Previously, we developed a chemostat system to study the behaviour and properties of a community of up to 10 species of oral bacteria. The present study describes modification of this system to incorporate removable and replaceable hydroxyapatite (the major mineral in human dental enamel) disks on which biofilms could develop. Hydroxyapatite disks were immersed in the chemostat for known time periods, and the bacterial content of biofilms determined by viable counting. Initial deposition rates were rapid, with all 10 species detected after 1 h, and the numbers of bacteria in biofilms continued to increase for 21 d. The species composition of biofilms reflected that of the surrounding fluid phase, and showed only limited signs of the type of 'species succession' which is observed in developing dental plaque in vivo, although anaerobic species increased in proportion in older biofilms. Four-day biofilms showed the least variability and were chosen as the 'standard biofilm' for more detailed study. Variability in the bacterial composition of 4-d biofilms was comparable both within a single chemostat run and between independent chemostat runs. Glucose pulsing in the absence of pH control resulted in the selection of cariogenic species; the disruption of the biofilm community was less marked than that of the equivalent planktonic culture. The model system has considerable potential in studying the effects of a variety of factors on biofilm development, as well as in comparing the efficacy of antimicrobial systems against biofilms.
The effect of aeration on the development of a defined biofilm consortium of oral bacteria was investigated in a two-stage chemostat system. An inoculum comprising 10 species, including both facultatively anaerobic and obligately anaerobic bacteria, and species associated with oral health and disease, was inoculated into an anaerobic first-stage chemostat vessel. The effluent from this chemostat was linked to an aerated [200 ml CO 2 /air (5:95, v/v) min –1 ] second-stage vessel, in which removable hydroxyapatite discs were inserted to allow biofilm formation. Comparisons were made of planktonic and biofilm communities in the aerated second-stage vessel by means of viable counts. Both planktonic and early biofilm communities were dominated by Neisseria subflava , comprising > 40% of total c>f.u. in the fluid phase, and > 80% of c.f.u. in 2 h biofilms. Obligate anaerobes persisted in this mixed culture, and succession in biofilms led them to predominate only after 7 d. Despite the continuous addition of air, the dissolved oxygen tension (dO 2 ) within the culture remained low (< 5% of air saturation), and the redox potential ( E h ) was –275 mV. In order to assess the significance of the presence of N. subflava in community development, a subsequent experiment omitted this aerobe from the inoculum, to produce a nine-species culture. The planktonic phase was predominated by three streptococcal species, Prevotella nigrescens and Fusobacterium nucleatum. Biofilms again underwent successional changes, with anaerobes increasing in proportion with time. In contrast to the culture including N. subflava , dO 2 was 50–60% of air saturation, and the E h was + 50 mV. In the final experiment, the rate of addition of first-stage culture was reduced to 1/10 of that in the previous experiment, in order to determine whether anaerobes were growing, rather than merely persisting in the aerated culture. The data for the planktonic phase indicated that the anaerobes were growing in aerated (dO 2 40–50%, E h +100 mV) conditions. Once again, anaerobes increased in proportion in older biofilms. The study indicates that mixed cultures can protect obligate anaerobes from the toxic effects of oxygen, both in the biofilm and planktonic modes of growth.
Medulloblastomas (MBs) are the most frequent malignant brain tumours in childhood and can be subdivided into the classic and the desmoplastic variant. The latter arises from cerebellar granule cell progenitors (GCPs) of the external granule cell layer (EGL). Its pathogenesis is linked to an overactivation of the Sonic Hedgehog-Patched (Shh-Ptc) pathway. By culturing murine GCPs in the presence or absence of the morphogen Shh, respectively, we identified the gene for the transcription factor Sox18 to be highly induced by Shh using DNA microarray and subsequent competitive RT-PCR. In situ hybridization showed that sox18 is expressed in the EGL of the postnatally developing cerebellum. However, immunohistological studies on sox18 deficient mice did not hint to an essential role in cerebellar development. mRNA expression analysis in human MBs showed that SOX18 is highly expressed in the desmoplastic variant pointing to a potential role in the genesis of this MB subtype.
