Drug Susceptibility Trends in Mastitis-Associated Klebsiella Species from Dairy Herds

Abstract

Mastitis remains a major challenge for the dairy industry, causing significant economic losses due to reduced milk yield, diminished milk quality, and increased veterinary costs. Klebsiella pneumoniae is recognized as a critical mastitis-causing pathogen due to its rapid disease progression, poor therapeutic response, and association with multidrug resistance (MDR). This study aimed to isolate Klebsiella species from mastitis-affected dairy cows and assess their antimicrobial susceptibility profiles. A total of 160 milk samples were collected from clinically confirmed mastitis cases across four dairy farms in the Lahore region. Among these, 34 isolates (21.25%) exhibited characteristic growth on Klebsiella selective media and lactose fermentation on MacConkey agar. Biochemical identification (API^® 20E) confirmed all isolates as Klebsiella pneumoniae. Antibiotic susceptibility testing was conducted using the Kirby-Bauer disc diffusion method following CLSI guidelines. Results demonstrated that nearly all isolates were MDR, showing complete resistance to amoxicillin and piperacillin and resistance to most tested antibiotics. Notably, all K. pneumoniae isolates were fully sensitive only to the combination of colistin and tigecycline, followed by variable sensitivity to cotrimoxazole, minocycline, ceftipime, imipenem, moxifloxacin, ceftazidime, and ceftriaxone. The findings emphasize the high prevalence of MDR K. pneumoniae in bovine mastitis and highlight the potential effectiveness of colistin-tigecycline combination therapy for future mastitis outbreaks. Strengthened antimicrobial stewardship and improved farm management practices are crucial to mitigate resistance development in dairy systems.