Kingella negevensis shares multiple putative virulence factors with Kingella kingae.

Kingella negevensis is a newly described gram-negative bacterium in the Neisseriaceae family and is closely related to Kingella kingae, an important cause of pediatric osteoarticular infections and other invasive diseases. Like K. kingae, K. negevensis can be isolated from the oropharynx of young children, although at a much lower rate. Due to the potential for misidentification as K. kingae, the burden of disease due to K. negevensis is currently unknown. Similarly, there is little known about virulence factors present in K. negevensis and how they compare to virulence factors in K. kingae. Using a variety of approaches, we show that K. negevensis produces many of the same putative virulence factors that are present in K. kingae, including a polysaccharide capsule, a secreted exopolysaccharide, a Knh-like trimeric autotransporter, and type IV pili, suggesting that K. negevensis may have significant pathogenic potential.

Necrotizing enterocolitis is preceded by increased gut bacterial replication, Klebsiella, and fimbriae-encoding bacteria.

Necrotizing enterocolitis (NEC) is a devastating intestinal disease that occurs primarily in premature infants. We performed genome-resolved metagenomic analysis of 1163 fecal samples from premature infants to identify microbial features predictive of NEC. Features considered include genes, bacterial strain types, eukaryotes, bacteriophages, plasmids, and growth rates. A machine learning classifier found that samples collected before NEC diagnosis harbored significantly more Klebsiella, bacteria encoding fimbriae, and bacteria encoding secondary metabolite gene clusters related to quorum sensing and bacteriocin production. Notably, replication rates of all bacteria, especially Enterobacteriaceae, were significantly higher 2 days before NEC diagnosis. The findings uncover biomarkers that could lead to early detection of NEC and targets for microbiome-based therapeutics.

Adhesion and invasion of gingival epithelial cells by Porphyromonas gulae.

Porphyromonas gulae, an animal periodontal pathogen, possess fimbriae classified into three genotypes (A-C) based on the diversity of fimA genes encoding FimA. Accumulating evidence suggests that P. gulae strains with type C fimbriae are more virulent as compared to those with other types. The ability of these organisms to adhere to and invade gingival epithelial cells has yet to be examined. P. gulae showed the greatest levels of adhesion and invasion at a multiplicity of infection of 100 for 90 min. P. gulae type C and some type B strains invaded gingival epithelial cells at significantly greater levels than the other strains, at the same level of efficiency as P. gingivalis with type II fimbriae. Adhesion and invasion of gingival epithelial cells by P. gulae were inhibited by cytochalasin D and sodium azide, indicating the requirements of actin polymerization and energy metabolism for those activities. Invasion within gingival epithelial cells was blocked by staurosporine, whereas those inhibitors showed little effects on adhesion, while nocodazole and cycloheximide had negligible effects on either adhesion or invasion. P. gulae proteases were found to be essential for adhesion and invasion of gingival epithelial cells, while its DNA and RNA, and protein synthesis were unnecessary for those activities. Additionally, α5ß1 integrin antibodies significantly inhibited adhesion and invasion by P. gulae. This is the first report to characterize P. gulae adhesion and invasion of human gingival epithelial cells.

Host cell-derived lactate functions as an effector molecule in Neisseria meningitidis microcolony dispersal.

The development of meningococcal disease, caused by the human pathogen Neisseria meningitidis, is preceded by the colonization of the epithelial layer in the nasopharynx. After initial adhesion to host cells meningococci form aggregates, through pilus-pilus interactions, termed microcolonies from which the bacteria later detach. Dispersal from microcolonies enables access to new colonization sites and facilitates the crossing of the cell barrier; however, this process is poorly understood. In this study, we used live-cell imaging to investigate the process of N. meningitidis microcolony dispersal. We show that direct contact with host cells is not required for microcolony dispersal, instead accumulation of a host-derived effector molecule induces microcolony dispersal. By using a host-cell free approach, we demonstrated that lactate, secreted from host cells, initiate rapid dispersal of microcolonies. Interestingly, metabolic utilization of lactate by the bacteria was not required for induction of dispersal, suggesting that lactate plays a role as a signaling molecule. Furthermore, Neisseria gonorrhoeae microcolony dispersal could also be induced by lactate. These findings reveal a role of host-secreted lactate in microcolony dispersal and virulence of pathogenic Neisseria.

