Luminol-enhanced chemiluminescence by Listeria monocytogenes: a test for rapid assessment of antimicrobial agents

Chemiluminescence of enterococci isolates from freshwater

All Enterococcus spp., isolated from environmental water samples (n=81), emitted a high chemiluminescence signal in the presence of luminol (10(-2) M). Kinetic studies of chemiluminescence show a close correlation between chemiluminescence and growth curves during the exponential phase, with a maximum chemiluminescence reached just before bacterial growth entered in the stationary phase. On the other hand, genera closely related to Enterococcus such as Streptococcus or Lactococcus produced a very weak chemiluminescent signal. Chemiluminescence of enterococci could therefore offer a rapid test, in aiding the identification of the genus Enterococcus and in the survey of the microbiological quality of water supplies.

Toxicity potential of disinfection agent in tannery wastewater

Wastewater from a tannery was investigated using chemical-specific analyses and assessment of the acute toxicity of the whole effluent over a 2-year period. The wastewater samples were overloaded with organic and inorganic compounds, and measured concentrations of the chemical parameters as well as dilution factors estimating acute toxicity, frequently exceeded the permissible limits for the discharge of wastewater from a tannery into the receiving stream. In the later part of the monitoring programme, the toxicity of the samples was significantly increased in comparison to the previous samples. The agent for hide disinfection was assumed to be the reason for the increased toxicity of the wastewater samples, and the extremely high acute and chronic toxicity of the agent to bacteria, algae, daphnids, and fish confirmed this suspicion. The most sensitive species was Daphnia magna; the 48 h EC50 was 0.70 x 10(-5)v/v% and the 21d IC25 was 0.40 x 10(-6)v/v% of the agent. After withdrawal of this highly toxic agent for hide disinfection from the technological process in the tannery, the toxicity of the wastewater declined to the previous level.

Effects of iron and oxygen species scavengers on Listeria spp. chemiluminescence

Listeria monocytogenes and Listeria innocua are able, under certain conditions, to produce chemiluminescence (CL), which is amplified by luminol. Kinetic studies of CL by L. monocytogenes and L. innocua show a close parallelism between CL and growth curves during the exponential phase, with a maximum of CL reached just before entrance of bacteria into the stationary phase. CL is tightly correlated with the release of oxygen compounds. The reactive oxygen species scavengers tryptophan, mannitol, and tiron, as well as cellobiose and high temperature, were assessed with regard to CL in the two Listeria species. Only tiron strongly reduced the CL emitted by L. monocytogenes and L. innocua. On the other hand, charcoal pretreatment of the growth medium inhibited the CL, whereas ferric citrate strongly increased the CL of L. monocytogenes and L. innocua. These data suggest that iron and superoxide radical are implicated in the CL produced by these bacteria, but this phenomenon is not correlated to virulence.

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

AIMS

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.

METHODS AND RESULTS

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.

CONCLUSION

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

SIGNIFICANCE AND IMPACT OF THE STUDY

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