[Antibiotic effect of wild Streptomyces strains isolated from Chilean soils]

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.

To demonstrate that the soil of the Southern region of Chile contains Streptomyces strains with antimicrobial activity towards pathogenic bacteria and fungi.

Two hundred fifty eight soil and sediment samples were collected from 148 places in Southern regions of Chile. They were cultured in Küster-Williams growth media and the presence of Streptomyces was confirmed by microscopic examination and biochemical characterization. The antimicrobial activity against reference microorganisms of each wild strain was tested using the disk method. Among active Streptomyces strains, 38 with the higher activity were selected and tested against 142 clinical microorganisms.

Seventy seven percent of soils were positive and 542 wild strains of Streptomyces were isolated; of these, 266 had antimicrobial activity. Fifty three percent 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 and T mentagrophytes. Among clinical microorganisms, 29% of S aureus strains were inhibited, while P aeruginosa, Alternaria sp, P vulgaris and Y enterocolitica strains were not inhibited. The most frequent Streptomyces morphotypes were those showing pigmented colonies with flexuous and spiral shaped chains of arthrospores.

Soils of the Southern region of Chile allow the growth of abundant native strains of Streptomyces with a promising antimicrobial activity.