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Assessment of Antimicrobial Activity of Plectasin Against Local Strains of Gram Negative and Positive Bacteria *O

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Assessment of Antimicrobial Activity of Plectasin Against Local Strains of Gram Negative and Positive Bacteria *O GSJ: Volume 6, Issue 10, October 2018 ISSN 2320-9186 107 GSJ: Volume 6, Issue 10, October 2018, Online: ISSN 2320-9186 www.globalscientificjournal.com ASSESSMENT OF ANTIMICROBIAL ACTIVITY OF PLECTASIN AGAINST LOCAL STRAINS OF GRAM NEGATIVE AND POSITIVE BACTERIA *O. O. Afolabi1, M. O. Adigun1, R.F. Peters2 , C. Okonofua1, U. Umar3 and O.E. Afuwape1 1Department of Biological Sciences, Crawford University, Faith City, Igbesa, Ogun State, Nigeria 2University Teaching Hospital, Idi-Araba, Lagos, Nigeria 3Department of Microbiology, Abubakar Tafawa Balewa University, Bauchi, Nigeria *[email protected]//+234 8023123868 ABSTRACT Bacterial infection remains a leading cause of mortality worldwide and this is worsened by the continuous emergence of antibiotic resistance. Defensins show broad spectrum antimicrobial activity and Plectasin 4431-s an organic peptide defensin that has not had its potential negative effects and extent of antimicrobial action clarified was screened against genetically diverse clinical isolates including Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Acinectobacter baumanii, Salmonella typhi, Klebsiella pneumoniae, Proteus mirabilis, Enterococcus faecalis and its antibiotic potential compared against other antibiotics which include levofloxacin-15µg, ceftriaxone-30µg, ciprofloxacin- 5µg, imipenem-30µg, cefuroxime-30µg. The range of Minimum Inhibitory Concentration (MIC) of plectasin was between 0.007mg/ml to 1.8mg/ml. MIC for Enterococcus faecalis was at 0.056mg/ml, MIC for Staphylococcus aureus was at 0.113mg/ ml and MIC for Klebsiella pneumoniae was at 1.8 mg/ml. There was no inhibitory effect on Escherichia coli between plectasin concentration 0.007mg/ml to 1.8mg/ml while similarly Proteus mirabilis, Acinectobacter baumanii, Salmonella typhi, Pseudomonas aeruginosa MIC was nil. Results show that Plectasin 4431-s showed significant antimicrobial activity against some Gram positive bacteria such as Staphylococcus aureus at concentration 0.113mg/ml to 1.8mg/ml and Enterococcus faecalis at concentration of 0.056mg/ml to 1.8mg/ml. For Gram-negative bacteria, Plectasin 4431-s showed insignificant inhibitory effect on the growth of Escherichia coli, Proteus mirabilis, Acinectobacter baumanii, Salmonella typhi, Pseudomonas aeruginosa. The minimum bactericidal concentration of plectasin against Enterococcus faecalis, Staphylococcus aureus and Klebsiella pneumoniae was 0.056mg/ ml, 0.113mg/ ml and 1.8 mg/ ml respectively. Results obtained suggest that plectasin could be an alternative antibiotic for clinical applications against bacterial infection mostly against Gram-positive bacteria on which they have significant antibacterial activity. This will be a novel strategy that can have major clinical implications in the fight against bacterial infections. Keywords: Plectasin, gram-positive, gram-negative, bacterial infection, antibiotic GSJ© 2018 www.globalscientificjournal.com GSJ: Volume 6, Issue 10, October 2018 ISSN 2320-9186 108 INTRODUCTION The epidemic of antimicrobial resistance is a growing public health threat. Bacteria have a high intracellular pressure, they must protect themselves from osmolysis with a rigid peptidoglycan, a meshwork of strands of glycan and peptide covalently cross-linked. Gram- negative bacteria, such as Escherichia coli and Pseudomonas aeruginosa, and Gram- positive bacteria, such as Staphylococcus aureus and Streptococcus pneumoniae, both have a peptidoglycan layer as part of their cell-wall structure. The peptidoglycan layer of Gram- positive bacteria is generally much thicker than that of Gram-negative bacteria, and constitutes the outermost layer. The peptidoglycan undergoes cross linking of the glycan strands by the action of transglycosidase, and of the peptide strands by the action of transglycosidase, and of the peptide strands by action of transpeptidase. In addition to Beta- lactams, vancomycin, considered a last resort among antibiotics, also targets peptidoglycan to block cell-wall biosynthesis. It binds to the D-Ala4-D-Ala5 moiety of pentapeptides and thereby keeps the substrates away from transpeptidase and transglycosidase. This substrate sequestion leads to the failure of peptidoglycan crosslinks, making the cell wall susceptible to osmolysis (Walsh, 2010). Although a large number of antibiotics are used clinically, the variety of targets that they inhibit is limited. Antibiotics are usually classified on the basis of chemical structure and mode of action. To understand how antibiotics work and why bacteria become resistance to them, a brief description of the targets of the main classes of antibiotics is