GipA Factor Supports Colonization of Peyer's Patches by Crohn's Disease-associated Escherichia Coli.

BACKGROUND: Adherent-invasive Escherichia coli (AIEC) associated with Crohn's disease target M cells lining Peyer's patches (PPs) through the expression of long polar fimbriae (LPF) and survive macrophage killing. Invasion of PPs constitutes a way to colonize the mucosa for bacteria able to escape or resist killing of underlying immune cells. We aimed to identify new virulence factors involved in PPs colonization by AIEC. METHODS: The presence of gipA (Growth in PPs) gene was determined by polymerase chain reaction. In vivo experiments were performed using CEABAC10 transgenic mice. Intramacrophagic behavior of AIEC was assessed in murine bone marrow-derived macrophages and human monocyte-derived macrophages. Cytokines production was quantified by ELISA. RESULTS: A higher prevalence of gipA-positive E. coli was observed in patients with Crohn's disease (27.3%) compared with controls (17.2%). Unlike non-AIEC strains, all gipA-positive AIEC strains also harbored lpfA. GipA deletion impaired AIEC translocation across M cells and their replication inside macrophages. GipA expression was induced by gastrointestinal (bile salts) and phagolysosomal (reactive oxygen species and acid pH) conditions. GipA deletion decreased lpfA mRNA level in AIEC bacteria. Survival of AIEC-ΔgipA bacteria was reduced in medium containing H2O2 or acidic pH. GipA deletion impaired AIEC colonization of PPs and dissemination to mesenteric lymph nodes in mice. CONCLUSIONS: GipA is required for optimal colonization of mouse PPs and survival within macrophages by AIEC, suggesting that this factor plays a role in AIEC promotion of Crohn's disease. Detection of gipA and lpfA could be a predictor for the presence of AIEC.

Radical-scavenging and Anti-inflammatory Activity of Quercetin and Related Compounds and Their Combinations Against RAW264.7 Cells Stimulated with Porphyromonas gingivalis Fimbriae. Relationships between Anti-inflammatory Activity and Quantum Chemical Parameters.

BACKGROUND/AIM: The flavonoid quercetin exerts significant anti-inflammatory activity against chronic infections, including periodontal disease. However, it is unclear whether combination of quercetin with other flavonoids enhances antioxidant and anti-inflammatory activity. To clarify the molecular mechanism responsible for the anti-inflammatory activity of quercetin, we investigated the antioxidant, cytotoxicity and anti-inflammatory activity of quercetin and its related compounds, catechin and epicatechin, and their combinations. MATERIALS AND METHODS: Radical-scavenging activities were determined by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, and cytotoxicity against RAW264.7 cells was determined using a cell counting kit (CCK-8). The inhibitory effects of these compounds on the mRNA expression of cyclooxygenase-2 (Cox2), tumor necrosis factor-alpha (Tnfα) and nitric oxide synthase 2 (Nos2), in RAW264.7 cells stimulated with Porphyromonas gingivalis (Pg) fimbriae, was also determined using real-time polymerase chain reaction analysis. The phenolic O-H bond dissociation enthalpy (BDE) and quantum chemical parameters were calculated on the basis of density function theory (DFT) BLYP/6-31G*. RESULTS: The DPPH(•) radical-scavenging activity (EC50) of quercetin, catechin and epicatechin was 5.5, 7.7 and 6.2 µM, respectively, whereas the cytotoxicity (LC50) was 4.45, 4.80 and 4.95 mM, respectively. Quercetin had slightly higher cytotoxicity and anti-DPPH(•) activity than catechin and epicatechin. The BDE for the three flavonoids at the 4'-OH in the B ring, which is the initial active site, was about 75 kcal/mol. Furthermore, various combinations of quercetin with catechin or epicatechin exerted an antagonistic effect on anti-DPPH(•) activity. Gene expression of Cox2, Tnfα and Nos2 stimulated by exposure to Pg-fimbriae was markedly suppressed by quercetin, but was not modulated by its combination with epicatechin. The 50% inhibitory concentration of quercetin for Cox2 expression was approximately 10 µM, while that of catechin and epicatechin was approximately 500 µM. Values of the quantum chemical parameters softness (σ) and electronegativity (χ) were highest for quercetin among the three flavonoids tested. CONCLUSION: The potent anti-inflammatory activity of quercetin appears to be attributable to its high σ and χ values. Quercetin may be applicable as a preventive agent against inflammatory periodontal disease as a manifestation of systemic disease.

