Abstract
Bacterial resistances to the existing antibiotics are increased and multidrug resistant bacteria pose a serious threat worldwide which cause morbidity and mortality throughout the world. Thus, new antibacterial agents are needed. The present study was focused on isolation of Actinomycetes with abilities to produce diffusible pigments in media from different parts of the East side of the Umm Jirsan cave, Saudi Arabia. Samples were collected at different depth of the soil surface and different distances from the cave entrance (30-550 m). Among 107 isolates, a total of 66 isolates were diffusible pigment actinomycete producers. Among the 66 pigment producing Actinomycetes, 12 isolates were selected based on the intensity and color of the pigment. These isolates were screened for their antibacterial activities against some tested microbial pathogen by different methods, cross streak method, Agar plug diffusion method and Agar well diffusion method. Strain SAG-85 was the most active isolate. The identification and biochemical characterization of the isolate SAG-85 were determined. It was belonging to genus Streptomyces. Furthermore, the extracellular pigment was extracted using ethyl acetate and this extract showed excellent antibacterial activities against Serratia marcescens, and MRSA but very weak effect on Staphylococcus aureus. In conclusion, Streptomyces species played a critical role as a source of pigments with antibacterial activities.