Chloe A. Autran, Joe. C. Dalton, Kevin G.Carnahan, Bahman Shafii, Mark. A. McGuire and Amin Ahmadzadeh
Staphylococcus aureus is a major infectious organism causing mastitis. Certain fatty acids have been shown to inhibit the growth of pathogens including Staphylococcus aureus. An in vitro experiment was conducted to determine the effects of prostaglandin F2α (PGF2α) on growth of S. aureus. Flasks containing tryptic soy broth (TSB) were inoculated with S. aureus Novel, and subsequently treated with PGF2α (dinoprost tromethamine) at concentrations of 0, 0.3, 0.6, 1.2, and 2.4 mg/ml. Cultures were incubated at 37°C for 24 h and sampled every 3 h. The entire experiment was conducted three times in duplicates. Bacterial growth was assessed by counting colony forming units (CFU) in triplicates. Data were analyzed by repeated measures analysis of variance and reduced and full dummy variable regression models to determine the effect of PGF2α concentrations on growth patterns of S. aureus
over time. There was an effect of treatment and treatment by time interaction (P<0.05) on mean log CFU, indicating that bacterial growth over 24 h was different across treatments. At time of inoculation (0 h), mean log CFU values were not different among treatments; however at 24 h, mean log CFU for each PGF2α treatment was different from control and decreased (P<0.05) with increasing concentrations of PGF2α. The predicted growth curve for each treatment was different (P<0.05) when compared with the control, and the rate of bacterial growth was less for 1.2 mg/ml PGF2α when compared with the control and 0.6 mg/ml. The bacterial growth was completely inhibited during the 24 h period in 2.4 mg/ml PGF2α treatment. Furthermore, a non-linear regression model was employed to estimate the dose response at the 24 h, and revealed that 1.2 mg/ml was the minimum inhibitory dose. These results provide evidence, for the first time, that PGF2α, in the form of dinoprost tromethamine, has bacteriostatic and bactericidal effects on S. aureus in vitro.
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