Microbes, cables, and an electrical touch

In nature, highly efficient and diverse consortia of microbes cycle carbon and other elements while generating energy for growth. Driving these reactions are organisms with the ability to extract electrons from the chemical substrates and transfer them to insoluble and soluble electron acceptors. One bacterial group in particular, Geobacter spp., can couple their respiratory metabolism to the reduction of insoluble minerals, such as iron and manganese oxides, and soluble toxic metals such as uranium. Key to these activities is the ability of the cells to transfer respiratory electrons extracellularly using an electroactive cell envelope containing abundant metalloproteins, including c-cytochromes, and conductive protein appendages or pili (known as nanowires). Thus, in addition to been ecological drivers of the cycling of carbon and metals in nature, these organisms show promise for the bioremediation of environments impacted with toxic metals. The electrical activity of Geobacter can also be mimicked in electrochemical reactors equipped with an electrode poised at a metabolically oxidizing potential, so that the electrode functions as an unlimited sink of electrons to drive the oxidation of electron donors and support cell growth. Electrochemical reactors are promising for the treatments of agricultural, industrial, and human wastes, and the electroactivity of these microbes can be used to develop materials and devices for bioenergy and bioremediation applications (AU)

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Group B Streptococcus pili mediate adherence to salivary glycoproteins.

Group B Streptococcus (GBS) is a leading cause of neonatal sepsis, pneumonia and meningitis, and is responsible for a rising number of severe invasive infections in adults. For all disease manifestations, colonisation is a critical first step. GBS has frequently been isolated from the oropharynx of neonates and adults. However, little is understood about the mechanisms of GBS colonisation at this site. In this study it is shown that three GBS strains (COH1, NEM316, 515) have capacity to adhere to human salivary pellicle. Heterologous expression of GBS pilus island (PI) genes in Lactococcus lactis to form surface-expressed pili demonstrated that GBS PI-2a and PI-1 pili bound glycoprotein-340 (gp340), a component of salivary pellicle. By contrast, PI-2b pili did not interact with gp340. The variation was attributable to differences in capacities for backbone and ancillary protein subunits of each pilus to bind gp340. Furthermore, while GBS strains were aggregated by fluid-phase gp340, this mechanism was not mediated by pili, which displayed specificity for immobilised gp340. Thus pili may enable GBS to colonise the soft and hard tissues of the oropharynx, while evading an innate mucosal defence, with implications for risk of progression to severe diseases such as meningitis and sepsis.

Virulence profiles of enterotoxigenic, shiga toxin and enteroaggregative Escherichia coli in South African pigs.

