Inhibitory activity against pathogenic bacteria of streptomycetes isolated from natural soil resources

Abstract

Bacterial  infections  still  remain  a  major  public  health  problem  worldwide,  particularly  caused  by  multidrug  resistant bacteria. Most bacterial diseases can be treated with antimicrobial agents. However, these drugs have been used so widely and so long that the infectious strains have rapidly adapted to resist the drugs, making the drugs less effective. Each year, million people become infected with the antibiotic-resistant bacteria and die as a result of these infections. Hence, discovery of  a new  drug  to  combat  these infections is  urgently  needed. Streptomycetes is  major  group  of  soil  bacteria  ubiquitous  in natural resources. These bacteria have shown to be a remarkably rich source of natural products, accounting for the production of two-thirds of available antibiotics. Thailand has been a land rich in natural bioresources, including soil microorganisms. Therefore, the objective of this work is to search streptomycetes isolated from Thai natural resources for antibacterial activity.  The  authors  have  isolated  fifty Streptomyces strains  from  soils  collected  from  various  geographic  natural  resources  of Thailand. The 50 different isolates were determined for antimicrobial activity against various standard strains of pathogenic bacteria using agar plug methods. The infectious bacteria include Enterococcus faecalis, Staphylococcus aureus, Klebsiella pneumoniae,  Acinetobacter  baumannii,  Pseudomonas  aeruginosa and Enterobacter  aerogenes.  The antimicrobial-producing Streptomycesisolates  exhibited  clear zone  of inhibition  around their  agar plugs  containing  the  colony.

Among the fifty Streptomyces,10 isolates (20 %) (strains SMC2, SMC30, SMC31, SMC47, SMC53, SMC56, SMC95, SMC146, SMC235 and SMC270) showed antimicrobial activities. Five strains (SMC30, SMC31, SMC56, SMC95, SMC270) showed growth inhibition against E. faecalis.Seven strains (SMC2, SMC30, SMC31, SMC53, SMC56, SMC235, SMC270) against S.  aureus. Two  strains  (SMC31,  SMC47)  against K.  pneumoniae. A strain  of  SMC47  against  A.  baumannii and E.  aerogenes, and  a  strain  of  SMC146  against P.  aeruginosa. The  potent  antibacterial  agents  of  Streptomyces candidates were  also  subject  to  extraction  and  assay  for  the  antimicrobial  activity  against  the  ESKAPE  pathogens.  The antimicrobial agent wil  be  further isolated  and  purified.  These will be useful as chemotherapeutics in the future.