The influence of commonly used selective agents on the growth of Listeria monocytogenes

The effects, upon addition of various selective agents to a rich growth medium (BHIEM) on the growth of Listeria monocytogenes and non-Listeria were studied in microtitre wells. A combination of nalidixic acid (0.1 g/l), acriflavine (0.02 g/l) and fosfomycin (0.1 g/l) added to the medium (BHIEMNAF) was found to be the least inhibitory to Listeria while at the same time, effectively inhibitory to non-Listeria organisms. Recovery of heat injured Listeria monocytogenes in BHIEM, BHIEMNAF and the two traditional Listeria-media, UVM I and II, was compared. Recovery in BHIEM was obtained within 24 h of incubation at 30°C, whereas recovery in BHIEMNAF took up to 48 h. Growth and recovery in UVM I and II never reached the same level as in BHIEM or BHIEMNAF.