Characterization of Fusobacterium nucleatum ATCC 23726 adhesins involved in strain-specific attachment to Porphyromonas gingivalis

Bacterial adherence is an essential virulence factor in pathogenesis and infection. Fusobacterium nucleatum has a central role in oral biofilm architecture by acting as a bridge between early Gram-positive and late Gram-negative colonizers that do not otherwise adhere to each other. In this study, we survey a key adherence interaction of F. nucleatum with Porphyromonas gingivalis, and present evidence that multiple fusobacterial adhesins have a role in the attachment of F. nucleatum ATCC 23726 to P. gingivalis in a highly strain-dependent manner. Interaction between these species displayed varying sensitivities to arginine, galactose and lactose. Arginine was found to hamper coaggregation by at least 62% and up to 89% with several P. gingivalis strains and galactose inhibition ranged from no inhibition up to 58% with the same P. gingivalis strains. Lactose consistently inhibited F. nucleatum interaction with these P. gingivalis strains ranging from 40% to 56% decrease in coaggregation. Among the adhesins involved are the previously described Fap2 and surprisingly, RadD, which was described in an earlier study for its function in attachment of F. nucleatum to Gram-positive species. We also provide evidence for the presence of at least one additional adhesin that is sensitive to arginine but unlike Fap2 and RadD, is not a member of the autotransporter family type of fusobacterial large outer membrane proteins. The strain-specific binding profile of multiple fusobacterial adhesins to P. gingivalis highlights the heterogeneity and complexity of interspecies interactions in the oral cavity.

Molecular Detection of Biofilm-Producing <i>Staphylococcus aureus</i>Isolates from National Orthopaedic Hospital Dala, Kano State, Nigeria

This study evaluated biofilm formation and antibiotic susceptibility in 36 clinical S. aureus isolates recovered from orthopaedic patients and detected the presence of intercellular adhesion and adhesin genes. Staphylococcus aureus was isolated from nasal swab, wound and urine specimens collected from orthopaedic patients in National Orthopaedic Hospital Dala, Kano over a period of three months. The isolates were identified using rapid identification kit for Staphylococcus species. The antibiotics susceptibility of the isolates was determined using modified disc diffusion method. Phenotypically, the biofilm formation was assessed using the Congo red agar method and microtitre plate assay. Polymerase chain reaction (PCR) analysis was used to detect biofilm-associated genes and characterize the isolates. The isolation rate of S. aureus from the samples (n = 134) was 26.8%, mainly from nasal swab (36%) and wound swab (36%). A total of 19 (52.7%) of the isolates showed positive for slime production. Majority of the isolates 29/36 (81.6%) were biofilm positive with only 2 (5.5%) and 5 (13.8%) as strong biofilm-formers and moderate biofilm-formers respectively. Molecular evaluation of the biofilm-associated genes in 12 S. aureus isolates revealed the prevalence of bbp genes (25%), clfA genes (16.6%) and the icaA (8.3%). None of the isolates harboured the fnbA and cna genes. There is no significant difference (P > 0.05) in the antibiotic resistance pattern between biofilm-positive and biofilm-negative S. aureus isolates. This result revealed that phenotypically most of the S. aureus isolates were biofilm formers but few of them chromosomally harbour the biofilm-associated genes.

Structures of SdrD from Staphylococcus aureus reveal the molecular mechanism of how the cell surface receptors recognize their ligands

Staphylococcus aureus is the most important Gram-positive colonizer of human skin and nasal passage,causing high morbidity and mortality.SD-repeat containing protein D(SdrD),an MSCRAMM(Microbial Surface Components Recognizing Adhesive Matrix Molecules)family surface protein,plays an important role in S.aureus adhesion and pathogenesis,while its binding target and molecular mechanism remain largely unknown.Here we solved the crystal structures of SdrD N2-N3 domain and N2-N3-B1 domain.Through structural analysis and comparisons,we characterized the ligand binding site of SdrD,and proposed a featured sequence motif of its potential ligands.In addition,the structures revealed for the first time the interactions between B1 domain and N2-N3 domain among B domain-containing MSCRAMMs.Our results may help in understanding the roles SdrD plays in S.aureus adhesion and shed light on the development of novel antibiotics.

Construction and application of carbohydrate microarrays to detect foodborne bacteria

The rapid detection of pathogenic bacteria is vital for the prevention of outbreaks of infectious diseases, including infections by the common foodborne bacteria E.coli and Salmonella Carbohydrate microarrays have been developed as a powerful method to investigate carbohydrate-protein interaction with only very small amounts of glycans, which show great potential for detect the carbohydrate mediated interaction with pathogens. Here, different mannose-coated microarrays were constructed and tested with E.coli(K-12 and BL-21) and Salmonella enterica strains(ATCC9184 and ATCC31685) exhibiting different mannose binding affinities. The optimized carbohydrate microarray was then applied to test the binding of 12 Salmonella enterica and 9 E.coli isolates from local patients for the first time and showed strong binding with certain serovars or subtypes. The results showed that microarray probed with the single mannose structure is not enough for the detection of bacteria with various serovars or subtypes, which contain a high degree of allelic variation in adhesin. We suggest that a complex carbohydrate microarray containing different glycan conformation may be needed for detection of different bacteria isolates.

Immunogenicity and protective immunity against otitis media caused by pneumococcus in mice of Hib conjugate vaccine with PsaA protein carrier

This study evaluated the immunogenicity and protective immunity of a Hemophilus influenzae b （Hib） polysaccharide conjugate vaccine with the pneumococcal surface adhesin A （PsaA） protein carrier in young mice. The Hib polysaccharide was conjugated with the rPsaA protein carrier, which was produced using recombinant DNA technology. A total of 15 young mice aged 3 weeks to 5 weeks were immunized with the conjugate vaccine, and another 15 young mice of the same age were immunized with the licensed Hib-tetanus toxoid （TT） vaccine. Furthermore, the third group of 15 young mice was inoculated with phosphate buffer saline as control. The immunized mice were inoculated with pneumococcus in the middle ear. Results showed that IgG antibody responses against both the PsaA protein and Hib polysaccharide were observed in the Hib-PsaA group. However, no statistical difference was observed in the titer of ｜gG against the Hib polysaccharide between Hib-PsaA and Hib-TT groups. The elimination rate of pneumococcus and the inflammation of the middle ear showed the effectiveness of protective immunity against otitis media caused by pneumococcus. Our results suggest that the Hib polysaccharide can be successfully conjugated with rPsaA via amide condensation. This new Hib-PsaA conjugate vaccine can induce both anti-PsaA and anti-Hib immune responses in young mice and elicit effective protection against acute otitis media caused by pneumococcus.