Attachment of Respiratory Pathogens and Candida to Denture Base Materials—A Pilot Study

Denture prostheses are an ideal and extensive reservoir for microorganisms to attach to their surfaces. The aim of the study was to elucidate interactions between materials for the fabrication of denture bases and the attachment of microorganisms, focusing on respiratory pathogens and Candida species. Specimens (6 mm × 1 mm) with a standardized surface roughness (Sa = 0.1 µm) were prepared from heat-pressed polymethyl methacrylate (PMMA), CAD/CAM-processed PMMA, and CAD/CAM-processed polyether ether ketone (PEEK). The specimens were randomly placed in the vestibular areas of complete upper dentures in seven patients and were removed either after 24 h without any oral hygiene measures or after a period of four weeks. The microorganisms adherent to the surface of the specimens were cultivated and subsequently analyzed using mass spectrometry (MALDI-TOF). The means and standard deviations were calculated, and the data were analyzed using a two-way analysis of variance (ANOVA) and Tukey post-hoc test where appropriate (α = 0.05). There was a significant increase (p ≤ 0.004) in the total bacterial counts (CFU/mL) between the first (24 h) and the second (four weeks) measurements. Regarding quantitative microbiological analyses, no significant differences between the various materials were identified. Respiratory microorganisms were detected in all samples at both measurement time points, with a large variance between different patients. Only after four weeks, Candida species were identified on all materials but not in all participants. Candida species and respiratory microorganisms accumulate on various denture base resins. While no significant differences were identified between the materials, there was a tendency towards a more pronounced accumulation of microorganisms on conventionally processed PMMA

Antimicrobial Susceptibility Profile of Rare Anaerobic Bacteria

Anaerobes play an important role in clinically relevant infections and resistance is increasing worldwide. We tested 120 rare anaerobic isolates belonging to 16 genera for antimicrobial resistance using the agar dilution method and compared those results to the time-saving E-test method. The susceptibility data for 12 antimicrobial substances (benzylpenicillin, ampicillin/sulbactam, piperacillin/tazobactam, imipenem, meropenem, cefoxitin, metronidazole, moxifloxacin, clindamycin, doxycycline, tigecycline, eravacycline) were collected. Susceptibility testing showed low resistance to β-lactam/β-lactamase inhibitor combinations and no resistance to carbapenems and tigecycline. We observed moderate to high rates of resistance to moxifloxacin and clindamycin which differed depending on the methodology used. The essential and categorical agreement was over 90% for ampicillin/sulbactam, meropenem, moxifloxacin, and tigecycline. For metronidazole and clindamycin, the essential agreement was below 90% but the categorical agreement was near or above 90%. Penicillin presented with the lowest categorical agreement of 86.7% and a very high very major error rate of 13.3%. The resistance rates reported in this study are concerning and show the importance of routine susceptibility testing. Further investigations are necessary to determine the reason for high error rates and how to improve susceptibility testing of fastidious anaerobes

Diversity of antimicrobial resistance genes in Bacteroides and Parabacteroides strains isolated in Germany

Objectives: Bacteroides spp. are normal constituents of the human intestinal microflora, but they are also able to cause severe diseases. The aim of this study was to determine the diversity of antibiotic resistance genes found in phenotypically resistant Bacteroides and Parabacteroides strains. Methods: A total of 71 phenotypically resistant Bacteroides spp. from human clinical specimens were screened for the antibiotic resistance genes cfiA, tetQ, tetM, tet36, cepA, cfxA, nim, ermG, ermF, bexA, blaVIM, blaNDM, blaKPC, blaOXA-48 and blaGES. The presence of these genes was compared with phenotypic resistance to ampicillin/sulbactam, cefoxitin, ceftolozane/tazobactam, piperacillin/tazobactam, imipenem, meropenem, meropenem/vaborbactam, clindamycin, moxifloxacin, tigecycline, eravacycline and metronidazole. Results: tetQ was the most frequently detected gene, followed by cfiA, ermF, cfxA, ermG, cepA, nim and bexA. None of the strains were positive for tetM, tet36, blaVIM, blaNDM, blaKPC, blaOXA-48 or blaGES. Resistance to the tested β-lactams was mainly linked to the presence of the cfiA gene. Clindamycin resistance correlated with the presence of the genes ermG and ermF. The bexA gene was found in six strains, but only two of them were resistant to moxifloxacin. Tigecycline and eravacycline showed good activities despite the frequent occurrence of tetQ. The nim gene was detected in six isolates, five of which were resistant to metronidazole. Conclusion: The findings of our study support the general belief that antimicrobial resistance within Bacteroides should be taken into consideration. This underlines the necessity of reliable routine antimicrobial susceptibility test methods for anaerobic bacteria and the implementation of antimicrobial surveillance programmes worldwide

