Isolation and Characterization of Antibiotic-producing Bacteria from the Salt Range of Kallar Kahar, Pakistan

Abstract

The emergence of antibiotic resistance in pathogenic bacteria has heightened the need for new antibiotics. Streptomycetes are filamentous gram-positive bacteria that are ubiquitous and present in saline soil and produce antibiotics as secondary metabolites under stressful conditions. Naturally, Streptomyces produce over two-thirds of antibiotics that are used clinically. Saline soil was collected from Kallar Kahar, Pakistan. The soil sample was serially diluted and three dilutions were plated on Streptomyces selection media (starch-casein agar and glucose yeast malt agar) after growing the culture, pure colonies were selected based on their morphological features and subsequently examined using Gram-staining. The antimicrobial activity of two selected strains (P1 and P2) was evaluated using the agar plug method and agar well diffusion method against both gram-positive (Bacillus subtilis) and gram-negative (Escherichia coli) pathogenic bacteria. In the agar plug method, the clear zone of inhibitions was not clearly visible against the test bacteria. The zone of inhibitions were only observed in agar well diffusion assay in which the P1 strain exhibited a diameter of 0.6mm against E. coli and 0.75mm against B. subtilis and the P2 strain showed antibacterial activity only against E. coli with a diameter of 0.75mm. The results were not significant, these slight zones of inhibition warrant further improvements in methods for isolation and purification of antibiotic-producing bacteria. Such methods should aim to enhance the efficiency of antibiotics.