Characterization of Corynebacterium uterequi isolates from mares in Brazil.

Overview

• This study investigates Corynebacterium uterequi isolated from mares in Brazil, focusing on its characteristics, antimicrobial susceptibility, biofilm formation, and implications as a pathogen in equine reproductive health.

Introduction and Background

• The genus Corynebacterium includes diverse bacteria that function as either normal microbiota or pathogens affecting humans and animals.
• Some species cause infections in horses, especially reproductive disorders such as endometritis (uterine inflammation), embryonic loss, and infertility.
• Corynebacterium uterequi has been identified as a potential pathogen associated specifically with reproductive problems in mares.
• Understanding C. uterequi is crucial due to its potential threat to equine reproductive health and economic impacts on horse breeding.

Research Objectives

• To isolate and characterize strains of Corynebacterium uterequi from mares in southern Brazil.
• To perform phenotypic, molecular, and phylogenetic analyses to confirm bacterial identity and explore its relation to other Corynebacterium species.
• To assess antimicrobial susceptibility against a broad panel of antibiotics to identify effective treatments.
• To examine the ability of the isolates to form biofilms under different glucose conditions.
• To evaluate biofilm eradication in response to varying antibiotic concentrations, focusing on both developing and mature biofilms.

Methodology

• Four isolates of C. uterequi were obtained from mares in southern Brazil.
• Phenotypic characterization involved assessing observable bacterial traits.
• Molecular and phylogenetic techniques confirmed the identity of the isolates and compared them to other species in the genus.
• Antimicrobial susceptibility testing was conducted using:
  • Disk diffusion method with 36 different drugs.
  • Microdilution method with five specific antibiotics: penicillin, gentamicin, doxycycline, clindamycin, and sulfamethoxazole + trimethoprim.
• Biofilm formation was evaluated at various glucose concentrations to mimic different nutrient environments.
• Minimum inhibitory concentration (MIC) values were determined for key antibiotics to identify effective doses.
• Biofilm eradication tests involved applying antibiotics at concentrations up to 8 times the MIC to both developing and mature biofilms.

Key Results

• Phylogenetic analysis confirmed all four isolates as Corynebacterium uterequi, grouping them closely with related species in the genus.
• All isolates showed susceptibility to antibiotics based on Clinical & Laboratory Standards Institute and Brazilian Committee on Antimicrobial Susceptibility Testing breakpoints relevant to related species.
• Isolates displayed the ability to form biofilms, but the strength of adhesion varied among samples and with glucose concentration.
• Antibiotic treatment was able to prevent or eradicate biofilms during their development stages effectively.
• However, mature biofilms demonstrated resistance and were not effectively eradicated even at high antibiotic concentrations (up to 8× MIC), highlighting persistence potential.

Conclusions and Implications

• Corynebacterium uterequi poses a significant pathogenic threat in equine reproductive infections primarily due to its biofilm-forming ability, which contributes to persistent infections.
• The variability in biofilm adhesion strength suggests that treatment effectiveness may depend on the stage of biofilm development and environmental factors.
• Standard antibiotics are effective against planktonic (free-floating) bacteria and early biofilm stages but less so against mature biofilms, pointing to challenges in treatment.
• These results underscore the need for:
  • Improved therapeutic strategies that target mature biofilms.
  • Further research on antimicrobial regimens or adjunct therapies (e.g., biofilm-disrupting agents) tailored for chronic uterine infections caused by C. uterequi.
  • Enhanced understanding of biofilm formation mechanisms in equine pathogens for better disease control.