An Assessment of the Bacterial Diversity found in Dental Unit Waterlines using the Illumina MiSeq

The importance of biofilm contamination control for dental unit waterlines: a multicenter assessment of the microbiota diversity of biofilm in dental unit waterlines

Background

The biofilm formation in Dental Unit Waterlines (DUWLs) could become an important cause of infection during dental care, which could put immunocompromised individuals at risk of cross-infection. The aim of this study was to characterize the microbial communities of biofilms among DUWLs using high-throughput sequencing technology.

Methods

Twenty-nine biofilm samples were obtained from 24 dental chair units at 5 hospitals and 2 dental clinics. The genomic DNA of the samples was extracted, then 16S rDNA and ITS2 gene were amplified and sequenced. Alpha-diversity and Beta-diversity were calculated with QIIME2 and the Kruskal - Wallis H-test was adopted for statistical analysis.

Results

Microbial communities with a high diversity of bacteria (377 genera) and fungi (83 genera) were detected in the biofilm samples. The dominant phylum of bacteria was Proteobacteria (93.27%) and that of fungi was Basidiomycota (68.15%). Potential human pathogens were detected including 7 genera of bacteria (Pseudomonas, Stenotrophomonas, Hafnia-Obesumbacterium, Burkholderia-Caballeronia-Paraburkholderia, Ralstonia, Enterobacter, Klebsiella) and 6 genera of fungi (Malassezia, Candida, Alternaria, Cryptococcus, Rhodotorula, Rhinocladiella).

Conclusions

This multicenter assessment revealed the infectious risk during dental care. It emphasized the importance of biofilm control due to biofilm accumulation and multiple kinds of opportunistic pathogens in DUWLs.

A laboratory ice machine as a cold oligotrophic artificial microbial niche for biodiscovery

Microorganisms are ubiquitously distributed in nature and usually appear as biofilms attached to a variety of surfaces. Here, we report the development of a thick biofilm in the drain pipe of several standard laboratory ice machines, and we describe and characterise, through culture-dependent and -independent techniques, the composition of this oligotrophic microbial community. By using culturomics, 25 different microbial strains were isolated and taxonomically identified. The 16S rRNA high-throughput sequencing analysis revealed that Bacteroidota and Proteobacteria were the most abundant bacterial phyla in the sample, followed by Acidobacteriota and Planctomycetota, while ITS high-throughput sequencing uncovered the fungal community was clearly dominated by the presence of a yet-unidentified genus from the Didymellaceae family. Alpha and beta diversity comparisons of the ice machine microbial community against that of other similar cold oligotrophic and/or artificial environments revealed a low similarity between samples, highlighting the ice machine could be considered a cold and oligotrophic niche with a unique selective pressure for colonisation of particular microorganisms. The recovery and analysis of high-quality metagenome-assembled genomes (MAGs) yielded a strikingly high rate of new species. The functional profiling of the metagenome sequences uncovered the presence of proteins involved in extracellular polymeric substance (EPS) and fimbriae biosynthesis and also allowed us to detect the key proteins involved in the cold adaptation mechanisms and oligotrophic metabolic pathways. The metabolic functions in the recovered MAGs confirmed that all MAGs have the genes involved in psychrophilic protein biosynthesis. In addition, the highest number of genes for EPS biosynthesis was presented in MAGs associated with the genus Sphingomonas, which was also recovered by culture-based method. Further, the MAGs with the highest potential gene number for oligotrophic protein production were closely affiliated with the genera Chryseoglobus and Mycobacterium. Our results reveal the surprising potential of a cold oligotrophic microecosystem within a machine as a source of new microbial taxa and provide the scientific community with clues about which microorganisms are able to colonise this ecological niche and what physiological mechanisms they develop. These results pave the way to understand how and why certain microorganisms can colonise similar anthropogenic environments.

