Screening The Carlson Lab Natural Product Library for Antibiotic Production

The misuse of antibiotics has deteriorated the efficacy of these medications and led to routine microbial infections becoming untreatable. New antibiotics are urgently needed to combat growing rates of antimicrobial resistance. Natural products make up more than half (55%) of all clinical antibiotics; natural products have either inspired or been directly approved as antibiotics since 1981, (Newman and Cragg, 2020, J. Nat. Prod.). The Carlson Lab Natural Product Library contains fractions and extracts from microbial and algal sources. Our work has been to screen the library for antibiotic compounds through 96-well plate liquid growth assay. The assay tests samples at varying concentrations against 4 pathogens three times (triplicate). Two hundred thirty-three total samples were tested as either crude extracts (fungi and gram-negative bacteria from algal surfaces) or fractions (marine and freshwater Actinomyces) and were tested against four bacteria known to cause human diseases (Staphylococcus aureus, Bacillus subtilis, Salmonella sp., and Eschericha coli) at 100 μg/mL, 50 μg/mL, and 25 μg/mL. Of the total extracts and fractions, 53 showed growth inhibition (about 23%). Eleven extracts inhibited both gram-positive pathogens and two extracts inhibited both gram negative and gram positive pathogens. There were a total of 54 inhibitions against gram-positive bacteria (S. aureus and B. subtilis) and 8 inhibitions against gram-negative bacteria (Salmonella and E. coli). Twenty showed inhibition at 100 μg/mL, 22 at 50 μg/mL, and 20 at 25 μg/mL.We will present our results so far and discuss the significance of these findings. Our future directions are to finish screening the remaining natural product extracts and fractions and to dereplicate any known antibiotics contained in our library.