Effects of triclosan-containing rinse on the dynamics and antimicrobial susceptibility of in vitro plaque ecosystems

Oral Microcosm Biofilms Grown under Conditions Progressing from Peri-Implant Health, Peri-Implant Mucositis, and Peri-Implantitis

Peri-implantitis is a disease influenced by dysbiotic microbial communities that play a role in the short- and long-term outcomes of its clinical treatment. The ecological triggers that establish the progression from peri-implant mucositis to peri-implantitis remain unknown. This investigation describes the development of a novel in vitro microcosm biofilm model. Biofilms were grown over 30 days over machined titanium discs in a constant depth film fermentor (CDFF), which was inoculated (I) with pooled human saliva. Following longitudinal biofilm sampling across peri-implant health (PH), peri-implant mucositis (PM), and peri-implantitis (PI) conditions, the characterisation of the biofilms was performed. The biofilm analyses included imaging by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM), selective and non-selective culture media of viable biofilms, and 16S rRNA gene amplification and sequencing. Bacterial qualitative shifts were observed by CLSM and SEM across conditions, which were defined by characteristic phenotypes. A total of 9 phyla, 83 genera, and 156 species were identified throughout the experiment. The phyla Proteobacteria, Bacteroidetes, Firmicutes, Fusobacteria, and Actinobacteria showed the highest prevalence in PI conditions. This novel in vitro microcosm model provides a high-throughput alternative for growing microcosm biofilms resembling an in vitro progression from PH-PM-PI conditions.

The cariogenic effect of starch on oral microcosm grown within the dual constant depth film fermenter

Evidence on the link between starch intake and caries incidence is conflicting, therefore the cariogenicity of starch compared with sucrose was explored using a dual Constant Depth Film Fermenter (dCDFF) biotic model system. Bovine enamel discs were used as a substrate and the dCDFF was inoculated using human saliva. CDFF units were supplemented with artificial saliva growth media at a constant rate to mimic resting salivary flow rate over 14 days. The CDFF units were exposed to different conditions, 2% sucrose or 2% starch 8 times daily and either no additional fluoride or 1450 ppm F- twice daily. Bovine enamel discs were removed at intervals (days 3, 7, 10 and 14) for bacterial enumeration and enamel analysis using Quantitative Light Induced Fluorescence (QLF) and Transverse Microradiography (TMR). Results showed that in the absence of fluoride there was generally no difference in mineral loss between enamel exposed to either sucrose or starch when analysed using TMR and QLF (P > 0.05). In the presence of fluoride by day 14 there was significantly more mineral loss under starch than sucrose when analysed with TMR (P < 0.05). It was confirmed that starch and sucrose are similarly cariogenic within the dCDFF in the absence of fluoride. With the aid of salivary amylase, the bacteria utilise starch to produce an acidic environment similar to that of bacteria exposed to sucrose only. In the presence of fluoride, starch was more cariogenic which may be due to the bacteria producing a more hydrophobic intercellular matrix lowering the penetration of fluoride through the biofilm. This is significant as it indicates that the focus on sugars being the primary cause of caries may need re-evaluating and an increase in focus on carbohydrates is needed as they may be similarly cariogenic as sugars if not more so.

Microbial virulence, molecular epidemiology and pathogenic factors of fluoroquinolone-resistant Haemophilus influenzae infections in Guangzhou, China

BACKGROUND

Fluoroquinolone-resistant Haemophilus influenzae (FRHI) has been reported worldwide but remain unclear in China.

METHODS

A total of 402 H. influenzae isolates collected from 2016 to 2017 were included. Antimicrobial susceptibility on 10 antibiotics was performed, and minimum inhibitory concentration of ciprofloxacin- and nalidixic acid-resistant strains were further determined by E-test strips, with risk factors also evaluated. Strains with resistance or reduced susceptibility to ciprofloxacin were subjected to sequencing of the quinolone resistance-determining regions (QRDR) and plasmid-mediated quinolone resistance genes by sequencing, with multi-locus sequence typing.

RESULTS

2.2% of H. influenzae strains were non-susceptible (7/402, 1.7%) or susceptible (2/402, 0.5%) to ciprofloxacin but NAL-resistant by E-test, and multidrug resistance was more common in fluoroquinolones non-susceptible H. influenzae group (p = 0.000). Infection risk factors included invasive procedure (p = 0.011), catching cold/previous contact with someone who had a cold (p = 0.019), fluoroquinolones use during previous 3 months (p = 0.003). With none of mutations obtained in gyrB, parE and other plasmid-mediated quinolone resistance genes, 7 and 4 strains were found for Ser-84-Leu substitutions in gyrA and one amino acid substitution in the QRDR of gyrA linked with one amino acid substitution in the QRDR of parC, respectively. In addition, five sequence types (ST) were identified, with ST1719 firstly found.

CONCLUSIONS

For the first time, this study has reported the incidence, risk factors, molecular determinants on fluoroquinolones resistance and ST of FRHI strains in mainland China, representing the first evidence of mutation of gyrA and parC in China and the new ST1719 worldwide.

Fungal mitochondrial oxygen consumption induces the growth of strict anaerobic bacteria

Fungi are commonly encountered as part of a healthy oral ecosystem. Candida albicans is the most often observed and investigated fungal species in the oral cavity. The role of fungi in the oral ecosystem has remained enigmatic for decades. Recently, it was shown that C. albicans, in vitro, influences the bacterial composition of young oral biofilms, indicating it possibly plays a role in increasing diversity in the oral ecosystem. C. albicans favored growth of strictly anaerobic species under aerobic culture conditions. In the present study, the role of mitochondrial respiration, as mechanism by which C. albicans modifies its environment, was investigated. Using oxygen sensors, a rapid depletion of dissolved oxygen (dO₂) was observed. This decrease was not C. albicans specific as several non-albicans Candida species showed similar oxygen consumption. Heat inactivation as well as addition of the specific mitochondrial respiration inhibitor Antimycin A inhibited depletion of dO₂. Using 16S rDNA sequencing, it is shown that mitochondrial activity, more than physical presence of C. albicans is responsible for inducing growth of strictly anaerobic oral bacteria in aerobic growth conditions. The described mechanism of dO₂ depletion may be a general mechanism by which fungi modulate their direct environment.

