BackgroundSecondary caries is responsible for 60 percent of all replacement restorations in the typical dental practice. The diversity of the bacterial sources and the different types of filling materials could play a role in secondary caries. The aim of this study was to determine and compare the microbial spectrum of secondary caries biofilms around amalgam and composite resin restorations.MethodsClinical samples were collected from freshly extracted teeth diagnosed with clinical secondary caries. Samples were categorized into four groups according to the types of restoration materials and the classification of the cavity. Biofilms were harvested from the tooth-restoration interface using a dental explorer and after dilution were incubated on special agars. The bacteria were identified using the biochemical appraisal system. Statistical calculations were carried out using SPSS11.5 software to analyze the prevalence of the bacteria involved in secondary caries.ResultsSamples from a total of four groups were collected: two groups were collected from amalgam restorations, each had 21 samples from both Class I and Class II caries; and the other two groups were from composite resin restorations, each had 13 samples from both class I and class II caries. Our results showed: (1) Anaerobic species were dominant in both restoration materials. (2) In terms of the types of individual bacteria, no significant differences were found among the four groups according to the geometric mean of the detected bacteria (P > 0.05). However, there were significant differences among the detected bacteria within each group (P < 0.05). The composition of each bacterium had no statistical difference among the four groups (P > 0.05), but showed significant differences among the detected bacteria in each group (P < 0.05). (3) Among the four groups, there were no significant differences for the detection rate of each bacterium (P > 0.05), however, the detection rate of each bacterium within each group was statistically different among the detected bacteria (P < 0.05).ConclusionsThe proportion of obligatory anaerobic species was much greater than the facultative anaerobic species in the biofilm of secondary caries. Statistically, the materials of restoration and the location of secondary caries did not show any significant effects on the composition of the microflora.
This study investigated the effect of carbon nanotubes (CNTs) and titanium dioxide (TiO2) incorporated in PDMS on biofilm formation and plantigrade settlement of Mytilus coruscus. TiO2 increased bacterial density, and CNTs also increased bacterial density but reduced diatom density in biofilms after 28 days. Further analysis was conducted between bacterial communities on glass, PDMS, CNTs (0.5 wt%) and TiO2 (7.5 wt%). ANOSIM analysis revealed significant differences (R > 0.9) between seven, 14, 21 and 28 day-old bacterial communities. MiSeq sequencing showed that CNTs and TiO2 impacted the composition of 28 day-old bacterial communities by increasing the abundance of Proteobacteria and decreasing the abundance of Bacteroidetes. The maximum decreased settlement rate in 28 day-old biofilms on CNTs and TiO2 was > 50% in comparison to those on glass and PDMS. Thus, CNTs and TiO2 incorporated in PDMS altered the biomass and community composition of biofilms, and subsequently decreased mussel settlement.
Silver nanoparticles (AgNPs) demonstrating good antimicrobial activity are widely used in many fields. However, the impact of AgNPs on the community structures of marine biofilms that drive biogeochemical cycling processes and the recruitment of marine invertebrate larvae remains unknown. Here, we employed MiSeq sequencing technology to evaluate the bacterial communities of 28-day-old marine biofilms formed on glass, polydimethylsiloxane (PDMS), and PDMS filled with AgNPs and subsequently tested the influence of these marine biofilms on plantigrade settlement by the mussel Mytilus coruscus. AgNP-filled PDMS significantly reduced the dry weight and bacterial density of biofilms compared with the glass and PDMS controls. AgNP incorporation impacted bacterial communities by reducing the relative abundance of Flavobacteriaceae (phylum: Bacteroidetes) and increasing the relative abundance of Vibrionaceae (phylum: Proteobacteria) in 28-day-old biofilms compared to PDMS. The settlement rate of M. coruscus on 28-day-old biofilms developed on AgNPs was lower by >30% compared to settlement on control biofilms. Thus, the incorporation of AgNPs influences biofilm bacterial communities in the marine environment and subsequently inhibits mussel settlement.
The 4-t-octylphenol (4-t-OP) biodegradation by alginate immobilized cells of Acinetobacter sp. was compared with its respective free cells in different media. The effects of different bead densities, pH values and practical applications of artificial seawater and wastewater on the biodegradation rate of 4-t-OP were investigated. Degradation kinetics of 4-t-OP by free and immobilized cells was well fitted with first order kinetic. The immobilized Acinetobacter sp. cells could enhance the efficiency of 4-t-OP degradation. The degradation rate and 4-t-OP half-life were 97.6% and 0.7 d, respectively. Increasing level of bead amount could also improve the degradation effects, when 400 beads per 100 mL were added, the degradation rate and 4-t-OP half-life were 96.5 % and 0.2 d respectively. The immobilized Acinetobacter sp. cells could degrade 4-t-OP both in artificial seawater and wastewater. The degradation rates were 87.7% and 84.3%, respectively, indicating its potential application of removing and biodegrading 4-t-OP under practical environment.
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