Appl. Environ. Microbiol., Aug 1997, 2961-2965, Vol 63, No. 8
MJ Loessner, M Rudolf and S Scherer
A511::luxAB is a recombinant derivative of a broad-host-range bacteriophage
specific for the genus Listeria, transducing bacterial bioluminescence into
infected cells. In this study, we have evaluated its use for rapid and easy
testing of contaminated foods and environmental samples for the presence of
viable Listeria cells, in comparison to the standard plating procedure.
With a short preenrichment step of 20 h, the system was capable of
detecting very low initial contamination rates in several foods
artificially contaminated with Listeria monocytogenes Scott A cells. In
ricotta cheese, chocolate pudding, and cabbage, less than one cell per g of
food could be clearly identified by comparing the light emission of
phage-infected samples to that of controls without lux phage. In foods
having a large and complex microbial background flora, such as minced meat
and soft cheese, at least 10 cells per g were necessary to produce a
positive bioluminescence signal. Of 348 potentially contaminated natural
food and environmental samples, 55 were found to be Listeria positive by
the lux phage method. The standard plating procedure detected 57 positive
samples. Some differences were observed with respect to the individual
samples, i.e., the lux phage procedure detected more positive samples among
the dairy products and environmental samples, whereas the plating procedure
revealed more contaminated meat and poultry samples. Overall, both methods
performed similarly, i.e., were equally sensitive. However, the minimum
time required for detection of Listeria with the luciferase phage assay was
24 h, which is much shorter than the 4 days needed by the standard plating
method. Furthermore, a most probable number technique with three parallels,
based on the use of A511::luxAB for differentiation of positive and
negative tubes, is described. The method enables rapid enumeration of low
levels of Listeria cells in several foods tested, against the background of
a competing microflora.
Copyright © 1997, American Society for Microbiology
Evaluation of luciferase reporter bacteriophage A511::luxAB for detection of Listeria monocytogenes in contaminated foods
Institut fur Mikrobiologie, Technische Universitat Munchen, Freising- Weihenstephan, Germany. M.J.Loessner@lrz.tu-muenchen.de
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