Specific binding of recombinant Listeria monocytogenes p60 protein to Caco-2 cells

P40 and P75 Are Singular Functional Muramidases Present in the Lactobacillus casei /paracasei/rhamnosus Taxon

Lactobacillus casei and Lactobacillus rhamnosus proteins P40 and P75 belong to a large family of secreted cell wall proteins that contain a carboxy(C)-terminal CHAP or NlpC/P60 superfamily domains. In addition to their peptidoglycan hydrolases activity, proteins in this family are specific antigens of pathogens, frequently responsible of interactions with the host. L. rhamnosus GG and L. casei BL23 purified P40 and P75 proteins have antiapoptotic activity by inducing the EGF/Akt pathway. The aim of this work was to study the genetics, phylogeny and dissemination of this family of proteins in the genus Lactobacillus as well as their characteristics and likely function. The scrutiny of their DNA encoding sequences revealed the presence of minisatellite DNA in the P75 encoding gene of L. casei/paracasei strains (cmuB) with intraspecific indels that gave raise to four different alleles (cmuB1-4), which are exclusive of this species. Phylogenic analyses suggest that both proteins are present mainly in the L. casei and Lactobacillus sakei phylogenomic groups. A P40 ancestral gene was possibly present in the common ancestor of Enterococcaceae, Lactobacillaceae and Streptococcaceae. P75 is also present in L. casei and L. sakei groups, but its evolution is difficult to explain only by vertical transmission. Antibodies raised against the N-terminal regions of P40 and P75 improved their immunological detection in culture supernatants as they recognized almost exclusively proteins of L. casei/paracasei/rhamnosus strains, highlighting their structural similarity, that allowed to detect them in different fermented dairy products that contained probiotic L. casei strains. Purified P40 and P75 proteins showed no evident lytic activity but they complemented L. casei BL23 cmuA and cmuB defective mutants, respectively, thus proving that they actively participate in cell division.

RpfF-dependent regulon of Xylella fastidiosa

ABSTRACT Xylella fastidiosa regulates traits important to both virulence of grape as well as colonization of sharpshooter vectors via its production of a fatty acid signal molecule known as DSF whose production is dependent on rpfF. Although X. fastidiosa rpfF mutants exhibit increased virulence to plants, they are unable to be spread from plant to plant by insect vectors. To gain more insight into the traits that contribute to these processes, a whole-genome Agilent DNA microarray for this species was developed and used to determine the RpfF-dependent regulon by transcriptional profiling. In total, 446 protein coding genes whose expression was significantly different between the wild type and an rpfF mutant (false discovery rate < 0.05) were identified when cells were grown in PW liquid medium. Among them, 165 genes were downregulated in the rpfF mutant compared with the wild-type strain whereas 281 genes were over-expressed. RpfF function was required for regulation of 11 regulatory and σ factors, including rpfE, yybA, PD1177, glnB, rpfG, PD0954, PD0199, PD2050, colR, rpoH, and rpoD. In general, RpfF is required for regulation of genes involved in attachment and biofilm formation, enhancing expression of hemagglutinin genes hxfA and hxfB, and suppressing most type IV pili and gum genes. A large number of other RpfF-dependent genes that might contribute to virulence or insect colonization were also identified such as those encoding hemolysin and colicin V, as well as genes with unknown functions.

Development and evaluation of a real-time polymerase chain reaction assay targeting iap for the detection of Listeria monocytogenes in select food matrices

Listeria monocytogenes is an intracellular foodborne pathogen that has been associated with severe human illnesses. Various rapid detection methods have been developed for the specific detection of this pathogen. In the present study, a real-time quantitative polymerase chain reaction (PCR) assay targeting iap, a gene encoding extracellular protein p60, was developed for L. monocytogenes. The PCR efficiency is above 85% and the limit of detection (LOD) is 30 copies of genome per reaction for all strains tested. The assay exhibited 100% inclusivity and exclusivity rates. The detection of L. monocytogenes in five food matrices, whole milk, soft cheese, turkey deli meat, smoked salmon, and alfalfa sprouts, was evaluated with and without enrichment. Without enrichment, the LOD for all food matrices were 4×10(3) CFU/mL food enrichment mix for whole milk and 4×10(4) CFU/mL for all other foods. With 24 h incubation in Buffered Listeria Enrichment Broth, the LOD was 3 CFU/25 g food for whole milk, turkey deli meat, and smoked salmon and 9 CFU/25 g food for soft cheese and alfalfa sprouts. With 48 h incubation, the LOD was 3 CFU/25 g food for all matrices. This quantitative PCR appears to be a promising alternative for rapid detection of L. monocytogenes in select foods.