Motivation: The significance of changes in functional connectivity (FC) measures involving white matter (WM) at preclinical stages of Alzheimer’s disease (AD) remains unclear. Goal(s): Our goal was to reveal alterations in correlations in BOLD signals between WM and gray matter (GM) in the AD continuum, focusing on preclinical AD. Approach: We used a novel bipartite graph model to evaluate network properties at multi-scales and compared preclinical AD, AD subjects with controls. Results: We found declines in local specific WM-GM FC and WM FC density, without a manifest decline in global efficiency of WM-involved functional networks in the preclinical AD group. Impact: Our observation of a decline in local WM-GM FC and WM FC density but an intact global efficiency of functional networks in preclinical AD may help explain why cognition remains normal despite the presence of pathology during the preclinical stage.
Mutacin II is an antibiotic that is produced by group II Streptococcus mutans. It inhibits the growth of other streptococci as well as many other gram-positive microorganisms by a hitherto unknown mechanism. Mutacin II possess bactericidal activity against susceptible cells. It transiently depolarizes the transmembrane electrical potential (delta psi) and the transmembrane pH gradient (delta pH) and partially inhibits amino acid transport. However, it rapidly depletes the intracellular ATP pool in glucose-energized cells and prevents the generation of ATP. It is concluded that mutacin II does not belong to the group of pore-forming antibiotics (type A) or to the type B antibiotics, which inhibit phospholipases or interfere with peptidoglycan biosynthesis. Mutacin II acts by inhibiting essential enzyme functions at the level of metabolic energy generation, an activity that has not yet been classified for antibiotics.
Abstract Background There is growing recognition that white matter microstructural integrity is affected in Alzheimer’s disease. The goal of this study was to characterize sex, racial/ethnic, and apolipoprotein (APOE)‐ε4 allele differences in white matter integrity. Methods This study included participants from ADNI, BLSA, ROS/MAP/MARS, and VMAP, all longitudinal cohorts of aging. This combined dataset included 6,837 imaging sessions from 2,619 participants age 50+ with diffusion MRI (dMRI) and demographic and clinical data (60% female, 31.4% APOE‐ε4 carriers, 78.9% White). dMRI was preprocessed using the PreQual pipeline. Free‐water (FW) correction was used to generate FW and FW‐corrected intracellular metrics including fractional anisotropy (FA FWcorr ), mean diffusivity (MD FWcorr ), axial diffusivity (AxD FWcorr ), and radial diffusivity (RD FWcorr ). Conventional and FW‐corrected metrics were harmonized using the Longitudinal ComBat package. Linear mixed‐effects models related sex, race/ethnicity, and APOE‐ε4 allele status to longitudinal diffusion metrics in 48 white matter tracts, adjusting for age at baseline, sex, education, race/ethnicity, APOE‐ε4 carrier status, cognitive status at baseline, and converter status. All models were corrected for multiple comparisons using the FDR approach. Result Sex differences in white matter were most notable in projection tracts (Figure 1A) and were primarily in FW‐corrected metrics. Females had lower FA FWcorr and higher RD FWcorr , indicative of worse microstructure, but lower AxD FWcorr . This sex difference was most pronounced for FA FWcorr in the ventral premotor projection tract (p=1.53x10 ‐62 ). There were global differences in white matter integrity by race/ethnicity (Figure 1B). Non‐Hispanic White participants tended to have higher conventional FA, FA FWcorr and AxD FWcorr and lower RD FWcorr . There was no association between APOE‐ε4 status and white matter integrity and no significant sex x race/ethnicity, sex x APOE‐ε4, or race/ethnicity x APOE‐ε4 interactions for conventional or FW‐corrected metrics when corrected for multiple comparisons. Conclusion There were striking sex and racial/ethnic (but not APOE‐ε4) differences in white matter tract integrity in a large cohort of aging adults. Female participants tended to have measures reflective of worse white matter integrity, and non‐Hispanic White participants tended to have measures reflective of greater integrity. Additional research exploring the etiology of these differences will be important to better understand disparities in Alzheimer’s disease.