Purulent lymphadenitis due to Halomonas hamiltonii: a case report

Halomonas hamiltonii is a gram-negative rod bacterium isolated from highly saline environments. H. hamiltonii has rarely been reported as a human pathogen. Herein, we present the first case report of a purulent lymphadenitis caused by H. hamiltonii worldwide. The patient was a previously healthy girl aged 1 year who was referred to our hospital for left axillary lymphadenitis. Although oral amoxicillin was administered, lymphadenitis did not improve, and an abscess developed. After incision and drainage, the abscess was reduced. No recurrence of lymphadenitis was observed. The pus culture was negative. However, the 16S ribosomal DNA was amplified by the melting temperature mapping method. The amplified 16S ribosomal DNA sequence revealed 99.7% identity of H. hamiltonii. To the best of our knowledge, this is the first case of H. hamiltonii infection in a lymph node. This pathogen should be considered when diagnosing purulent lymphadenitis in healthy patients with lymphadenopathy of unknown origin.

Assessment of microbiota diversity in dental unit waterline contamination

BACKGROUND

Dental unit waterlines (DUWLs) provide water for handpieces, air/water syringes, and mouth-rinse water outlets. DUWL contamination can negatively affect the operating environment and public health. Therefore, it is important to elucidate the bacterial concentrations and microbial composition in the DUWLs from different dental specialties.

METHODS

We collected 350 5-mL dental water samples (from high-speed handpieces, air/water syringes, and mouth-rinse water outlets) from 60 dental chair units (DCUs) at a dental hospital to determine the bacterial concentrations by culture methods. Meanwhile, to investigate the diversity and community structure of microbe in the DUWLs, 17 high-quality DNA from 60 250-mL air/water syringe water samples, which were collected from the same 60 DCUs, were analyzed using 16S rDNA high-throughput sequencing.

RESULTS

The median bacterial concentration was 166 (31.5, 672.5) CFU/mL and the range was 0-3,816,000 CFU/mL. Only 42.6% of the water samples had bacterial concentrations below 100 CFU/mL. The Kruskal-Wallis H-test revealed that the water samples from three dental specialties had significantly different bacterial concentrations (H = 27.441, P < 0.01). High-throughput sequencing results showed significant differences in bacterial community structure between periodontics and the other two dental specialties. In the samples from three dental specialties, 508 OTUs were detected, with 160, 182 and 176 OTUs unique to the periodontics, endodontics and prosthodontics specialties, respectively. Linear discriminant analysis (LDA) effect size (LEfSe) suggested that Hydrocarboniphaga, Zoogloea, Aquabacterium, and Hydrogenophaga were enriched in the periodontics specialty; Acinetobacter, Geothrix, and Desulfovibrio were enriched in the prosthodontics specialty; and Alistipes, Clostridium XIVa, and Serratia were enriched in the endodontics specialty. Seven potentially human-pathogenic genera (Pseudomonas, Acinetobacter, Sphingomonas, Ochrobactrum, Rhizobium, Brevundimonas, and Methylobacterium) with relative abundance exceeding 1% were also detected in the DUWLs.

CONCLUSIONS

The bacterial concentrations and microbial composition were influenced by different dental specialties, so a validated disinfection protocol should be used to control DUWL contamination in different dental specialties.

Legionnaires' disease in dental offices: Quantifying aerosol risks to dental workers and patients

Legionella pneumophila is an opportunistic bacterial respiratory pathogen that is one of the leading causes of drinking water outbreaks in the United States. Dental offices pose a potential risk for inhalation or aspiration of L. pneumophila due to the high surface area to volume ratio of dental unit water lines-a feature that is conducive to biofilm growth. This is coupled with the use of high-pressure water devices (e.g., ultrasonic scalers) that produce fine aerosols within the breathing zone. Prior research confirms that L. pneumophila occurs in dental unit water lines, but the associated human health risks have not been assessed. We aimed to: (1) synthesize the evidence for transmission and management of Legionnaires' disease in dental offices; (2) create a quantitative modeling framework for predicting associated L. pneumophila infection risk; and (3) highlight influential parameters and research gaps requiring further study. We reviewed outbreaks, management guidance, and exposure studies and used these data to parameterize a quantitative microbial risk assessment (QMRA) model for L. pneumophila in dental applications. Probabilities of infection for dental hygienists and patients were assessed on a per-exposure and annual basis. We also assessed the impact of varying ventilation rates and the use of personal protective equipment (PPE). Following an instrument purge (i.e., flush) and with a ventilation rate of 1.2 air changes per hour, the median per-exposure probability of infection for dental hygienists and patients exceeded a 1-in-10,000 infection risk benchmark. Per-exposure risks for workers during a purge and annual risks for workers wearing N95 masks did not exceed the benchmark. Increasing air change rates in the treatment room from 1.2 to 10 would achieve an ∼85% risk reduction, while utilization of N95 respirators would reduce risks by ∼95%. The concentration of L. pneumophila in dental unit water lines was a dominant parameter in the model and driver of risk. Future risk assessment efforts and refinement of microbiological control protocols would benefit from expanded occurrence datasets for L. pneumophila in dental applications.