Arginine Exposure Decreases Acidogenesis in Long-Term Oral Biofilm Microcosms

Arginine is used in dental health formulations to help prevent dental cavities. This study assessed the effects of the long-term dosing of laboratory dental plaques with an arginine dentifrice. Data indicate that the addition of arginine dentifrice during sucrose challenge significantly increased plaque pH, thus potentially mitigating cariogenesis. Several functional groups of bacteria associated with tooth decay were significantly decreased in the laboratory plaques during exposure to the arginine dentifrice.

Arginine is an important pH-elevating agent in the oral cavity. It has been incorporated in oral hygiene formulations to mitigate sensitivity and to prevent caries. In this investigation, the effects of sustained arginine dosing of dental plaque microcosms on bacteriological composition and pH were evaluated under controlled conditions. Plaque microcosms were established in constant-depth film fermentors (CDFFs) using salivary inocula and fed continuously with artificial saliva. To simulate resting and cariogenic states, the CDFFs were supplemented with sterile water or 5% sucrose, respectively. Plaques were then dosed twice daily with a dentifrice with 1.5% arginine arginine added (DA) or without arginine (DN). This regimen continued for over 3 weeks, after which fermentors were maintained without dosing. Microcosms were analyzed by differential viable counting, with a pH microelectrode, and by eubacterial DNA profiling. Sucrose dosing was associated with significantly (P < 0.001) decreased pH, significantly (P < 0.05) increased counts of total aerobes, Gram-negative anaerobes, aciduric species, acidogenic species, arginine utilizing species, bifidobacteria, lactobacilli and streptococci, and significant (P < 0.05) changes in DNA profiles. Plaques dosed with DA had a significantly (P < 0.001) higher pH than those dosed with DN, with or without sucrose supplementation. Dosing with DA but not DN significantly (P < 0.05) decreased counts of all functional bacterial groups apart from the total anaerobes in cariogenic plaques, and in resting plaques, dosing with DA significantly (P < 0.05) decreased counts of streptococci, lactobacilli, bifidobacteria, and acidogenic bacteria. In summary, sustained exposure of oral microcosms to arginine in formulation significantly increased plaque pH and significantly reduced the viability of cariogenic bacterial species.

IMPORTANCE Arginine is used in dental health formulations to help prevent dental cavities. This study assessed the effects of the long-term dosing of laboratory dental plaques with an arginine dentifrice. Data indicate that the addition of arginine dentifrice during sucrose challenge significantly increased plaque pH, thus potentially mitigating cariogenesis. Counts of several functional groups of bacteria associated with tooth decay were significantly decreased in the laboratory plaques during exposure to the arginine dentifrice.

In vitro biofilm models to study dental caries: a systematic review

The aim of this systematic review is to characterize and discuss key methodological aspects of in vitro biofilm models for caries-related research and to verify the reproducibility and dose-response of models considering the response to anti-caries and/or antimicrobial substances. Inclusion criteria were divided into Part I (PI): an in vitro biofilm model that produces a cariogenic biofilm and/or caries-like lesions and allows pH fluctuations; and Part II (PII): models showing an effect of anti-caries and/or antimicrobial substances. Within PI, 72.9% consisted of dynamic biofilm models, while 27.1% consisted of batch models. Within PII, 75.5% corresponded to dynamic models, whereas 24.5% corresponded to batch models. Respectively, 20.4 and 14.3% of the studies reported dose-response validations and reproducibility, and 32.7% were classified as having a high risk of bias. Several in vitro biofilm models are available for caries-related research; however, most models lack validation by dose-response and reproducibility experiments for each proposed protocol.

Dental Biofilm and Laboratory Microbial Culture Models for Cariology Research

Dental caries form through a complex interaction over time among dental plaque, fermentable carbohydrate, and host factors (including teeth and saliva). As a key factor, dental plaque or biofilm substantially influence the characteristic of the carious lesions. Laboratory microbial culture models are often used because they provide a controllable and constant environment for cariology research. Moreover, they do not have ethical problems associated with clinical studies. The design of the microbial culture model varies from simple to sophisticated according to the purpose of the investigation. Each model is a compromise between the reality of the oral cavity and the simplification of the model. Researchers, however, can still obtain meaningful and useful results from the models they select. Laboratory microbial culture models can be categorized into a closed system and an open system. Models in the closed system have a finite supply of nutrients, and are also simple and cost-effective. Models in the open system enabled the supply of a fresh culture medium and the removal of metabolites and spent culture liquid simultaneously. They provide better regulation of the biofilm growth rate than the models in the closed system. This review paper gives an overview of the dental plaque biofilm and laboratory microbial culture models used for cariology research.

Inhibition of Streptococcus mutans biofilm formation using extracts from Assam tea compared to green tea

OBJECTIVE

Streptococcus mutans, a gram-positive oral bacterium, has been identified as one of the principal etiological agents of human dental caries. To clarify the nature of the difference anti-biofilm effect against S. mutans between Assam tea from Camellia sinensis var. assamica, partially fermented, and green tea from Camellia sinensis, non-fermented, active agents from the teas were purified.

METHODS

Effects of Assam tea and green tea samples on biofilm were assessed by using the conventional titer plate method and the human saliva-coated hydroxyapatite discs. The purification and identification of inhibitors were performed by using ultrafiltration with centrifugal filter devices and high performance liquid chromatography.

RESULTS

Assam tea has stronger biofilm inhibition activity against S. mutans than green tea. A substance of <10kDa in mass in Assam tea had a high concentration of galloylated catechins and a stronger biofilm inhibiting activity than green tea. In contrast, substances >10kDa in mass from green tea included higher concentrations of polysaccharides composed of galacturonic acid, such as pectin, that enhance biofilm formation.

CONCLUSIONS

The higher concentrations of galloylated catechins in Assam tea may assist in prevention of dental caries, whereas in green tea, this mode of inhibition was likely offset by the presence of pectin. Purification of catechins in partially fermented Assam tea with lower-molecular-weight polysaccharide than pectin may be useful for developing oral care products such as toothpaste and oral care gel pastes.

Oral bacteria adherence to suture threads: an in vitro study

PURPOSE

This study investigated the adherence of oral microorganisms to different types of suture threads.

