Relationship between in vitroantimicrobial sensitivity of bovine subclinical mastitis isolates and treatment outcome in lactating dairy cows

Document Type : Full paper (Original article)


1 Department of Clinical Sciences, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran

2 Department of Clinical Sciences, School of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad, Iran


The objective of the present study was to determine whether there was an association between the in
vitroantimicrobial sensitivity test results of subclinical mastitis pathogensand bacteriological cure following
intramammary treatment using a combination of nafcillin, penicillin, and streptomycin (NPS). Eighty-six
intramammary pathogens from 43 cows were examined inthis study. Most intramammary infections were
due to coagulase-negative staphylococci, coliforms, and environmental streptococci. The antibiotic
sensitivity to NPS was determined using the Kirby-Bauer disc diffusion method. Bacteriological cure rates
for sensitive, intermediate, and resistant isolates in the standard treatment group (3 intramammary infusions of NPS once daily) were 84.4, 88.9, and 100%, respectively. These figures in the extended treatment group (6 intramammary infusions of NPS once daily) were 100% for the 3 categories. Bacteriological cure was not associated with the sensitivity test result. Based on this study, Kirby-Bauer sensitivity test results were not useful as predictors of the bacteriological outcome ofsubclinical mastitis treated with intramammary NPS.