Dr. David John
University of South Florida St. Petersburg
Many current antibacterial agents on the market are derived from compounds naturally produced by bacteria. This experiment was conducted to isolate and assess possible antibacterial strains, namely Actinomycetes, from 50 mL of marine and terrestrial samples collected from nine locations around the St. Petersburg area. The agar plates were prepared with Jensen’s AMM agar and inoculated with bacterial samples which had been diluted by factor 1:100 and heated. Three plates were initially assigned to a sample to test against three laboratory bacteria by the overlay method. Then isolates were selected and inoculated onto TSA and BHI agar plates to test against ten common pathogenic bacteria, or relatives of pathogenic bacteria, by lateral streaking. Overlays were also done for some isolates on AMM agar, and a test was performed to measure inhibition over time. The strains yielded from the terrestrial samples appeared to have far greater effectiveness against the test bacteria than those from the marine samples. One terrestrial isolate in particular showed effectiveness against all ten bacteria, whereas the marine samples showed little to no effectiveness against any of the bacteria with the exception of one. The Gram stains performed for four best terrestrial isolates revealed purple rods, indicating Gram-positive Bacillus species but not Actinomycetes. The strains were identified via DNA extraction, amplification and sequencing, as Brevibacillus choshinensis, Brevibacillus laterosporus, Bacillus amyloliquefaciens subsp. plantarum and Bacillus amyloliquefaciens. Extraction of the unknown compounds with dichloromethane and subsequent IR spectroscopy revealed a similar-looking molecule produced by all four isolates, with amine, arene and ketone or ester groups.
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Reybitz, Arianna M., "Isolating and Testing Antibiotic-Producing Bacteria from Marine and Terrestrial Samples from St. Petersburg, FL" (2015). USFSP Honors Program Theses (Undergraduate). 185.