was identified. However, a
transfer of the phenotypic resistance was possible. Furthermore, G-268-2
contained the mcr-1 gene, combining phenotypical carbapenem- as well as
colistin resistance in one isolate. Carbapenem-resistant Enterobacteriaceae
have been found in three out of 45 investigated chicken flocks. This finding
is alarming and emphasizes the importance of intervention strategies to
contain the environmental spread of resistant bacteria in animals and humans