Antimicrobial resistance of Staphylococcus aureus and Streptococcus agalactiae isolated from milk from cows with mastitis

Abstract

The indiscriminate use of antibiotics without prior in vitro sensitivity test is the main cause of failure for the treatment of mastitis in the Ayacucho región. In order to assess the antimicrobial resistance of Síaphylococcus aureus and Sírepíococcus agalacíiae causing bo- vine mastitis, the isolation, identification and antibiogram of the bacteria under study were carried out to find the resistance against five antibiotics. Samples were collected at the Allpachaca farm that belongs to the National University of San Cristóbal de Huamanga (Aya- cucho, Perú), located at coordinates 13°23'30.79 "S; 74° 15'56.48 "W, at an altitude of 3528 meters above sea level. In the field, 94 dairy cows were studied using the California Mastitis Test (CMT), which resulted in 35 cows with subclinical mastitis. In the laboratory, the isolation and the identification of S. aureus and S. agalacíiae were carried out, later the antibiogram was carried out using the method of Bauer et al. (1966). Then 35.2% of S. aureus and 12.7% S. agalacíiae were isolated. The results of the antibiogram show that S. agalacíiae was 22% resistant to penicillin, 22% to cephalexin and 33.3% sulfatrimethoprim, whereas tetra- cycline, amoxicillin plus clavulanic acid were 100% sensitive. On the other hand, .S. aureus was 52% resistant to penicillin and amoxicillin plus clavulanic acid 28%, while cephalexin, tetracycline and sulfatrimethoprim were 100% sensitive.