METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS INHIBITED BY ENDOGENOUS ANTIBIOTICS FROM STREPTOMYCES ZAOMYCETICUS
Joshua Arias1, Luis Mota-Bravo, Lili Mesak.
University of California, Irvine, Irvine, CA.
Methicillin-resistant Staphylococcus aureus (MRSA) strains are resistant to most beta-lactam antibiotics. In 2012, there were over 75,000 reported cases of MRSA infections worldwide, with an overall mortality rate of 3.08%. In a survey of bacteria isolated from soils from Southern California we found Streptomyces zaomyceticus, a Gram-positive bacterium known to produce antibiotics. The objectives of this study were to screen for antibiotics produced by S. zaomyceticus, determine whether they inhibit MRSA, purify them, and determine their thermal stability for further chemical analysis. Actinobacteria identified as S. zaomyceticus were grown on ISP2 agar and overlaid with 0.05% triphenyltetrazolium chloride and either S. aureus ATCC 25923 (MSSA) or 43300 (MRSA) to confirm the presence of antibiotics. Extracts were tested for antibiotic activity using a thin-layer chromatography (TLC) overlay with MRSA and MSSA, and a solvent system was developed for best compound separation and fractionation by flash and high-performance liquid chromatography. Finally, the extract was incubated at 20, 37, 50, and 60 degrees Celsius to measure antibiotic thermal stability. The optimal separation solvent ratio for the extract was 9.75:0.25 dichloromethane:methanol. S. zaomyceticus produced 5 antibiotics (Rf = 0.857, 0.386, 0.243, 0.157, 0.057), which were all stable at temperatures of at least 60 degrees Celsius and active against MSSA and MRSA. S. zaomyceticus is known to produce zaomycin; however, our results indicate that our strain produces 5 antibiotics that can be separated by TLC, and all of them are active against MRSA. Future studies will focus on determining the structure and mechanisms of these compounds.