Anti-Bacterial Activity of Endophytic Streptomyces sp. towards Acinetobacter baumannii

Aims: To screen fifty-six endophytic streptomyces isolates for anti-bacterial activity on two clinical strains of Acinetobacter baumannii (carbapenem sensitive and resistant).
Place and Duration of Study: Universiti Kebangsaan Malaysia; between May 2011 and February 2012.
Methods: In this study, 56 isolates of endophytic Streptomyces sp. and their extracts were screened for anti-bacterial activity against A. baumannii. The compound’s profile was obtained for determination of active metabolites
Results: The bioassay showed that 14 isolates namely “Strain Universiti Kebangsaan” (SUK) had anti-bacterial activity towards A. baumannii. Isolates SUK 31, SUK 56 and SUK 15 showed 100% inhibition, while SUK 8 and SUK 10 showed more than 50% inhibition. These 3 isolates proceeded with secondary metabolites extraction using ethyl acetate. Disc diffusion test showed the zone of inhibition towards sensitive and resistant strain of A. baumannii; by SUK 15 at 11 and 8 mm, while SUK 31 at 7 and 10 mm, respectively. Minimum inhibition concentration (MIC) and minimum bactericidal concentration (MBC) of SUK 8 were 1.0mg/mL and 4.0mg/mL, respectively. On the other hand, SUK 15, SUK 31 and SUK 56 had the same MIC and MBC values at 2.0mg/mL. Then again, there was no difference between the MIC and MBC values for both strains of A. baumannii. Analysis of profile extract components of one selected extract, SUK 8, showed that there was at least nine polar compounds that had been successfully separated using a Thin Layer Chromatography (TLC) technique.
Conclusion: Endophytic Streptomyces sp. exhibits an anti-bacterial activity against resistant and sensitive strains of A.baumannii, thus might be a potential drug candidate.