The polio eradication endgame: Why immunization and continued surveillance is critical.

The poliovirus is very close to being eradicated from the world. To this end, the four main objectives of the World Health Organization's Polio Eradication & Endgame Strategic Plan 2013-2018 are to: detect and interrupt all poliovirus transmission; strengthen immunization systems and withdraw oral polio vaccine; contain poliovirus and certify interruption of transmission; and plan polio's legacy. There is a need to maintain vigilance for circulating vaccine-derived polioviruses as well as maintaining both epidemiological and laboratory surveillance for polio at this critical point in history. Despite the elimination of indigenous wild poliovirus transmission in Canada, the risk of wild poliovirus importation from endemic countries, and the risk of importation of circulating vaccine strains remains. Due to this ongoing risk, active surveillance of acute flaccid paralysis (AFP) in children less than 15 years of age remains important. At least one stool specimen from all suspect AFP cases should be sent to the National Microbiology Laboratory at the Public Health Agency of Canada for polio isolation and testing to support and verify Canada's polio-free status. An added benefit of this is that it may also help identify other non-polio enteroviruses, such as enterovirus D68.

National surveillance for non-polio enteroviruses in Canada: Why is it important?

A widespread outbreak of enterovirus D68 (EV-D68) was detected in association with respiratory illness in children across Canada and the United States during the autumn of 2014. The majority of cases were mild, but some were associated with more severe illness requiring hospitalization; some of the cases also had neurological symptoms including paralysis, and three deaths were reported in British Columbia. EV-D68 is one of many enteroviruses that include Coxsackieviruses, echovirusesand polio virus. Other than polio virus, there are no vaccines available for the prevention of enterovirus infections, nor are there any antiviral medications that have been approved for their treatment. More than 46 different serotypes have been identified to be circulating in Canada over the last 25 years. Until 2014, EV-D68 was rare. Routine genotyping surveillance done by Canada's National Microbiology Laboratory (NML) identified only 85 isolates of EV-D68 between 1991 and 2013, while 282 were detected between July and October 2014. The complexity of the epidemiology of these enteroviruses demonstrates the need for genotype surveillance, to detect outbreaks spatially and temporally, to determine their relative incidence and impact on the population, and to investigate evolutionary trends, such as recombination events, that are thought to play an important part in strain variation and emergence of epidemic strains. In particular, it is important to carry out virological testing on unusual cases of paralysis in children, and to genotype and sequence any viruses identified. Submission of specimens (virus cultures, stool, cerebrospinal fluid or respiratory specimens) from any such cases to the National Centre for Enteroviruses at NML is encouraged.

Surveillance summary of hospitalized pediatric enterovirus D68 cases in Canada, September 2014.

BACKGROUND: Enterovirus D68 (EV-D68) has been detected infrequently and has not been associated with severe disease in Canada. In the early fall of 2014, following an unusual case increase in the United States, clusters of EV-D68 among children and some adults manifesting severe symptoms were reported in Canada. OBJECTIVE: To provide an initial epidemiological summary of pediatric cases hospitalized with EV-D68 in Canada. METHODS: A time-limited surveillance pilot was conducted collecting information on pediatric cases (less than 18 years of age) hospitalized with EV-D68 between September 1 and 30, 2014. RESULTS: In total, 268 cases were reported from Ontario (n=210), Alberta (n=45), and British Columbia (n=13). Of the 268 reported cases, 64.9% (n=174) were male; the sex difference was statistically significant (p<0.01). Age was reported for 255 cases, with a mean age for males of 5.4 years and for females of 5.3 years. For cases with data available, 6.8% (18/266) were admitted to an intensive care unit. Of those where clinical illness was recorded, respiratory illness alone was present in 98.3% (227/231), neurologic illness alone was present in 0.4% (n=1), and both illnesses were present in 0.9% of cases (n=2); cases with neither respiratory nor neurologic illness were rare (n=1). Of the 90 cases with additional clinical information available, 43.3% were reported as having asthma. No deaths were reported among the 268 cases. CONCLUSION: The EV-D68 outbreak in Canada in September 2014 represents the beginning of a novel outbreak associated with severe illness in children. These findings provide the first epidemiological summary of severe cases of EV-D68 as an emergent respiratory pathogen in Canada. The continued investigation of this pathogen is necessary to build on these results and capture the full spectrum of associated illness.

The effect of environmental pH on the physiology and surface structures of Salmonella serotype enteritidis phage type 4.

