Elsevier

Veterinary Microbiology

Volume 145, Issues 3–4, 26 October 2010, Pages 366-372
Veterinary Microbiology

Short communication
Fecal microbiota of horses in the clinical setting: Potential effects of penicillin and general anesthesia

https://doi.org/10.1016/j.vetmic.2010.03.023Get rights and content

Abstract

Antimicrobial treatment is associated with the spread of antimicrobial resistance and disturbances in the ecological balance of intestinal microbiota. In horses, the main adverse effect of antimicrobial treatment is colitis. We used culture and 16S rRNA gene based molecular methods to monitor the prevalence of antimicrobial resistance and changes in predominant fecal populations during penicillin treatment and general anesthesia of horses in the clinical setting. After 5 days of parenteral administration of penicillin, fecal Escherichia coli were resistant to multiple unrelated antimicrobial agents when compared to the pre-exposure situation. Denaturing gradient gel electrophoresis (DGGE) profiles indicated that horses have an extremely diverse fecal microbiota, with marked differences between individual horses. Most of the variation in DGGE profiles could be attributed to horse-specific factors, and penicillin, general anesthesia or both could not explain the remaining variation. Within-animal variation remained less than between-animal variation despite treatment. However, real-time PCR quantification (qPCR) indicated subclinical changes in selected bacterial groups of the penicillin treated horses.

Introduction

The equine intestinal microbiota consists of hundreds of different bacterial species of which more than 99% are anaerobic (Jones, 2000). The composition and activity of this microbiota have a profound effect on the health, growth, development and performance of the animal (Daly and Shirazi-Beechey, 2003). Despite its importance, the microbial community of the equine hindgut has received remarkably little scientific attention (Daly et al., 2001, Endo et al., 2007, Mackie and Wilkins, 1988) compared to the intestinal microbiota of other species (Eckburg et al., 2005, Simpson et al., 2000, Simpson et al., 2002, Sundset et al., 2009). Antimicrobial treatment is associated with an alteration of the intestinal microbiota, which in horses may result in potentially life-threatening colitis (Båverud et al., 1997, Gustafsson et al., 1997). Further, it has been shown that the antimicrobial resistance patterns of enteric bacteria change in response to antimicrobial exposure (Grønvold et al., 2010, Houndt and Ochman, 2000). The emergence of antimicrobial resistant bacteria is a growing threat to public health in general, as it is a major cause of treatment failure in infectious diseases in humans as well as animals.

Understanding the effect of various interventions upon the complex microbial ecosystem of the intestinal microbiota requires both basic knowledge of the composition of the microbiota and a convenient method for its study. To reflect bacterial diversity in fecal samples molecular approaches give more reliable results than culture-based methods because most intestinal bacteria are not culturable (Eckburg et al., 2005). Still, no single method can accurately describe the total community in complex ecosystems such as the intestinal tract. In this study we used an integrated approach consisting of culture-based analysis of Escherichia coli for antimicrobial susceptibility, and DGGE analysis of 16S rRNA gene amplicons and qPCR analysis to monitor the fecal microbiota of 12 horses in the clinical setting.

There are many controversies in equine antimicrobial therapy (Hollis and Wilkins, 2009). Penicillin is a commonly used, narrow spectrum antimicrobial agent considered to be relatively benign, especially with regard to the equine gastrointestinal tract. The aims of this study were to monitor the prevalence of antimicrobial resistance among fecal E. coli during penicillin treatment, general anesthesia or both, and investigate the diversity of equine fecal microbiota. In addition, we aimed to monitor potential changes in predominant fecal bacterial populations of horses during penicillin treatment, general anesthesia or both.

Section snippets

Animals and treatments

Twelve horses of different age, breed and sex and with no history of antimicrobial treatment or diarrhoea in the previous 6 months were included in the study (Table 1). All horses were client owned patients presented to the Norwegian School of Veterinary Science (NSVS) for various reasons (Table 1). While hospitalized, all horses were fed the same diet consisting of dry hay ad libitum and standard amounts of pellet grain. Horses subject to general anesthesia were starved 12 h before being

Analysis of antimicrobial resistance

In pre-treatment samples, E. coli from 10 of the 12 horses had a susceptibility pattern reflecting the normal intrinsic susceptibility to the 10 antimicrobial agents included (Table 2). After 5 days with penicillin treatment E. coli from five of the six horses treated with penicillin showed additional resistance to several (≥3) antimicrobials compared to E. coli tested in pre-treatment samples. E. coli tested from the three horses that had general anesthesia without antimicrobial treatment

Discussion and conclusions

Monitoring the antimicrobial susceptibility pattern revealed increased prevalence of resistance to several unrelated antimicrobial agents among fecal E. coli in five out of six horses after 5 days of parenteral penicillin treatment. Such increase in resistance is consistent with previous studies showing that resistance patterns of enteric bacteria change in response to antibiotic exposure (Grønvold et al., 2010, Houndt and Ochman, 2000). However, in those studies the antimicrobial exposure

Acknowledgements

The authors acknowledge Ann Øye (NSVS) and Aud Kari Fauske (NSVS) for assistance with qPCR, and Akershus University Hospital for providing bacterial reference strains. We would also like to thank Dr. Isaac Cann (University of Illinois at Urbana-Champaign) for insightful discussions and support.

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