Human gut-derived commensal suppresses generation of T-cell response to gliadin in humanized mice by modulating gut microbiota.

The human intestinal tract is colonized by a large number of diverse microorganisms that play various important physiologic functions. In inflammatory gut diseases including celiac disease (CeD), a dysbiotic state of microbiome has been observed. Interestingly, this perturbed microbiome is normalized towards eubiosis in patients showing recovery after treatment. The treatment has been observed to increase the abundance of beneficial microbes in comparison to non-treated patients. In this study, we investigated the effect of Prevotella histicola or Prevotella melaninogenica, isolated from the duodenum of a treated CeD patient, on the induction and maintenance of oral tolerance to gliadin, a CeD associated subgroup of gluten proteins, in NOD.DQ8.ABo transgenic mice. Conventionally raised mice on a gluten free diet were orally gavaged with bacteria before and after injection with pepsin trypsin digested gliadin (PTD-gliadin). P. histicola suppressed the cellular response to gliadin, whereas P. melaninogenica failed to suppress an immune response against gliadin. Interestingly, tolerance to gliadin in NOD.DQ8.ABo mice may be associated with gut microbiota as mice gavaged with P melaninogenica harbored a different microbial diversity as compared to P. histicola treated mice. This study provides experimental evidence that gut microbes like P. histicola from treated patients can suppress the immune response against gliadin epitopes.

Antibacterial Efficacy of Silver Nanoparticles on Endometritis Caused by Prevotella melaninogenica and Arcanobacterum pyogenes in Dairy Cattle.

Bovine postpartum diseases remain one of the most significant and highly prevalent illnesses with negative effects on the productivity, survival, and welfare of dairy cows. Antibiotics are generally considered beneficial in the treatment of endometritis; however, frequent usage of each antibiotic drug is reason for the emergence of multidrug resistance (MDR) of the pathogenic microorganisms, representing a major impediment for the successful diagnosis and management of infectious diseases in both humans and animals. We synthesized silver nanoparticles (AgNPs) with an average size of 10 nm using the novel biomolecule apigenin as a reducing and stabilizing agent, and evaluated the efficacy of the AgNPs on the MDR pathogenic bacteria Prevotella melaninogenica and Arcanobacterium pyogenes isolated from uterine secretion samples. AgNPs inhibited cell viability and biofilm formation in a dose- and time-dependent manner. Moreover, the metabolic toxicity of the AgNPs was assessed through various cellular assays. The major toxic effect of cell death was caused by an increase in oxidative stress, as evidenced by the increased generation of reactive oxygen species (ROS), malondialdehyde, protein carbonyl content, and nitric oxide. The formation of ROS is considered to be the primary mechanism of bacterial death. Therefore, the biomolecule-mediated synthesis of AgNPs shows potential as an alternative antimicrobial therapy for bovine metritis and endometritis.

Lactobacillus brevis CD2 inhibits Prevotella melaninogenica biofilm.

OBJECTIVE: To evaluate the ability of the probiotic strain Lactobacillus brevis CD2 to inhibit the opportunistic anaerobe Prevotella melaninogenica (PM1), a well-known causative agent of periodontitis. MATERIALS AND METHODS: The inhibitory effect of Lactobacillus CD2 on Prevotella PM1 biofilm was assessed both by exposing the anaerobe to the supernatant of the probiotic strain and by growing the two strains to obtain single or mixed biofilms. The inhibitory effect of CD2 on PM1 was also checked by the agar overlay method. RESULTS: The development of PM1 biofilm was strongly affected (56% decrease in OD value) by the CD2 supernatant after 96 h. A dose-dependent biofilm reduction was also observed at 1/10 and 1/100 dilutions of supernatant. Confocal microscopy on the mixed biofilms revealed the ability of CD2 to prevail on PM1, greatly reducing the biofilm of the latter. CONCLUSIONS: It has been hypothesized a multifactorial nature of the inhibition mechanism, the strong adherence ability of CD2 strain together with the released metabolites presumably contributing to the reduction in the PM1 biofilm detected by confocal microscopy.

An evaluation of bacterial contamination of barriers used in periapical tissue regeneration: Part 1--Bacterial adherence.

