A simple chemiluminescence-based method for rapid enumeration of Listeria spp. microcolonies

Listeria monocytogenes is capable, under certain conditions, of producing chemiluminescence which is amplified by luminol. This property was used to detect and count microcolonies of Listeria spp. in a few hours, without the use of a microscope.

After trapping Listeria cells on polyvinylidene fluoride membranes, a chemiluminescence mixture was sprayed onto the membrane. The chemiluminescent spots emitted were analysed by a charge-coupled device camera connected to a data-processing system, which restored the intensity of the signals into three dimensional images. The intensity of the luminescence of microcolonies was improved by addition of cellobiose, and by brief exposure to u.v. light.

Microcolonies of Listeria spp. can be imaged and counted by luminol-enhanced chemiluminescence with a photon-counting system.

This method can be applied to the rapid detection and counting of Listeria spp. in raw milk.