Abstract
BackgroundTo tackle the problem of antibiotic resistance, an extensive search for novel antibiotics is one of the top research priorities. Around 60% of the antibiotics used today were obtained from the genus Streptomyces. The river sediments of Bangladesh are still an unexplored source for antibiotic-producing bacteria (APB). This study aimed to isolate novel APB from Padma and Kapotakkho river sediments having the potential to produce antibacterial compounds with known scaffolds by manipulating their self-protection mechanisms.ResultsThe antibiotic supplemented starch-casein-nitrate agar (SCNA) media were used to isolate antibiotic-resistant APB from the river sediments. The colonies having Streptomyces-like morphology were selectively purified and their antagonistic activity was screened against a range of test bacteria using the cross-streaking method. A notable decrease of the colony-forming units (CFUs) in the antibiotic supplemented SCNA plates compared to control plates (where added antibiotics were absent) was observed. A total of three azithromycin resistant (AZR) and nine meropenem resistant (MPR) isolates were purified and their antagonistic activity was investigated against a series of test bacteria including Shigella brodie, Escherichia coli, Pseudomonas sp., Proteus sp., Staphylococcus aureus, and Bacillus cereus. All the AZR isolates and all but two MPR isolates exhibited moderate to high broad-spectrum activity. Among the isolates, 16S rDNA sequencing of NAr5 and NAr6 were performed to identify them up to species level. The analyses of the sequences revealed that both belong to the genus Streptomyces.ConclusionsThe results from these studies suggest that manipulation of the self-resistance property of APB is an easy and quick method to search for novel APB having the potential to produce potentially novel antibacterial compounds with known scaffolds.
Highlights
To tackle the problem of antibiotic resistance, an extensive search for novel antibiotics is one of the top research priorities
Antibiotic supplementation in the starch-casein-nitrate agar (SCNA) media reduced the load of colonies on the isolation plates In this study, two antibiotics namely, azithromycin and meropenem were used separately to isolate drugresistant actinomycetes with potential of producing antibiotics to which they possess self-resistance mechanisms
It was found that the antibiotic supplementation killed the susceptible bacterial species present in the sample and reduced the number of bacteria on the isolation plates by 4–6 folds compared to the control plates where no antibiotics were added
Summary
To tackle the problem of antibiotic resistance, an extensive search for novel antibiotics is one of the top research priorities. Using the isolation chip (iChip), teixobactin, a new class of antibiotics with novel scaffolds, was discovered from Eleftheria terrae, an unculturable soil bacteria [8]. Another new class of antibiotics, lugdunin, was discovered from Staphylococcus lugdunensis, a gram-positive bacterium colonising the human nasal cavity [9]. WAC4229 by selecting the GPA-producing organisms using vancomycin [4] These recent success stories on the discovery of novel antimicrobial compounds suggest that if the relatively untapped sources are explored with novel strategies, there is still a chance of obtaining new antibiotics with novel scaffolds
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