Actin polymerization drives septation of Listeria monocytogenes namA hydrolase mutants, demonstrating host correction of a bacterial defect

The Gram-positive bacterial cell wall presents a structural barrier that requires modification for protein secretion and large-molecule transport as well as for bacterial growth and cell division. The Gram-positive bacterium Listeria monocytogenes adjusts cell wall architecture to promote its survival in diverse environments that include soil and the cytosol of mammalian cells. Here we provide evidence for the enzymatic flexibility of the murein hydrolase NamA and demonstrate that bacterial septation defects associated with a loss of NamA are functionally complemented by physical forces associated with actin polymerization within the host cell cytosol. L. monocytogenes ΔnamA mutants formed long bacterial chains during exponential growth in broth culture; however, normal septation could be restored if mutant cells were cocultured with wild-type L. monocytogenes bacteria or by the addition of exogenous NamA. Surprisingly, ΔnamA mutants were not significantly attenuated for virulence in mice despite the pronounced exponential growth septation defect. The physical force of L. monocytogenes-mediated actin polymerization within the cytosol was sufficient to sever ΔnamA mutant intracellular chains and thereby enable the process of bacterial cell-to-cell spread so critical for L. monocytogenes virulence. The inhibition of actin polymerization by cytochalasin D resulted in extended intracellular bacterial chains for which septation was restored following drug removal. Thus, despite the requirement for NamA for the normal septation of exponentially growing L. monocytogenes cells, the hydrolase is essentially dispensable once L. monocytogenes gains access to the host cell cytosol. This phenomenon represents a notable example of eukaryotic host cell complementation of a bacterial defect.

Protease treatment affects both invasion ability and biofilm formation in Listeria monocytogenes

Listeria monocytogenes is a notably invasive bacterium associated with life-threatening food-borne disease in humans. Several surface proteins have been shown to be essential in the adhesion of L. monocytogenes, and in the subsequent invasion of phagocytes. Because the control of the invasion of host cells by Listeria could potentially hinder its spread in the infected host, we have examined the effects of a protease treatment on the ability of L. monocytogenes to form biofilms and to invade tissues. We have chosen serratiopeptidase (SPEP), an extracellular metalloprotease produced by Serratia marcescens that is already widely used as an anti-inflammatory agent, and has been shown to modulate adhesin expression and to induce antibiotic sensitivity in other bacteria. Treatment of L. monocytogenes with sublethal concentrations of SPEP reduced their ability to form biofilms and to invade host cells. Zymograms of the treated cells revealed that Ami4b autolysin, internalinB, and ActA were sharply reduced. These cell-surface proteins are known to function as ligands in the interaction between these bacteria and their host cells, and our data suggest that treatment with this natural enzyme may provide a useful tool in the prevention of the initial adhesion of L. monocytogenes to the human gut.

A P60 mutant of Listeria monocytogenes is impaired in its ability to cause infection in intragastrically inoculated mice

A spontaneous P60 mutant of Listeria monocytogenes was less able to cause systemic infection in A/J mice, following intragastric inoculation, than the parental wild type strain (SLCC 5764, serotype 1/2a). Significantly fewer CFU were recovered from internal organs (spleen, liver, gall bladder) and from the cecum of mice inoculated intragastrically with the P60 mutant than mice inoculated with wild type L. monocytogenes. The P60 mutant also exhibited a diminished ability to invade and multiply within Caco-2 intestinal epithelial cells. These findings indicate that P60 is required for maximal virulence of L. monocytogenes in the gastrointestinal tract of mice.

