Biological characteristics and antibacterial activity against gram-positive bacteria of Microbacterium sp. C21 isolated from soil

Abstract

Most commercial antibiotics are derived from Streptomyces. The search for new potential microbial sources (non-Streptomyces) for antibacterial activity is proposed to prevent drug resistance by current pathogenic microbes. Strain C21 was isolated from soil, with small colonies (0.8-1.2 mm in size) on an intensive soil extract medium (ISEM). Sequence analysis of the 16S rRNA gene revealed strain C21 belongs to the group of bacteria that are difficult to cultivate, and
is considered a candidate for novel species of genus Microbacterium. Except for R2A medium, strain C21 was only able to grow in nutrient-poor media such as NB/3, TSB/10, and R4/10. N-acetylglucosamine, maltose, D-glucose, L-proline, L-rhamnose, inositol, sodium acetate and 3-hydroxybutyric acid were suitable carbon sources for the growth of strain C21. Crude extract from fermentation liquid of strain C21 can inhibit Enterococcus faecalis CCARM 5168 at a concentration of 16 µg/ml, 8 µg/ml for E. faecalis CCARM 5171, 32 µg/ml for E. faecalis CCARM 5024, 64 µg/ml for E. faecium CCARM 5025, 32 µg/ml for Streptococcus agalactiae CCARM 4504, and 8 µg/ml for S. pyogenes CCARM 4520. Results of this study established a basis for future studies on finding potential antibacterial compounds from difficult-to-culture bacteria.