The incidence of food-poisoning caused by Salmonella serotype Enteritidis PT4 has increased. Implicated food products display pH levels between 4 and 9. Accordingly, the effect of growth at extremes of pH on the presence of surface structures and the carriage of a 38-MDa plasmid was determined by growing a clinical isolate of Enteritidis PT4 in a chemostat. Steady-state growth was possible over the pH range 4.35-9.45, corresponding to the pH extremes associated with key reservoirs implicated in outbreaks. Without pH control, cultures stabilised at pH 7.10. Growth at extremes of pH had significant effects on the distribution of cell surface structures; at pH 9.45, only 3% of cells were fimbriate compared with 52% at pH 7.10 and 20% at pH 4.35. The proportion of motile cells and the presence of flagella was also reduced at extremes of pH. A 38-MDa plasmid was present in cells grown in the chemostat at pH 7.10, but not in cells grown at pH 4.35 or pH 9.45. Thus, environmental pH may have a significant impact on the virulence potential of Enteritidis PT4.

Generalized hypervigilance in fibromyalgia: evidence of perceptual amplification.

The hypervigilance model of pain perception states that chronic pain patients have a heightened sensitivity to pain (e.g. low threshold and tolerance) because of increased attention to external stimulation and a preoccupation with pain sensations. This study tested the hypothesis that individuals with fibromyalgia, a chronic pain disorder of undetermined origin, have a generalized hypervigilant pattern of responding that extends beyond the pain domain. Twenty fibromyalgia out-patients, 20 rheumatoid arthritis (RA) patients, and 20 normal controls served as subjects. The RA and normal control subjects were age and sex matched to the fibromyalgia patients. Subjects were tested for pain tolerance, pain threshold, and noise tolerance and were asked to complete a number of questionnaires that assessed hypervigilance. As predicted, the responses of the fibromyalgia patients to both the pain and auditory stimuli were consistent with the generalized hypervigilance hypothesis. These patients had significantly lower threshold and tolerance values than the RA patients, who in turn, had lower values than the normal control subjects. The results of the psychological questionnaires revealed that the fibromyalgia and RA patients preferred lower levels of external stimulation than the control subjects. The outcome of this study supports the generalized hypervigilance hypothesis, suggesting that fibromyalgia patients have a perceptual style of amplification. The implications of these findings for understanding the role of biological, cognitive, and perceptual factors in pain disorders are discussed.

Survival of Salmonella enteritidis Pt4 and Salm. typhimurium Swindon in aerosols.

Small particle aerosols of plate-grown Salmonella enteritidis and Salm. typhimurium were generated and maintained within a rotating drum at 75% relative humidity and 24 degrees C for 2 h. Plate-grown organisms were found to be more aerosol-stable than broth-grown organisms. Differences were observed between the two species; plate-grown Salm. typhimurium retained 100% viability after 2 h compared to approximately 70% for plate-grown Salm. enteritidis. A large proportion of cells of both serotypes remained viable in aerosols after 2 h, confirming the potential for airborne transmission for these organisms, e.g. within henhouses and during food processing.

The effect of litigation status on adjustment to whiplash injury.

STUDY DESIGN: This retrospective study examined the effect of civil litigation on reports of pain and disability in chronic pain patients who sustained whiplash injuries after a motor vehicle accident. OBJECTIVES: To examine the effect of litigation on adjustment to chronic pain. SUMMARY OF BACKGROUND DATA: A common methodologic weakness with many studies in this area is the composition of the nonlitigant group, which often includes individuals who have completed litigation as well as those who opted not to litigate. This introduces a confound in that litigant and nonlitigant groups differ not only with respect to litigation status but with respect to any factors that predispose one to litigate. METHODS: Questionnaire data were obtained from 41 patients (current litigants) in the process of litigation and 21 patients (postlitigants) who had completed litigation. Subjects completed self-report measures assessing demographic characteristics, psychological distress, sleep disturbance, employment status, and various pain indices. RESULTS: There were no significant group differences in demographic characteristics, employment status, or psychological distress. Litigants, however, reported more pain than did postlitigants. Group differences in pain reports remained statistically significant even after controlling for length of time since accident and initial severity of the injuries. CONCLUSIONS: That litigation status did not predict employment status suggests that secondary gain does not figure prominently in influencing the functionality of these patients. The rather robust effect of litigation status on pain reports is discussed with respect to the potential mediational role of the stress of litigation.