METHODS

Pieces of thread were distributed on 24-well plates, according to the following groups: (G1) nylon, (G2) silk, (G3) polyglactin 910, (G4) polyglactin 910 with triclosan. Blank control (G5) consisted of one thread from each group. Adherence to thread tests was performed to observe adhesion of total microorganisms from saliva or two isolates of Prevotella intermedia (ATCC49046) and Fusobacterium nucleatum (ATCC51190). Brain-heart infusion (BHI) medium with or without bacterial inoculum (1.8 × 10(7) CFU/mL) was added to each well of microplates. The microplates were incubated in an anaerobic chamber at 37 °C, for 5 days for biofilm formation.

RESULTS

There was no difference between the groups as regard to adhesion of F. nucleatum (p > 0.05). For P. intermedia, the threads in G1 and G4 showed a lower level of adhesion (p < 0.05), with no difference between them. Against total microorganisms, G1 presented a lower level of adherence (p < 0.05), followed by G4; and no difference was observed between G2 and G3.

CONCLUSIONS

Total microorganisms and P. intermedia have different affinities to the tested suture threads, whereas F. nucleatum presented a similar adherence level. Among the threads, nylon (G1), followed by polyglactin 910 with triclosan (G4) presented the lowest microbial adherence level.

Bacteriological effects of dentifrices with and without active ingredients of natural origin

Compounds of natural origin are increasingly used as adjuncts to oral hygiene. We have adopted four distinct approaches to assess the antibacterial activity of dentifrices containing natural active ingredients against oral bacteria in several test systems. Corsodyl Daily (CD), Kingfisher Mint (KM), and Parodontax fluoride (PF) were compared to a dentifrice containing fluoride (Colgate Cavity Protection [CCP]) and one containing triclosan (Colgate Total [CT]). The growth inhibitory and bactericidal potency of the formulations were determined for 10 isolated oral bacteria. Effects of single exposures of simulated supragingival plaques were then determined by epifluorescence and confocal microscopy, while the effects of repeated exposures were quantified by viable counting. Additionally, dense plaques, maintained in continuous culture, were repeatedly dosed, and the outcome was assessed by viable counting and eubacterial DNA profiling. The test dentifrices exhibited variable specificity and potency against oral bacteria in axenic culture. Of the herbal formulations, KM caused the largest viability reductions in simulated supragingival plaques, with CT causing the greatest reductions overall. Following single exposures, CD caused moderate reductions, while PF had no effect. After multiple dosing, all formulations significantly reduced numbers of total, facultative, and Gram-negative anaerobes, but only KM and CT caused greater reductions than the fluoride control. KM also reduced counts of streptococci (rank order of effectiveness: CT > KM > CCP > PF > CD). Marked changes in eubacterial DNA profiles were not detected for any herbal formulation in dense plaques, although KM markedly reduced viable counts of streptococci, in agreement with supragingival data. While both nonherbal comparators displayed antibacterial activity, the triclosan-containing formulation caused greater viability reductions than the herbal and nonherbal formulations.

Oral bacterial communities in individuals with type 2 diabetes who live in southern Thailand

Type 2 diabetes mellitus is increasingly common in Thailand and elsewhere. In the present investigation, the bacteriological composition of saliva and supragingival plaque in Thai diabetics with and without active dental caries and in nondiabetics was determined by differential culture and eubacterial DNA profiling. Potential associations between fasting blood sugar and glycosylated hemoglobin (biomarkers of current and historical glucose control, respectively) with decayed, missing, and filled teeth and with salivary Streptococcus and Lactobacillus counts were also investigated. The incidence of active dental caries was greater in the Thai diabetics than in nondiabetics, and the numbers of total streptococci and lactobacilli were significantly higher in supragingival plaque from diabetics than in nondiabetics. Lactobacillus counts in the saliva and supragingival plaque of diabetics with active caries were significantly higher than those in diabetics without active caries. Oral eubacterial DNA profiles of diabetic versus nondiabetic individuals and of diabetics with active caries versus those without active caries could not be readily differentiated through cluster analysis or multidimensional scaling. The elevated caries incidence in the Thai diabetics was positively associated with numbers of bacteria of the acidogenic/acid-tolerant genera Streptococcus and Lactobacillus. Lactobacillus bacterial numbers were further elevated in diabetics with active caries, although salivary eubacterial DNA profiles were not significantly altered.

Continuous culture of sessile human oropharyngeal microbiotas

The microbiota of the human oropharynx plays an important role in health through involvement in the aetiology of infection and the carriage of adventitious pathogens. Despite this, there are few models available for the preclinical assessment of novel antimicrobials directed to the human throat. We have profiled bacterial consortia sampled from the palatine tonsil and posterior pharyngeal wall microbiotas of healthy adult volunteers (n = 10) using differential culture and 16S rRNA gene sequencing, together with PCR-denaturing gradient gel electrophoresis. The data generated were used to assess the validity of an oropharyngeal microcosm system based on replicated constant-depth film fermenters (CDFFs; n = 5), which were continuously fed using an artificial airway surface liquid. Developed microcosms exhibited significant homology to ex situ consortia according to principal components analysis, whilst compositional reproducibility was apparent in replicated models for tonsillar and pharyngeal inocula. Differential viable count data and Shannon-Weiner diversity indices indicated that representative tonsil and pharyngeal model systems achieved dynamic compositional stability about 6 days after inoculation which could be maintained for ≥20 days. In conclusion, the CDFF facilitated the continuous maintenance of bacteriologically stable microcosms that were compositionally similar to ex situ inocula.

Topical effect of a medically prescribed pediatric antibiotic on dental biofilm: a cross-over, in situ study

Objective

This study aimed to investigate the possible topical effect of a broad-spectrum antibiotic on dental biofilm formed in situ in the absence or presence of sucrose.

Methods

A crossover study was conducted in three phases of 14 days each, during which 11 volunteers wore palatal devices containing 6 enamel blocks covered with meshes to allow biofilm formation. Dental blocks were extraorally submitted to a 20% sucrose solution at three different frequencies of exposure (0, 3 and 8 times/day), and to a suspension of amoxicillin/clavulanate potassium (A/CP) or a placebo (P) suspension at an 8-hour time interval application regimen. On the 14^th day of each phase, biofilms were collected for microbiological (conventional culture) and molecular (Denaturing Gradient Gel Electrophoresis – DGGE) analyses.

