Assessment in the mouse of cefoperazone as a treatment for mastitis

The value of cefoperazone in mastitis therapy was assessed in the mouse model of mastitis primarily by its effect on bacterial cell numbers in the gland. In addition histological studies showed that the drug was not an irritant in the mammary gland. Pharmacokinetic studies showed that it was slowly absorbed from the gland (six days to absorb 500 micrograms) but was easily removed by milking. In ascending order of efficacy cefoperazone (500 micrograms/gland) was active against four-hour-old intramammary infections caused by Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, Streptococcus agalactiae and Strep uberis. The effect against Staph aureus was titrated down to a dose of 50 micrograms/gland. Cefoperazone was not bactericidal against intracellular staphylococci but it did sensitise them to the action of lytic enzyme. Cefoperazone and cloxacillin behaved similarly against progressive staphylococcal mastitis. Both antibiotics significantly reduced the bacterial numbers when four-hour-old infections were treated but the effect on 26-hour-old infections was perceptible only when each antibiotic was assayed against saline treatment in the mouse. The results suggest that further studies in dairy cattle should be undertaken.