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[Identification of Listeria monocytogenes by PCR method]
1Institute of Microbiology and Epidemiology, Academy of Military Medical Sciences, Beijing.
Objective:
To establish a rapid, sensitive and specific polymerase chain reaction (PCR) method for detection of Listeria monocytogenes (LM).
Methods:
A pair of oligonucleotide primers were designed with hylA gene as target sequence. Fiftyfour strain of standard LM and 21 strains of irelevant bacteria were amplified and confirmed by PCR technique. Thirty-three strains of listeria isolated from food at home were identified by PCR and routine methods.
Results:
A 743-bp DNA fragment with a conservative Hind II site could be amplified by PCR, showing excellent features of LM. Limit to detection for pure culture was 55 colony forming units (CFU). Eighteen of 54 strains were identified as LM by both methods, with a completely coincident result. PCR was strongly inhibited as used in detection for food. If food was cultured for 25 hours for proliferation in listeria enrichment broth, then the culture was chemically extracted, the purified bacteria after heat lysis could react as PCR templates and the inhibitory effects could be greatly reduced. Milk inoculated artificially with four colony forming units of LM could be specifically detected by PCR.
Conclusion:
PCR can be used in rapid, sensitive and specific identification of LM.