Appl. Environ. Microbiol., Apr 1996, 1133-1140, Vol 62, No. 4
MJ Loessner, CE Rees, GS Stewart and S Scherer
Specific transfer and expression of bacterial luciferase genes via
bacteriophages provides an efficient way to detect and assay viable host
cells. Listeria bacteriophage A511 is a genus-specific, virulent myovirus
which infects 95% of Listeria monocytogenes serovar 1/2 and 4 cells. We
constructed recombinant derivative A511::luxAB, which carries the gene for
a fused Vibrio harveyi LuxAB protein inserted immediately downstream of the
major capsid protein gene (cps). Efficient transcription is initiated by
the powerful cps promoter at 15 to 20 min postinfection. Site-specific
introduction of the luciferase gene into the phage genome was achieved by
homologous recombination in infected cells between a plasmid carrying A511
DNA flanking luxAB and phage DNA. Recombinants occurred in the lysate at a
frequency of 5 x 10(-4) and were readily identified by the bioluminescent
phenotype conferred on newly infected host cells. A511::luxAB can be used
to directly detect Listeria cells. Following infection and a 2-h incubation
period, numbers as low as 5 x 10(2) to 10(3) cells per ml were detected by
using a single-tube luminometer. Extreme sensitivity was achieved by
including an enrichment step prior to the lux phage assay; under these
conditions less than 1 cell of L. monocytogenes Scott A per g of
artificially contaminated salad was clearly identified. The assay is
simple, rapid, inexpensive, and easy to perform. Our findings indicate that
A511::luxAB is useful for routine screening of foods and environmental
samples for Listeria cells.
Copyright © 1996, American Society for Microbiology
Construction of luciferase reporter bacteriophage A511::luxAB for rapid and sensitive detection of viable Listeria cells
Institut fur Mikrobiologie, Technische Universitat Munchen, Freising, Germany.
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