Locally-isolated protease-producing Bacillus spp. from soil inhibits biofilm formation of Staphylococcus aureus

Abstract

Pathogens form biofilms to increase their resistance to environmental stress and antibacterial compounds. The rhizosphere is a rich source of microorganisms producing industrially important compounds including those with antimicrobial and biofilm inhibitory activities. Four isolates from soil collected from Taguig City, Philippines, were subjected to phenotypic and genotypic characterization, screening for protease production, and biofilm inhibition assays. Colony morphology and microscopic analyses indicated the isolates were putative Bacillus species. Upon DNA extraction, 16S rRNA gene was amplified, and based on their sequences, the isolates were confirmed to be Bacillus spp. Isolate AHP was B. cereus, isolate DJA was Priestia megaterium, formerly known as B. megaterium and isolates SJS and SKA were Bacillus spp.-all of which produced protease. Although the cell-free supernatants (CFS) of the isolates did not inhibit the growth of Staphylococcus aureus 1258, Citrobacter freundii ATCC24864, Salmonella Typhimurium ATCC13311, Escherichia coli ATCC11229, and E. coli O157:H7, biofilm formation of S. aureus was inhibited by all CFS, with B. cereus AHP showing the highest biofilm inhibition at 46%, followed by Bacillus sp. SKA (39%), P. megaterium DJA (36%), and Bacillus sp. SJS (31%). Even though further studies are warranted, the bioactivities of these isolates indicate potential use for pharmaceutical purposes due to their ability to produce protease and inhibition of biofilm formation of a common bacterial pathogen.