High-Zinc Supplementation of Weaned Piglets Affects Frequencies of Virulence and Bacteriocin Associated Genes Among Intestinal Escherichia coli Populations

Vanessa C Johanns; Lennard Epping; Torsten Semmler; Fereshteh Ghazisaeedi; Antina Lübke-Becker; Yvonne Pfeifer; Inga Eichhorn; Roswitha Merle; Astrid Bethe; Birgit Walther; Lothar H Wieler

doi:10.3389/fvets.2020.614513

High-Zinc Supplementation of Weaned Piglets Affects Frequencies of Virulence and Bacteriocin Associated Genes Among Intestinal Escherichia coli Populations

Front Vet Sci. 2020 Dec 16:7:614513. doi: 10.3389/fvets.2020.614513. eCollection 2020.

Affiliations

¹ Advanced Light and Electron Microscopy (ZBS-4), Robert Koch Institute, Berlin, Germany.
² Microbial Genomics (NG1), Robert Koch Institute, Berlin, Germany.
³ Center for Infection Medicine, Institute of Microbiology and Epizootics, Freie Universität Berlin, Berlin, Germany.
⁴ Nosocomial Pathogens and Antibiotic Resistance (FG13), Robert Koch Institute, Wernigerode, Germany.
⁵ Institute for Veterinary Epidemiology and Biostatistics, Freie Universität Berlin, Berlin, Germany.
⁶ Robert Koch Institute, Berlin, Germany.

Abstract

To prevent economic losses due to post-weaning diarrhea (PWD) in industrial pig production, zinc (Zn) feed additives have been widely used, especially since awareness has risen that the regular application of antibiotics promotes buildup of antimicrobial resistance in both commensal and pathogenic bacteria. In a previous study on 179 Escherichia coli collected from piglets sacrificed at the end of a Zn feeding trial, including isolates obtained from animals of a high-zinc fed group (HZG) and a corresponding control group (CG), we found that the isolate collection exhibited three different levels of tolerance toward zinc, i.e., the minimal inhibitory concentration (MIC) detected was 128, followed by 256 and 512 μg/ml ZnCl_2. We further provided evidence that enhanced zinc tolerance in porcine intestinal E. coli populations is clearly linked to excessive zinc feeding. Here we provide insights about the genomic make-up and phylogenetic background of these 179 E. coli genomes. Bayesian analysis of the population structure (BAPS) revealed a lack of association between the actual zinc tolerance level and a particular phylogenetic E. coli cluster or even branch for both, isolates belonging to the HZG and CG. In addition, detection rates for genes and operons associated with virulence (VAG) and bacteriocins (BAG) were lower in isolates originating from the HZG (41 vs. 65% and 22 vs. 35%, p < 0.001 and p = 0.002, resp.). Strikingly, E. coli harboring genes defining distinct pathotypes associated with intestinal disease, i.e., enterotoxigenic, enteropathogenic, and Shiga toxin-producing E. coli (ETEC, EPEC, and STEC) constituted 1% of the isolates belonging to the HZG but 14% of those from the CG. Notably, these pathotypes were positively associated with enhanced zinc tolerance (512 μg/ml ZnCl₂ MIC, p < 0.001). Taken together, zinc excess seems to influence carriage rates of VAGs and BAGs in porcine intestinal E. coli populations, and high-zinc feeding is negatively correlated with enteral pathotype occurrences, which might explain earlier observations concerning the relative increase of Enterobacterales considering the overall intestinal microbiota of piglets during zinc feeding trials while PWD rates have decreased.

Keywords: E. coli; bacteriocins; gut; pig; virulence associated genes; zinc.