A simple chemiluminescence-based method for rapid enumeration ofListeriaspp. microcolonies

Abstract

Aims: Listeria monocytogenes is capable, under certain conditions, of producing chemiluminescence which is ampli®ed by luminol. This property was used to detect and count microcolonies of Listeria spp. in a few hours, without the use of a microscope. Methods and Results: After trapping Listeria cells on polyvinylidene¯uoride 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. Conclusions: Microcolonies of Listeria spp. can be imaged and counted by luminol-enhanced chemiluminescence with a photon-counting system. Signi®cance and Impact of the Study: This method can be applied to the rapid detection and counting of Listeria spp. in raw milk.

On the use of capillary cytometry for assessing the bactericidal effect of TiO2. Identification and involvement of reactive oxygen species

“…Luminol is the most commonly used CL probe for measuring ROS concentration in biological systems, more specifically that of O 2˙− , identified using superoxide dismutase (SOD) scavenger which is one of the most important antioxidative enzymes, playing an important role in the balance between oxidation and antioxidation of the organism. 23,25,26 The aim of this paper is thus to first highlight the use of capillary cytometry for evaluating the bactericidal efficiency of the liquid phase photocatalytic treatment toward S. aureus, E. coli, and P. aeruginosa bacteria, and to compare the results with counts on agar plate, known as the traditional numeration method. 12,27 Further, the identification of the ROS implied in the photocatalytic process was monitored by CL and correlated with cell viability and the observed bactericidal effect.…”

Chemiluminescence of enterococci isolates from freshwater

“…We have previously shown that the addition of luminol increases 10‐fold the CL produced by L. monocytogenes [24] and used this property to develop a simple CL‐based method for rapid enumeration of Listeria spp. microcolonies in raw milk [18]. Huycke et al .…”

“…It has been reported that different bacterial species such as Listeria monocytogenes [17], Listeria innocua [18] and lactic acid bacteria [19] produce a weak chemiluminescence (CL). This phenomenon is correlated with the production of superoxide anion, H 2 O 2 and other reactive oxygen species (ROS) [20].…”

“…We have previously shown that the addition of luminol increases 10-fold the CL produced by L. monocytogenes [24] and used this property to develop a simple CLbased method for rapid enumeration of Listeria spp. microcolonies in raw milk [18]. Huycke et al [25] recently reported that under inhibition of bacterial respiration E. faecalis produced large amounts of extracellular superoxide, which is generated in the presence of fermentable sugar (glucose, gentobiose, cellobiose or D-mannose) by the cell membrane through univalent reduction of oxygen by reduced demethylmenaquinone.…”