Both Candida albicans and lactobacilli are common colonizers of carious lesions in children and adolescents. The purpose of this study is to compare the velocity of acid production between C. albicans and several Lactobacillus species at different pH levels and concentrations of glucose. Washed, pure resting-cell suspensions were obtained by culturing a total of 28 oral isolates comprising the species C. albicans, Lactobacillus rhamnosus, Lactobacillus paracasei paracasei, Lactobacillus paracasei tolerans and Lactobacillus delbrueckii lactis. Acid production from glucose was determined at a constant pH of 7.0, 5.5, 5.0 and 4.0 by repeated titrations with NaOH in an automated pH-stat system. Acid formation rates of yeast and lactobacilli proved to be similar at both neutral and low pH, while in a moderately acidic environment C. albicans produced less acid than the lactobacilli. Ion chromatographic analysis of the cell-free medium after titration revealed pyruvate to be the predominant organic acid anion secreted by C. albicans. The proportion of organic acids to overall acid production by the yeast was below 10% at neutral conditions, in contrast to 42–66% at pH 4.0. Compared to lactobacilli, yeast required a concentration of glucose that was about 50 times higher to allow acid production at half the maximum speed. Considering the clinical data in the literature about the frequency and proportions of microorganisms present in early childhood caries lesions, the contribution of oral lactobacilli as well as C. albicans to overall microbial acid formation appears to be important.

A range of opportunistic pathogens have been associated with dental unit water systems (DUWS), particularly in the biofilms that can line the tubing. This study therefore aimed to assess the microbiology of DUWS and biofilms in general dental practices across seven European countries, including the United Kingdom (UK), Ireland (IRL), Greece (GR), Spain (ES), Germany (D), Denmark (DK) and the Netherlands (NL). Water supplied by 51% of 237 dental unit water lines exceeded current American Dental Association recommendations of < or = 200 colony-forming units (CFU) ml(-1). Microbiological loading of the source waters was between 0 (Denmark, the Netherlands and Spain) and 4.67 (IRL) log CFU ml(-1); water line samples from the DUWS ranged from 1.52 (ES) to 2.79 (GR) log CFU ml(-1); and biofilm counts ranged from 1.49 (GR) to 3.22 (DK) log CFU.cm(-2). Opportunistic pathogens such as legionellae (DK and ES), including Legionella pneumophila SG1 (DK and GR), and Mycobacterium spp. (DK, NL, GR, D and ES) were recovered occasionally. Presumptive oral streptococci (ES and NL), oral anaerobes (GR), Candida spp. (UK, NL and ES) and blood (GR and IRL) were detected at relatively low frequencies, but their presence indicated a failure of the 3-in-1 antiretraction valve, leading to back siphonage of oral fluids into the water and biofilm phase. These findings confirm that a substantial proportion of DUWS have high levels of microbial contamination, irrespective of country, type of equipment and source water. The study emphasizes the need for effective mechanisms to reduce the microbial burden within DUWS, and highlights the risk of occupational exposure and cross-infection in general dental practice.

Water delivered by dental unit water systems (DUWS) in general dental practices can harbor high numbers of bacteria, including opportunistic pathogens. Biofilms on tubing within DUWS provide a reservoir for microorganisms and should be controlled. This study compared disinfection products for their ability to meet the American Dental Association's guideline of <200 CFU · ml ؊1 for DUWS water. Alpron, BioBlue, Dentosept, Oxygenal, Sanosil, Sterilex Ultra, and Ster4Spray were tested in DUWS (n ‫؍‬ 134) in Denmark, Germany, Greece, Ireland, The Netherlands, Spain, and the United Kingdom. Weekly water samples were tested for total viable counts (TVCs) on yeast extract agar, and, where possible, the effects of products on established biofilm (TVCs) were measured. A 4-to 5-week baseline measurement period was followed by 6 to 8 weeks of disinfection (intermittent or continuous product application). DUWS water TVCs before disinfection ranged from 0 to 5.41 log CFU · ml ؊1 . Disinfectants achieved reductions in the median water TVC ranging from 0.69 (Ster4Spray) to 3.11 (Dentosept) log CFU · ml ؊1 , although occasional high values (up to 4.88 log CFU · ml ؊1 ) occurred with all products. Before treatment, 64% of all baseline samples exceeded American Dental Association guidelines, compared to only 17% following commencement of treatment; where tested, biofilm TVCs were reduced to below detectable levels. The antimicrobial efficacies of products varied (e.g., 91% of water samples from DUWS treated with Dentosept or Oxygenal met American Dental Association guidelines, compared to 60% of those treated with Ster4Spray). Overall, the continuously applied products performed better than those applied intermittently. The most effective products were Dentosept and Oxygenal, although Dentosept gave the most consistent and sustained antimicrobial effect over time.