The reliability of examination for tenderness in patients with myofascial pain, chronic fibromyalgia and controls.

OBJECTIVE: To establish the reliability with which tenderness could be evaluated in patients with chronic myalgias, using dolorimetry and palpation. METHODS: Three blinded examiners using pressure dolorimetry and digital palpation compared 19 paired tender points and 8 paired control points in 4 matched groups of 6 patients with fibromyalgia (FM), myofascial pain, pain controls, and healthy controls. RESULTS: Good interrater and test-retest reliability were found for dolorimetry scores. There were significant differences in tenderness ratings by dolorimetry between the diagnostic groups, with the patients with FM and myofascial pain having the greatest tenderness, the normals having the least tenderness, and the pain controls having tenderness levels midway between the patients with FM or myofascial pain and the normals. In all patients, control points had higher pain thresholds than tender points. One-third of patients with localized pain complaints demonstrated a significant relationship between region of clinical pain complaint and measured tenderness thresholds by dolorimetry. In ratings of tenderness by digital palpation, there was very good intrarater reliability over 26 of 27 paired points, and good interrater reliability at 75% of the points. One-half of patients with localized pain complaints demonstrated a significant relationship between region of clinical pain complaint and number of tender points by palpation. CONCLUSION: Both dolorimetry and palpation are sufficiently reliable to discriminate control patients from patients with myofascial pain and FM, but may not discriminate patients with myofascial pain from those with FM. Neither method appears to correlate well with the location of the clinical pain complaint, regardless of diagnosis.

The effect of growth rate and haemin on the virulence and proteolytic activity of Porphyromonas gingivalis W50.

Porphyromonas gingivalis strain W50 was grown under haemin-limitation and haemin-excess conditions in a chemostat at pH 7.5. The maximum specific growth rate (mumax) was determined at both haemin concentrations (mumax = 0.236 +/- 0.052 and 0.271 +/- 0.039 h-1, respectively). This enabled dilution rates to be adjusted so that the virulence and enzyme activity of haemin-limited and haemin-replete cells could be compared at identical relative growth rates (murel) of 0.25, 0.50 and 0.75 of their respective mumax. The data showed that the fastest growing cells were significantly more virulent than those grown more slowly, irrespective of haemin concentration. However, at each growth rate tested, cells grown under haemin-excess conditions were always more virulent than haemin-limited cells. Trypsin-like enzyme activity of whole cultures was also greater at each growth rate under haemin-excess conditions while, conversely, collagenolytic activity was generally higher in haemin-limited cultures. Thus, although growth rate had an effect on the virulence and enzyme activity of P. gingivalis, the availability of haemin for growth was the most significant factor.

The impact of contextual cues on the interpretation of and response to physical symptoms: a vignette approach.

This study examined the impact of two contextual cues--stress and aging--on conceptualizations of, and health care responses to, physical symptoms. Eighty-three undergraduates each read four vignettes describing a woman experiencing physical symptoms indicative of either heart attack, depression, ulcer, or flu. Subjects were randomly assigned to one of six age/stress cue combinations. Consistent with predictions, physical symptoms presented with stress cues were less likely to be attributed to acute illness and were seen as more variable. The effect was most pronounced for heart attack symptoms, which, when presented with stress cues, were also less likely (1) to be identified as a heart attack, (2) to be attributed to chronic illness, (3) to elicit recommendations to seek medical care, (4) and to be regarded as serious. The age manipulation did not exert an effect. Implications of these findings and limitations of the vignette approach are discussed.

Comparison of properties of collected cells and cells from the culture vessel during continuous culture of Streptococcus mutans Ingbritt.

In continuous-culture studies chemostat effluents are usually collected into a receiving flask in an ice bath to obtain enough cells for an experiment. It is assumed that the properties of these are not significantly different from those of the culture in the chemostat vessel. This assumption has been tested for the dental pathogen Streptococcus mutans Ingbritt. Collected supernatant fluid and cells were compared with supernatant fluid and cells taken directly from the culture vessel, for four major groups of culture properties: viability and biomass, concentrations of metabolites and nutrients, activities of selected enzymes, and glycolytic rates. The assumption held true except for glycolytic rate during endogenous metabolism. It is suggested that comparison of collected and culture vessel cells is an important control which should be done in all continuous culture studies of microbial physiology and biochemistry, but that the properties of Strep. mutans cells collected on ice up to 16 h do reflect those of cells actively growing in the chemostat.

