Bacterial extracellular vesicles: towards realistic models for bacterial membranes in molecular interaction studies by surface plasmon resonance

One way to mitigate the ongoing antimicrobial resistance crisis is to discover and develop new classes of antibiotics. As all antibiotics at some point need to either cross or just interact with the bacterial membrane, there is a need for representative models of bacterial membranes and efficient methods to characterize the interactions with novel molecules -both to generate new knowledge and to screen compound libraries. Since the bacterial cell envelope is a complex assembly of lipids, lipopolysaccharides, membrane proteins and other components, constructing relevant synthetic liposome-based models of the membrane is both difficult and expensive. We here propose to let the bacteria do the hard work for us. Bacterial extracellular vesicles (bEVs) are naturally secreted by Gram-negative and Gram-positive bacteria, playing a role in communication between bacteria, as virulence factors, molecular transport or being a part of the antimicrobial resistance mechanism. bEVs consist of the bacterial outer membrane and thus inherit many components and properties of the native outer cell envelope. In this work, we have isolated and characterized bEVs from one Escherichia coli mutant and three clinical strains of the ESKAPE pathogens Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa. The bEVs were shown to be representative models for the bacterial membrane in terms of lipid composition with speciesstrain specific variations. The bEVs were further used to probe the interactions between bEV and antimicrobial peptides (AMPs) as model compounds by Surface Plasmon Resonance (SPR) and provide proof-of-principle that bEVs can be used as an easily accessible and highly realistic model for the bacterial surface in interaction studies. This further enables direct monitoring of the effect induced by antibiotics, or the response to host-pathogen interactions.

Goldilocks Dilemma: LPS Works Both as the Initial Target and a Barrier for the Antimicrobial Action of Cationic AMPs on E. coli

Antimicrobial peptides (AMPs) are generally membrane-active compounds that physically disrupt bacterial membranes. Despite extensive research, the precise mode of action of AMPs is still a topic of great debate. This work demonstrates that the initial interaction between the Gram-negative E. coli and AMPs is driven by lipopolysaccharides (LPS) that act as kinetic barriers for the binding of AMPs to the bacterial membrane. A combination of SPR and NMR experiments provide evidence suggesting that cationic AMPs first bind to the negatively charged LPS before reaching a binding place in the lipid bilayer. In the event that the initial LPS-binding is too strong (corresponding to a low dissociation rate), the cationic AMPs cannot effectively get from the LPS to the membrane, and their antimicrobial potency will thus be diminished. On the other hand, the AMPs must also be able to effectively interact with the membrane to exert its activity. The ability of the studied cyclic hexapeptides to bind LPS and to translocate into a lipid membrane is related to the nature of the cationic charge (arginine vs. lysine) and to the distribution of hydrophobicity along the molecule (alternating vs. clumped tryptophan).

Can the absolute configuration of cyclic peptides be determined with vibrational circular dichroism?

Cyclic peptides show a wide range of biological activities, among others as antibacterial agents. These peptides are often large and flexible with multiple chiral centers. The determination of the stereochemistry of molecules with multiple chiral centers is a challenging and important task in drug development. Chiroptical spectroscopies such as vibrational circular dichroism (VCD) can distinguish between different stereoisomers. The absolute configuration (AC) of a stereoisomer can be determined by comparing its experimental spectra to computed spectra of stereoisomers with known AC. In this way, the AC of rigid molecules with up to seven chiral centers has been assigned (Bogaerts et al., Phys. Chem. Chem. Phys., 2020, 22, 18014). The question arises whether this is possible with more conformationally flexible molecules such as cyclic peptides. We here investigate to what extent the AC of cyclic peptides can be determined with VCD. More specifically, we investigate the maximum number of chiral centers a cyclic peptide can have in order to be able to unambiguously assign the AC with VCD. We present experimental and computed IR and VCD spectra for a series of eight tetrapeptides and hexapeptides with two, three and four chiral centers. We use our recently developed computational protocol with a conformational search based on sampling with meta-dynamics. We use visual inspection to compare the computed spectra of different stereoisomers with an experimental spectrum of the corresponding cyclic peptide with known AC. We find that the AC of the investigated cyclic peptides with two chiral centers can be unambiguously assigned with VCD. This is however not possible for all of the cyclic peptides with three chiral centers and for none of those with four chiral centers. At best, one can limit the number of possible stereoisomers in those cases. Our work shows that other techniques are needed to assign the AC of cyclic peptides with three or more chiral centers. Our study also constitutes a warning that the spectra of all stereoisomers should be computed before attempting to match to an experimental spectrum, to avoid an accidental erroneous match.