Results

In the absence of sucrose exposure (SE) and at the 3-time daily frequency, dental biofilms treated with A/CP showed lower total biofilm weight and lower counts of total microbiota than the ones treated with P (p>0.05). A/CP presented higher counts of Candida spp. when compared with P in the presence of SE, especially at the 8-time daily frequency (p<0.05). Considering the DGGE analysis, the mean number of bands was higher for P (p>0.05), regardless of SE. However, DGGE profiles demonstrated large interindividual variability.

Conclusion

Both conventional culture and DGGE have demonstrated some differences on total microbiota of dental biofilms when exposed to the A/CP or P suspensions, mainly in the absence of sucrose, which suggests a possible topical effect of the sugar-free A/CP suspension on dental biofilm.

Rapid detection of rpoB mutations in rifampin resistant M. tuberculosis from sputum samples by denaturing gradient gel electrophoresis

OBJECTIVE

To establish a rapid detection method for identifying rpoB mutations associated with rifampin (RIF) resistance in sputum specimens.

METHODS

We detected rpoB mutations directly in 90 sputum specimens collected from suspected tuberculosis patients using PCR-based denaturing gradient gel electrophoresis (DGGE) and compared these results with those obtained by rpoB sequencing and conventional drug susceptibility testing.

RESULTS

The positive detection rate of Mycobacterium tuberculosis (M. tuberculosis) was 52.2% by Acid-Fast Bacilli staining and 72.2% by conventional mycobacterial culture. In contrast, the positive rate was significantly higher (93.3%) by PCR-based detection of the rpoB gene in the same specimens. Furthermore, 75% of the tested specimens presented abnormal patterns compared with the wild-type pattern (standard H37Rv strain) analysed by DGGE. A total of 12 different patterns, representing 12 different rpoB mutations, were observed in the 63 abnormal patterns. The match rate of rpoB mutations detected by DGGE reached 96.9% when compared to DNA sequencing.

CONCLUSION

Our findings indicate that PCR-based DGGE is a rapid and reliable bio-technique for direct detection of rpoB mutations associated with RIF resistance in the sputum of suspected tuberculosis patients.

Antimicrobial sutures and prevention of surgical site infection: assessment of the safety of the antiseptic triclosan

This article is based on a second Hygienist Panel meeting held in London on 16-17 June 2010. The Panel discussed the current use of antimicrobials and care bundles in the prevention of surgical site infection; the need to comply with good antibiotic stewardship, to reduce the risk of antibiotic-resistant and emergent organisms; and the need to revisit the use of antiseptics. The discussion was driven by concerns of the use of triclosan, which had been raised by a publication from the Scientific Committee on Consumer Products of the Directorate General for Health and Consumers, European Commission. Uncertainties that excessive use of triclosan for preservation and in cosmetics could select naturally resistant environmental organisms or induce reduced triclosan-susceptibility or antibiotic resistance were considered. It was concluded that the uses of triclosan with demonstrable health benefits, as in some medical applications (such as antimicrobial sutures), need to be distinguished from those where there is no proven benefit, such as its use in certain consumer products. The addition of triclosan to a product must be substantiated in any claim of preventive or therapeutic health benefit. Triclosan is the most widely studied biocide and this same level of information should be available for other topically used antimicrobials, which are widely used in surgical practice and chronic wound care.

Bacteriological effects of a Lactobacillus reuteri probiotic on in vitro oral biofilms

OBJECTIVE

Despite the targeted and incidental exposure of the oral cavity to probiotic bacteria, relatively little information is available concerning their bacteriological effects or ecological fate in this environment. We have investigated the effects of an oral probiotic bacterium, Lactobacillus reuteri on salivary biofilm microcosms.

DESIGN

Nascent in vitro plaques in hydroxyapatite disc model and mature continuous culture plaques within constant depth film fermenters (CDFFs) were exposed to probiotic strains of L. reuteri. Microbial composition was assessed using differential viable counting and CDFF plaques were additionally characterised using qPCR and PCR-DGGE.

RESULTS

Probiotic dosing of nascent plaques was associated with significant increases in lactobacilli and Gram-negative anaerobes in both biofilm and planktonic phases, and with elevated counts of streptococci in the planktonic phase that were not accompanied by decreases in pH. In mature CDFF plaques, differential culture indicated that whilst significant increases in lactobacillus counts occurred during dosing, numbers of other bacterial groups and pH did not significantly change. Monitoring the probiotic strain in CDFFs using selective culture and qPCR indicated that the exogenous bacterium reached and maintained c. 5 log(10)CFU/mm(2) during dosing and 20 days after cessation. The apparent lack of marked bacterial inhibition by L. reuteri in both model systems was supported by the absence of antagonism in binary antagonism assays.

CONCLUSION

The largest compositional changes occurred in nascent plaques where the addition of lactobacilli caused significant increases in streptococci and Gram-negative anaerobes, the latter possibly via lactate syntrophy. Exogenous L. reuteri persisted in mature plaque microcosms after dosing ceased.

Evaluation of the specificity and effectiveness of selected oral hygiene actives in salivary biofilm microcosms

The microbiological effects of biocidal products used for the enhancement of oral hygiene relate to the active compound(s) as well as other formulation components. Here, we test the specificities of selected actives in the absence of multiple excipients. Salivary ecosystems were maintained in tissue culture plate-based hydroxyapatite disc models (HDMs) and modified drip-flow biofilm reactors (MDFRs). Test compounds stannous fluoride (SF), SDS, triclosan (TCS), zinc lactate (ZL) and ZL with SF in combination (ZLSF) were delivered to the HDMs once and four times daily for 6 days to MDFRs. Plaques were characterized by differential viable counting and PCR–denaturing gradient gel electrophoresis (DGGE). TCS and SDS were the most effective compounds against HDM plaques, significantly reducing total viable counts (P<0.05), whilst SF, ZL and ZLSF were comparatively ineffective. TCS exhibited specificity for streptococci (P<0.01) and Gram-negative anaerobes (P<0.01) following a single dosing and also on repeated dosing in MDFRs. In contrast to single exposures, multiple dosing with ZLSF also significantly reduced all bacterial groups, whilst SF and ZL caused significant but transient reductions. According to PCR–DGGE analyses, significant (P<0.05) reductions in eubacterial diversity occurred following 6 day dosing with both TCS and ZLSF. Concordance of MDFR eubacterial profiles with salivary inocula ranged between 58 and 97 %. TCS and ZL(SF) exhibited similar specificities to those reported for formulations. TCS was the most potent antibacterial, after single and multiple dosage regimens.