Enterotoxigenic Escherichia coli (ETEC) and shiga toxin E. coli (STEC) are important causes of colibacillosis in piglets. Recently, enteroaggregative E. coli heat-stable enterotoxin 1 (EAST-1) has been implicated in pig diarrhoea. This study investigated the prevalence of enterotoxin [heat-labile toxins (LT), heat-stable toxin a (STa), heat-stable toxin b (STb)], shiga toxins (Stx1, Stx2, Stx2e), enteroaggregative heat-stable E. coli (EAST-1), associated fimbriae (F4, F5, F6, F41, F18ab, F18ac) and non-fimbrial adhesins [adhesin involved in diffuse adherence 1 (AIDA-1), attaching and effacing factor, porcine attaching- and effacing-associated factor] in South African pigs. A total of 263 E. coli strains were isolated from Landrace (n = 24), Large White (n = 126), Duroc (n = 28) and indigenous (n = 85) breeds of piglets aged between 9 and 136 days. PCR was used in the analysis. Virulent genes were detected in 40.3% of the isolates, of which 18.6, 0.4 and 17.5% were classified as ETEC, STEC and enteroaggregative E. coli (EAEC), respectively. Individual genes were found in the following proportions: STb (19.01%), LT (0.4%), STa (3.4%), St2xe (1.1%) and EAST-1 (20.2%) toxins. None of the tested fimbriae were detected in ETEC and STEC isolates. About one third of the ETEC and STEC isolates was tested negative for both fimbrial and non-fimbrial adhesins. Twenty-five pathotypes from ETEC-, EAEC- and STEC-positive strains were identified. Pathotypes EAST-1 (30.2%), STb (13.2%) and STb/AIDA-1 (10.4%) were most prevalent. The study provided insight on possible causes of colibacillosis in South African pigs.

The fimbriae of enteroaggregative Escherichia coli induce epithelial inflammation in vitro and in a human intestinal xenograft model.

BACKGROUND: Enteroaggregative Escherichia coli (EAEC) are increasingly recognized as an important agent of inflammatory and often persistent diarrhea. Although previous studies report on the inflammatory aspects of EAEC pathogenesis, the mechanisms by which EAEC trigger these events are not well understood. METHODS: EAEC strains harboring mutations in known EAEC virulence determinants were tested in an in vitro model of transepithelial migration of polymorphonuclear neutrophils (PMNs) and in human intestinal xenografts in severe-combined immunodeficient (SCID-HU-INT) mice, a novel model for studying EAEC disease in vivo. RESULTS: Expression of aggregative adherence fimbriae (AAFs), the principal adhesins of EAEC, was required for EAEC-induced PMN transepithelial migration in vitro. Moreover, constructed plasmids encoding AAF gene clusters demonstrated that the AAF adhesins are sufficient for triggering this event in a nonpathogenic E. coli background. Furthermore, with use of the SCID-HU-INT mouse model, severe tissue damage and infiltration of inflammatory cells was observed in the human tissue after EAEC infection. These pathological marks were strongly related to AAF expression, thus clearly confirming our in vitro findings. CONCLUSIONS: The present work establishes EAEC as an important inflammatory pathogen and the AAF adhesins as inducers of potentially detrimental immune responses.

La infección urinaria y su prevención / Urinary Tract Infections and Their Prevention

Contexto: En este artículo se revisan diferentes aspectos acerca de la prevención de las infecciones del tracto urinario que incluyen: la confirmación de la existencia de dichas infecciones, la aplicación de medidas higiénico-dietéticas, la profilaxis antibacteriana-preferentemente la toma de una única dosis nocturna diaria oral de un antibiótico o quimioterápico con elevada excreción urinaria y buena tolerancia-, la administración de vacunas elaboradas con Escherichiacoli y otros bacilos gramnegativos completos con fracciones inmunoestimulantes o fimbrias tipo 1 de E. coli por vías parenteral u oral. Objetivo: Revisión de las nuevas medidas de prevención de las infecciones del tracto urinario. Adquisición y síntesis de evidencia: Se revisan diferentes aspectos microbiológicos, la fisiopatología y los factores de virulencia de E. coli uropatógenos productores de fimbrias de tipos 1y P. Se analiza la relación entre los grupos sanguíneos y la infección del tracto urinario en los individuos secretores y no secretores. Conclusiones: El uso de vacunas inactivadas con fenol y administradas por vía mucosa, el empleode inhibidores de la adherencia y de la formación de biopelículas bacterianas y el uso de estimuladores del adenosín-monofosfato cíclico se presentan como nuevas medidas preventivas de la infección urinaria, particularmente para el grupo de mayor incidencia, representado por las mujeres entre la pubertad y la menopausia (AU)

