Antibiotic Producing Potentials of Three Freshwater Actinomycetes Isolated from the Eastern Cape Province of South Africa

Timothy Sibanda,Anthony I Okoh,Ademola O Olaniran,Leonard V Mabinya,Kim Bernard,David A Akinpelu,Ntsikelelo Mazomba

doi:10.3390/ijms11072612

Abstract

Crude extracts of three actinomycetes species belonging to Saccharopolyspora (TR 046 and TR 039) and Actinosynnema (TR 024) genera were screened for antibacterial activities against a panel of several bacterial strains. The extracts showed antibacterial activities against both gram-negative and gram-positive test bacteria with inhibition zones ranging from 8 to 28 mm (TR 046); 8 to15 mm (TR 039); and 10 to 13 mm (TR 024). The minimum inhibitory concentrations ranged from 0.078 to 10 mg/mL (TR 046); 5 to >10 mg/mL (TR 039); and 1.25 to 5 mg/mL (TR 024). Time-kill studies revealed that crude extract of TR 046 showed strong bactericidal activity against Bacillus pumilus (ATCC14884), reducing the bacterial load by 104 cfu/mL and 102 cfu/mL at 4× MIC and 2× MIC, respectively, after 6 h of exposure. Similarly, against Proteus vulgaris (CSIR 0030), crude extract of TR 046 achieved a 0.9log10 and 0.13log10 cfu/mL reduction at 5 mg/mL (4× MIC) and 1.25 mg/mL (2× MIC) after 12 h of exposure. The extract was however weakly bactericidal against two environmental bacterial strains (Klebsiella pneumoniae and Staphylococcus epidermidis); and against Pseudomonas aeruginosa (ATCC 19582): the extract showed bacteriostatic activities at all concentrations tested. These freshwater actinomycetes appear to have immense potential as a source of new antibacterial compound(s).

Highlights

Actinomycetes are Gram-positive bacteria, which are noteworthy for their antibiotic production, producing more than 70% of all currently known antibiotics [1,2]
In this study we investigate antibiotic production by three freshwater actinomycete strains which were isolated from the Tyume River in the Eastern Cape Province of South Africa and identified to belong to the Saccharopolyspora (TR 046 and TR 034) and Actinosynnema (TR 024) genera [12]
When the crude extracts of each of the test actinomycetes were assessed against a total of 32 test bacteria at a concentration of 10 mg/mL, extract obtained from Saccharopolyspora (TR 046) was observed to be active against nine test bacteria with zones of inhibition ranging from 8-28 mm (Table 1)

Summary

Introduction

Actinomycetes are Gram-positive bacteria, which are noteworthy for their antibiotic production, producing more than 70% of all currently known antibiotics [1,2]. The antibiotic substances they produce display antibacterial, antifungal, antitumor, antiprotozoic and antiviral properties [3]. These natural antibiotics have been shaped by evolution to make them effective in killing microorganisms as a competitive tool. Antibiotics produced by actinomycetes are normally composed of heterogeneous and biologically active compounds [9]

Methods

Results

Conclusion