Expression of HLA class II antigens in marginal periodontitis of patients with Down's syndrome

The expression of HLA Class II antigens on the surfaces of immunocompetent cells and the presence of CD1a+ cells (Langerhans cells) are important components of antigen presentation. Quantitative variations in HLA class II expression on antigen-presenting cells play a role in immune regulation. An indirect immunofluorescent technique was used on cryostat sections to reveal such differences qualitatively or quantitatively between chronic marginal periodontitis (CMP) in patients with Down's syndrome (DS) and in otherwise normal patients (NP). We found increased frequency of HLA Class II (HLA-expression on inflammatory cells and on keratinocytes of the oral gingival epithelium) in CMP of DS patients compared to sections from NP. The expression of HLA-DR was more frequent on the keratinocytes of the pocket epithelium in NP than in DS. There were significantly higher numbers of CD1a+ cells and ratios of HLA-DR+/CD1a+ cells and HLA-DP+/CD1a+ cells in the DS group compared to the NP group. Our conclusion is that there is a more pronounced inflammatory process in the gingival sites with CMP of DS patients compared to CMP in NP. The findings also indicate that there is a highly activated immune response in CMP of DS patients.

Spontaneous gingival antibody production to Fusobacterium nucleatum outer membrane in patients with adult periodontitis

The local antibody response to Fusobacterium nucleatum outer membrane (FnOM) was analyzed in patients with adult periodontitis (AP) at the single cell level. Furthermore, we analyzed whether periodontal hygienic treatment could alter the antibody response. The number of IgG- and IgM-producing cells were investigated in gingival samples collected from 20 patients with AP. The patients were divided into 2 groups, before (BT, n = 9) and after (AT, n = 11) periodontal hygienic treatment. Four healthy gingival samples were used as controls. The results obtained showed that local antibody production against FnOM occurred in gingiva of patients with AP, but not in healthy gingiva. The IgG anti-FnOM was the predominant isotype observed. However, there was no statistically significant difference between the BT and AT groups. These results indicate that periodontal hygienic treatment was not sufficient to alter significantly the number of IgG- and IgM-secreting cells present in gingival tissue of AP patients, but it promoted a reduction of IgG anti-FnOM secreting cells. The presence of anti-FnOM antibodies in AP but not in control patients indicates that this bacteria may play a role in the pathogenesis of periodontal disease.

Epithelial expression of HLA class II antigens and Fc gamma receptors in patients with adult periodontitis

The distribution of HLA class II (DR, DP, DQ) and Fc gamma R (I, II, III) was analyzed in the epithelia of patients with advanced marginal periodontitis using cryostat sections incubated with monoclonal antibodies (MoAb) against the Langerhans cell (LC) (CD1a) and various subtypes of HLA class II and Fc gamma R, and the indirect immunofluorescence technique. In the oral gingival epithelium (OGE), LC were concentrated subjacent to the connective tissue papillae, while in the pocket epithelium (PE), they were most abundant at the gingival margin. HLA-DP, DQ, and DR stained LC in both OGE and PE. HLA-DQ+ LC were significantly fewer than DP+ and DR+ LC. HLA-DR also stained keratinocytes (KC) in the whole extension of both OGE and PE. HLA-DP was also observed on KC, but not HLA-DQ. Fc gamma R II stained both LC and focal areas of KC. In PE FC gamma R II+ LC were concentrated near the bottom of the pocket, while in the OGE, they were concentrated at the gingival margin. Fc gamma R III was present only on KC, especially in the basal and suprabasal layer. The results indicate that the epithelial cells are actively involved in the development and maintenance of the inflammation of periodontal disease.

