Effects of APO-Lactoferrin on the Minimum Inhibitory Concentrations of Eight Antimicrobials with S. Aureus, S. Uberis, and E. Coli Strains Isolated from Bovine Mammary Glands
The minimum inhibitory concentrations (MICs) of eight antimicrobials (penicillin, cloxacillin, cephapirin, ceftiofur, novobiocin, enroflocxacin, erythromycin, and pirlimycin) in combination with 0, 0.3, and 5.0 mg/ml of apo-Lactoferrin (apo-Lf) were determined against Staphylococcus aureus, Streptococcus uberis, and Escherichia coli strains isolated from bovine mammary glands. The MICs of the antimicrobials displayed dramatic increases in MICs from <0.5 µg/ml in Mueller-Hinton Broth (MHB) to >64.0 µg/ml in MHB supplemented with 5.0 mg/ml of apo-Lf (MHB5) against S. aureus. Similar results were obtained against S. uberis with the exception of penicillin which demonstrated no increase in the MIC. Finally, the 𝛽-lactams, enrofloxacin, and pirlimycin displayed no remarkable change in MICs against E. coli, while erythromycin and novobiocin demonstrated drastic reductions in MICs from 32.0 and > 64.0 µg/ml in MHB to 8.0 and 16.0 µg/ml in MHB5, respectively. Enrofloxacin and pirlimycin displayed no change in MICs against E. coli. These results indicate that Lf may affect the activity of antimicrobials used to treat bovine mastitis. This effect may need to be considered in selecting the most efficacious treatment.