Rapid detection of Listeria monocytogenes in ham samples using immunomagnetic separation followed by polymerase chain reaction.
OBJECTIVE
To develop a 24-h system for the detection of Listeria monocytogenes in ham.


RESULTS
An immunomagnetic separation (IMS) of bacteria directly from ham followed by extraction of DNA and detection using a new multiplex polymerase chain reaction (PCR) was used. The PCR method used one primer pair targeted at the listeriolysin O gene of L. monocytogenes and the other pair for a region of the 23S rRNA genes of Listeria, giving products of 706 and 239 bp, respectively. The combined IMS/PCR was calculated to be capable of detecting as few as 1.1 L. monocytogenes cells g-1 in a 25-g ham sample.


CONCLUSIONS
The process produced acceptable results, but the IMS step is the main barrier to further improvement of sensitivity. The DNA isolation was the most time-consuming step in the process.


CONCLUSIONS
A 24-h test for the presence of L. monocytogenes will be useful to the food industry and significantly assist in the timely investigation of outbreaks.
Hudson
J A
JA
Institute of Environmental Science and Research (ESR) Ltd, Christchurch Science Centre, PO Box 29-181, Ilam, Christchurch, New Zealand. andrew.hudson@esr.cri.nz
Lake
R J
RJ
Savill
M G
MG
Scholes
P
P
McCormick
R E
RE
D004269:DNA, Bacterial / Q000032:analysis; D005516:Food Microbiology; D018189:Immunomagnetic Separation / Q000379:methods*; D008089:Listeria monocytogenes / Q000235:genetics / Q000302:isolation & purification*; D008461:Meat Products / Q000382:microbiology*; D016133:Polymerase Chain Reaction / Q000379:methods*; D011786:Quality Control
D004269:DNA, Bacterial