Comparative evaluation of adhesion, surface properties, and surface protein composition of Listeria monocytogenes strains after cultivation at constant pH of 5 and 7

AIMS

To analyse the cellular mechanisms that influence Listeria monocytogenes adhesion onto inert surfaces under acidic growth conditions.

METHODS AND RESULTS

The adhesion capability of all the strains was significantly reduced after cultivation at constant pH 5 than at constant pH 7 and the cell surface was significantly less hydrophobic at pH 5 than at 7. At pH 5, the analyses of surface protein composition revealed that the flagellin was downregulated for all strains, which was confirmed by the absence of flagella and the P60 protein was upregulated for L. monocytogenes EGD-e, X-Li-mo 500 and 111. The use of L. monocytogenes EGD mutants revealed that flagellin could be involved in the adhesion process, but not P60 protein. It was also observed that the hydrophobic character was not linked to the presence or the absence of flagellin or P60 protein at the cell surface of L. monocytogenes.

CONCLUSIONS

The decrease of L. monocytogenes adhesion at pH 5 could be attributed to the downregulation of the flagellin synthesis under the acidic conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Conservation of food product at pH 5 will delay bacterial adhesion and biofilm formation during food processing on inert surfaces when the product is contaminated with L. monocytogenes.

Adhesion characteristics of Listeria adhesion protein (LAP)-expressing Escherichia coli to Caco-2 cells and of recombinant LAP to eukaryotic receptor Hsp60 as examined in a surface plasmon resonance sensor

Listeria adhesion protein (LAP) is an important adhesion factor in Listeria monocytogenes and interacts with its cognate receptor, mammalian heat shock protein 60 (Hsp60). The genetic identity of LAP was determined to be alcohol acetaldehyde dehydrogenase (Aad). A recombinant Escherichia coli strain expressing aad confirmed the involvement of Aad in adhesion to Caco-2 cells. Binding kinetics (ka) of recombinant LAP (rLAP) to Hsp60 was examined in a surface plasmon resonance sensor and was determined to be 5.35 x 10(8) M(-1) s(-1) and it was equivalent to the binding of anti-Hsp60 antibody (ka = 2.15 x 10(9) M(-1) s(-1)) to Hsp60. In contrast, Internalin B, an adhesion/invasion protein from L. monocytogenes, used as a control, had binding kinetics (ka) of only 2.9 x 10(6) M(-1) s(-1). The KD value of rLAP was 1.68 x 10(-8) M, which was significantly lower than Internalin B (KD = 6.5 x 10(-4) M). These results suggest that Hsp60 has significantly higher avidity for anti-Hsp60 antibody and LAP than Internalin B. In summary, LAP is identified as an alcohol acetaldehyde dehydrogenase and binding of recombinant E. coli to Caco-2 cells or rLAP to Hsp60 protein was found to be highly specific.

Characterization of Listeria monocytogenes protein Lmo0327 with murein hydrolase activity

Listeria monocytogenes is an ubiquitous gram-positive, opportunistic food-borne human and animal pathogen. To date, five L. monocytogenes autolysins have been characterized: p60, p45, Ami, MurA and Auto and the preliminary results of our studies show that FlaA, a flagellar protein of L. monocytogenes, also has murein-degrading activity. In this study, a gene coding a 144 kDa protein (Lmo0327) with murein hydrolase activity was identified from a lambda Zap expression library of L. monocytogenes EGD genomic DNA, using a direct screening protocol involving the plating of infected Escherichia coli XL1-blue MRF' cells onto medium containing Bacillus subtilis murein, a substrate for autolytic proteins. Protein Lmo0327 has a signal sequence, a N-terminal LRR domain and a C-terminal wall-anchoring LPXTG motif. In order to examine the roles of this enzyme and the putative transcription regulator coded by gene lmo0326 located upstream of lmo0327, both structural genes were insertionally inactivated by site-specific integration of a temperature-sensitive plasmid. We show that Lmo0327 is a surface protein covalently linked to murein and that the putative transcription regulator Lmo0326 can be assumed to positively regulate the expression of gene lmo0327. The enzyme, which we have shown to have murein-hydrolysing activity, plays a role in cell separation and murein turnover.