required. The main classes of antibiotics inhibit four classical targets; cell wall biosynthesis, protein biosynthesis, DNA and RNA biosynthesis, and (IV) folate biosynthesis (Walsh, 2009). Inhibition of Bacterial Cell Wall Biosynthesis Since bacteria have a high intracellular pressure, they must protect themselves from osmolysis with a rigid peptidoglycan, a meshwork of strands of glycan and peptide covalently cross-linked. Gram-negative bacteria, such as Escherichia coli and Pseudomonas aeruginosa, and Gram-positive bacteria, such as Staphylococcus aureus and Streptococcus pneumoniae, both have a peptidoglycan layer as part of their cell-wall structure. The peptidoglycan layer of Gram-positive bacteria is generally much thicker than that of Gram- negative bacteria, and constitutes the outermost layer. The peptidoglycan undergoes cross linking of the glycan strands by the action of transglycosidase, and of the peptide strands by the action of transglycosidase, and of the peptide strands by action of transpeptidase. In addition to Beta-lactams, vancomycin, considered a last resort among antibiotics, also targets peptidoglycan to block cell-wall biosynthesis. It binds to the D-Ala4-D-Ala5 moiety of pentapeptides and thereby keeps the substrates away from transpeptidase and GSJ© 2018 www.globalscientificjournal.com GSJ: Volume 6, Issue 10, October 2018 ISSN 2320-9186 109 transglycosidase. This substrate sequestion leads to the failure of peptidoglycan crosslinks, making the cell wall susceptible to osmolysis (Walsh, 2010). Inhibition of Protein Biosynthesis Protein biosynthesis, a central reaction for cellular function, is catalyzed by ribosomes, composed of two nucleoprotein subunits,30s and 50s subunits with about two-thirds RNA and one- thirds protein, in prokaryotes (Ban et al., 2010).This machinery of prokaryotes differs substantially from the eukaryotic counterpart, which explains the effectiveness and selective toxicity of many clinically important antibiotics. The X-ray structure of 30s and 50s subunits (Schluenzen et al., 2010) and of 70S ribosome reveals the architecture of this gain protein biosynthesis machinery in detail, and the peptidyltransferase activity deriving from the catalytic ribozyme domain of the 23S rRNA with no obvious assistance from protein subunits. Due to the large number of steps involved in protein biosynthesis, initiation, elongation and termination, it is not surprising that there are many steps to be blocked, or that many clinically useful antibiotics that interact with the conserved sequences of 16S rRNA of the 30S subunits (Aminoglycoside and tetracycline) and the 23S rRNA of the 50S subunit (macrolides, chloramphenicol, lincosamides, and quinupristin- dalfopristin) have been found (Carter et al., 2010). Inhibition of DNA And RNA Biosynthesis DNA replication is an essential process for all organisms. Bacteria chromosomal DNA is packed in a highly twisted (supercoiling) state in the cell, and dynamically changes its structure during the replication process (Sherratt, 2003). The enzymes involved in interconversion of a topologically different form of the DNA are called topoisomerases. The DNA topoisomerase are classified into type I and type II type I topoisomerase transiently breaks either one strand at a time, while type II topoisomerase breaks both strands at the same time (Maxwell, 2009). Due to the essential character of DNA replication, it is natural that microorganisms such as Streptomycetes produce metabolites such as novobiocin and coumermycin that kill their neighbours by inhibiting the DNA replication process, the target of which has been found to be type II topoisomerase, specifically DNA gyrase. Nalidixic acid, the prototype quinolone, was discovered to possess antibacterial activity in 1962 and was approved for urinary tract infections in 1964. This finding led to more potent quinolone antibiotics, such as norfloxacin, ciprofloxacin, ofloxacin, and gatifloxacin, called Fluoroquinolones due to the presence of a fluorine substituent. These quinolones target the GSJ© 2018 www.globalscientificjournal.com GSJ: Volume 6, Issue 10, October 2018 ISSN 2320-9186 110 DNA gyrase and affect the double-strand cleavage double-strand religation equilibrium in the gyrase catalytic reaction, in such a way that the cleaved complex accumulates by stabilization of the complex in the presence of quinoles. A second type II topoisomerase, known as topoisomerase IV, is also implicated in DNA replication and decatenation of knotted daughter chromosomes at the end of bacterial DNA replication, and thus is an important target, probably the primary one in Staphylococcus aureus. Transcription is an essential process for decoding genetic information from DNA to RNA in all organisms. RNA polymerase of bacteria composed of different subunits with a stoichiometry to form the core enzyme catalyzes transcription Rifampicin is a semisynthetic
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