Relevance of Sensitivity Testings (MIC) of S. aureus to Predict the Antibacterial Action in Milk

Abstract

Bacterial susceptibility testings were carried out in parallel Iso-sensitest broth (ISB) and bovine milk cultures using 16 antibacterials and 4 sensitive strains of mastitic isolates of Staphylococcus aureus.Bacterial activities were analyzed by continuous turbidity monitoring (broth cultures), continuous fluorometric monitoring of the resazurin-reducing redox activity, and by analyzing the triphenyltetrazolium (TTC)-reducing capacity at the end of the incubation period.To obtain an equipotent bacteria-suppressing activity, milk cultures required in general several times more antibiotic than the respective ISB cultures. Antibacterial activities of sulfadoxinetrimethoprim, vancomycin, novobiocin, macrolides, aminoglycosides and oxytetracycline were most effectively suppressed by milk. Aminoglycosides suffered additionally from reduction of oxygen in the incubation environment. The b-lactams (penicillin G, oxacillin, cephalothin, ceftiofur, ampicillin, ampicillin-clavulanic acid), gentamicin and enrofloxacin showed extremely variable sensitivity results depending on the S. aureuslmilk combination.

Pharmacokinetics, milk penetration and PK/PD analysis by Monte Carlo simulation of marbofloxacin, after intravenous and intramuscular administration to lactating goats

“…Moreover, evidence indicates that PK/PD endpoints for fluoroquinolones in milk may be higher than in plasma. Louhi, Inkinen, Myllys, and Sandholm () and Fang and Pyörälä () reported a lower in vitro antimicrobial susceptibility of S. aureus and E. coli to enrofloxacin when cultured in milk compared to broth. These findings may result in higher cut‐off values for MFX in milk compared to serum, by increasing MIC value in milk.…”

Synergistic interactions between cefalexin and kanamycin in Mueller-Hinton broth medium and in milk

“…The bacteriostatic and bactericidal concentrations of antibiotic required are usually larger in milk than in broth media (Krabbenhoft et al. 1965; Owens and Watts 1987; Louhi et al. 1992; Ganière et al.…”

“…In order to better reflect the actual in vivo activity in the udder, some authors have recommended the use of milk‐based medium for minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) determinations (Owens and Watts 1987; Louhi et al. 1992; Ganière et al.…”

Efficacy of Targeted 5-day Combined Parenteral and Intramammary Treatment of Clinical Mastitis Caused by Penicillin-Susceptible or Penicillin-Resistant Staphylococcus aureus

“…As regards the pharmacokinetics of the antimicrobials used here, with parenterally administered penicillin G at the dosing we used, therapeutic concentrations in the udder for susceptible S. aureus strains can be maintained [8]. Spiramycin penetrates well into the udder and milk when administered parenterally at the dosage used in this study [8], but milk strongly reduces its antibacterial activity [13]. Information about the pharmacokinetics of systemic amoxycillin-clavulanic acid suspension in dairy cows is almost totally lacking, but in view of the low dose used here as recommended by the manufacturer and according to the literature which is available [20], therapeutic concentrations could hardly be achieved in the udder.…”