High dietary zinc supplementation increases the occurrence of tetracycline and sulfonamide resistance genes in the intestine of weaned pigs

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Abstract

Background

Dietary zinc oxide is used in pig nutrition to combat post weaning diarrhoea. Recent data suggests that high doses (2.5 g/kg feed) increase the bacterial antibiotic resistance development in weaned pigs. Therefore, the aim of this study was to investigate the development of enterobacterial antibiotic resistance genes in the intestinal tract of weaned pigs.

Findings

Weaned pigs were fed diets for 4 weeks containing 57 (low), 164 (intermediate) or 2425 (high) mg kg ⁻¹ analytical grade ZnO. DNA extracts from stomach, mid-jejunum, terminal ileum and colon ascendens were amplified by qPCR assays to quantify copy numbers for the tetracycline ( tetA) and sulfonamide ( sul1) resistance genes in Gram-negative bacteria. Overall, the combined data (n = 336) showed that copy numbers for tetracycline and sulfonamide resistance genes were significantly increased in the high zinc treatment compared to the low ( tetA: p value < 10 ⁻⁶; sul1: p value = 1 × 10 ⁻⁵) or intermediate ( tetA: P < 1.6 × 10 ⁻⁴; sul1: P = 3.2 × 10 ⁻⁴) zinc treatment. Regarding the time dependent development, no treatment effects were seen 1 week after weaning, but significant differences between high and low/intermediate zinc treatments evolved 2 weeks after weaning. The increased number of tetA and sul1 copies was not confined to the hind gut, but was already present in stomach contents.

Conclusions

The results of this study suggest that the use of high doses of dietary zinc beyond 2 weeks after weaning should be avoided in pigs due to the possible increase of antibiotic resistance in Gram-negative bacteria.

Electronic supplementary material

The online version of this article (doi:10.1186/s13099-015-0071-3) contains supplementary material, which is available to authorized users.

Related collections

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Dietary doses of 2,500 ppm ZnO-Zn reduced bacterial activity (ATP accumulation) in digesta from the gastrointestinal tracts of newly weaned piglets compared to that in animals receiving 100 ppm ZnO-Zn. The amounts of lactic acid bacteria (MRS counts) and lactobacilli (Rogosa counts) were reduced, whereas coliforms (MacConkey counts) and enterococci (Slanetz counts, red colonies) were more numerous in animals receiving the high ZnO dose. Based on 16S rRNA gene sequencing, the colonies on MRS were dominated by three phylotypes, tentatively identified as Lactobacillus amylovorus (OTU171), Lactobacillus reuteri (OTU173), and Streptococcus alactolyticus (OTU180). The colonies on Rogosa plates were dominated by the two Lactobacillus phylotypes only. Terminal restriction fragment length polymorphism analysis supported the observations of three phylotypes of lactic acid bacteria dominating in piglets receiving the low ZnO dose and of coliforms and enterococci dominating in piglets receiving the high ZnO dose. Dietary doses of 175 ppm CuSO(4)-Cu also reduced MRS and Rogosa counts of stomach contents, but for these animals, the numbers of coliforms were reduced in the cecum and the colon. The influence of ZnO on the gastrointestinal microbiota resembles the working mechanism suggested for some growth-promoting antibiotics, namely, the suppression of gram-positive commensals rather than potentially pathogenic gram-negative organisms. Reduced fermentation of digestible nutrients in the proximal part of the gastrointestinal tract may render more energy available for the host animal and contribute to the growth-promoting effect of high dietary ZnO doses. Dietary CuSO(4) inhibited the coliforms and thus potential pathogens as well, but overall the observed effect of CuSO(4) was limited compared to that of ZnO.

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Author and article information

Contributors

Wilfried Vahjen: Wilfried.Vahjen@fu-berlin.de

Dominika Pietruszyńska: d.pietruszynska@wp.pl

Ingo C. Starke: Ingo.Starke@fu-berlin.de

Jürgen Zentek: Juergen.Zentek@fu-berlin.de

Journal

Journal ID (nlm-ta): Gut Pathog

Journal ID (iso-abbrev): Gut Pathog

Title: Gut Pathogens

Publisher: BioMed Central (London )

ISSN (Electronic): 1757-4749

Publication date (Electronic): 26 August 2015

Publication date PMC-release: 26 August 2015

Publication date Collection: 2015

Volume: 7

Electronic Location Identifier: 23

Affiliations

Institute of Animal Nutrition, Freie Universität Berlin, Berlin, Germany

Article

Publisher ID: 71

DOI: 10.1186/s13099-015-0071-3

PMC ID: 4551370

PubMed ID: 26322131

SO-VID: 6770f981-cdf0-4f7c-9d75-7e3220930015

License:

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.