Airborne particles and microorganisms in a dental clinic: Variability of indoor concentrations, impact of dental procedures, and personal exposure during everyday practice

This study presents for the first time comprehensive measurements of the particle number size distribution (10 nm to 10 μm) together with next-generation sequencing analysis of airborne bacteria inside a dental clinic. A substantial enrichment of the indoor environment with new particles in all size classes was identified by both activities to background and indoor/outdoor (I/O) ratios. Grinding and drilling were the principal dental activities to produce new particles in the air, closely followed by polishing. Illumina MiSeq sequencing of 16S rRNA of bioaerosol collected indoors revealed the presence of 86 bacterial genera, 26 of them previously characterized as potential human pathogens. Bacterial species richness and concentration determined both by qPCR, and culture-dependent analysis were significantly higher in the treatment room. Bacterial load of the treatment room impacted in the nearby waiting room where no dental procedures took place. I/O ratio of bacterial concentration in the treatment room followed the fluctuation of I/O ratio of airborne particles in the biology-relevant size classes of 1-2.5, 2.5-5, and 5-10 μm. Exposure analysis revealed increased inhaled number of particles and microorganisms during dental procedures. These findings provide a detailed insight on airborne particles of both biotic and abiotic origin in a dental clinic.

Unravelling nitrogen removal and nitrous oxide emission from mainstream integrated nitrification-partial denitrification-anammox for low carbon/nitrogen domestic wastewater

Stable supply of nitrite is often a major obstacle for achieving mainstream anammox due to washout failure of nitrite oxidizers (NOB) at low influent ammonia of municipal wastewater. In this study, an integrated nitrification, partial denitrification and anammox (INPDA) as a one-stage mainstream nitrogen removal alternative was established in a low-oxygen sequencing batch biofilm reactor treating synthetic sewage. The overall nitrogen removal and nitrous oxide (N₂O) emission were mainly investigated at 50 mg/L NH₄⁺-N influent with a low carbon/nitrogen (C/N) of 2.5. Continuous operation demonstrated that as high as 98.8% NH₄⁺-N and 94.1% TN were removed in SBBR system. Cyclic experiment verified sequential completion of nitrification, partial denitrification and anammox were responsible for high-rate TN removal. During one typical cycle, the trend of N₂O emission was characterized by firstly rapid rise, then fluctuant decrease followed by rapid decrease and finally slow disappearance. The maximum N₂O emission rate reached up to 6.7 μg/(L·min) occurred at 75 min. High-throughput sequencing revealed the co-existence of nitrifying, denitrifying and anammox species and large detection of key functional genes (Hzs, Hdh, Hao, Nor) in an oxygen-limited SBBR, thereby highly correlating nitrogen removal and N₂O emission characteristics. Nitrogen metabolic pathways analysis further suggest denitratation(NO₃^--N to NO₂^--N)-based anammox is a main route for mainstream nitrogen removal. Moreover, N₂O might be generated by both hydroxylamine oxidation step in nitrification and also heterotrophic denitrification pathway. The research findings provide more deep understandings of enhanced nitrogen removal and mitigated N₂O footprint from a single mainstream anammox-based system.