Abstract
In this study, the cell free modified tryptone soya broth (pH 7.4 ± 0.2) of Bacillus subtilis URID 12.1 showed significant antimicrobial activity against multidrug-resistant strains of Staphylococcus aureus, S. epidermidis, Streptococcus pyogenes and Enterococcus faecalis. The partially purified antimicrobial molecule was found to be resistant to extremes of pH and temperatures and also to higher concentrations of trypsin and proteinase K. The antimicrobial molecule was purified by a three-step method that included reversed-phase high performance liquid chromatography (RP-HPLC). The minimum inhibitory concentration (MIC) values were determined for 14 species of bacteria using a microbroth dilution technique. The HPLC-purified fraction showed the MICs ranging from 0.5 to 16 μg/ml for methicillin and vancomycin-resistant Staphylococcus aureus (MVRSA) and methicillin-resistant Staphylococcus epidermidis (MRSE) strains. The molecular mass of the antimicrobial compound was determined to be 842.37 Da. The same antimicrobial fraction showed negligible haemolytic activity against human red blood cells even at a concentration as high as 100 μg/ml. Because of its significant antimicrobial activity at low MIC values coupled with its non-haemolytic property, it may prove to be a novel antimicrobial lead molecule.
Highlights
Antimicrobial peptides (AMPs) represent a defense system against invading pathogenic bacteria and are effective therapeutically against antibiotic-resistant bacteria by causing rapid killing
The antimicrobial activity of the URID 12.1 was tested against the S. aureus Microbial Type Culture Collection (MTCC) 96 as the indicator strain
Acid, and alkaline treatment, the inhibition zones produced by the partially purified antimicrobial compound remained almost the same (Table 1). This observation indicated that antimicrobial compound was very stable
Summary
Antimicrobial peptides (AMPs) represent a defense system against invading pathogenic bacteria and are effective therapeutically against antibiotic-resistant bacteria by causing rapid killing. Nonribosomal peptides represent a large family of bioactive secondary metabolites produced by bacteria and fungi. Many of these peptides turned out to be important antibiotics like iturin, gramicidin, and bacitracin. The production of antibiotics is considered to be a major step in enhancing the competitiveness of producing organism under an environment with limited resource (Grossman, 1995). Bacillus is an important genus producing an umpteen number of ribosomal and nonribosomal peptides with bioactivity (Tamehiro et al, 2002).
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