Actinomycetes, antimicrobial activity

Antimicrobial Activity. The elfamycins antimicrobial specificity and lack of toxicity in animals can be explained in view of species-dependent specificity of elfamycin binding to EE-Tu. Inefficient cellular uptake or the presence of a nonresponding EE-Tu were cited as responsible factors for the natural resistance in Halohacterium cutiruhrum (67), Lactobaci//us brevis (68), and in actinomycetes (5,69). The low activity of elfamycins against S. aureus was also attributed to an elfamycin-resistant EE-Tu system (70). However, cross-resistance with other antibacterial agents has not been observed (71). 

A long-lasting open question in the study of Actinomycetes is why this group of bacteria produce such highly diverged compounds as secondary metabolites. It is well known that some of the compounds exhibit antimicrobial activities, which leads to a plausible argument that the defensive function of these compounds is essential for the life of this kind of bacteria in the natural environment, although this simple idea does not fully explain the marked diversity of structure and activity of the secondary metabolites. 

In recent years there has been a growing awareness of the potential value of marine and river sediments as sources of actinomycetes that produce useful metabolic products. Approximately 16% of the strains obtained from marine sediments displayed antimicrobial activity, consisting primarily of the inhibition of Gram-positive bacteria [9]. Actinomycetes were also isolated from sediments obtained from the Hudson River. Of 165 isolates obtained, 22 exhibited significant antifungal activity. All but three of the active substances contained polyene antibiotics and most of the bioactive actinomycetes were identified as streptomycetes [10]. These observations of the production of antibiotics resulted from laboratory cultivation it is not known whether the bioactive actinomycetes are also capable of producing antibiotics in the aquatic environments. 

Lipopeptides are versatile biosurfactants produced by bacterial and actinomycetes species. A remarkable property of lipopeptides is their antimicrobial activity. Many lipopep-tide are well-known antibiotics some of them are explained below. 

Borgave, S. B., Joshi, A. A., Kelkar, A. S., Kanekar, P. P. Screening of atkaliphUic, haloalka-UphiUc bacteria and alkalithermophilic actinomycetes isolated form alkaline soda lake of Lonar, India for antimicrobial activity. Int J Pharma Bio Sci. 2012, 3(4), 258-274. 

The phenazine ring system is common to some thirty microbial metabolites and antimicrobial assay shows many of them to be active against gram-positive bacteria, fungi and actinomycetes. The... 

It is well known that terrestrial microorganisms, in particular the Streptomycetes, as well as Gram-positive soil bacteria of the order, Actinomycetales are the major soirrce of antimicrobial agents. These are produced as complex secondary metabolites which resirlt in billions of US dollars per year in sales. The soil-dwelling filamentous Streptomyces coelicolor is responsible for over half the naturally-derived antibiotics in current use today. Actinomycetes are foimd in a wide variety of habitats, including aquatic and terrestrial habitats and are especially abimdant in soils of different types. Soil samples from various locations have been screened all over the world with the objective of isolating actinomycetes with the ability to produce bioactive compoimds. However most of the screenings have concentrated on the isolation of mesophilic actinomycetes. The information on secondary metabolites produced by actinomycetes is compiled by Tabarez (2005, 2006). An immense variety of active secondary metabolites with different properties have been isolated from actinomycetes. 

Hotta, K., Saito, N., Okami, Y. Studies on a new aminoglycoside antibiotic, istamycins, from an actinomycete isolated from a marine environment. JAntibiot. 1980, 33,1502-1509. Hsueh, P. R., Chen, W. H., Teng, L. J., Luh, K. T. Nosocomial infections due to methiciUin-resistant Staphylococcus aureus and vancomycin-resistant enterococci at a University Hospital in Taiwan from 1991 to 2003 resistance trends, antibiotic usage and in vitro activities of newer antimicrobial agents. Int J Antimicrob Ag. 2005,26(1), 43 9. Kharat, K., Kharat, A., Hardikar, B. P. Antimicrobial and cytotoxic activity oiStreptomyces sp. from Lonar Lake. Afr JBiotechnol. 2009, 8(23), 6645-6648. 

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