Abstract: Geographical specific data is required to guide empirical antimicrobial selection in equine neonates. Objective: Evaluate antibiograms and survival in foals from a United Kingdom (UK)-based hospital to guide antimicrobial selection. Methods: Blood and synovial fluid samples from 208 foals ≤ 30 days old admitted to Rossdales Equine Hospital from 2018 to 2023. Methods: Retrospective cohort study. Antimicrobial susceptibility was assessed by disc diffusion method. Bacterial culture and susceptibility and foal survival were recorded. The effects of the presence of positive culture or multidrug resistance (MDR) isolates on survival were evaluated using univariable mixed effects logistic regression. Results: Ninety-one isolates were identified from 381 samples from 208 foals. Predominantly gram-positive (75%, 68/91; 95% confidence interval [CI]: 65%-83%) isolates were identified, and Enterococcus (26%, 24/91; 95% CI: 18%-37%) was the most commonly isolated bacteria. MDR was identified in 21% of isolates (19/91; 95% CI: 13%-31%). Enterococcus was the most frequent MDR isolate (7/19). The combination of ampicillin and amikacin showed in vitro susceptibility in 90% (81/90; 95% CI: 82%-95%) of aerobic isolates. In total, 87% of foals were discharged from the hospital (180/208; 95% CI: 81%-91%). No association was identified between survival and the presence of positive culture or MDR isolates. Conclusions: Retrospective design; missing data for prior antimicrobial treatment, reason for admission and admission variables. Conclusions: Ampicillin and amikacin are appropriate combination first-line antimicrobial treatments in this population. Many Gram-positive isolates were identified, most notably Enterococcus. Culture and susceptibility guided antimicrobial choices remain crucial, especially given the unpredictable susceptibility of Enterococcus and the frequency of MDR Enterococcus isolates identified.
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Overview
This study analyzed bacterial cultures and their antibiotic susceptibilities from equine neonates at a UK hospital to guide effective antimicrobial treatment for foals with infections.
The research also investigated the relationship between bacterial infections, multidrug resistance, and survival outcomes in these foals.
Background and Objective
Equine neonates (foals ≤ 30 days old) are susceptible to bacterial infections that can be life-threatening, requiring timely and appropriate antimicrobial treatment.
Antibiotic resistance patterns vary by geographic location, so localized data is crucial to inform empirical antimicrobial choices before culture results are available.
The objective was to evaluate bacterial isolates, their antibiotic susceptibility patterns (antibiograms), and survival rates in foals admitted to Rossdales Equine Hospital in the UK from 2018 to 2023.
Methods
Samples analyzed included 381 blood and synovial fluid samples collected from 208 foals aged 30 days or younger.
Bacterial culture was performed to identify types of bacteria present in the samples.
Antimicrobial susceptibility testing was conducted using the disc diffusion method to determine which antibiotics could inhibit bacterial growth effectively.
The study design was retrospective, analyzing previously collected data over a 5-year period.
Statistical analysis included univariable mixed effects logistic regression to assess if there was a relationship between positive bacterial culture or presence of multidrug-resistant (MDR) bacteria and foal survival outcomes.
Results
A total of 91 bacterial isolates were identified from the 381 samples of 208 foals.
Most isolates were gram-positive bacteria (75%), with Enterococcus being the most commonly isolated genus (26% of isolates).
Multidrug resistance was found in 21% of all isolates, with Enterococcus also being the predominant MDR species.
The antibiotic combination of ampicillin (a beta-lactam antibiotic) and amikacin (an aminoglycoside) was effective in vitro against 90% of aerobic bacterial isolates.
Out of all foals, 87% survived to hospital discharge, indicating a generally high recovery rate.
Statistical analysis did not find a significant association between survival and either having a positive bacterial culture or the presence of multidrug-resistant organisms.
Conclusions and Clinical Implications
Ampicillin combined with amikacin is recommended as a first-line empirical antimicrobial regimen for foals with suspected bacterial infections in this UK hospital setting.
High prevalence of gram-positive bacteria, especially Enterococcus, highlights the need to consider these organisms when selecting antibiotics.
Enterococcus spp. showed unpredictable antibiotic susceptibility and frequent multidrug resistance, necessitating culture and sensitivity testing to guide effective treatment.
Culturing and susceptibility tests remain critical because empirical therapy might not cover resistant organisms effectively.
The study’s retrospective design and missing data on prior antimicrobial use and admission details limit the generalizability and detailed interpretation of the findings.
Study Limitations
Retrospective nature means data was dependent on existing records, which may have been incomplete or inconsistent.
Information on previous antimicrobial treatments before admission and reasons for admission were missing or incomplete, which could impact antimicrobial resistance patterns and outcomes.
Admission clinical variables were not fully accounted for, potentially influencing survival analysis.
Summary
This study informs veterinarians at UK equine hospitals about the bacterial pathogens commonly affecting foals and their antibiotic resistance profiles.
By identifying ampicillin plus amikacin as effective empirical therapy in most cases, it supports rational antibiotic use to improve clinical outcomes and reduce resistance risks.
Given the frequency of multidrug-resistant Enterococcus species, culture and susceptibility testing remain essential to tailor optimal antimicrobial therapy in equine neonates.
Cite This Article
APA
Graham AE, Colgate VA, Floyd EF.
(2025).
Antibiograms of Bacterial Cultures From Equine Neonates at a United Kingdom Hospital: 381 Samples (2018-2023).
J Vet Intern Med, 39(5), e70198.
https://doi.org/10.1111/jvim.70198
Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, UK.
Colgate, Victoria A
Rossdales Equine Hospital, Suffolk, UK.
Floyd, Emily F
Rossdales Equine Hospital, Suffolk, UK.
MeSH Terms
Animals
Horses
Retrospective Studies
Horse Diseases / microbiology
Horse Diseases / drug therapy
Horse Diseases / mortality
Anti-Bacterial Agents / pharmacology
Anti-Bacterial Agents / therapeutic use
Animals, Newborn
United Kingdom / epidemiology
Microbial Sensitivity Tests / veterinary
Hospitals, Animal
Drug Resistance, Multiple, Bacterial
Female
Male
Bacteria / drug effects
Conflict of Interest Statement
This retrospective paper discusses the susceptibility testing of amoxicillin, piperacillin and tazobactam, clarithromycin, ceftriaxone, amikacin, rifampicin, doxycycline, ampicillin, ticarcillin and clavulanic acid, erythromycin, cefotaxime, azithromycin, cefquinome, and marbofloxacin but not used in the study. The authors declare no conflicts of interest.
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