Abolfazl Rafati Zomorodi - Department of Bacteriology and Virology, Shiraz Medical School, Shiraz University of Medical Sciences, Shiraz, Iran
Gholamreza Hashemitabar - Department of Pathobiology, Faculty of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad, Iran
Fatemeh Aflakian - Department of Pathobiology, Faculty of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad, Iran.

Background and Aim : In the dairy industry, bovine mastitis (BVM) is indicated as a significantconcerning result of economic loss worldwide. Bacterial infections are introduced as the mainreason for BVM; subsequently, antibiotic therapy has been propounded as the first line of combatin mastitis cases because antibiotic residue in milk will develop diminishing antibiotic resistanceto the environment. P. aeruginosa, a non-fermentative gram-negative rod-shaped bacterium, iswidely associated with several infections, specially BVM. Also, P. aeruginosa is listed as a criticalpriority pathogen by the World Health Organization due to emerging multi-, extended- and pandrugresistance P. aeruginosa isolates. The present study was performed to aim to assess theantimicrobial susceptibility pattern among phenotypic resistant P. aeruginosa isolates from clinicalmastitis from Mashhad, northeast Iran.Methods : The current study was conducted on a collection of P. aeruginosa isolates from clinicalmastitis cases kept at the Microbiology laboratory, faculty of veterinary, Ferdowsi University ofMashhad. A total of ۵۰ P. aeruginosa isolates from clinical mastitis cases were subjected in thecurrent study. The Kirby-Bauer method was used to determine all isolates' antimicrobialsusceptibility patterns. The colistin broth disc elution method (CBDE) was used as CLSI (۲۰۲۲)recommended demonstrating the colistin-resistant isolates.Results : The antimicrobial susceptibility testing has revealed the highest resistance againstmeropenem ۴۰ isolates (۸۰%); however, aztreonam has shown a significant sensitivity (۱۰۰%).Also, all isolates were sensitive to tobramycin and gentamycin. The CBDE test has determined ۳colistin-resistance isolates.Conclusion : The emergence of colistin-resistance P. aeruginosa is a global issue that indicatesantimicrobial stewardship is necessary to manage increasing antimicrobial resistance.

Bovine mastitis, Colistin, P. aeruginosa