Listeria is a rod-shaped, Gram-positive bacteria. There are 17 known species in listeria genus, of which two, L. monocytogenesand L. ivanoviiare pathogenic. L. monocytogenesis the cause of listeriosis, a serious disease that is especially dangerous to those with impaired immune systems such as the elderly, pregnant women and new-borns. Even though listeriosis is an infrequent disease, it has a high mortality rate of more than 20%. Listeriosis incubation period in humans may be up to three months. The disease also affects livestock.
Listeria can stay undetected for long periods of time. L. monocytogenes can live in many environmental niches such as soil as a saprophyte but is capable of transforming into a pathogen after ingestion.The high environmental adaptability of Listeria is contingent upon their ability to sense changes that signal environmental/ host localization. As such,in order for the accumulating profiles to be of any relevant use, there must be sufficient ingenuity to isolate and prompt the target species to grow.
There are several points of contact within the dairy industry that lead to contamination with Listeria. Listeria persists through a relationship with biofilm forming bacteria that survive the pasteurization process. These biofilms can harbour spoilage related microorganisms and initiate a cycle of contamination.
Given the danger and cost of listeriosis, an efficient and reliable method for the detection of trace L. monocytogenescontamination is needed. A promising approach is the detection of metabolic signature of the bacteria in the form of volatile organic compounds (VOC). Pathogenic bacteria are capable of producing a large variety of VOCs.Common bacterial VOCs are alcohol-based such as 1-butanol and tridecanol, found in high abundance in bacterial cultures(1).However, only a very small fraction of the metabolites are produced exclusively by one species. A combination of VOCs, rather than single biomarkers, will be necessary for discrete species identification.
It has been found that 1-hexanol and 1-heptadecene are goodVOC indicators to distinguish between bacterial and viral positive cultures (1). Indole and its derivatives may be good biomarkers for the formation of the biofilm (2,3).
Y. Yu et al. have described the VOC composition of cultured L. monocytogenes (4). Tait et al.could detect 2-nitrophenol and 3-fluoroaniline, specific to L. monocytogenes, based on the activity of β-glucosidase and hippuricase enzymes, provided that the samples containedat least 1−1.5×102CFU ml-1of milk prior to incubation (5). In further work in 2017, exogenous benzyl alcohol was detected in the presence of α-mannosidase and D-alanyl aminopeptidase. It was possible to differentiate between L. monocytogenes and L. ivanovii, based on VOC response from α-mannosidase activity(6).
Picomole technology is based on the measurement of infrared absorption with cavity ring-down spectroscopy (IR-CRDS). It is specifically capable of detecting individual gas compounds as well as the composite signature of the VOCs associated with pathogens. The above-referenced VOCs associated with L. monocytogenes have absorption in mid-infrared which makes them good candidates for detection by IR-CRDS.
1. Abd El Qader A, Lieberman D, Shemer Avni Y, Svobodin N, Lazarovitch T, Sagi O, et al. Volatile organic compounds generated by cultures of bacteria and viruses associated with respiratory infections. Biomed Chromatogr. 2015 Dec;29(12):1783–90.
2. Hu M, Zhang C, Mu Y, Shen Q, Feng Y. Indole Affects Biofilm Formation in Bacteria. Indian J Microbiol. 2010 Oct;50(4):362–8.
3. Scherzer R, Gdalevsky GY, Goldgur Y, Cohen-Luria R, Bittner S, Parola AH. New tryptophanase inhibitors: Towards prevention of bacterial biofilm formation. Journal of Enzyme Inhibition and Medicinal Chemistry. 2009 Apr;24(2):350–5.
4. Yu Y, Sun X, Liu Y, Pan Y, Zhao Y. Odor fingerprinting of Listeria monocytogenesrecognized by SPME–GC–MS and E-nose. Canadian Journal of Microbiology. 2015 May;61(5):367–72.
5. Tait E, Perry JD, Stanforth SP, Dean JR. Bacteria detection based on the evolution of enzyme-generated volatile organic compounds: Determination of Listeria monocytogenes in milk samples. Analytica Chimica Acta. 2014 Oct;848:80–7.
6. Taylor C, Lough F, Stanforth SP, Schwalbe EC, Fowlis IA, Dean JR. Analysis of Listeria using exogenous volatile organic compound metabolites and their detection by static headspace–multi-capillary column–gas chromatography–ion mobility spectrometry (SHS–MCC–GC–IMS). Analytical and Bioanalytical Chemistry. 2017 Jul;409(17):4247–56.