Antimicrobial effects of probiotics against selected pathogenic and spoilage bacteria in cheese-based dips

Spot-on lawn, spot and streak, co-culturing techniques and HPLC analysis were used for the detection and screening of inhibitory activity produced by probiotic bacteria against spoilage and pathogenic bacteria. After incubation, plates were examined for either zones of inhibition and for other effects of suppression around the wells/spots and streaks or cfu/g of target bacteria. The spore-formers were inhibited by the probiotic organisms to a greater extent than the non-spore formers. The inhibitory effect of all probiotic bacteria was weakest against E. coli and strongest against B. cereus. S. aureus was inhibited to a greater extend by B. animalis and by L. rhamnosus. The order of probiotic bacteria in terms of level of inhibition on agar plates (and zone of inhibition in mm) was L. rhamnosus (21) L. acidophilus (19) = L. casei (19) L. paracasei subsp. paracasei (18) B. animalis (15) P. freudenreichii subsp. shermanii (11). Though co-culturing of target organisms with probiotic bacteria in reconstituted skim milk showed inhibitory effect against target organisms; however, in French onion dip, there was no additive effect in controlling the bacterial population except that for B. cereus. Varying quantities of organic acids (acetic, lactic, formic, propionic, butyric, benzoic and phenyllactic) that were responsible for the inhibition were detected.