ANTIMICROBIAL EFFECT OF WILD STREPTOMYCES STRAINS ISOLATED FROM CHILEAN SOILS

Background: The soils of the southern part of Chile, that are isolated , cold, humid, poorly oxygenated and with a low acidity could contain new strains of antimicrobial producing Streptomyces. Aim: To demonstra te that the soil of the Southern region of Chile contains Streptomyces strains with antimicrobial activity towards pathogenic bacteria and f ungi. Material and methods: Two hundred fifty eight soil and sediment samples were collected from 148 places in Southern regions of Chile. T hey were cultured in Kuster-Williams growth media and the presence of Streptomyces was confirmed by microscopic examination and biochemical characterization. The antimicrobial activity against reference microor ganisms of each wild strain was tested using the disk method Among act ive Streptomyces strains, 38 with the higher-activity were selected an d rested against 142 clinical microorganisms. Results: Seventy seven p ercent of soils were positive and 542 wild strains of Streptomyces wer e isolated of these 266 had antimicrobial activity. Fifty three percen t of isolates had activity against S aureus 43% against B subtilis and 0.7% against E coli. Most Streptomyces were active against more than one organism. When there was activity against single organisms, these were mostly eucariotic, such as C albicans wild T mentagrophytes. Amon g clinical microorganisms, 23% of S aureus strains were inhibited whil e P aeruginosa, Alternaria sp, P vulgaris and Y enterocolitica strains were not inhibited. The most frequent Streptomyces morphotypes were t hose showing pigmented colonies with flexuous and spiral shaped chains of arthrospores. Conclusions: Soils of the Southern region of Chile a llow the growth of abundant native strains of Streptomyces with a prom ising antimicrobial activity.