Naturally-Derived Antibiotics from Streptomyces zaomyceticus inhibit MRSA

Saturday, 14 February 2015
Exhibit Hall (San Jose Convention Center)
Joshua Daniel Arias, University of California, Irvine, Irvine, CA
Methicillin-Resistant Staphylococcus aureus (MRSA) strains are resistant not only to beta-lactams, but to other classes of antibiotics. In 2012, there were over 75,000 reported cases of MRSA infections worldwide, with an overall mortality rate of 3.08%. Streptomyces zaomyceticus, a Gram-positive bacteria, is known only to produce Zaomycin, an antibiotic that has not been researched extensively. Studying S. zaomyceticus and its antibiotic compounds would be beneficial in the ongoing battle against MRSA and overall antibiotic resistance in bacterial pathogens. The objectives of this study were (1) to screen for potential antibiotic compounds from S. zaomyceticus, (2) to determine whether these compounds inhibit MRSA or not, (3) to purify these compounds, and (4) to determine their thermal stability for future elucidation of their chemical structures. Actinobacteria identified as S.  zaomyceticus were collected from the environment and were grown on International Streptomyces Project (ISP2) agar plates. They were then overlaid with S. aureus ATCC 25923 (MSSA) and 43300 (MRSA) in order to determine the extent of their antibiotics’ effectiveness. S. zaomyceticus was then grown on ISP2 agar plates, homogenized, and extracted using ethyl acetate. These extracts were then tested for antibiotic activity using thin layer chromatography (TLC) overlays with MSSA and MRSA to determine the solvent ratio that would obtain the best separation of compounds with antibiotic activity. High-Performance Liquid Chromatography and flash chromatography was used to detect and separate antibiotics from S. zaomyceticus extract. Finally, the extract was incubated at temperatures of 20, 37, 50, and 60 degrees Celsius to measure the thermal stability of the antibiotics. Orange-colored extract (152 mg) was collected from one liter of ethyl acetate extract. The optimal separation solvent ratio for this extract was 9.75:0.25 dichloromethane:methanol. S. zaomyceticus was discovered to produce five antibiotics (Rf = 0.857, 0.386, 0.243, 0.157, 0.057), and the compound with the Rf value of 0.243 was able to be purified using flash chromatography. All antibiotics were stable at temperatures of at least 60 degrees Celsius and active against both MSSA and MRSA. Determining the structure and mechanisms of all these compounds is crucial for future studies of S. zaomyceticus.