Staphylococcus aureus-induced
mastitis in cattle causes important financial losses in the dairy industry due to lower yield and bad milk quality. Although S. aureus is susceptible to many antimicrobials in vitro, treatment often fails to cure the infected udder. Hence, comprehensive evaluation of antimicrobials against S. aureus
mastitis is desirable to direct treatment strategies. The mouse
mastitis model is an elegant tool to evaluate antimicrobials in vivo while circumventing the high costs associated with bovine experiments. An evaluation of the antimicrobial efficacy of the intramammary (imam) applied
first generation cephalosporins cefalexin, cefalonium,
cefapirin and
cefazolin, was performed using the S. aureus mouse
mastitis model. In vivo determination of the effective dose 2log(10) (ED(2log10)), ED(4log10), protective dose 50 (PD(50)) and PD(100) in mouse
mastitis studies, support that in vitro MIC data of the
cephalosporins did not fully concur with the in vivo clinical outcome.
Cefazolin was shown to be the most efficacious
first generation cephalosporin to treat S. aureus
mastitis whereas the MIC data indicate that cefalonium and
cefapirin were more active in vitro. Changing the
excipient for imam application from
mineral oil to
miglyol 812 further improved the antimicrobial efficacy of
cefazolin, confirming that the
excipient can influence the in vivo efficacy. Additionally, statistical analysis of the variation of S. aureus-infected,
excipient-treated mice from fourteen studies emphasizes the strength of the mouse
mastitis model as a fast, cost-effective and highly reproducible screening tool to assess the efficacy of antimicrobial compounds against intramammary S. aureus
infection.