Antimicrobial activity of actinobacteria from a sanitary landfill in Pangasinan, Philippines

Abstract

The study was conducted to determine if actinobacteria isolated from Urdaneta City Sanitary Landfill soil have antimicrobial potential. Actinobacteria were selectively isolated using serial dilution of composite soil samples from the said landfill, followed by spread plating onto starch casein agar. Primary antimicrobial screening using cross-streak method followed by secondary screening using agar-well method were performed for the actinobacteria isolates obtained. Antimicrobial activity were detected by the presence of zone of inhibition. The minimum inhibitory concentration (MIC), and minimum bactericidal or fungicidal concentration (MBC) for the isolates with the highest zone of inhibition against each test organism in the secondary screening were then determined. And, the identities of these isolates were determined using molecular identification based on 16S rRNA gene sequencing. A total of eight putative actinobacteria isolates based on their cultural characteristics were obtained from the landfill soil samples. The isolates with the highest zone of inhibition in the secondary screening against B. subtilis BIOTECH 1563, E. coli BIOTECH 1634, and C. albicans ATCC14053 were AB-1, AB- 7 and AB-6, respectively. The MIC of AB-1, AB-7 and AB-6 were 50-75%, 20%, 20-25%, respectively. The MBC of AB-7 is 25%. BLAST analysis of 16s rRNA sequences with 99% identity revealed that isolate AB-1 belongs to the species Amycolatopsis tucumanensis, AB-7 belongs to Streptomyces nogolater, and AB-6 belongs to Streptomyces enissocaesilis. This is the first report of A. tucumanenesis to be isolated in sanitary landfill in the Philippines, and S. nogalater and S. enissocaesilis in sanitary landfill worldwide. This study signifies that sanitary landfill soil is a promising source of antimicrobial producing actinobacteria. In future studies, bioactive metablites from these species can be extracted, purified and screened.