Chapter 4: In vitro biofilm models: an overview

Observing naturally occurring biofilms in situ or ex situ has revealed the wide distribution of sessile microbial communities. The ubiquity, variety and complexity of biofilms is now widely accepted by microbiologists. While they are associated with many beneficial functions such as nutrient cycling, bioremediation and colonization resistance, adverse effects including recalcitrance, their involvement in industrial fouling, contamination and infection have made biofilms a priority research topic. We know that most biofilms, other than within certain infections and laboratory flasks, are composed of multiple species and that there is arguably no unifying biofilm architecture. Biofilms do however share certain properties including the presence of gradients of nutrients, gasses and metabolic products, relatively increased cell density, deposition of extracellular polymeric substances and marked recalcitrance towards antimicrobial treatments. Much of our understanding of biofilm physiology and micro-ecology originates from experiments using in vitro biofilm models. Broadly speaking, such models may be used to replicate environmental conditions within the laboratory or to focus on selected variables such a growth rate or fluid flow, etc. This chapter provides an overview of some commonly used biofilm models including microtitre plate systems, flow cells, the constant depth film fermenter, annular reactors and the perfused biofilm fermenter. While perfused biofilm fermenters, in particular, enable growth rate to be controlled within thin, relatively homogenous, quasi steady-state biofilms through modulation of flow rate nutrient availability, other models provide representative modelling of in situ conditions where steady states may be uncommon.

An in vitro evaluation of hydrolytic enzymes as dental plaque control agents

The plaque-control potential of commercially available amylase, lipase and protease was evaluated by observing their effects on coaggregation and on bacterial viability within various plaque microcosms. A quantitative coaggregation assay indicated that protease significantly inhibited the extent of coaggregation of Actinomyces naeslundii and Streptococcus oralis (P <0.05) and of Porphyromonas gingivalis and S. oralis. Amylase significantly (P <0.05) increased the coaggregation of A. naeslundii versus Fusobacterium nucleatum and A. naeslundii versus P. gingivalis. Concomitant challenge of constant-depth film fermenter-grown plaques with the enzymes did not result in detectable ecological perturbations (assessed by differential culture and denaturing gradient gel electrophoresis). Similar dosing and analysis of multiple Sorbarod devices did not reveal increases in bacterial dispersion which could result from disaggregation of extant plaques. A short-term hydroxyapatite colonization model was therefore used to investigate possible enzyme effects on early-stage plaque development. Whilst culture did not indicate significant reductions in adhesion or plaque accumulation, a vital visual assay revealed significantly increased aggregation frequency following enzyme exposure. In summary, although hydrolytic enzymes negatively influenced binary coaggregation, they did not cause statistically significant changes in bacterial viability within plaque microcosms. In contrast, enzyme exposure increased aggregation within extant plaques.

In vitro models for oral malodor

A model is a representation of some real phenomena and contains aspects or elements of the real system to be modeled. The model reflects (or duplicates) the type of behavior (or mechanisms) seen in the real system. The main characteristic of any model is the mapping of elements or parameters found in the system being studied (e.g. tongue dorsum biofilm in situ) on to the model being devised (e.g. laboratory perfusion biofilm). Such parameters include correct physico-chemical (abiotic) conditions as well as biotic conditions that occur in both model and reality. The main purpose of a model is to provide information that better explains the processes observed or thought to occur in the real system. Such models can be abstract (mental, conceptual, theoretical, mathematical or computational) or 'physical', e.g. in the form of a real disaggregated in vitro system or laboratory model. A wide range of different model systems have been used in oral biofilm research. These will be briefly reviewed with special emphasis on those models that have contributed most to knowledge in breath odor research. The different model systems used in breath odor research are compared. Finally, the requirements for developing an overall 'bad breath model' from considering the processes as a whole (real oral cavity, substrates in saliva, biotransformation by tongue microflora, odor gases in the breath) and extending this to the detection of malodor by the human nose will be outlined and discussed.

Common therapeutic approaches for the control of oral biofilms: microbiological safety and efficacy

Triclosan is widely employed in many consumer and healthcare products. The increasing employment of triclosan in a range of consumer products where there is no proven benefit for hygiene has been severely criticised. Laboratory studies demonstrate theoretical risks that the wide-scale use of triclosan might compromise its efficacy as well as the activity of third-party antibiotics. The precautionary principle would dictate against the use of triclosan, at least in those products where there was no demonstrable health benefit. The theoretical risks, however, are not supported by either field or clinical studies, or by laboratory studies using bacterial microcosms. Numerous clinical studies, as well as historical data, demonstrate the clinical benefits of hygiene adjuncts such as triclosan and triclosan/copolymer in oral care products where these compensate for deficiencies in mechanical hygiene (brushing and flossing). The balance of risk and benefit is firmly in favour of the continued use of dentifrices (toothpastes) and mouthwashes containing active agents such as triclosan.

Microbial colonization of the upper gastrointestinal tract in patients with Barrett's esophagus

BACKGROUND

Barrett's esophagus (BE) is a complication of chronic gastroesophageal reflux disease, in which patients are at greatly increased risk of esophageal dysplasia and adenocarcinoma. Over the past 2 decades, there has been an increase in the incidence of both BE and adenocarcinoma; however, the involvement of microorganisms in BE is uncertain. The aim of this study was to characterize microbial communities in esophageal aspirate specimens and on distal esophageal mucosal samples from patients with BE.

METHODS

Biopsy and aspirate specimens were obtained by endoscopic examination from 7 patients with BE and 7 control subjects without BE. Samples were cultured under aerobic, anaerobic, and microaerophilic conditions for yeasts and bacteria, including Helicobacter pylori. Bacterial isolates were identified by 16S ribosomal RNA gene sequencing. Fluorescence microscopic examination was also used to determine the spatial localization of these organisms on mucosal surfaces. Significant colonization was detected in 6 patients with BE and in 4 control subjects.