In situ characterization of mononuclear cells in marginal periodontitis of patients with Down's syndrome

An indirect immunofluorescence technique on cryostat sections was used to study the cellular composition in chronic marginal periodontitis (CMP) of patients with Down's syndrome (DS). The findings were compared with CMP lesions in otherwise normal patients (NP). The distribution and amount of CD22+ cells (B lymphocytes), CD3+ cells (pan T lymphocytes), CD4+ cells (helper T subset), CD8+ cells (suppressor/cytotoxic T subset), and CD11c+ cells (in tissue, mainly monocytes and macrophages) were investigated. Morphologic studies showed a denser inflammatory infiltrate in DS than in NP. Countings showed significant differences in cell distribution (p = 0.0003) and cell profiles (p = 0.0273) between the two groups. The median CD4+/CD8+ ratio in DS (2.73) was significantly higher (p = 0.0024) than found in gingival inflammatory lesions from NP (1.08). The present study shows that DS patients have a different, more pronounced, immune response in CMP than NP.

The composition of gingival inflammatory cell infiltrates in children studied by enzyme histochemistry

Gingival biopsies were obtained from 23 children, aged 5-11 years (8.6 +/- 1.8 years). Specimens were taken from areas of the gingiva adjacent to the teeth which were to be extracted because of caries or its sequelae and which clinically had a gingival index score of at least 1. Staining for alpha-naphthyl acetate esterase with unspecific esterase at pH 5.8 (ANAE) permitted identification of T lymphocytes, monocytes/macrophages, plasma cells and non-reactive (ANAE-negative) cells. Cells which tentatively were identified as "natural killer" (NK) cells were also observed. Differential cell counting was performed for 10 specimens, selected on the basis of the presence of a well-defined inflammatory infiltrate, clear morphology throughout and good ANAE staining. Cell counts confirmed earlier studies showing that lymphocytes predominate in the inflammatory infiltrates in childrens' gingivitis. T lymphocytes dominated particularly in the periphery of the most densely infiltrated areas. Relatively few plasma cells were seen. It was concluded that T lymphocytes dominate in the inflammatory infiltrate in childrens' gingivitis.

Outer membrane proteins of Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus studied by SDS-PAGE and immunoblotting

This investigation characterized and compared outer membrane proteins (OMP) of the closely related Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus by means of SDS-PAGE patterns and reactions on immunoblots with rabbit antiserum against A. actinomycetemcomitans FDC Y4. Reactions with serum from a patient with Papillon Lefévre syndrome (PLS), from whom periodontal wild strains of A. actinomycetemcomitans had been isolated, were also studied. OMP were purified with selective solubilization from lyophilized cells of 10 wild and 4 reference strains of A. actinomycetemcomitans and 4 reference strains of H. aphrophilus. OMP profiles from wild and reference strains of A. actinomycetemcomitans were similar while those from A. actinomycetemcomitans and H. aphrophilus differed. The most prominent difference was absence of a heat modifiable protein in H. aphrophilus strains. Immunoblotting revealed strong common antigens in most strains, including a heat modifiable protein with mol wt 34 kDa, as well as a 29 kDa and a 16.5 kDa protein. Treatment with pronase and sodium periodate confirmed the protein nature of the major OMP antigens.

