Rapid enumeration of Listeria monocytogenes in artificially contaminated cabbage using real-time polymerase chain reaction.
A quantitative real-time polymerase chain reaction (PCR) detection method specific for Listeria monocytogenes was developed, and studies involving pure culture showed that the response of the assay was linear over 7 log10 (log) cycles. The method was then applied to the detection of L. monocytogenes artificially inoculated onto cabbage, a vegetable chosen because it is a major component of coleslaw, which has been associated with an outbreak of listeriosis. After being allowed to attach to the food, cells were washed from the cabbage leaf surface and recovered by centrifugation. The DNA was purified by an organic solvent extraction technique and analyzed by real-time PCR. In this matrix, the method again produced a linear response over 7 log cycles from 1.4 x 10(2) to 1.4 x 10(9) CFU of L. monocytogenes in 25 g of cabbage, and analysis of the reproducibility of the system showed that log differences in L. monocytogenes numbers added to cabbage could be reliably distinguished. The system allowed quantitative results to be obtained within 8 h and was relatively inexpensive, showing good potential for routine analytical use.
Christchurch Science Centre, Institute of Environmental Science and Research, New Zealand. angela.hough@esr.cri.nz
Angela J
AJ
Hough
Sally-Ann
SA
Harbison
Marion G
MG
Savill
Laurence D
LD
Melton
Graham
G
Fletcher
D001937:Brassica / Q000382:microbiology*; D015169:Colony Count, Microbial; D004269:DNA, Bacterial / Q000032:analysis*; D005516:Food Microbiology; D008089:Listeria monocytogenes / Q000235:genetics / Q000302:isolation & purification*; D016133:Polymerase Chain Reaction / Q000191:economics / Q000379:methods*; D015203:Reproducibility of Results
D004269:DNA, Bacterial