RESULTS

Overall, 46 bacterial species belonging to 16 genera were detected, with 10 species being common in both groups. Both aspirate and biopsy samples from patients with BE contained complex populations of bacteria. Uniquely, high levels of Campylobacter species (Campylobacter concisus and Campylobacter rectus), which have been linked to enteritis, periodontal infections, and tumor formation in animals, were found in 4 (57%) of 7 patients with BE but in none of the control subjects. Microscopic examination revealed that bacteria on mucosal biofilms often occurred in microcolonies.

CONCLUSIONS

The occurrence of nitrate-reducing Campylobacter species in patients with BE may suggest that there is a link in either the initiation, maintenance, or exacerbation of disease processes leading to adenocarcinoma formation.

Caries-related plaque microcosm biofilms developed in microplates

In vivo dental plaque biofilms consist of complex communities of oral bacteria that are a challenge to replicate in vitro. The aim of this investigation was to establish human dental plaque microcosms in microplates to reflect conditions that are relevant to dental caries. Microcosm plaque biofilms were initiated from the saliva of two different donors, grown for up to 10 days in 24-welled microplates on Thermanox coverslips in various types of artificial saliva with and without sucrose, which were replaced daily. Microbiota composition of 40 species associated with oral health and dental caries was monitored in the plaques using Checkerboard DNA-DNA hybridization analysis. pH was measured as an indicator of cariogenic potential. The composition of the saliva inocula was different, and yielded plaque microcosms with different composition and growth responses to sucrose. Artificial saliva type and presence of sucrose, and the resulting growth and pH conditions, modified the growth of individual species and hence the ecological profile of the microplate plaques during development. Complex population shifts were observed during development, and older plaques comprised predominantly facultative anaerobic species. Sucrose supplementation limited the decline of Streptococci over time but did not increase the abundance of mutans Streptococci. Sucrose at 0.15% increased levels of caries-associated species including Lactobacillus fermentum, Lactobacillus acidophilus and Actinomyces gerensceriae; these were further increased with sucrose at 0.5%, in addition to Actinomyces israelii, Rothia dentocariosa and Capnocytophaga gingivalis. The microplate plaques demonstrated complex community dynamics that appeared to reflect the maturation of natural plaques, and sucrose induced a cariogenic plaque composition and pH.

Effect of triclosan on Salmonella typhimurium at different growth stages and in biofilms

Triclosan is a potent biocide that is included in a diverse range of products. This research was aimed to investigate the susceptibility of planktonic and biofilm-associated Salmonella enterica serovar Typhimurium to triclosan, and to identify potential mechanisms of adaptation. The effect of triclosan was studied on planktonic Salmonella (log and stationary phases), on biofilm-associated cells, on bacteria derived from disrupted biofilms and on a biofilm-deficient mutant. An eight-log reduction of exponentially growing cells was observed with 1000 micro g mL(-1) triclosan within 10 min, a 3.6-log reduction in stationary cells and a 6.3-log reduction in stationary cells of a biofilm-deficient mutant (P<0.05). Biofilm-associated cells were tolerant (1-log reduction). However, biofilm-derived cells showed sensitivity to triclosan similar to stationary-phase cells. Triclosan induced the transcription of fabI and micF. Within biofilms, triclosan also up-regulated the transcription of acrAB, encoding for an efflux pump, marA, and the cellulose-synthesis-coding genes bcsA and bcsE. Thus, Salmonella within biofilms could experience reduced influx, increased efflux and enhanced exopolysaccharides production. Our results demonstrated that the tolerance of Salmonella towards triclosan in the biofilm was attributed to low diffusion through the extracellular matrix, while changes of gene expression might provide further resistance to triclosan and to other antimicrobials.

Molecular analysis of the subgingival microbiota in health and disease

This investigation provides molecular analyses of the periodontal microbiota in health and disease. Subgingival samples from 47 volunteers with healthy gingivae or clinically diagnosed chronic periodontitis were characterized by PCR-denaturing gradient gel electrophoresis (DGGE) with primers specific for the V2-V3 region of the eubacterial 16S rRNA gene. A hierarchical dendrogram was constructed from band patterns. All unique PCR amplicons (DGGE bands) were sequenced for identity. Samples were also analyzed for the presence of Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, and Tannerella forsythensis by multiplex PCR. Associations of patient age, gender, and smoking status together with the presence of each unique band and putative periodontal pathogens with disease were assessed by logistic regression. Periodontal pockets were colonized by complex eubacterial communities (10 to 40 distinct DGGE bands) with substantial individual variation in the community profile. Species diversity in health and disease was determined by the Shannon-Weaver index of diversity and compared by the Mann-Whitney U test. Sequence analyses of DGGE amplicons indicated the occurrence of many nontypical oral species and eubacteria previously associated with this environment. With the exception of T. forsythensis, the putative pathogens were not detected by DGGE. Multiplex PCR, however, detected T. forsythensis, A. actinomycetemcomitans, and P. gingivalis in 9% 16%, and 29% of the patients with disease, respectively. The presence of A. actinomycetemcomitans was significantly associated with disease (P < 0.01). Statistical analyses indicated that the presence of Treponema socranskii and Pseudomonas sp. was a significant predictor of disease (P < 0.05) and that there was no significant difference (P > 0.05) in terms of eubacterial species diversity between health and disease.

Triclosan and Antimicrobial Resistance in Bacteria: An Overview

Triclosan is a widely used biocide that is considered as an effective antimicrobial agent against different microorganisms. It is included in many contemporary consumer and personal health-care products, like oral and dermal products, but also in household items, including plastics and textiles. At bactericidal concentrations, triclosan appears to act upon multiple nonspecific targets, causing disruption of bacterial cell wall functions, while at sublethal concentrations, triclosan affects specific targets. During the 1990s, bacterial isolates with reduced susceptibility to triclosan were produced in laboratory experiments by repeated exposure to sublethal concentrations of the agent. Since 2000, a number of studies have verified the occurrence of triclosan resistance amongst dermal, intestinal, and environmental microorganisms, including some of clinical relevance. Of major concern is the possibility that triclosan resistance may contribute to reduced susceptibility to clinically important antimicrobials, due to either cross-resistance or co-resistance mechanisms. Although the number of studies elucidating the association between triclosan resistance and resistance to other antimicrobials in clinical isolates has been limited, recent laboratory studies have confirmed the potential for such a link in Escherichia coli and Salmonella enterica. Thus, widespread use of triclosan may represent a potential public health risk in regard to development of concomitant resistance to clinically important antimicrobials.

