Abstract

A total of 83 actinobacteria isolates were successfully revived from cryovials stored in -80°C FRIM actinobacteria culture collection (FACC). Based on macromorphological observation, Streptomyces-like group is predominant among all the isolates. The representative actinobacteria isolates were grown in three different fermentation media (M1, M2 and M3) and a total of 249 culture broth extracts obtained were evaluated for in vitro antitrypanosomal activity against Trypanosoma brucei brucei strain BS221. Five extracts (2.0%) exhibited strong activity (score 3) with an IC₅₀ value ≤ 1.56 µg ml^-1 and 34 extracts (13.7%) exhibited moderate activity (score 2) of 1.56 µg ml^-1 < IC₅₀ ≤ 12.5 µg ml^-1 . Extracts showing score 3 and score 2 activities were further tested for cytotoxicity. Eight extracts exhibited good selectivity with a SI (Selectivity Index) value ≥ 20. Among the isolates showing good selectivity, isolate FACC-A032 that belonged to the genus Streptomyces produced extract with the highest antitrypanosomal activity (IC₅₀ = 0.23 µg ml^-1) and high selectivity (SI = 76.417). Growth profile study of isolates FACC-A032 in medium M3 exhibited maximum antitrypanosomal activity at day eight of fermentation with IC₅₀ = 0.15 µg ml^-1 and SI = 154.75. This is the first study of in vitroantitrypanosomal activity of soil actinobacteria isolated from Malaysian forest.

Key words: Antitrypanosomal, trypanosomiasis, actinobacteria, Alamar blue assay, Streptomyces.