I have observed the presence of inhibition zones against L. monocytogenes by lactic acid bacteria isolated from African foods.
After seeing inhibition zones, bacteria was cultivated in liquid medium to test it in supernatant, but I get not get inhibition zones.
The questions, that I have asked myself while reading your entry were: Did antimicrobial expressed in liquid medium? What method was used to detect inhibition after the liquid culture? What were the centrifugation conditions in order to retrieve a supernatant containing the antimicrobial? Maybe method which combines cultures on solid and liquid media would be more efficient?
Good luck with further tests! Best regards!
inhibition zones on agar plates with lactic acid bacteria can be caused by a number of things: low pH (lactic acid, acetic acid), peroxide, nutrient depletion etc, so they are not always caused by bacteriocins....
Are you growing the bacteria in the same medium as the plates (LB Plates and LB Broth for example). Also, production of bacteriocins may be dependent on sensing of other bacteria near by. You could try adding some spent media from a Listeria culture to your culture of lactobacillus and see if that induces production of the growth inhibiting compounds.
Isothermal microcalorimetry (IMC) is an extremely sensitive, quantitative, real-time method for evaluating the effects of antimicrobials in ANY medium. See:
https://en.wikipedia.org/wiki/Isothermal_microcalorimetry#Microbiology
https://en.wikipedia.org/wiki/Isothermal_microcalorimetry#Pharmacodynamics
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