It is difficult to distinguish mutans streptococci on the species level, and even more so on the subspecies level. Intact cell matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) (ICM) was applied to reference strains of five of the species of the mutans group (Streptococcus criceti, Streptococcus downei, Streptococcus mutans, Streptococcus ratti, Streptococcus sobrinus), nonmutans streptococci (Streptococcus oralis, Streptococcus mitis, Streptococcus salivarius, and Streptococcus sanguinis), and 177 mutans streptococci isolated from saliva of 10 children. From the analysis of the reference strains, readily distinguishable ICM mass spectra were obtained for the different species. Based on multivariate statistical analysis, a correct and unambiguous assignment was made of the spectra of 159 isolated mutans streptococci to S. mutans and 16 isolates to S. sobrinus. Two isolates were sorted out and were identified by sequencing of their 16S rRNA genes as Streptococcus anginosus. In addition, ICM indicated a misclassification for some reference strains (AHT, V 100 and E 49) and re-classified AHT and E 49 as S. ratti and V 100 as S. sobrinus. This was confirmed by 16S rDNA sequencing. Based on a statistical similarity analysis of the spectra of reference strains and a quantitative assessment of the reproducibility of ICM, the isolates identified as either S. mutans or S. sobrinus were phenotyped on the subspecies level. In the population of the clinical isolates, 14 unambiguously different S. mutans and three different S. sobrinus phenotypes were detected. ICM proved to be a powerful tool for a differentiation of mutans streptococci down to the subspecies level.

To exert anticaries effects, probiotics are described to inhibit growth and biofilm formation of cariogenic bacteria such as Streptococcus mutans (SM). We screened 8 probiotics and assessed how SM growth or biofilm formation inhibition affects cariogenicity of probiotic-SM mixed-species biofilms in vitro. Growth inhibition was assessed by cocultivating probiotics and 2 SM strains (ATCC 20532/25175) on agar. Probiotics were either precultured before SM cultivation (exclusion), or SM precultured prior to probiotic cultivation (displacement). Inhibition of SM culture growth was assessed visually. Inhibition of SM biofilm formation on bovine enamel was assessed using a continuous-flow short-term biofilm model, again in exclusion or displacement mode. The cariogenicity of mixed-species biofilms of SM with the most promising growth and biofilm formation inhibiting probiotic strains was assessed using an artificial mouth model, and enamel mineral loss (ΔZ) was measured microradiographically. We found limited differences in SM growth inhibition in exclusion versus displacement mode, and in inhibition of SM 20532 versus 25175. Results were therefore pooled. Lactobacillus acidophilus LA-5 inhibited significantly more SM culture growth than most other probiotics. L. casei LC-11 inhibited SM biofilm formation similarly to other alternatives but showed the highest retention of probiotics in the biofilms (p < 0.05). Mineral loss from SM monospecies biofilms (ΔZ = 9,772, 25th/75th percentiles: 6,277/13,558 vol% × µm) was significantly lower than from mixed-species SM × LA-5 biofilms (ΔZ = 24,578, 25th/75th percentiles: 19,081/28,768 vol% × µm; p < 0.01) but significantly higher than from SM × LC-11 biofilms (ΔZ = 4,835, 25th/75th percentiles: 263/7,865 vol% × µm; p < 0.05). Probiotics inhibiting SM culture growth do not necessarily reduce the cariogenicity of SM-probiotic biofilms. Nevertheless, SM biofilm formation inhibition may be relevant in the reduction of cariogenicity.