Listeria monocytogenes protein p60 affects hemolytic activity and uptake of bacteria by macrophages

Bacillus subtilis strains expressing listeriolysin O (LLO) and simultaneously LLO and p60 protein were constructed. The effect of p60 protein on hemolytic activity and on the invasion of professional phagocytes was demonstrated in the absence of other virulence factors of L. monocytogenes. The hemolytic activity of LLO in the presence of p60 protein decreased which indicates that p60 promoted adhesion and subsequent invasion of professional phagocytes.

The multifunctional Staphylococcus aureus autolysin aaa mediates adherence to immobilized fibrinogen and fibronectin

Staphylococci can cause a wide spectrum of infections, including endocarditis, osteomyelitis, and sepsis, which is reflected by the numerous virulence factors they produce, among them a recently identified new class of adhesins, namely, the multifunctional autolysins/adhesins. Here we report the identification and molecular characterization of Aaa, a novel autolysin/adhesin from Staphylococcus aureus. The gene encoding Aaa was cloned from the clinical isolate Staphylococcus aureus 4074. DNA sequence analysis revealed that aaa encodes a deduced protein of 334 amino acids with a predicted molecular mass of 35.8 kDa. Aaa contains three N-terminal repetitive sequences that comprise features of a peptidoglycan-binding domain, the LysM domain. The expression of aaa by Escherichia coli and its subsequent characterization revealed that Aaa possesses bacteriolytic activity as well as adhesive properties, such as binding to extracellular matrix proteins. Real-time biomolecular interaction analysis demonstrated that the interaction of Aaa with fibrinogen, fibronectin, and vitronectin is dose dependent and saturable and occurs with a high affinity. Furthermore, we demonstrate that Aaa binds to the Aalpha and Bbeta chains of fragment D of fibrinogen. Immunofluorescence microscopy revealed that Aaa is located at the cell surface. Finally, an aaa knockout mutant showed reduced adherence to surface-adsorbed fibrinogen and fibronectin, strongly suggesting a role for Aaa in the colonization of host factor-coated polymer surfaces and/or host tissue.

Enhanced synthesis of internalin A in aro mutants of Listeria monocytogenes indicates posttranscriptional control of the inlAB mRNA

Listeria monocytogenes mutants with deletions in aroA, aroB, or aroE exhibited strong posttranscriptional upregulation of internalin A (InlA) and InlB synthesis, which resulted in a more-than-10-fold increase in InlA-mediated internalization by epithelial Caco-2 cells and a 4-fold increase in InlB-mediated internalization by microvascular endothelial cells (human brain microvascular endothelial cells) compared to the wild-type strain. The increase in InlA and InlB production was not due to enhanced PrfA- and/or sigma factor B (SigB)-dependent inlAB transcription but was caused by enhanced translation of the inlAB transcripts in the aro mutants. All inlA(B) transcripts had a 396-nucleotide upstream 5' untranslated region (UTR). Different deletions introduced into this UTR led to significant reductions in InlA and InlB synthesis; enhanced translation of all of the truncated transcripts in the aro mutants was, however, still observed. Thus, translation of the inlAB transcripts was subject to two modes of posttranscriptional control, one mediated by the UTR structure and the other mediated by the aro mutation. The latter mode of control seemed to be related to the predominantly anaerobic metabolism of the aro mutants.

Glucose and nutrient concentrations affect the expression of a 104-kilodalton Listeria adhesion protein in Listeria monocytogenes