OBJECTIVE: To compare the adherence of Prevotella melaninogenica and Enterococcus faecalis to 3 guided tissue regeneration membranes: Atrisorb, Lambone, and OsseoQuest. It was hypothesized that OsseoQuest would show increased bacterial adherence compared to Lambone and Atrisorb. METHOD AND MATERIALS: The barriers were suspended in trypticase soy broth containing an inoculum of either P melaninogenica or E faecalis. The samples were incubated under appropriate conditions for 6, 24, and 48 hours. Following incubation, each membrane was mixed in fresh media in a vortex machine to dislodge adherent bacteria. The vortexed media was quantitatively assessed using serial dilutions for viable cell count. RESULTS: E faecalis exhibited higher adherence compared to P melaninogenica with time. Of the membranes tested, Lambone displayed the least bacterial adherence. CONCLUSION: An analysis of the results indicated that bacterial adherence was time-dependent for all membranes. Membrane structure, chemical configuration, hydrophobicity, and bacterial cell surface structure were suggested as factors contributing to variance in bacterial adherence.

Mechanism of oxidative DNA damage induction in a strict anaerobe, Prevotella melaninogenica.

We investigated the mechanism of the oxidative DNA damage induction by exposure to O(2) in Prevotella melaninogenica, a strict anaerobe. Flow cytometry with hydroethidine and dichlorofluorescein diacetate showed that O(2) exposure generated O(2)*-) and H(2)O(2). Results of electron spin resonance with alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone and ethanol showed that O(2) exposure also induced *OH radical generation in P. melaninogenica loaded with FeCl(2) but not in samples without FeCl(2) loading. In P. melaninogenica, O(2) exposure increased 8-hydroxydeoxyguanosine (8OHdG), typical of oxidative DNA damage. Catalase inhibited the increase, but the *OH radical scavengers did not. Phenanthroline, a membrane-permeable Fe and Cu chelator, increased the 8OHdG induction. In FeCl(2)-loaded samples, induction of 8OHdG decreased. Addition of H(2)O(2) markedly increased 8OHdG levels. These results indicate that in P. melaninogenica, exposure to O(2) generated and accumulated O(2)* and H(2)O(2), and that a crypto-OH radical generated through H(2)O(2) was the active species in the 8OHdG induction.

A hemagglutinating variant of Prevotella melaninogenica isolated from the oral cavity.

Strains resembling Prevotella melaninogenica were isolated from healthy subjects and patients with periodontal disease and were identified using: a 5-test phenotypic screen; commercial identification kits; and a 16S rRNA-based polymerase chain reaction (PCR) method. Eleven clinical isolates closely resembling P. melaninogenica, and all from patients with periodontitis, were able to agglutinate erythrocytes. In the electron microscope, hemagglutinating isolates showed fimbria-like structures, that were not seen on non-hemagglutinating isolates. Some strains were further classified with PCR-restriction fragment-length polymorphism (RFLP) of 16S rRNA genes. Amplified 16S rDNA was digested using five different endonucleases, separated with agarose gel electrophoresis, stained and photographed. Photographs were then scanned, digitized and a distance matrix calculated using Dice coefficient, where the presence or absence of a band was used as a character. The distance matrix was plotted as a phenogram. At 70% similarity six clusters were seen. Type strains of separate Prevotella species did not fall into any cluster. Hemagglutinating isolates fell into three clusters: four clustered with the type strains of P. melaninogenica and Prevotella veroralis; four with other P. melaninogenica isolates and two hemagglutinating isolates clustered together Prevotella loescheii. The PCR-RFLP results showed that the hemagglutinating strains did not form a homogenous group inside the Prevotella genus.

Periodontal bone loss in mice induced by different periodontopathic organisms.

Periodontal bone loss in mice orally inoculated with Peptostreptococcus anaerobius, Pept. magnus and Actinobacillus actinomycetemcomitans was compared to that in sham-inoculated mice. Six-to-8-week-old BALB/c mice were inoculated with 1 x 10(5), 1 x 10(7) or 1 x 10(9) colony-forming units (c.f.u.) of bacteria in 50 microliters of medium. Ten mice received each concentration of bacteria and 10 sham-inoculated mice acted as controls. Five mice from each of the groups were killed 6 weeks after inoculation and the remaining five mice at 12 weeks. Right hemimandibles were defleshed, stained and bone loss was measured using an image analyser. All the organisms tested were associated with bone loss. Animals that had received Pept. anaerobius and Pept. magnus had up to 18% more bone loss than those sham inoculated. In contrast, mice inoculated with A. actinomycetemcomitans had up to 38% more bone loss than the sham-inoculated animals, this amount of loss occurring at the lowest inoculation of 1 x 10(5) c.f.u. These data demonstrate a differential ability of micro-organisms to cause periodontal bone loss in mice.