Bacterial Colonization and Tissue Compatibility of Denture Base Resins

Currently, there is minimal clinical data regarding biofilm composition on the surface of denture bases and the clinical tissue compatibility. Therefore, the aim of this experimental study was to compare the bacterial colonization and the tissue compatibility of a hypoallergenic polyamide with a frequently used PMMA resin tested intraorally in a randomized split-mouth design. Test specimens made of polyamide (n = 10) and PMMA (n = 10) were attached over a molar band appliance in oral cavity of 10 subjects. A cytological smear test was done from palatal mucosa at baseline and after four weeks. The monolayers were inspected for micronuclei. After four weeks in situ, the appliance was removed. The test specimens were immediately cultivated on non-selective and selective nutrient media. All growing colonies were identified using VITEK-MS. The anonymized results were analyzed descriptively. A total of 110 different bacterial species could be isolated, including putative pathogens. An average of 17.8 different bacterial species grew on the PMMA specimens, and 17.3 on the polyamide specimens. The highest number of different bacterial species was n = 24, found on a PMMA specimen. On the two specimens, a similar bacterial distribution was observed. Micronuclei, as a marker for genotoxic potential of dental materials, were not detected. This study indicates that the composition of bacterial biofilm developed on these resins after four weeks is not influenced by the type of resin itself. The two materials showed no cytological differences. This investigation suggests that polyamide and PMMA are suitable for clinical use as denture base material

Relationship between Phenotypic and Genotypic Resistance of Subgingival Biofilm Samples in Patients with Periodontitis

The phenotypic expression of antibiotic resistance genes (ARGs) can hamper the use of antibiotics as adjuncts to subgingival instrumentation in the treatment of periodontitis patients. The aim of the study was to analyze the relationship between the phenotypic and genotypic resistance against ampicillin-sulbactam, clindamycin, doxycycline and metronidazole of subgingival biofilm samples from 19 periodontitis patients. Samples were analyzed with shotgun sequencing and cultivated anaerobically for 7 days on microbiological culture media incorporating antibiotics. All growing isolates were identified to the species level using MALDI-TOF-MS and sequence analysis of the 16S ribosomal RNA (rRNA) gene. Phenotypic resistance was determined using EUCAST-breakpoints. The genetic profile of eight patients matched completely with phenotypical resistance to the tested antibiotics. The positive predictive values varied from 1.00 for clindamycin to 0.57 for doxycycline and 0.25 for ampicillin-sulbactam. No sample contained the nimI gene. It can be concluded that antibiotic resistance may be polygenetic and genes may be silent. Every biofilm sample harboring erm genes was phenotypic resistant. The absence of cfx and tet genes correlated to 100%, respectively, to 75%, with the absence of phenotypic resistance. The absence of nimI genes leads to the assumption that constitutive resistance among several species could explain the resistance to metronidazole

Antimicrobial Susceptibility of Clinical Oral Isolates of Actinomyces spp.

Actinomyces species play an important role in the pathogenesis of oral diseases and infections. Susceptibility testing is not always routinely performed, and one may oversee a shift in resistance patterns. The aim of the study was to analyze the antimicrobial susceptibility of 100 well-identified clinical oral isolates of Actinomyces spp. against eight selected antimicrobial agents using the agar dilution (AD) and E-Test (ET) methods. We observed no to low resistance against penicillin, ampicillin-sulbactam, meropenem, clindamycin, linezolid and tigecycline (0–2% ET, 0% AD) but high levels of resistance to moxifloxacin (93% ET, 87% AD) and daptomycin (83% ET, 95% AD). The essential agreement of the two methods was very good for benzylpenicillin (EA 95%) and meropenem (EA 92%). The ET method was reliable for correctly categorizing susceptibility, in comparison with the reference method agar dilution, except for daptomycin (categorical agreement 87%). Penicillin is still the first-choice antibiotic for therapy of diseases caused by Actinomyces spp

Associations between Immunological and Microbiological Findings.

<p>n: positive identifications from the 46 microbiologically characterized individuals; SI: stimulation index;</p>1<p>activation of Th1-response;</p>2<p>activation of B-cell-maturation;</p>3<p>negative regulation of innate immunity;</p>4<p>no B-cell stimulation;</p>5<p>positive regulation of innate immunity;</p>6<p>activation of humoral immunity (Th2).</p><p>Associations between Immunological and Microbiological Findings.</p

Percentage of Memory B-cells.

<p>Memory B-cells as percentage of CD19⁺ B-cells measured by flow cytometry. Explorative analysis revealed a higher level of memory B-cells in patients with moderate chronic periodontitis (median of 33.03%) compared with healthy subjects and patients with aggressive periodontitis (median of 19.39%/15.06%). With a median of 19.39% for all subject groups, an increase in memory B-cells in patients with moderate chronic periodontitis is statistically significant (p = 0.01).</p

Mean Clinical Parameters of Study Patients.

<p>IPI: interproximal plaque index; PD: probing depth; CAL: clinical attachment level; BOP: bleeding on probing; bone loss: maximum of radiographic bone loss.</p><p>Mean Clinical Parameters of Study Patients.</p

Carriers of Individual Cultivated Species among Different Subject Groups.

<p>* <0.05; ** <0.001.</p><p>Carriers of Individual Cultivated Species among Different Subject Groups.</p