Novel class of antimicrobials from the marine isolates of actinomycetes and their potential screening against multidrug-resistant bacterial strains.

Microbial pathogenesis contributes a significant proportion to the global human mortality rate. Further, the outbreak of antimicrobial-resistant strains represents an alarming threat to human and animal healthcare, which drives scientific research on searching for novel antimicrobials. The present study is one such initiative to isolate new classes of antibiotics from the marine actinomycetes to combat the perpetual increase of multidrug-resistant strains. The soil samples from Tamil Nadu, India's coastal regions, were collected, and eight isolates of the actinomycete species (S1, S1b, S2, S3, S4b, S4W, S4R, S5) were recovered. From their 16S rRNA sequencing, the isolates belonged to Streptomyces sp.; the phylogenetic tree was constructed through the neighbour-joining method. Further, the secondary metabolites of all the isolates were screened against ATCC strains, Staphylococcus aureus (ATCC 25923), Enterococcus faecalis (ATCC 29212), Escherichia coli (ATCC 25927) and Acinetobacter baumanni (ATCC 19606) and multidrug-resistant (MDR) strains, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecalis (VRE), carbapenem-resistant Klebsiella pneumonia (OXA) and colistin-cephalosporin resistant Escherichia coli (MCR). Of the eight isolates, S1b and S3 showed good inhibition for all the strains tested and their genomic sequences were sequenced and submitted to Genbank, MK641472 (S1b) & MK641473 (S3). Conclusively, their metabolites were purified using LC-MS and no resemblances were found with standard classes of antimicrobials such as nitrofurans, sulfonamides, fluoroquinolones, tetracyclines, chloramphenicols or ivermectins, which suggests that these metabolites are novel and could be exploited for the prospective antimicrobial research. [ABSTRACT FROM AUTHOR]