Blood culture isolates and antimicrobial sensitivities from 1621 critically ill neonatal foals (2005-2022).

Bloodstream infections in critically ill newborn foals were studied over 17 years to identify the responsible bacteria and their antibiotic resistance patterns. The research compared findings to a previous period and highlighted changes in bacterial types and antimicrobial resistance, providing guidance for effective treatment.

Study Background and Purpose

• Neonatal sepsis (blood infection) is a major cause of illness and death in newborn foals.
• Effective treatment depends on early use of appropriate antibiotics and supportive care.
• The study aimed to analyze bacterial species found in blood cultures from critically ill foals admitted to an ICU between 2005-2022 and examine their antibiotic sensitivities.
• A secondary aim was to compare the data with findings from an earlier study conducted at the same ICU from 1999-2004 to identify trends over time.

Methods

• Retrospective study of blood cultures collected from foals aged 7 days or younger admitted to Scone Equine Hospital ICU.
• Blood samples were collected upon admission to the ICU to detect bacterial infections.
• Bacterial isolation and identification were performed, followed by antibiotic susceptibility testing using the Kirby-Bauer disc diffusion method, a standard laboratory technique to assess bacterial resistance.
• Statistical analysis compared results from two periods (1999-2004 and 2005-2022) using Fisher’s exact test, with significance set at P < 0.05.

Results

• Out of 1621 blood cultures, 380 (23.4%) were positive for bacterial infection.
• A total of 402 bacterial isolates were identified; some samples had multiple isolates.
• Bacterial classification:
  • 55.5% were Gram-positive bacteria (223/402)
  • 42.6% were Gram-negative bacteria (171/402)
  • 1.7% were anaerobic bacteria (7/409)
• A significant increase in the proportion of Gram-positive bacterial isolates was observed when compared to the earlier study period (P = 0.002).
• Gram-negative bacteria showed a significant increase in resistance to seven out of the nine tested antibiotics over time, indicating rising antimicrobial resistance.

Implications and Conclusions

• The study provides updated information about the types of bacterial pathogens commonly causing bloodstream infections in critically ill neonatal foals in Australia.
• Identification of changing patterns in bacterial species (increase in Gram-positive organisms) influences empirical antibiotic choices when culture results are unavailable.
• The increase in antibiotic resistance, especially among Gram-negative bacteria, highlights the need for routine culture and sensitivity testing to guide effective antimicrobial therapy.
• Judicious use of antibiotics in equine medicine is critical to prevent further development of resistance and ensure treatments remain effective.
• Veterinarians should use this data to optimize early antimicrobial therapy for neonatal foals with sepsis, improving survival and outcomes.