Individual microflora beget unique oral microcosms

AIMS

To examine the efficacy of the multiple Sorbarod device (MSD) for the reproduction of inter-individual variations in oral microbiotas. The MSD supports sessile growth on parallel cellulose filters, perfused with artificial saliva. This enables biofilms (BF) to be grown and sampled, together with released cells in eluted medium (perfusates, PAs).

METHODS AND RESULTS

Two sets of triplicate MSDs were established. One set was inoculated using fresh saliva from three separate volunteers; the second set was inoculated from one saliva donor. Both were incubated in an anaerobic cabinet. BF and PA were analysed at 24-h intervals by PCR-denaturing gradient gel electrophoresis (DGGE) of 16S rDNA. Hierarchical dendrograms were constructed in order to sort community fingerprints over time, based on community relatedness. The MSD supported complex oral communities, as evidenced by DGGE (>20 distinct DGGE bands) and confocal scanning laser microscopy. DGGE band sequencing revealed bacteriological diversity and a high incidence of anaerobic species, including Prevotella sp. Dendrograms demonstrated marked inter-individual variation in the relative species abundance within salivary inocula from different volunteers (DV) and each associated MSD (all >45%, majority c. 85% concordance). Less variation was shown between triplicate models established using saliva from a single volunteer (SV) (all >58%; majority c. 95% concordance). PAs clustered together with the associated biofilms and inocula in the majority of cases for the DV MSDs whilst SV MSD community profiles clustered between replicate MSDs.

CONCLUSIONS

Data indicate that marked inter-individual variations in human salivary composition can be partially replicated in individualized MSD microcosms.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the in vitro reproduction of individual oral microbiotas and suggests that taking inter-individual variability into account will increase the relevance of microcosm studies.

Effects of a Lactobacillus casei Synbiotic on Serum Lipoprotein, Intestinal Microflora, and Organic Acids in Rats

The main aim of this study was to evaluate the effectiveness of 3 synbiotic diets: 1) containing Lactobacillus casei ASCC 292 and fructooligosaccharides (LF diet); 2) containing L. casei ASCC 292 and maltodextrin (LM diet); and 3) containing L. casei ASCC 292, fructooligosaccharide, and maltodextrin (LFM diet) to reduce serum cholesterol in male Wistar rats. The effect of the synbiotic diets on intestinal microflora, concentration of organic acids, and the possibility of translocation of lactobacilli were also investigated. The LFM diet lowered serum total cholesterol and triglyceride levels, whereas the LM diet increased serum high-density lipoprotein cholesterol level. However, synbiotic diets did not contribute to a change in low-density lipoprotein cholesterol level compared with the control diet. There was a decrease in the population of staphylococci, bacteroides, Escherichia coli, and total coliforms in most bowel regions with the LFM diet compared with the control (which did not contain any synbiotic). In general, the LFM diet contributed to a higher concentration of lactic acid that may have contributed to the decrease in the population of pathogenic microorganisms compared with the control. Fructooligosaccharide was the preferred substrate for production of acetic acid. Results from this study showed that the synbiotic diet that contained L. casei ASCC 292, fructooligosaccharide, and maltodextrin beneficially altered cholesterol levels and produced a healthier bowel microbial population without translocation of lactobacilli to other organs.

Effects of chronic triclosan exposure upon the antimicrobial susceptibility of 40 ex-situ environmental and human isolates

BACKGROUND

Triclosan (TCS) exposure of Escherichia coli selects for tolerant clones, mutated in their enoyl-acyl carrier protein reductase (FabI). It has been inferred that this phenomenon is widespread amongst bacterial genera and might be associated with resistance to third party agents.

METHODS

Ex-situ, low passage isolates of enteric, human axilla, human oral origin and bacteria isolated from a domestic drain, together with selected type cultures were exposed to escalating concentrations of TCS over 10 passages using a gradient plate technique. One fresh faecal isolate of E. coli was included as a positive control. TCS susceptibility was determined for all strains before and after exposure, whilst enteric isolates were additionally assessed for susceptibility towards chlorhexidine, tetracycline, chloramphenicol, nalidixic acid and ciprofloxacin, and the oral isolates towards chlorhexidine, tetracycline and metronidazole.

RESULTS

Triclosan exposure of E. coli markedly decreased TCS susceptibility. TCS susceptibility also decreased for Klebsiella oxytoca, Aranicola proteolyticus and Stenotrophomonas maltophilia. Susceptibility of the remaining 35 strains to TCS and the other test agents remained unchanged.

CONCLUSIONS

These data suggest that selection for high level resistance by TCS exposure is not widespread and appears to be confined to certain enteric bacteria, especially E. coli. Change in TCS susceptibility did not affect susceptibility towards chemically unrelated antimicrobials.

SIGNIFICANCE AND IMPACT

Acquired high-level TCS resistance is not a widespread phenomenon.

Evaluation of the antibacterial effect of a triclosan-containing floor used in the food industry

Antibacterial surfaces are increasingly used in the food industry. In the present study, the antibacterial effect of a triclosan-containing industrial floor was assessed. A poultry processing plant, which had a floor that contained triclosan, was visited, and the floor was sampled for bacteria. A high bacterial diversity was found on the floor. Testing showed that bacteria isolated from the floor showed a sensitivity to triclosan that covered a range of MICs from 0.07 to >40 ppm. Staphylococci were the most sensitive, and Pseudomonas fluorescens and Serratia marcescens were the most tolerant. The MICs of triclosan for the strains isolated from the floor were similar to the control strains from the corresponding genera or species of other origin. Thus, the floor seemed not to select for strains that were tolerant to triclosan or that led to the development of resistance to triclosan. Laboratory studies showed that the ability of bacteria to survive under dry conditions on coupons of the floor was similar to that for stainless steel and that the survival of the bacteria on the floor was not linked to their tolerance of triclosan, as determined by the MICs of triclosan. Adherence studies showed that bacteria were able to adhere to coupons of the floor; however, no thick biofilm developed after 3 days of incubation. In an agar plate assay, the floor produced inhibition zones against staphylococci, which are known to be very sensitive to triclosan, whereas no inhibition zones were observed for other bacteria tested. In conclusion, the antibacterial effect of the floor seemed to be very low. Because the concentration of triclosan in the floor was low compared to what has been reported for other triclosan-incorporated surfaces, sufficient amounts of triclosan may not have been available on the surface of the floor to kill the bacteria.

