Formulation of Chrysomycin A Cream for the Treatment of Skin Infections

Abstract

Chrysomycin A, a compound derived from marine microorganisms, proved to have a specific great in vitro inhibitory effect on methicillin-resistant Staphylococcus aureus (MRSA). It exhibits high safety for the skin, as well as a better therapeutic effect than the current clinical drug, vancomycin. Nevertheless, its poor water solubility highly limits the application and reduces the bioavailability. In view of this, we developed a cream of chrysomycin A (CA) to enhance the solubility for the treatment of skin infection, while avoiding the possible toxicity caused by systemic administration. A comprehensive orthogonal evaluation system composed of appearance, spreading ability, and stability was established to find the optimal formula under experimental conditions. The final product was odorless and easy to be spread, with a lustrous, smooth surface. The particle size of the product met Chinese Pharmacopoeia specifications and the entire cream showed long-term stability in destructive tests. The in vitro and in vivo studies indicated that CA cream had a similar anti-MRSA activity to commercially available mupirocin, showing its potential as an efficacious topical delivery system for skin infections treatment.

Keywords: MRSA; chrysomycin A; cream; skin infections; topical administration.

Figure 1

Appearances and particle sizes of the testing samples during formulation screening. (A) Nine prepared cream samples displayed differences in spreading. No. 1, 2, 5, and 9 were easy to spread, and others were relative sticky. (B) The distribution of the water phase, oil phase, and CA crystal were uniform, and no crystal with a size larger than 180 μm was found in all samples.

Figure 2

Appearance of optimized sample and its particle size under microscope. (A) The optimized cream showed as a uniform yellowish-green paste with lustrous, smooth surface, and was easy to spread. (B) The distribution of the water phase, oil phase, and CA crystal were uniform, and no crystal with a size larger than 180 μm was found in all samples.

Figure 3

Stability of chrysomycin A cream and HPLC calibration curve of CA. (A) No stratification was observed after the study of low temperature resistance, centrifugal stability study, thermal stability study, indicating that the cream was uniform and stable. (B) HPLC calibration curve of CA and its equation.

Figure 4

In vitro antibacterial activity of free chrysomycin A against MRSA USA 300 and Pseudomonas aeruginosa PAO1. CA, MUP and FD were dissolved in DMSO, respectively. VAN and PB were dissolved in pure water. The MIC was determined to be the dose of antibiotic that inhibited bacterial growth by >95%. CA has a good inhibitory effect on Gram-positive bacteria Staphylococcus aureus USA300, while displaying poor activity against Gram-negative bacteria Pseudomonas aeruginosa PAO1.

Figure 5

In vitro antibacterial activity of chrysomycin A cream. (A) Kindy–Bauer method. Methanol extract of each formulation was added to a circular filter paper with a diameter of 15 mm. The filter papers were placed on TSA plate to observe inhibition zones. (B) CA cream exhibits a similar ability to ERY ointment to reduce bacteria survival. The MIC of different formulations was determined by detecting the bacteria survival. (C) MRSA (OD₆₀₀ = 0.5) was treated with CA formulations to further test the anti-MRSA activity of CA and CA cream, MUP was used as positive control. CA and CA cream treatment resulted in the eradication of living cells to the limit of detection. Statistical analysis was expressed as the mean ±SD, using a one-way ANOVA or Student’s t-test. The data were considered as statistically significant difference when *** p < 0.001 versus the indicated group.

Figure 6

In vitro and in vivo antibacterial activities of CA cream. The number of S. aureus in infected skin was determined by the number of colonies in the TSA plate. Statistical analysis was expressed as the mean ±SD, using a one-way ANOVA or Student’s t-test. The data were considered as statistically significant difference when *** p < 0.001 versus the indicated group.