A high proportion of bacterial isolates from septic neonatal foals in Ontario express multidrug resistance and low susceptibility to first-line antimicrobials.

Overview

• This study investigated the types of bacteria found in sick neonatal foals in Ontario and examined how resistant these bacteria are to commonly used antibiotics.
• The findings revealed a high presence of multidrug-resistant bacteria, which are less susceptible to first-line antibiotic treatments.

Study Purpose and Population

• Goal: To describe the bacterial species isolated from sick neonatal foals (≤ 30 days old) and analyze their resistance patterns to antibiotics.
• Population: 60 neonatal foals, mostly Thoroughbreds, admitted to the Ontario Veterinary College between 2020 and 2023.
• Samples: 62 bacterial culture samples were collected, yielding 104 bacterial isolates.

Bacterial Isolates Identified

• A total of 34 bacterial species/genera were identified from the samples.
• Most frequent isolates included:
  • Enterococcus species (22%)
  • Streptococcus equi subsp. zooepidemicus (17%)
  • Escherichia coli (12%)
  • Actinobacillus equuli subsp. haemolyticus (8%)
  • Staphylococcus aureus (8%)

Antimicrobial Susceptibility Findings

• Overall, the highest antibiotic susceptibility for all isolates combined was found for:
  • Chloramphenicol (74% susceptible)
  • Ceftiofur (68%)
  • Enrofloxacin (64%)
• Gram-positive bacteria showed highest susceptibility to:
  • Chloramphenicol (87%)
  • Ampicillin (75%)
  • Rifampin (70%)
• Gram-negative bacteria were most susceptible to:
  • Enrofloxacin (81%)
  • Ceftiofur (71%)
• A combination therapy of amikacin plus ampicillin exhibited the highest susceptibility overall at 78%.

Multidrug Resistance (MDR) Analysis

• Multidrug resistance was common, with 78% of all isolates resistant to multiple antibiotics.
• Breakdown by gram stain:
  • 66% of gram-positive isolates were multidrug-resistant.
  • 93% of gram-negative isolates were multidrug-resistant.

Conclusions and Implications

• The predominance of Streptococcus equi subsp. zooepidemicus and Enterococcus species, alongside diverse equine and environmental bacteria, was confirmed.
• There is a concerning high rate of multidrug resistance among bacterial isolates from septic neonatal foals in this Ontario population.
• First-line antibiotics commonly used are showing low efficacy due to resistance.
• The study highlights the urgent need for continuous monitoring of antibiotic susceptibility patterns in foal populations.
• Effective antimicrobial stewardship programs are recommended to manage and reduce the development of resistant bacterial strains in neonatal foals.