Infectious oral necrosis (cancrum oris) in Nigerian children: a review.

The devastating orofacial gangrenous disease known as cancrum oris (noma) is still commonly seen in underprivileged Nigerian children. These children are usually victims of such stressors as chronic malnutrition, numerous endemic communicable diseases and severe adverse physical conditions which may lead to depletion of their adaptive resources or produce physiological maladaptation to additional stressors. Measles is the most common infection preceding the development of noma in Nigerian children. Acquired immunodeficiency as well as the impaired endocrine balance of the chronically malnourished permits, for example, widespread infection with the measles virus. Anergy resulting from the combination of malnutrition and measles virus infection promotes selective overgrowth and invasion by an infective consortium consisting of anaerobic organisms and other species capable of elaborating necessary growth factors for the former. Because of the pre-existing depletion of adaptive physiologic resources in the malnourished child, the infection is not readily contained locally as necrotizing ulcerative gingivitis but instead spreads rapidly to the next naturally occurring anatomical barriers. This is then followed by continuing necrosis and possible sequestration as exemplified by noma.

Significance of encapsulated Bacteroides melaninogenicus and Bacteroides fragilis groups in mixed infections.

Organisms of the Bacteroides melaninogenicus and Bacteroides fragilis groups are often found mixed with facultatively anaerobic organisms in infections. The relative importance of these Bacteroides groups and facultative anaerobic pathogens in mixed infections was investigated in a subcutaneous abscess model in mice. This was determined by observing the effect of antimicrobial therapy directed against one or both organisms present in the abscess. Clindamycin or metronidazole was used for treatment of infections caused by Bacteroides species, and either gentamicin, penicillin, ampicillin, or oxacillin was used for treatment of infections caused by facultative flora. In almost all instances the aerobic counterparts in the infection were more important than the unencapsulated Bacteroides species. On the other hand, encapsulated B. melaninogenicus group organisms were found to be more important in abscess formation than were group A streptococci, Streptococcus pneumoniae, Klebsiella pneumoniae, Haemophilus influenzae, and Staphylococcus aureus. Encapsulated B. fragilis group organisms were found to be more important than or as important as Escherichia coli and group D streptococci and less important than S. aureus, group A streptococci, and K. pneumoniae in induction of subcutaneous abscesses. This study demonstrates that encapsulated Bacteroides species are a factor that should be considered in the treatment of mixed infections with antibiotics.

Effect of anaerobic bacteria on killing of Proteus mirabilis by human polymorphonuclear leukocytes.

Killing of Proteus mirabilis by human polymorphonuclear leukocytes was tested in the presence of different Bacteroides species. In vitro experiments showed that anaerobic bacteria interfered with the killing of aerobic bacteria. However, this inhibitory effect was not a property of all Bacteroides species. Bacteroides gingivalis W83 showed the greatest inhibitory effect of the five Bacteroides strains tested. Killing of P. mirabilis was inhibited by the culture supernatant of B. gingivalis but not by washed cells. Two factors were found in the supernatant of B. gingivalis to account for the inhibitory effect. One was heat stable with a molecular weight of less than 3,500 and inhibited the killing activity of leukocytes, and the other was heat labile and partly inactivated the complement system. The killing experiments paralleled chemiluminescence measurements.

Bactericidal effect of pooled human serum on Bacteroides melaninogenicus, Bacteroides asaccharolyticus and Actinobacillus actinomycetemcomitans.

Bacteria belonging to the species B. melaninogenicus ss. melaninogenicus (two strains), B. melaninogenicus ss. intermedius (five strains), B. asaccharolyticus (seven strains), and Actinobacillus actinomycetemcomitans (four strains) were tested under anaerobic conditions for their sensitivity to the bactericidal effect of pooled human serum. The A. actinomycetemcomitans strains were not killed to any extent by the serum. Both B. melaninogenicus ss. melaninogenicus strains were killed by serum. The sensitivity to serum among the strains of B. asaccharolyticus and B. melaninogenicus ss. intermedius was diverse. There was no correlation between the sensitivity to serum among the strains and the levels of specific antibodies in the serum. The bactericidal activity of serum was only effective if the complement system was present in serum. All strains initiated activation of complement and binding of a C3 component to the cell surface both in normal and MgEGTA chelated serum. The possible role of serum bactericidal activity in the pathogenesis of oral infections is unclear.