A method for identifying antibacterial agents comprises depleting bacteria of a strain comprising a luxAB construct of Ca.sup.2+, incubating the Ca.sup.2+ depleted bacteria with an agent the antibacterial effect of which shall be determined, recording the light emitted by the bacteria upon addition of an aldehyde, the incubation being carried out at a temperature which is at least 10.degree. C. higher than the temperature at which the light is emitted by the bacteria. Also disclosed are corresponding probes and antibacterial agents identified by the method.