In vitro efficacy of teat disinfectants against Staphylococcus aureus strains isolated from bovine mastitis in Brazil

Abstract Text:

The present study sought to explore the in vitro efficacy of four antiseptics against Staphylococcus aureus isolated from milk of dairy cows with mastitis. The efficacy of chlorhexidine (2.0%), chlorine (2.5%), quaternary ammonium (4%), lactic acid (2.0%) and iodine (0.6%) was accessed in concentrations conventionally used as commercial antiseptics before and after teat dipping. We used 50 S. aureus strains isolated from milk of 50 different dairy herds located at Minas Gerais, Sao Paulo, Parana and Rio Grande do Sul States - Brazil. The efficacy of antiseptics were evaluated by incubation of S. aureus with the disinfectant at four different times (15”, 30”, 60” and 300”). We used 0.8 mL of each antiseptic, 0.2 of sterile milk and 1.2 mL of a bacteria solution (MacFarland scale 1) for all treatments and testing times. The activity of the antiseptics was accessed by bacteria growth in Brain-heart infusion broth and 5% sheep blood agar plates. If there was no bacteria growth in Brain-heart infusion broth and blood agar plates, the antiseptic was regarded as efficient. Statistical analysis was performed using Cochran's Q test. We found higher activity of quaternary ammonium (98 % at all testing times) and chlorhexidine (84 % at 15”, 90 % at 30”, 94 % at 60”, and 96 % at 300”) against S. aureus at all testing times (P = 0.001), followed by iodine (46 % at 15”, 56 % at 30”, 66 % at 60”, and 78 % at 300”) and chlorine (30 % at 15”, 40 % at 30”, 48 % at 60”, and 64 % at 300”). Lactic acid showed the worst results (4 % at 15”, 4 % at 30”, 8 % at 60”, and 14 % at 300”) at all testing times and its use should not be recommended. Due to variation in sensitivity and resistance of S. aureus to antiseptics, the appropriateness of a given intervention should be based on efficacy in the specific application.

Keywords: Dairy cow, intramammary infection, milking, teat dip