Untersuchungen zum Vorkommen und zur Stabilität von Colistin-Resistenzdeterminanten in pathogenen Escherichia coli-Isolaten aus klinischem Untersuchungsgut von Schweinen
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Beschreibung
Colistin is a reserve antibiotic, representing one of the final therapeutic options in human medicine for the treatment of infections caused by multidrug-resistant Gram-negative bacteria. The global spread of mobile colistin resistance (mcr) genes, including in food-producing animals, endangers the crucial function of colistin and represents a substantial risk to public health. The presence of mcr genes in commensal porcine E. coli has been subject of numerous studies. In contrast, there is a paucity of knowledge regarding the distribution of these genes in pig-associated pathotypes of E. coli, which are responsible for diseases in pigs. A total of 10,573 porcine E. coli isolates obtained from pigs in Germany between July 2000 and December 2021 were analysed for the presence of virulence-associated genes (VAGs) and resistance genes mcr-1 to mcr-10 using multiplex PCR. The majority of isolates were identified as one of several E. coli pathovars that have been previously associated with disease in pigs. These included enterotoxigenic E. coli (ETEC, 31.9 %), edema disease E. coli (EDEC, 12.8 %), attaching and effacing E. coli (AEEC, 12.4 %), and shigatoxin-encoding E. coli (STEC, 3.5 %). The mcr gene was detected in 10.2 % of the isolates examined, with mcr-1 (8.4 %) and mcr-4 (1.6 %) being most frequently detected. Resistance genes mcr-2 (0.02 %), mcr-3 (0.03 %), and mcr-5 (0.3 %) were also identified sporadically in isolates, in contrast to mcr-6 to mcr-10, which were not detected. There was a steady increase in the mcr-1 detection rates until 2015 (15.2 %), followed by a decline to 11.4 % in 2016 and 6.3 % in 2017. Enterotoxigenic and shigatoxin-encoding E. coli (ETEC/STEC hybrid) and EDEC were most frequently positive for mcr genes (21.9 % and 17.6 %, respectively). Whole genome sequencing of 220 representative mcr-positive E. coli strains revealed the presence of several known mcr variants, including mcr 1.1, mcr-1.26, mcr 3.12, mcr-4.1, mcr-4.2, mcr-4.3, mcr-4.6, and mcr-5.1, as well as three new mcr variants, mcr-1.36, mcr-4.8, and mcr-5.5. The most frequently identified mcr-1 gene was found to be localized on plasmid types IncX4 (83 %), IncHI2 (13 %) and IncI2 (4 %), while the majority of mcr-4 genes (97.1 %) were observed to be present on ColE10 plasmids.
In addition to inspected isolates from Germany, 1,936 porcine pathogenic E. coli strains from 17 European countries, which were isolated between 2010 and 2020, were also examined for the presence of mcr-1 and mcr-2. The mcr-1 gene was detected in the majority of E. coli strains from Hungary, Spain, Italy, and Portugal (33.3 - 60.7 %). A previously unknown mcr-2 gene variant (mcr-2.8) was detected in two ETEC isolates obtained from two pigs from a farm in Belgium. In addition to the localization of mcr-2 on IncX4 plasmids (n = 8) and the chromosome (n = 1), a previously unknown IncP-like plasmid was identified as harbouring mcr-2.1 in three isolates from one farm in Belgium.
Three pig farms in Germany were identified retrospectively on the basis of defined criteria where mcr-positive E. coli isolates had been detected for at least four consecutive years. To investigate whether the recurrent occurrence of certain E. coli pathotypes and plasmids in individual pig farms was due to the continuous presence or repeated reintroduction of E. coli strains, 87 representative isolates from a total of 154 E. coli were whole genome sequenced. The occurrence of VAGs, resistance genes, and plasmid types were analysed using bioinformatic methods. A high prevalence of 42 %, 30.8 %, and 57.7 % was observed for mcr 1.1-positive isolates obtained from farms 1, 2, and 3, respectively. Additionally, one ETEC-like isolate from farm 3 was identified as positive for mcr-4.8. Based on the determination of sequence types, virulence and resistance gene profiles, no clonal E. coli lineages were identified on any of the farms. The analysis revealed the presence of E. coli isolates of sequence types ST10 and ST131, which are considered to be E. coli with zoonotic potential, as carriers of mcr genes on the three farms under investigation. The mcr-1.1 genes were identified on identical plasmids in farm 1 (IncHI2), farm 2 (IncX4) and farm 3 (IncX4, IncI2) over a period of several years.
This study highlights the need for further development of existing surveillance approaches that can identify potential risk factors for the introduction, maintenance and dissemination of colistin-resistant microorganisms through comprehensive and continuous data collection in livestock farms. This allows targeted measures to be taken in order to mitigate these risks.
Autor*in
Lisa Göpel
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E-Coli Restistenzen Bakterien Viren Erreger Schweine Colistin Reserveantibiotikum Colistin-resistente Mikroorganismen