Context: This article reviews diverse aspects of the prevention of urinary tract infections, including confirmation of the diagnosis, application of hygiene and dietary measures, antibacterial prophylaxis (preferably consisting of a single nocturnal oral dose per day of an antibiotic or drug with high urinary excretion and good tolerance), and administration of vaccines made with Escherichia coli and other Gram-negative bacilli, consisting of immunostimulating fractions of E. coli strains or E. coli type-1 fimbriae administered through the parenteral or oral route. Objective: We aimed to review the new preventive measures against urinary tract infections. Acquisition and synthesis of evidence: We reviewed various microbiological aspects, as well as the physiopathology and virulence factors of uropathogenic E. coli strains expressing type-1 and P fimbriae. The association between blood groups and urinary tract infections in blood group antigen-secretors and non secretors was analyzed. Conclusions: New preventive measures against urinary tract infection consist of the use of phenol-inactivated vaccines administered via the mucosal route, inhibitors of bacterial adherence and biofilm formation and cyclic adenosine monophosphate stimulators, especially in women aged between puberty and menopause, who show the highest incidence of these infections (AU)

Autotransporters and virulenceof enteroaggregative E. coli

EAEC, enteroaggregative E. coli; EPEC, enteropathogenic E. coli; ETEC, enterotoxigenic E. coli; EIEC,enteroinvasive E. coli; STEC, shiga-toxin producing E. coli; DAEC, diffusely adhering E. coli; AA, agregative adherence; OMP, outer membrane protein; AAF, aggregative adherence fimbriae; ECP, E. coli common pilus; T1SS, type I secretion system; EAST-1,enteroaggregative E. coli heat stable enterotoxin 1; ORF, open reading frame; Pet, plasmid-encoded toxin; Pic, protein involved in colonization; ShET1, Shigella enterotoxin 1; HlyE, hemolysin E; OM, outer membrane; T5SS, type V secretion system; TPS, twopartner secretion; SPATE, serine protease autotransporter of the Enterobacteriaceae; ER, endoplasmic reticulum; Shmu, Shigellamucinase; cAMP, cyclic adhenosin monophosphate; cGMP, cyclic guanosine monophosphate; STa, heat-stable toxin a; GC-C, guanylyl cyclase C; IL, interleukin; IEC, intestinal epithelial cells; MAPK, mitogen-activating protein kinase; TLR5, toll-like receptor 5; TNFá, tumour necrosis factor á; GRO, growth-related gene product; ICAM-1, intercellular adhesion molecule 1;GM-CSF, granulocyte-macrophage colony-stimulating factor.

M1T1 group A streptococcal pili promote epithelial colonization but diminish systemic virulence through neutrophil extracellular entrapment.

Group A Streptococcus is a leading human pathogen associated with a diverse array of mucosal and systemic infections. Cell wall anchored pili were recently described in several species of pathogenic streptococci, and in the case of GAS, these surface appendages were demonstrated to facilitate epithelial cell adherence. Here we use targeted mutagenesis to evaluate the contribution of pilus expression to virulence of the globally disseminated M1T1 GAS clone, the leading agent of both GAS pharyngitis and severe invasive infections. We confirm that pilus expression promotes GAS adherence to pharyngeal cells, keratinocytes, and skin. However, in contrast to findings reported for group B streptococcal and pneumococcal pili, we observe that pilus expression reduces GAS virulence in murine models of necrotizing fasciitis, pneumonia and sepsis, while decreasing GAS survival in human blood. Further analysis indicated the systemic virulence attenuation associated with pilus expression was not related to differences in phagocytic uptake, complement deposition or cathelicidin antimicrobial peptide sensitivity. Rather, GAS pili were found to induce neutrophil IL-8 production, promote neutrophil transcytosis of endothelial cells, and increase neutrophil release of DNA-based extracellular traps, ultimately promoting GAS entrapment and killing within these structures.

Quimioprofilaxis en la infección del tracto urinario / Chemoprophylaxis in urinary tract infection

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Role of bacterial biofilms in urinary tract infections.