16S rDNA PCR-denaturing gradient gel electrophoresis in determining proportions of coexisting Actinobacillus actinomycetemcomitans strains

Certain serotypes of Actinobacillus actinomycetemcomitans seem to prefer coexistence in vivo. The 16S rDNA PCR-denaturing gradient gel electrophoresis (DGGE) was tested for its capability to distinguish coexisting A. actinomycetemcomitans strains of different serotypes or genetic lineages and to determine their proportions in vitro. The migration pattern of the PCR amplicon from serotype c differed from those of the other serotypes. Contrary to the strains of serotypes c, d, and e, strains of serotypes a, b, and f consistently demonstrated intra-serotype migration patterns similar to each other. Since the migration patterns differed between serotype c and b strains a strain of each was used to determine their proportional representation in a strain mixture. The strains were distinguishable from each other above the 5% PCR-DGGE detection level (12.5 ng DNA/1.5 x 10(6) cells). DGGE provides a promising tool for in vitro studies on the coexistence of different genetic lineages of A. actinomycetemcomitans.

Development and characterization of a simple perfused oral microcosm

AIMS

To validate perfused, inline, filter-based fermentation systems (multiple Sorbarod devices, MSD) for their ability to maintain stable oral bacterial communities. MSD enable replicate (n=5) microcosm biofilms (BF) to be established and sampled, together with their perfusates (PA, cells in eluted medium).

METHODS AND RESULTS

Fresh saliva from human volunteers was used to inoculate MSD, incubated in an anaerobic cabinet and perfused with artificial saliva at 7 ml h(-1). BF within Sorbarod filters and cells eluted in the PA were analysed at 24-h intervals by differential bacteriological culture and checkerboard DNA-DNA hybridization (CKB, 40 oral species). Dynamic stability was apparent after 2-3 days within both BF and PA as evidenced by culture, CKB data and pH measurements. BF harboured large numbers of anaerobic species and facultative anaerobes [ca 10-11 log10 colony-forming units (CFU)/filter] comprising considerable numbers of streptococci and Gram-negative species. PA contained ca 9-10 log(10) CFU ml(-1) suggesting an apparent mean growth rate of 0.1 h(-1) for the BF, as a whole corresponding to a mean generation time of 10 h. CKB analysis revealed considerable bacterial diversity within the respective MSD. Inter-individual variations in the relative species abundance of inocula was broadly reproduced in the MSD (BF and PA), although considerable variation was apparent between triplicate models established using saliva from one saliva donor or from three individual donors. The dominance of Gram-negative species, indicated by culture was supported by CKB analysis (major species, Prevotella melaninogenica and Fusobacterium nucleatum).

CONCLUSIONS

Data obtained from the various analytical approaches showed a high degree of congruence. The MSD enables the maintenance of complex, stable salivary microcosms and represents a simple, reproducible tool for modelling individual oral bacterial ecosystems.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the utility of the MSD for studying the micro-ecology of the oral cavity.

PCR-based diagnostics for anaerobic infections

Conventional methods to identify anaerobic bacteria have often relied on unique clinical findings, isolation of organisms, and laboratory identification by morphology and biochemical tests (phenotypic tests). Although these methods are still fundamental, there is an increasing move toward molecular diagnostics of anaerobes. In this review, some of the molecular approaches to anaerobic diagnostics based on the polymerase chain reaction (PCR) are discussed. This includes several technological advances in PCR-based methods for the detection, identification, and quantitation of anaerobes including real-time PCR which has been successfully used to provide rapid, quantitative data on anaerobic species on clinical samples. Since its introduction in the mid-1980s, PCR has provided many molecular diagnostic tools, some of which are discussed within this review. With the advances in micro-array technology and real-time PCR methods, the future is bright for the development of accurate, quantitative diagnostic tools that can provide information not only on individual anaerobic species but also on whole communities.

Effects of quaternary-ammonium-based formulations on bacterial community dynamics and antimicrobial susceptibility

Quaternary ammonium compounds (QACs) are widely used as adjuncts to hygiene in domestic cleaning products. Current concern that the increased use of such biocides in consumer products might contribute to the emergence of antibiotic resistance has led us to examine the effects of a QAC-containing domestic cleaning fluid on the population dynamics and antimicrobial susceptibility of domestic sink drain biofilm communities. QAC susceptibilities of numerically dominant, culturable drain bacteria (15 genera, 17 species) were determined in vitro before and after repeated QAC exposure (14 passages). A fully characterized drain microcosm was then exposed to short-term (12 days) and long-term (3 months) dosing with a QAC-containing domestic detergent (QD). QAC exposure of isolated cultures caused both increases (three species) and circa twofold decreases (six species) in QAC susceptibility. The susceptibility of Ralstonia sp. was considerably decreased following 14 consecutive QAC passages. Control drain microcosm biofilms maintained dynamic stability, as evidenced by culture and denaturing gradient gel electrophoresis (DGGE) analysis. Bacterial population densities were largely unaffected during short-term exposure to use levels of QD, although 50% QD caused circa 10-fold viability reductions. DGGE analysis supported these observations; identified the major microcosm genera as Pseudomonas, Pseudoalteromonas, Erwinia, and Enterobacter, and showed that aeromonads increased in abundance under 10 to 50% QD. Long-term exposure of the microcosms to QD did not significantly alter the pattern of antimicrobial susceptibility. These data demonstrate the recalcitrance of domestic drain biofilms toward QAC and that although repeated QAC exposure of drain isolates in pure culture results in susceptibility change in some test bacteria, such changes do not necessarily occur within complex communities.