Effect of milk on antibacterial activity of tetracycline against Escherichia coli and Staphylococcus aureus isolated from bovine mastitis.
The susceptibility of mastitis-causing Escherichia coli and Staphylococcus aureus to two commonly used antibiotics, tetracycline and penicillin G, was tested in raw milk and in Muller-Hinton (MH) broth by introducing a pH indicator, bromocresol purple, which was shown to be a simple, sensitive, and rapid method. The minimum inhibitory concentration (MIC) of penicillin G in milk was the same as those in MH broth, whereas the MIC of tetracycline in milk was 4 to 32 times that in MH. An irreversible binding between tetracycline and large molecules of milk, which might be due to a hydrophobic interaction, was demonstrated by a dialysis test, suggesting the observed impairing effect was due to the action of milk on the tetracycline being tested. Further investigation revealed that much of the reduction of tetracycline's activity in milk was attributable to the milk protein casein, while other heat-sensitive components in milk also play some roles.
Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Midoriku, Yokohama 226-8501, Japan.
Ying
Y
Kuang
Haoyu
H
Jia
Kazuhiko
K
Miyanaga
Yasunori
Y
Tanji
D000818:Animals; D000900:Anti-Bacterial Agents / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D002417:Cattle; D004926:Escherichia coli / Q000187:drug effects* / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary*; D005260:Female; D008414:Mastitis, Bovine / Q000188:drug therapy / Q000382:microbiology*; D008892:Milk / Q000009:adverse effects* / Q000737:chemistry; D011485:Protein Binding; D013203:Staphylococcal Infections / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D013752:Tetracycline / Q000037:antagonists & inhibitors* / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D013752:Tetracycline