In vitro evaluation of the antimicrobial effect of commercially available mastitis medications combined with EDTA-Tris on bacteria that cause mastitis in cattle.

A study was conducted to evaluate the antimicrobial activity of selected commercial mastitis medications with and without EDTA-Tris by comparing minimum inhibitory concentrations and minimum bactericidal concentrations in vitro. Solutions containing 5 mM EDTA/50 mM Tris potentiated the antimicrobial action of seven commercially available mastitis medications when reacted in vitro with Staphylococcus aureus, Streptococcus uberis, and Pseudomonas aeruginosa. Lesser potentiation was observed for Escherichia coli, whereas no potentiation was observed for Klebsiella pneumoniae. The incorporation of EDTA-Tris solutions into mastitis medications may reduce the amount of antibiotics necessary for therapy and may prevent formation of antibiotic-resistant forms.