Growth media and environmental conditions influence the expression of adhesion and invasion proteins in Listeria monocytogenes. Here, the expression of the 104-kDa Listeria adhesion protein (LAP) was studied in nutrient-rich media (Trypticase soy broth [TSB] and brain heart infusion [BHI]), minimal medium (Luria-Bertani [LB]), or nutrient-deficient medium (peptone water [PW]) by immunoblotting, enzyme-linked immunosorbent assay (ELISA), and immunoelectron microscopy. Also, the effect of incorporating different concentrations of glucose on LAP expression was studied. Immunoblotting showed that LAP expression was at least twofold higher in LB medium than in TSB or BHI, while PW supported very poor cell growth and LAP expression. ELISA and immunoblotting results showed that higher concentrations of glucose (>1.6 g/liter) lowered the culture pH and suppressed LAP expression by more than 75%; however, the addition of K(2)HPO(4) reduced this effect. L. monocytogenes cells grown in LB media with lower concentrations of glucose showed higher adhesion to Caco-2 cells (3,716 and 4,186 cpm of attached bacteria for 0 and 0.2 g of glucose/liter, respectively), while L. monocytogenes cells grown in LB with higher glucose concentrations exhibited lower adhesion (2,126 and 2,221 cpm for 1.6 and 3.2 g of glucose/liter, respectively). A LAP-negative L. monocytogenes strain (A572) showed low adhesion profiles regardless of the amount of glucose added. Transmission electron microscopy revealed that LAP is localized mainly in the cytoplasm, with only a few molecules located on the cell surface. Growth in LB with high glucose (3.2 g/liter) showed the presence of only a few molecules in the cells, corroborating the results observed with ELISA or immunoblotting. In summary, nutrient-rich media and high concentrations of glucose suppressed LAP expression, which possibly is due to the changes in the pH of the media during growth from the accumulation of sugar fermentation by-products.

Surface proteins and the pathogenic potential of Listeria monocytogenes

On the basis of the recently determined genome sequence of Listeria monocytogenes, we performed a global analysis of the surface-protein-encoding genes. Only proteins displaying a signal peptide were taken into account. Forty-one genes encoding LPXTG proteins, including the previously known internalin gene family, were detected. Several genes encoding proteins that, like InlB and Ami, possess GW modules that attach them to lipoteichoic acids were also identified. Additionally, the completed genome sequence revealed genes encoding proteins potentially anchored in the cell membrane by a hydrophobic tail as well as genes encoding P60-like proteins and lipoproteins. We describe these families and discuss their putative implications for host-pathogen interactions.

Listeria pathogenesis and molecular virulence determinants

The gram-positive bacterium Listeria monocytogenes is the causative agent of listeriosis, a highly fatal opportunistic foodborne infection. Pregnant women, neonates, the elderly, and debilitated or immunocompromised patients in general are predominantly affected, although the disease can also develop in normal individuals. Clinical manifestations of invasive listeriosis are usually severe and include abortion, sepsis, and meningoencephalitis. Listeriosis can also manifest as a febrile gastroenteritis syndrome. In addition to humans, L. monocytogenes affects many vertebrate species, including birds. Listeria ivanovii, a second pathogenic species of the genus, is specific for ruminants. Our current view of the pathophysiology of listeriosis derives largely from studies with the mouse infection model. Pathogenic listeriae enter the host primarily through the intestine. The liver is thought to be their first target organ after intestinal translocation. In the liver, listeriae actively multiply until the infection is controlled by a cell-mediated immune response. This initial, subclinical step of listeriosis is thought to be common due to the frequent presence of pathogenic L. monocytogenes in food. In normal individuals, the continual exposure to listerial antigens probably contributes to the maintenance of anti-Listeria memory T cells. However, in debilitated and immunocompromised patients, the unrestricted proliferation of listeriae in the liver may result in prolonged low-level bacteremia, leading to invasion of the preferred secondary target organs (the brain and the gravid uterus) and to overt clinical disease. L. monocytogenes and L. ivanovii are facultative intracellular parasites able to survive in macrophages and to invade a variety of normally nonphagocytic cells, such as epithelial cells, hepatocytes, and endothelial cells. In all these cell types, pathogenic listeriae go through an intracellular life cycle involving early escape from the phagocytic vacuole, rapid intracytoplasmic multiplication, bacterially induced actin-based motility, and direct spread to neighboring cells, in which they reinitiate the cycle. In this way, listeriae disseminate in host tissues sheltered from the humoral arm of the immune system. Over the last 15 years, a number of virulence factors involved in key steps of this intracellular life cycle have been identified. This review describes in detail the molecular determinants of Listeria virulence and their mechanism of action and summarizes the current knowledge on the pathophysiology of listeriosis and the cell biology and host cell responses to Listeria infection. This article provides an updated perspective of the development of our understanding of Listeria pathogenesis from the first molecular genetic analyses of virulence mechanisms reported in 1985 until the start of the genomic era of Listeria research.