Bacterial urinary tract infections represent the most common type of nosocomial infection. In many cases, the ability of bacteria to both establish and maintain these infections is directly related to biofilm formation on indwelling devices or within the urinary tract itself. This chapter will focus on the role of biofilm formation in urinary tract infections with an emphasis on Gram-negative bacteria. The clinical implications of biofilm formation will be presented along with potential strategies for prevention. In addition, the role of specific pathogen-encoded functions in biofilm development will be discussed.

Contribution of Moraxella catarrhalis type IV pili to nasopharyngeal colonization and biofilm formation.

Moraxella catarrhalis is a gram-negative mucosal pathogen of the human respiratory tract. Although little information is available regarding the initial steps of M. catarrhalis pathogenesis, this organism must be able to colonize the human mucosal surface in order to initiate an infection. Type IV pili (TFP), filamentous surface appendages primarily comprised of a single protein subunit termed pilin, play a crucial role in the initiation of disease by a wide range of bacteria. We previously identified the genes that encode the major proteins involved in the biosynthesis of M. catarrhalis TFP and determined that the TFP expressed by this organism are highly conserved and essential for natural transformation. We extended this initial study by investigating the contribution of TFP to the early stages of M. catarrhalis colonization. TFP-deficient M. catarrhalis bacteria exhibit diminished adherence to eukaryotic cells in vitro. Additionally, our studies demonstrate that M. catarrhalis cells form a mature biofilm in continuous-flow chambers and that biofilm formation is enhanced by TFP expression. The potential role of TFP in colonization by M. catarrhalis was further investigated using in vivo studies comparing the abilities of wild-type M. catarrhalis and an isogenic TFP mutant to colonize the nasopharynx of the chinchilla. These results suggest that the expression of TFP contributes to mucosal airway colonization. Furthermore, these data indicate that the chinchilla model of nasopharyngeal colonization provides an effective animal system for studying the early steps of M. catarrhalis pathogenesis.

Characterization of fimbriae extracts from porcine enterotoxigenic Escherichia coli strains carrying F6 (987P) antigen / Caracterización de los extractos de fimbrias de cepas porcinas de Escherichia coli enterotoxigénica con el antígeno F6 (987P)

Fimbrial extracts from porcine enterotoxigenic Escherichia coli (ETEC) strains carrying F6 (987P) intestinal colonization factor antigen were obtained using the thermal shock method. The extracts were analyzed by SDSPAGE and immunoblotting using different fimbriae-specific antisera. Two major protein bands with molecular masses of 17.5 and 21.9 kDa were detected. The 21.9-kDa band was identified as the major subunit of F6 fimbrial antigen in strains of serogroups O9 and O141. The 17.5-kDa band was associated with porcine strains of serogroups O9 and O20 (AU)

Los extractos de fimbrias obtenidos usando el método de choque térmico a partir de cepas de origen porcino de Escherichia coli (ETEC) enterotoxigénica con el antígeno de colonización intestinal F6 (987P) fueron analizados por SDS-PAGE e immunotransferencia usando diferentes antisueros específicos frente a antígenos de fimbrias. Se detectaron dos bandas principales de proteínas de 17,5 kDa y 21,9 kDa según la cepa ensayada. La banda de 21,9 kDa fue identificada como la subunidad estructural principal del antígeno de fimbria F6 y se observó en las cepas de los serogrupos O9 yO141. La banda de 17,5 kDa se asoció a las cepas porcinas de los serogrupos O9 y O20 (AU)

Prevalence of the lpfO113 gene cluster among Escherichia coli O157 isolates from different sources.