Insertional inactivation of the Streptococcus mutans spaP gene was used to construct an isogenic mutant (834) of strain NG8 (serotype c) which lacked the major cell surface-associated protein referred to as P1 (15). Results of several studies suggest that P1 is involved in the adherence of S. mutans to saliva-coated apatite surfaces. With an in vitro model system of hydroxyapatite (HA) beads coated with parotid saliva (PS) and additional HA surfaces coated with PS and in situ-formed glucan, it was observed that mutant 834 adhered poorly to the PS/HA surfaces. In contrast, both parent and mutant strains bound to the PS-glucan/HA surface. Groups of intact and desalivated rats were infected with each strain to determine relative capacities to induce dental caries. Rats were fed a highly cariogenic diet containing 56% sucrose for 3 to 5 weeks. Each strain colonized the rodent model and caused similar levels of smooth-surface caries under these dietary conditions. It was concluded that P1 influences the ability of organisms to adhere to saliva-coated surfaces and possibly affects primary colonization of the oral cavity in the absence of a glucan surface but has no effect on glucan-mediated adherence in vitro or in vivo.
Cellular immediate-early genes are rapidly induced by a diverse range of agents and conditions. Since many cIE genes encode known or potential transcription factors, they are believed to couple extracellular stimuli to long-lasting alterations in cellular phenotype through the regulation of gene transcription. In addition, the localization of the products of cIE genes has been used as a method for determining the cellular sites of action of particular agents in the nervous system. However, the methods of analysis are tedious, and the results may be ambiguous because of cross-reaction of reagents with related proteins. To further the utility of this approach, a bacterial gene encoding beta-galactosidase (lac Z) has been fused, in frame, into the fourth exon of c-fos, and this fos-lac Z fusion gene has been introduced into the germ line of mice. We have analyzed the expression of beta-galactosidase (under the control of the c-fos promoter) in the developing and adult nervous systems of these transgenic mice. As far as can be determined, the constitutive and stimulated expression of the transgene accurately reflects the expression of cognate c-fos in both cultured cells and the intact animal. This study has also revealed novel sites of constitutive and induced expression of c-fos that were overlooked using conventional analysis. In particular, constitutive expression of c-fos is associated with cells that are entering terminal differentiation and are destined to die. In addition, induced expression of the transgene in adult brain mirrors the pattern of neurotoxicity elicited by kainic acid.(ABSTRACT TRUNCATED AT 250 WORDS)
During aging of human skin, a number of intrinsic and extrinsic factors cause the alteration of the skin’s structure, function and cutaneous physiology. Many studies have investigated the influence of the skin microbiome on these alterations, but the molecular mechanisms that dictate the interplay between these factors and the skin microbiome are still not fully understood. To obtain more insight into the connection between the skin microbiome and the human physiological processes involved in skin aging, we performed a systematic study on interconnected pathways of human and bacterial metabolic processes that are known to play a role in skin aging. The bacterial genes in these pathways were subsequently used to create Hidden Markov Models (HMMs), which were applied to screen for presence of defined functionalities in both genomic and metagenomic datasets of skin-associated bacteria. These models were further applied on 16S rRNA gene sequencing data from skin microbiota samples derived from female volunteers of two different age groups (25–28 years (‘young’) and 59–68 years (‘old’)). The results show that the main bacterial pathways associated with aging skin are those involved in the production of pigmentation intermediates, fatty acids and ceramides. This study furthermore provides evidence for a relation between skin aging and bacterial enzymes involved in protein glycation. Taken together, the results and insights described in this paper provide new leads for intervening with bacterial processes that are associated with aging of human skin.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)