Detection of Listeria monocytogenes in Italian-style soft cheeses.
OBJECTIVE
A rapid detection system specific for Listeria monocytogenes and based on the polymerase chain reaction (PCR) was developed.


RESULTS
Primers annealing to the coding region of the actA gene, critically involved in virulence and capable of discrimination between two different alleles naturally occurring in L. monocytogenes, have been utilized. The procedure was applied to recover L. monocytogenes cells in artificially contaminated fresh Italian soft cheeses (mozzarella, crescenza and ricotta). Low levels of L. monocytogenes were detected in mozzarella and crescenza homogenates (0.04-0.4 and 4 CFU g(-1), respectively) whereas in ricotta the detection limit was higher (40 CFU g(-1)).


CONCLUSIONS
This PCR-based assay is highly specific as primers used recognize the DNA from different L. monocytogenes strains of clinical and food origin, while no amplification products result with any other Listeria spp. strains.


CONCLUSIONS
This study highlighted a low-cost and rapid procedure that can be appropriated for the detection in real time of low L. monocytogenes levels in soft cheese.
Longhi
C
C
Department of Public Health Sciences, University, La Sapienza, P.le A. Moro, Rome, Italy.
Maffeo
A
A
Penta
M
M
Petrone
G
G
Seganti
L
L
Conte
M P
MP
D001426:Bacterial Proteins / Q000235:genetics; D002611:Cheese / Q000382:microbiology*; D004269:DNA, Bacterial / Q000032:analysis; D004587:Electrophoresis, Agar Gel; D005516:Food Microbiology; D008089:Listeria monocytogenes / Q000302:isolation & purification*; D008565:Membrane Proteins / Q000235:genetics; D016133:Polymerase Chain Reaction / Q000379:methods; D012680:Sensitivity and Specificity; D013048:Specimen Handling / Q000379:methods
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D008565:Membrane Proteins; C072980:actA protein, Listeria monocytogenes