Effect of acid adaptation on the fate of Listeria monocytogenes in THP-1 human macrophages activated by gamma interferon.
In Listeria monocytogenes the acid tolerance response (ATR) takes place through a programmed molecular response which ensures cell survival under unfavorable conditions. Much evidence links ATR with virulence, but the molecular determinants involved in the reactivity to low pHs and the behavior of acid-exposed bacteria within host cells are still poorly understood. We have investigated the effect of acid adaptation on the fate of L. monocytogenes in human macrophages. Expression of genes encoding determinants for cell invasion and intracellular survival was tested for acid-exposed bacteria, and invasive behavior in the human myelomonocytic cell line THP-1 activated with gamma interferon was assessed. Functional approaches demonstrated that preexposure to an acidic pH enhances the survival of L. monocytogenes in activated human macrophages and that this effect is associated with an altered pattern of expression of genes involved in acid resistance and cell invasion. Significantly decreased transcription of the plcA gene, encoding a phospholipase C involved in vacuolar escape and cell-to-cell spread, was observed in acid-adapted bacteria. This effect was due to a reduction in the quantity of the bicistronic plcA-prfA transcript, concomitant with an increase in the level(s) of the monocistronic prfA mRNA(s). The transcriptional shift from distal to proximal prfA promoters resulted in equal levels of the prfA transcript (and, as a consequence, of the inlA, hly, and actA transcripts) under neutral and acidic conditions. In contrast, the sodC and gad genes, encoding a cytoplasmic superoxide dismutase and the glutamate-based acid resistance system, respectively, were positively regulated at a low pH. Morphological approaches confirmed the increased intracellular survival and growth of acid-adapted L. monocytogenes cells both in vacuoles and in the cytoplasm of interferon gamma-activated THP-1 macrophages. Our data indicate that preexposure to a low pH has a positive impact on subsequent challenge of L. monocytogenes with macrophagic cells.
Conte
Maria Pia
MP
Department of Public Health Sciences, University La Sapienza, 00185 Rome, Italy.
Petrone
Gloria
G
Di Biase
Assunta Maria
AM
Longhi
Catia
C
Penta
Michela
M
Tinari
Antonella
A
Superti
Fabiana
F
Fabozzi
Giulia
G
Visca
Paolo
P
Seganti
Lucilla
L
D000222:Adaptation, Physiological / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics; D001427:Bacterial Toxins; D018938:Caco-2 Cells; D002460:Cell Line; D003470:Culture Media; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D005968:Glutamate Decarboxylase / Q000235:genetics; D006360:Heat-Shock Proteins / Q000235:genetics; D006460:Hemolysin Proteins; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007371:Interferon-gamma / Q000494:pharmacology; D007424:Intracellular Fluid / Q000382:microbiology; D019344:Lactic Acid / Q000494:pharmacology; D008089:Listeria monocytogenes / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development / Q000502:physiology; D008262:Macrophage Activation; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000276:immunology / Q000382:microbiology; D008565:Membrane Proteins / Q000235:genetics; D010454:Peptide Termination Factors; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D013482:Superoxide Dismutase / Q000235:genetics; D015534:Trans-Activators / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D010738:Type C Phospholipases / Q000235:genetics; D014774:Virulence
D001426:Bacterial Proteins; D001427:Bacterial Toxins; D003470:Culture Media; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D006460:Hemolysin Proteins; D008565:Membrane Proteins; D010454:Peptide Termination Factors; D015534:Trans-Activators; C069761:internalin protein, Bacteria; C072980:actA protein, Listeria monocytogenes; D019344:Lactic Acid; D007371:Interferon-gamma; D013482:Superoxide Dismutase; C116114:sodC protein, E coli; D010738:Type C Phospholipases; D005968:Glutamate Decarboxylase; D043265:Phosphatidylinositol Diacylglycerol-Lyase; C038705:hlyA protein, Listeria monocytogenes