Sensitivity to acetic acid, ability to colonize abiotic surfaces and virulence potential of Listeria monocytogenes EGD-e after incubation on parsley leaves.
OBJECTIVE
To investigate how the survival of Listeria monocytogenes on parsley leaves may affect its ability to sustain process-related harsh conditions and its virulence.


RESULTS
Parsley seedlings were spot inoculated with stationary phase cells of L. monocytogenes EGD-e and incubated for 15 days. Each day, bacterial cells were harvested and enumerated, and their ability to survive acetic acid challenge (90 min, pH 4.0), to colonize abiotic surfaces and to grow as biofilms was assessed. After a 3-log decrease over the first 48 h, the population stabilized to about 10(6) CFU g(-1) until the sixth day. After the sixth day, L. monocytogenes was no longer detected, even after specific enrichment. Incubation on parsley leaves affected the ability of L. monocytogenes to survive acetic acid challenge (90 min, pH 4.0) and to adhere to stainless steel although the ability to grow as biofilm was preserved. To further investigate these physiological alterations, the mRNA levels of six target genes (bsh, clpC, groEL, inlA, opuC, prfA) was quantified using reverse transcription qPCR after 5 h of incubation on parsley leaves. A decrease was observed in all but one (bsh) target, including groEL and clpC which are involved in resistance to salt and acid. Moreover, the decrease in the levels of inlA, prfA and opuC transcripts after incubation on parsley suggested a repression of some genes involved in pathogenicity. In vitro assessment of mammalian cell adherence and invasion using Caco-2 cells confirmed the repression of the virulence factor InlA; however, the virulence potential in vivo in the chick embryo model was not affected.


CONCLUSIONS
Listeria monocytogenes did undergo rapid changes to adapt its physiology to the phyllosphere.


CONCLUSIONS
This study highlights the physiological changes undergone by L. monocytogenes during/after survival on parsley leaves.
Rieu
A
A
Laboratoire de Recherche En Vigne et Vin REVV, Université de Bourgogne, IUVV, Dijon, France.
Guzzo
J
J
Piveteau
P
P
D019342:Acetic Acid / Q000494:pharmacology*; D000818:Animals; D001422:Bacterial Adhesion; D018441:Biofilms; D018938:Caco-2 Cells; D002642:Chick Embryo; D006801:Humans; D008089:Listeria monocytogenes / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity* / Q000502:physiology*; D050296:Microbial Viability; D028528:Petroselinum / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology; D011137:Polystyrenes; D012329:RNA, Bacterial / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D013193:Stainless Steel; D014774:Virulence
D011137:Polystyrenes; D012329:RNA, Bacterial; D012333:RNA, Messenger; D013193:Stainless Steel; D019342:Acetic Acid