MEDICINE: INFECTIOUS DISEASES


Alterations in the Fecal Microbiome of Horses with Antimicrobial-Associated Diarrhea Compared with Antibiotic-Treated and Non-Treated Healthy Case Controls


Carolyn E. Arnold, DVM, DACVS*; Rachel Pilla, PhD; Keith Chaffin, MS, DACVIM; Joerg Steiner, MedVet, DMV, PhD, DACVIM, DECVIM-CA, AGAF; and Jan Suchodolski, MedVet, DVM, AGAF, DACVM


Horses with antimicrobial-associated diarrhea (AAD) have severe alterations of their fecal micro- biome compared with control horses and minor changes compared with horses on antibiotics that maintained normal feces. Other factors may contribute to the development of diarrhea. Authors’ address: Texas A&M University, College of Veterinary Medicine, College Station, TX 77843; e-mail: carnold@cvm.tamu.edu. *Corresponding and presenting author. © 2020 AAEP.


1. Introduction


Horses receiving antimicrobials may develop diar- rhea due to changes in the gastrointestinal micro- biome. This matched case-controlled study compared the fecal microbiome in hospitalized horses on antibi- otics that developed diarrhea (AAD), hospitalized horses on antibiotics that did not develop diarrhea (ABX), and a healthy, non-hospitalized control popu- lation (CON).


2. Materials and Methods


Naturally voided fecal samples were collected from AAD horses (n  17) the day that diarrhea devel- oped and matched to ABX (n  15) and CON (n  31) horses for diet, antimicrobial agent, and dura- tion of antimicrobial therapy ( 5 days or  5 days). Illumina sequencing of 16S rRNA genes on fecal DNA was performed. Alpha and beta diversity metrics were generated using QIIME 2.0. A


Kruskal-Wallis with Dunn’s post-test and analysis of similarities (ANOSIM) testing was used for sta- tistical analysis.


3. Results


Microbiome composition in AAD was significantly different from CON (ANOSIM, R  0.568, P  .001) and ABX (ANOSIM, R  0.121, P  .0012). The microbiome of AAD and ABX horses had significantly decreased richness and evenness than CON horses (P  .05). Actinobacteria (q  0.0192) and Bacte- roidetes (q0.0005) were different between AAD and CON. Verrucomicrobia was markedly decreased in AAD compared to ABX and CON (q  0.0005).


4. Discussion


Horses with AAD have a dysbiosis compared to CON horses, and show minor differences in bacterial com- munity composition to ABX horses.


Research Abstractfor more information, contact the corresponding author NOTES


438 2020  Vol. 66  AAEP PROCEEDINGS


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