Variation in the composition of gingival inflammatory cell infiltrates

Biopsy specimens were taken at gingivectomy from 18 adult patients undergoing treatment for chronic marginal periodontitis. They were embedded so that the cut surface of the gingiva was parallel to the top of the block to obtain a comprehensive view in a transversal plane of the inflammatory cell infiltrate near the bottom of the pocket. Sections were stained with HES or with toluidine blue for histological description, and acid alpha-naphthyl acetate esterase (ANAE) was used to differentially stain T lymphocytes, plasma cells and monocytes/macrophages. Sections stained with HES showed that the density and size of the cell infiltrates varied along the circumference of a tooth over very short distances and on various surfaces on neighbouring teeth. Differential counts of cells stained for ANAE demonstrated great variation in the composition of the cell infiltrates, particularly along the pocket epithelium. The predominating ANAE positive cell type in this area was T lymphocytes, while in the central connective tissue, plasma cells predominated. There was no systematic covariation between the localization of the gingiva (i.e. mesial, facial, etc.) and the composition of the cell infiltrates. The local variation in the composition of the cellular infiltrate most likely reflects local variability in the noxious substances (i.e. plaque composition) within the periodontal pocket, and in the resulting local inflammatory response.

Deposits of immunoglobulins, complement, and immune complexes in inflamed human gingiva

Gingival biopsy specimens from 20 patients with moderate to advanced periodontitis were obtained from inflamed sites with pockets of 5 mm or more. Sections were studied by an immunofluorescence technique, using polyclonal rabbit or goat anti-IgG, anti-IgM, anti-C1q, anti-C3a, and anti-C3c and mouse monoclonal anti-C9. Prewashed ethanol-fixed and nonwashed ethanol-fixed or frozen specimens showed many plasma cells staining for IgG or C3a, suggesting the possible occurrence of a receptor for C3a in plasma cells. Plasma cells containing IgM were also seen. Deposits of IgG and IgM with C1q, C3a, and C3c, suggesting immune complexes, were demonstrated by a double staining technique, combining fluorescein (FITC) or rhodamine (TRITC)-labeled anti-immunoglobulins with TRITC- or FITC-conjugated antibody to C3a, C3c, and C1q. The complexes were located mainly within or around vessel walls. Deposits of C3a and C1q were found in vessel walls, in the basement membrane zone of oral gingival epithelium, or diffusely distributed in the tissues. Deposits of C3c were found to a lesser extent and only in vessel walls. Mouse monoclonal anti-C9, visualized with FITC-labeled rabbit anti-mouse and swine anti-rabbit antiserum, showed granular deposits of C9, mainly in the basement membrane zone of oral gingival epithelium. The study indicates the involvement of immune complex vasculitis in inflammatory periodontal lesions. Also, our observations of the occurrence of deposits of complement factors support the hypothesis that complement factors play an important role in the immunopathology of the periodontal lesion.

Host responses to bacteria and bacterial products in periodontal disease: immunosuppressive effects of periodontitis-related microorganisms?

Several recent investigations indicate that some patients with adult periodontitis have lowered serum antibody levels or reduced lymphoproliferative responses to certain periodontitis-related microorganisms. Many such patients tend to show increased responses after therapy. Some suggested mechanisms of such responses are reviewed and the possible significance of immunosuppressive effects of periodontitis-related microorganisms are briefly discussed.

A baseline study of periodontal conditions among youths and adults in Portugal

A study was undertaken in 1979 to obtain baseline data of periodontal disease and treatment needs among rural and urban Portuguese. From Montemor-o-Novo, Alentejo and from Lisbon, 255 persons (121 males, 134 females) aged 15-44 yr were selected by a stratified quota sampling method and examined under field conditions using both Russell's Periodontal Index (P.I.), slightly modified, and components of a proposed new WHO method. The latter formed the basis for estimation of treatment need according to the Community Periodontal Index for Treatment Needs (CPITN). Periodontal disease as assessed by the P.I. exhibited epidemiologic characteristics which in several respects were similar to those reported in other populations. Severity increased with increasing age and there were trends towards more severe disease in males than in females, and more severe disease in rural than in urban districts. Relatively few cases of advanced periodontitis were detected by the P.I. as applied in this study. The underestimation of disease prevalence inherent in the scoring method, the high tooth mortality and the fact that only relatively young individuals were studied may have contributed to this finding. Great need for various types of periodontal therapy were found through CPITN assessments. However, relatively few individuals were in need of "complex periodontal therapy" as assessed by the CPITN.

