In the present study, antibacterial activity of crude and modified L. acidophilus
supernatant against 28 clinical isolates of gram negative and gram positive pathogens have been
evaluated using the cup-cut plate and time-killing curve methods. The isolates were isolated from
different patients and selected as the most resistant strains when challenged with antibiotics already
in clinical practice. The crude cell-free L. acidophilus supernatants demonstrated wide antibacterial
spectrum against the vast majority of the pathogenic strains where the diameter of the zone of
inhibition around the cups containing the supernatants ranged between 10 and 15.5 mm. Modifying
the MRS media by adding 1%v/v olive oil to L. acidophilus culture during the incubation period
resulted in a supernatant with significantly weak antibacterial activity as compared to crude
supernatant. In that almost most of the isolates were completely resistant to the antibacterial activity
of the modified L. acidophilus supernatant. In contrast, the antibacterial activity of the crude
supernatant was significantly enhanced by adding 1%v/v olive oil to the cell-free L. acidophilus
supernatants collected 48 hours post-incubation as compared to the crude 48hrs supernatant without
olive oil. This is evident by the remarkable differences of the diameter of the zone of inhibition
among the conditions. In a kinetic study the lactobacillus sensitive MRSA and P. aeruginosa
showed comparable and significant susceptibility to the antibacterial activity of crude and modified
L. acidophilus, although they were isolated from different patients. In conclusion, the mixing of cellfree L. acidophilus supernatant with olive oil (1%v/v) produced a new compound with very good
antibacterial activity as compared to controls.
Keywords: L. acidophilus supernatant, Anti-bacterial, MRSA, Olive oil