AUTHOR=Borowiak Maria , Baumann Beatrice , Fischer Jennie , Thomas Katharina , Deneke Carlus , Hammerl Jens Andre , Szabo Istvan , Malorny Burkhard 

TITLE=Development of a Novel mcr-6 to mcr-9 Multiplex PCR and Assessment of mcr-1 to mcr-9 Occurrence in Colistin-Resistant Salmonella enterica Isolates From Environment, Feed, Animals and Food (2011–2018) in Germany

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.00080

DOI=10.3389/fmicb.2020.00080

ISSN=1664-302X

ABSTRACT=<p>The polymyxin antibiotic colistin has been used in decades for treatment and prevention of infectious diseases in livestock. Nowadays, it is even considered as last-line treatment option for severe human infections caused by multidrug- and carbapenem-resistant Gram-negative bacteria. Therefore, the discovery of plasmid-mediated mobile colistin resistance (<italic>mcr</italic>) genes raised major public health concern. The aim of our study was to analyze colistin-resistant <italic>Salmonella enterica</italic> strains from animals, food, feed and the environment collected at the National Reference Laboratory for <italic>Salmonella</italic> in Germany on the presence of <italic>mcr-1</italic> to <italic>mcr-9</italic> genes. Altogether 407 colistin-resistant (MIC &gt;2 mg/L) <italic>Salmonella</italic> isolates received between 2011 and 2018 were selected and screened by PCR using a published <italic>mcr-1</italic> to <italic>mcr-5</italic> as well as a newly developed <italic>mcr-6</italic> to <italic>mcr-9</italic> multiplex PCR protocol. 254 of 407 (62.4%) isolates harbored either <italic>mcr-1</italic> (<italic>n</italic> = 175), <italic>mcr-4</italic> (<italic>n</italic> = 53), <italic>mcr-5</italic> (<italic>n</italic> = 18) or <italic>mcr-1</italic> and <italic>mcr-9</italic> (<italic>n</italic> = 8). The number of <italic>mcr</italic>-positive isolates ranged from 19 (2017) to 64 (2012) per year. WGS revealed that none of our isolates harbored the <italic>mcr-9.1</italic> gene. Instead, two novel <italic>mcr-9</italic> variants were observed, which both were affected by frameshift mutations and are probably non-functional. The <italic>mcr</italic>-harboring isolates were mainly derived from animals (77.2%) or food (20.1%) and could be assigned to ten different <italic>Salmonella</italic> serovars. Many of the isolates were multidrug-resistant. Co-occurrence of <italic>mcr-1</italic> and AmpC or ESBL genes was observed in eight isolates. Our findings suggest that <italic>mcr</italic> genes are widely spread among colistin-resistant <italic>Salmonella</italic> isolates from livestock and food in Germany. Potential transfer of <italic>mcr</italic>-harboring isolates along the food chain has to be considered critically.</p>