Effect of oral hygiene instructions given by paraprofessional personnel

A study was undertaken in order to test the effect of hygiene instructions given by specially trained chair-side assistants and to test the value of depuration prior to instructions. Chair-side assistants were trained to motivate and instruct patients in oral hygiene methods. The 71 participants (12 female and 59 male employees of the same industrial firm) were divided into three groups. Group C received depuration (one visit) prior to oral hygiene instruction, Group B hygiene instructions only, and Group A depuration only. Following instructions, the participants were examined after 4, 12 and 24 weeks with respect to: DMFT, Gingival Index, Retention Index, plaque surface and periodontal pockets greater than or equal to 4 mm. The results showed a reduction in plaque surfaces from baseline to 24 weeks in Groups B and C of 67% and 70% (difference not significant). Slight improvement was noted in Group A. Significant improvement was also observed in Gingival Index scores and pocket depths. Significant differences were not found between the groups with respect to Retention Index scores. Smoking did not influence the program. The effects of instructions were retained after 6 months. It is concluded that the use of this kind of personnel is highly effective and expedient, and that the present model can be useful in preventive dental health work.

Ultrasonic scaling of maxillary teeth causing tinnitus and temporary hearing shifts

The possible effects of ultrasonic scaling of all maxillary teeth for a total of 5 min on the inner ears of 20 healthy young adults, 22-36 years of age, were investigated by means of pure tone audiometry. Audiograms were obtained just before and immediatley after scaling. Temporary shifts in hearing threshold (TTS) of 10-20 dB, mostly at 7--8 kHz, ersisting for up to 30 min, were recorded in eight of the individuals. Three patients reported high-pitched tinnitus lasting for 20-30 min after ultrasonic scaling. When audiograms were obtained 3--5 weeks later in the same 20 individuals before and immediatley after they had kept their mouths open for 5 min, but with no scaling performed, TTS was recorded in three of the individuals. TTS after opening only was less pronounced than TTS after ultrasonic scaling, both with regard to severity and duration.

Periodontal disease and oral hygiene in an Alaskan Eskimo population

Periodontal tissues and oral hygiene conditions of 75 inhabitants of an inland Alaskan village population were studied. Living habits had changed considerably since dental examinations and dietary studies were done eight years previously. Periodontal disease was severe and followed the same pattern as that in other populations, except that the influence of age alone was not so pronounced.

FATE OF BACILLUS CEREUS IN CULTURED AND DIRECT ACIDIFIED SKIMMILK AND CHEDDAR CHEESE1

Germination, growth, sporulation, and. survival of Bacillus cereus 7 was determined in cultured (Streptococcus lactis C10) and direct acidified (lactic acid) skimmilks. For cultured systems, B. cereus increased initially at approximately the same rate in milks with or without streptococci. However, as the acidity of the milk increased, vegetative B. cereus cells failed to survive but spore counts remained unchanged. B. cereus organisms did not influence acid production or multiplication of the lactic streptococci. In direct acidified skimmilk, spore germination and outgrowth and vegetative cell multiplication decreased as the pH of the system was lowered from 6.5 to 5.0. In skimmilk at pH 5.0, vegetative cells failed to multiply and spore germination ceased. In Cheddar cheese manufacture, B. cereus multiplied rapidly during the period from the end of cooking to milling of the curd. B. cereus survived in the spore state in Cheddar cheese during 52 weeks curing.