Abstract

Background:
Increasing antimicrobial resistance poses a serious threat to both animal and public health. Identifying the factors that play a role in resistance will contribute to preventive measures and strategies to address this problem.

Aim:
This study investigated the roles of veterinarians' approaches to the treatment of mastitis in dairy cows and the antimicrobial compounds used in the field isolates on the development of resistance.

Methods:
A face-to-face questionnaire was conducted to determine veterinarians' approaches to the treatment of mastitis, the challenges they faced in treatment, and the antimicrobial compounds they used. In addition, Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) were isolated and identified from milk samples of 248 cows with mastitis in 60 farms across 26 different regions in two provinces located in eastern Turkey and their resistance to the antimicrobial compounds used by veterinarians in the field was determined by the disc diffusion. Antimicrobial usage and resistance percentages were z-score standardized and analyzed using K-means clustering, with the four-cluster solution selected based on silhouette analysis.

Results:
The questionnaire survey revealed that veterinarians treated mastitis based on clinical signs and their own experience. They were often forced to use multiple antimicrobial compounds due to the difficulties in treatment, but despite this, the treatment of mastitis resulted in failure in most cases. A large majority of veterinarians stated they were willing to perform microbiological cultures and antibiograms if available, but noted a lack of adequate laboratory services. The results of the antimicrobial susceptibility testing conducted on E. coli isolates revealed that the highest resistance rate (93.2%) was observed against ampicillin-sulbactam, while no resistance was detected against ertapenem, tigecycline, and nitrofurantoin antimicrobial compounds used in human medicine. Among S. aureus isolates obtained from milk samples with mastitis, the highest resistance rate was 100% against benzylpenicillin, followed by erythromycin (78%), clindamycin (75%), and lincomycin (74%). Although high resistance was detected to some commonly used antimicrobials (amoxicillin and penicillin), K-means analysis identified a low-use–high-resistance profile (Cluster II), with significantly higher resistance rates in both E. coli (p < 0.05) and S. aureus (p < 0.001). Furthermore, high resistance was detected to antimicrobial compounds mostly used in human medicine rather than in the treatment of mastitis or other ruminant diseases including rifampicin, linezolid, tobramycin and levofloxacin.

Conclusion:
Although the extensive use of antimicrobial compounds can lead to antimicrobial resistance, no direct link was established between the use of antimicrobial compounds in the treatment of mastitis and the development of resistance in bacteria in this study. Given that many factors play a role in the development of antimicrobial resistance, the issue must be addressed with a holistic approach in order to implement necessary measure. The detection of high resistance to critically important antimicrobial compounds used in human medicine in this study underliness the urgent need for new regulatory measures in this area in some countries, including Turkey.

Key words: Antimicrobial resistance; Escherichia coli; Questionnaire survey; Staphylococcus aureus; Veterinarians.