Abstract
Bacteria active against multi-drug resistant pathogens, isolated by direct selection of colonies from clover silage samples, produce zones of inhibition against two Gram-negative (Klebsiella pneumoniae Ni9 and Pseudomonas aeruginosa MMA83) and two Gram-positive (Staphylococcus aureus ATCC25923 and Listeria monocytogenes ATCC19111) pathogens. Isolates BGSP7, BGSP9, BGSP11 and BGSP12 produced the largest zones of inhibition against all four pathogens when grown in LB broth with aeration at 37°C. Isolates BGSP7, BGSP9, BGSP11 and BGSP12 were identified as Brevibacillus laterosporus and pulsed field gel electrophoresis and extracellular protein profiles showed that three different strains (BGSP7, BGSP9 and BGSP11) were isolated. A semi-native SDS-PAGE (sodium dodecyl sulphate-polyacrylamide gel electrophoresis) gel overlay assay showed that BGSP7 and BGSP9 produce small antimicrobial molecules of about 1.5 kDa, while BGSP11 produces antimicrobial molecules of 1.5 and 6 kDa active against S. aureus ATCC25923. Amino acid analysis of two antimicrobial molecules (1583.73 Da; from BGSP7 and 1556.31 Da; from BGSP11) revealed that they have a similar composition and differ only by virtue of the presence of a methionine which is present only in BGSP11 molecule. Genome sequencing of the three isolates revealed the presence of gene clusters associated with the production of non-ribosomally synthesized peptides (brevibacillin, bogorol, gramicidin S, plipastatin and tyrocin) and bacteriocins (laterosporulin, a lactococcin 972-like bacteriocin, as well as putative linocin M18, sactipeptide, UviB and lantipeptide-like molecules). Ultimately, the purification of a number of antimicrobial molecules from each isolate suggests that they can be considered as potent biocontrol strains that produce an arsenal of antimicrobial molecules active against Gram-positive and Gram-negative multi-resistant pathogens, fungi and insects.
Highlights
The acquisition and spread of antibiotic resistance among pathogenic bacteria poses a great threat to public health, especially in light of the paucity of new antibiotics being developed [1]
Clover silage samples were assayed for antipathogenic potential and three new Br. laterosporus strains (BGSP7, BGSP9 and BGSP11) were isolated showing strong antimicrobial activity against Gram-positive and Gram-negative food-borne spoilage and pathogenic bacteria from humans, animals and plants
The bioactive compounds produced by Br. laterosporus SA14 include antimicrobial peptides which are medically important substances that may be used for alternative treatment of MRSA infection [73]
Summary
The acquisition and spread of antibiotic resistance among pathogenic bacteria poses a great threat to public health, especially in light of the paucity of new antibiotics being developed [1]. There is a need for new antimicrobials that can be used as alternatives to conventional antibiotics. Antimicrobial peptides and bacteriocins are considered as such potential alternatives [2, 3]. Bacteriocins are ribosomally synthesized peptides with antimicrobial activity produced by many bacterial species. Class I are represented by antimicrobial peptides that have been enzymatically modified; Class II, which encompasses non-modified or minimally modified peptides, that are further divided into several subgroups; Class III, containing the large, unmodified heat sensitive antimicrobial proteins with bacteriolytic or some other mechanism of action
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