Interesting to read about your experiment. Is that lactobacillus strain from a commercial probiotic preparation or one of your own isolates? if its a new strain there are several established assays in literature to define its probiotic potential. the usual methods to study antagonostic activity employ both an agar based assay (like the one you describe. this is usually aimed at detecting bacteriocin production by the lactobacillus strain) or a broth based (co-culture) method. with reference to your assay ..i dont understand what you mean by floor of the plate..do you mean a lawn culture on agar surface?. Unless we take into consideration the growth rates of both these diverse organisms, inoculum size etc. It would be difficult to demonstrate in vitro activity. How do you make your probiotic inoculum. Is it a log phase culture (age?). Perhaps you can try different concentrations of probiotic inocula and see. You can also try the streak line method. you can find papers on these online. Hope my comments were of some use.

Just to add to Girish's comments. An agar test is much less sensitive to the presence of bacteriocins, should the Lactobacillus be producing them, than a broth test. Furthermore Lactobacillus usually has a preference for anaerobic conditions so a broth like brain heart infusion or tryptone soya broth with added cysteine may help. You will then have to perform viable counts after a period of exposure on a differential medium such as blood enriched TSA agar. The broth method may also be able to tell you a whether differences in growth rates play a role. However, for competitive exclusion you will have to choose another model system. They are published. You may also want to add lactose to your media.

Add to Jackie comments...

as i have work on this lactobacillus and given solution to one of the manufacturing company called UNISANKYO in hyderabad....

i have isolated the lactolacillus on BLOOD AGAR and chocklet agar, on fully Anaerobic conditions ONLY[ choose anaerobic jar method], the most important the collection of the sample is also anaerobically, then you will get the very good growth on the agarplates....

normally in probiotics, when you grow the lactobacillus, there will be a ENAEMY [which not alloe the lactobaciullus to grow] that is lactobacillus cervaciae , BUT lactobacillus Bolardi is the friend .

after you grow the culture on these palte anaeriobically, you must perform the Gramstaining, and folloe by IDENTIFICATION CONFIRMATION with ready made kit called Elichrom IDs system for YEAST, if you fing the Ids, Lactobacillus bolardi then you are going on the write track for the development of lactobacillus probiotics.

one more better media plate called PETRIFILM ANAEROBIC / AEROBIC COUNT THIS PRODUCT IS FROM 3m USA THE PER FILM COST WILL BE Rs:- 25/- per plate.

i have grown on these plate, [lactobacillus] and subculture on sheep blood agar [sandwitch agar method with soyabean casin diagest agar] and chocklet agar... this will help you to grow your organisam properly and understand the friend or enemy organisam for this lactobacillus.

further to know on these you can write to me and i can support more on this, if you want to know more about the elichrom IDS and Petrifilm please write to me so i will mail the same.

have you used standard bacterial inoculum size? . my best suggestion is try to prepare different inoculum size of both staph as well as Lactobacilli and try with all ....definitely you will get the zone of inhibition . try with other media suggested by the authors. try also with different quantity of Lactobacilli eg. 50, 100 200 microliters ( to be placed in the wells).

Hi

Different inoculum size fail to produce inhibitory zone. I'll try a anaerobic culture media in following days and post here my findings.

Best regards