Domestic farm animals represent an important reservoir of infection for Shiga toxin-producing Escherichia coli (STEC). Nevertheless the bacterial factors required to colonise these hosts are poorly defined. In this study, the prevalence of a recently described fimbrial gene cluster, lpfO113, among human and animal isolates of STEC was investigated. lpfO113 has been shown to play a role in the adherence of STEC O113:H21 to epithelial cells. Here the presence of the lpfAO113 gene (predicted to encode a major fimbrial subunit) was examined by PCR in E. coli of serogroups O157 and O26 isolated from pigs (n=38), cattle (n=10), and humans (n=9). In addition, we tested for several other genetic virulence markers including Shiga toxin (stx), intimin (eae), the translocated intimin receptor (tir), EHEC-hemolysin (ehx) and F18 fimbriae (fedA). Overall 45 of the 57 strains (79%) possessed the lpfAO113 gene as determined by the presence of a 573 bp PCR product. Moreover, there was a close correlation between the presence of the lpfAO113 marker and the absence of the eae gene. lpfAO113 was found in all of pig isolates, suggesting a possible role in colonisation of the porcine host. In addition, several E. coli strains isolated from pigs had two fimbrial gene markers, fedA and lpfAO113. lpfAO113 was not present in strains of E. coli O157:H7 as described previously. Overall these results show that lpfAO113 is widely distributed among eae-negative E. coli isolates and thus may represent an important adherence factor in this group of pathogens.

Association between the porcine Escherichia coli F18 receptor genotype and phenotype and susceptibility to colonisation and postweaning diarrhoea caused by E. coli O138:F18.

Porcine postweaning Escherichia coli enteritis is a cause of significant morbidity and mortality in pigs worldwide, and effective prevention remains an unsolved problem. This study examined the correlation between susceptibility of pigs to experimental infection with an E. coli F18 strain and the porcine intestinal F18 receptor genotypes. Thirty-one pigs classified as either belonging to the susceptible or the resistant genotype were inoculated with cultures of an E. coli O138:F18 isolated from a pig with postweaning diarrhoea. Susceptibility to colonisation and diarrhoea was assessed by clinical observations, faecal shedding of the challenge strain, histopathology and microscopic adhesion tests. Ten of 14 (71.4%) genetically susceptible pigs and one of 17 (5.9%) resistant pigs developed diarrhoea attributable to the challenge strain. There was no difference in susceptibility between homozygotic and heterozygotic susceptible pigs. Faecal shedding of the challenge strain correlated with the genetic receptor profile. Twenty pigs examined immunohistochemically revealed focal to extensive small intestinal mucosal colonisation by E. coli O138:F18 in nine of 10 susceptible and three of 10 resistant pigs. Results of in vitro adhesion assays performed with F18 cells on enterocyte preparations from 24 pigs, showed complete concordance with the F18 genotypes. In conclusion, this study showed a high correlation between the porcine intestinal F18 receptor genotypes and susceptibility to disease. However, pigs of the resistant F18 receptor genotype were not entirely protected against intestinal colonisation by E. coli F18.

Fimbriae and adherence of Strenotrophomonas maltophilia to epithelial cells and to abiotic surfaces

Stenotrophomonas maltophilia is an emerging nosocomial bacterial pathogen associated with several infectious diseases and opportunistic infections, especially in immunocompromised patients. These bacteria adhere avidly to medical implants and catheters forming a biofilm that confers natural protection against host immune defences and different antimicrobial agents. The nature of the bacterial surface factors involved in biofilm formation on inert surfaces and in adherence of S. maltophilia to epithelial cells is largely unknown. In this study, we identified and characterized fimbrial structures produced by S. maltophilia. The S. maltophilia fimbriae 1(SMF-1) are composed of a 17 kDa fimbrin subunit which shares significant similarities with the Nterminal amino acid sequences of several fimbrial adhesins (G, F17, K99 and 20K) found in Escherichia coli pathogenic strains and the CupA fimbriae of Pseudomonas aeruginosa. All of the clinical S. maltophilia isolates tested produced the 17 kDa fimbrin. Antibodies raised against SMF-1 fimbriae inhibited the agglutination of animal erythrocytes, adherence to HEp-2 cells and biofilm formation by S. maltophilia.High resolution electron microscopy ovided evidence of the presence of fimbriae acting as bridges between bacteria adhering to inert surfaces or to cultured epithelial cells. This is the first characterization of fimbriae in this genus. We provide compelling data suggesting that the SMF-1 fimbriae are involved in haemagglutination, biofilm formation and adherence to cultured mammalian cells...