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Listeria monocytogenes is a Gram-positive intracellular bacterium responsible for severe opportunistic infections in humans and animals. Signature-tagged mutagenesis (STM) was used to identify a gene named fbpA, required for efficient liver colonization of mice inoculated intravenously. FbpA was also shown to be required for intestinal and liver colonization after oral infection of transgenic mice expressing human E-cadherin. fbpA encodes a 570-amino-acid polypeptide that has strong homologies to atypical fibronectin-binding proteins. FbpA binds to immobilized human fibronectin in a dose-dependent and saturable manner and increases adherence of wild-type L. monocytogenes to HEp-2 cells in the presence of exogenous fibronectin. Despite the lack of conventional secretion/anchoring signals, FbpA is detected using an antibody generated against the recombinant FbpA protein on the bacterial surface by immunofluorescence, and in the membrane compartment by Western blot analysis of cell extracts. Strikingly, FbpA expression affects the protein levels of two virulence factors, listeriolysin O (LLO) and InlB, but not that of InlA or ActA. FbpA co-immunoprecipitates with LLO and InlB, but not with InlA or ActA. Thus, FbpA, in addition to being a fibronectin-binding protein, behaves as a chaperone or an escort protein for two important virulence factors and appears as a novel multifunctional virulence factor of L. monocytogenes. [ABSTRACT FROM AUTHOR]

Entry of Listeria monocytogenes into epithelial cells requires expression of inlA, the first gene of an operon comprising two genes: inlA, which encodes internalin, a 800-amino-acid protein, and inlB, which encodes a 630-amino-acid protein. We report here that the inl locus is transcribed on two transcripts in constant relative ratio: a 5 kb transcript spanning inlA and inlB, and a 2.9 kb transcript that covers only inlA. The promoter is located 397 bp from the GTG initiator of inlA and displays in its -35 region a palindrome similar to that found in promoters controlled by the pleiotropic activator prfA. Transcription of the inl focus is, as are several other L. monocytogenes virulence genes, activated by prfA and regulated by temperature--with higher expression at 37°C versus 25°C--and bacterial growth state. It is maximal during exponential growth and correlates with maximal invasivity of the bacteria in the human epithelial cell line Caco-2. It also correlates with maximum amounts of internalin present on the bacterial surface. Internalin is also detected in substantial amounts in culture supernatants. Taken together, these data suggest that surface-bound internalin plays an important role in bacterial entry but do not exclude a role for the released form. [ABSTRACT FROM AUTHOR]

Evidence for pleiotropic activation of virulence genes in Listeria monocytogenes is presented. A complementation study of a spontaneous prfA-deletion mutant and analysis of cassette and transposon insertion mutants showed that the gene prfA activates the transcription of four independent genes which code for a phosphatidyl-inositol-specific phospholipase C (gene plcA), listeriolysin O (gene hlyA), a metallo-protease (gene prtA) and a lecithinase (gene prtC). Transcription of prfA is not constitutive. During the growth phase, two peaks of prfA transcript accumulation were observed: the first was during exponential growth, and the second was at the beginning of the stationary phase, in addition, two prf4-specific transcripts of 2.2 kb and 1 kb are detected. Early in exponential growth, prfA is co-transcribed with plcA which lies upstream prfA, giving rise to the 2.2 kb plcA-prfA transcript, in late-exponential growth and at the beginning of the stationary phase, prfA transcripts of 1 kb are predominantly detected. Our results demonstrate that since prfA controls plcA transcription, it also regulates its own synthesis. [ABSTRACT FROM AUTHOR]

Presents a letter to the editor regarding gram-positive bacterial proteins involved in cell recognition.