Isolation of antibiotic producing microorganisms by screening for antibiotic resistance

Abstract: The worldwide use of antibiotics has rapidly increased since the discovery of the secondary metabolite penicillin made by Alexander Fleming in 1928. Since then, thousands of useful secondary metabolites of microbial origin have been discovered. About 80 % of these substances originate from Actinomycetes and in particularly Streptomyces species. Lately, the search have been focused upon finding rare-actinomycetes where the chance of discover a novel secondary metabolite is larger. The use of antibiotics the past decades has led to a rapid evolution in microorganisms where naturally occurring resistance genes to antibiotics are spreading fast, hence the need for new antibiotics increases. New isolation and screening methods applied on samples from under-explored ecological niches like marine environments and plant endophytes are examined to increase the change of finding new useful antimicrobial metabolites. In the current work, samples were collected from a broad range of ecological niches; five marine samples from the west coast of Sweden, two plant samples and one sample from lichen from the middle of Sweden and one sample of bat guano from the Philippines. The samples were plated onto three different media containing one of five different antibiotics in two concentrations. Two hundred and thirty-five bacterial isolates were collected and 64 isolates were identified by sequencing their 16S rDNA. Using 58 of these isolates, a phylogenetic tree were constructed on the genus and species level. A PCR-screening covering four genes in different enzymatic pathways for secondary metabolite production were done on all samples to evaluate the theoretical ability to produce the most important types of secondary metabolites. Finally to determine production of antibacterial activity a zone-inhibition assay against one species of Staphylococcus and one species of Pseudomonas were performed on 14 isolates.