Journal of Veterinary Clinics (한국임상수의학회지)

The Korean Society of Veterinary Clinics (한국임상수의학회)
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Diagnosis of Subclinical Mastitis-Causing Pathogens Using MALDI-TOF Mass Spectrometry in a Certified Organic Dairy Farm in Korea

  • Sung Jae Kim (Department of Companion Animal Health, Kyungbok University) ;
  • Hyun-Tae Kim (Department of Clinical Sciences and Advanced Medicine, School of Veterinary Medicine, University of Pennsylvania) ;
  • Yo-Han Kim (College of Veterinary Medicine and Institute of Veterinary Science, Kangwon National University)
  • Received : 2023.11.17
  • Accepted : 2023.11.28
  • Published : 2023.12.31
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Abstract

We identified mastitis-causing pathogens using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) in an organic dairy farm and evaluated the effects of antimicrobial restriction on antimicrobial susceptibility. A total of 43 Holstein cows without any clinical sign of mastitis were used in this study, and 172 quarter milk samples were cultured on blood agar plates for 24 hours at 37℃. Subsequently, bacterial species were identified and antimicrobial susceptibility tests were performed. The subclinical mastitis infection rates in the cows and quarters were 58.1% (25/43) and 25.6% (44/172), respectively. In the species identification, Staphylococcus aureus (40.9%) was the most prominent isolate, followed by S. chromogenes (22.7%), S. epidermis (18.2%), S. simulans (11.4%), S. haemolyticus (2.3%), S. muscae (2.3%), and S. xylosus (2.3%). In the antimicrobial susceptibility test, all isolates were 100% susceptible to 24 of 28 antibiotics, except for benzylpenicillin, cefalotin, cefpodoxime, and trimethoprim/sulfamethoxazole. The resistance rates of S. aureus, S. chromogenes, and S. muscae isolates to trimethoprim/sulfamethoxazole were 27.8%, 10%, and 100%, respectively, and the resistance rates of S. epidermis and S. xylosus to benzylpenicillin were 50% and 100%, respectively. S. chromogenes, S. epidermis, S. simulans, S. haemolyticus, and S. xylosus were resistant to cefalotin and cefpodoxime. In conclusion, restrictions on antimicrobial use for organic dairy farm certification have resulted in a high Staphylococcus spp. infection rate. Therefore, our study indicates the importance of mastitis management strategies implemented by farmers together with veterinary practitioners, even if mastitis does not appear clinically in organic dairy farms.

Keywords

Acknowledgement

This study was supported by 2022 Research Grant from Kangwon National University.

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