Antimicrobial resistance patterns of bacteria isolated from milk samples of mastitic goats in Waghimra Zone, Amhara, Ethiopia

Abstract

ABSTRACT Mastitis is a multifactorial disease with major consequences for production, animal welfare, and public health, yet it remains less studied in goats than in cows. Moreover, reports of antimicrobial resistance among bacteria isolated from mastitic goats are scarce. In Ethiopia, treatment decisions for mastitis largely rely on empirical clinical experience rather than routine antimicrobial susceptibility testing. To address this gap, a cross-sectional study was conducted from November to December 2024 in Waghimra, Amhara, Ethiopia, to identify the major bacterial causes of mastitis and to evaluate their antimicrobial susceptibility patterns. Bacterial isolation, identification, and antimicrobial susceptibility testing followed standard protocols, and statistical analyses were performed using Stata 17 and WHONET software. The overall goat-level mastitis prevalence was 24.69% (98/397), comprising 2.52% (10/397) clinical and 22.28% (88/395) subclinical mastitis. Staphylococcus spp. (47/129; 36.43%) was the predominant isolate, followed by E. coli (12/129; 9.30%) and Klebsiella spp. (3/129; 2.33%). All Staphylococcus isolates were resistant to ampicillin (37/37; 100%) and showed considerable resistance to tetracycline (16/37; 43.24%), but remained highly susceptible to kanamycin (36/37; 97.30%), chloramphenicol, and gentamicin (35/37; 94.59% each). E. coli and Klebsiella spp. were highly susceptible to most antimicrobials tested, except ampicillin. Multidrug resistance was detected in 13.46% (7 out of 52) of isolates, occurring exclusively among Staphylococcus spp. Subclinical mastitis, mainly caused by Staphylococcus spp., was highly prevalent in the study area, showing complete ampicillin resistance and considerable tetracycline resistance. These findings have important implications for milk production, animal welfare, and public health, given local raw milk consumption.