Ultrastructure and enzyme activities of a virulent and an avirulent variant of Bacteroides gingivalis W50.

The ultrastructure and enzyme activity of an avirulent, weakly-pigmenting, colonial variant (W50/BE1) was compared with that of the highly-virulent parent strain, Bacteroides gingivalis W50, in an attempt to identify significant virulence factors. Electron microscopy of thin sections of the organisms showed strain W50 to possess a 3-4-fold thicker layer of material external to the outer membrane. No significant differences between the strains were found with respect to collagen- or hyaluronic acid-breakdown activities at assay pH 7.5. However, cultures of strain W50 had over 3-fold more trypsin-like activity (P less than 0.01) than the avirulent variant. These results, when taken with other data, suggest that a thick external layer on the cell surface together with high trypsin-like activity might be important virulence factors of B. gingivalis.

Isolation of colonial variants of Bacteroides gingivalis W50 with a reduced virulence.

The spontaneous appearance of unusual colony forms was observed during prolonged growth of Bacteroides gingivalis W50 in a chemostat. Two variants were selected for further study which could be distinguished from the parent strain by the rate and intensity of pigmentation of their colonies. For example, after anaerobic incubation for 14 days, variant W50/BR1 produced brown colonies whereas those of the parent strain were black; in contrast, variant W50/BE1 did not show signs of pigmentation until incubation had continued for 21 days. In subsequent studies in the chemostat, variant W50/BE1 bred true even after prolonged growth whereas other colony forms appeared after incubation of variant W50/BR1 for 14 days. The relatedness of W50/BR1 and W50/BE1 to the parent strain was confirmed by comparisons of the whole-cell fatty-acid profiles, the patterns of pre-formed enzymes and by the metabolic end products after growth. However, the variants did differ from the parent strain in their virulence in a mouse pathogenicity model. The parent strain killed all mice given infective doses greater than 5 x 10(8) cfu whereas W50/BR1 was much less virulent (2 out of 10 mice killed and higher infective doses needed for higher mortality rates) and W50/BE1 was avirulent at all infective doses tested.

Effect of environmental pH on enzyme activity and growth of Bacteroides gingivalis W50.

Since the pH of the gingival crevice increases from below neutrality in health to above pH 8 in disease, we decided to investigate the effect of environmental pH on the growth and enzyme activity of Bacteroides gingivalis W50. Cells were grown in a chemostat under hemin-excess conditions over a range of pH values; stable growth was observed only between pH 6.7 and 8.3, with the maximum yields obtained between pH 7.0 and 8.0. The enzyme profile of cells varied markedly with pH. Enzymes with a specificity for gingival connective tissue (collagenase, hyaluronidase) were produced optimally at or below neutral pH, whereas trypsinlike activity increased with the growth pH and was maximal at pH 8.0. Chymotrypsinlike activity was generally low, although its activity was highest at the extremes of growth pH, i.e., at pH 6.7 and 8.3. Inhibitor studies provided evidence that the breakdown of collagen involved the concerted action of both a collagenase and the trypsinlike enzyme. The ratio of trypsin to collagenolytic activity rose from 1:1 during growth at neutral pH and below to almost 7:1 during growth at pH 8.3. Thus B. gingivalis appears to be uniquely adapted as a periodontopathic organism in that under environmental conditions likely to prevail during the initial stages of pocket development it produces maximally those enzymes with a tissue-damaging potential. Then, as the pH of the pocket rises during the host inflammatory response, the activity of the trypsinlike enzyme increases markedly, which may enable cells to inactivate key components of the host defenses such as immunoglobulins and complement.

A mixed-culture chemostat system to predict the effect of anti-microbial agents on the oral flora: preliminary studies using chlorhexidine.

A mixed-culture chemostat system, composed of nine bacterial species representative of plaque in health and disease, has been assessed as an improved laboratory method of evaluating the likely in vivo effects of antimicrobial agents used in dentistry. The advantages of the system include reproducibility, the long-term stable cultivation of bacteria under controllable conditions, and repeated sampling, for bacteriological and biochemical studies, without disrupting the stability of the community. The effects of (i) the continuous provision of chlorhexidine (CHX) and (ii) three pulses of CHX (final concentration in both experiments = 0.24 mmol/L) on the composition of the chemostat communities were monitored. Only L. casei survived the continuous provision of CHX; the other bacteria were killed and were lost at different rates which generally corresponded to their known sensitivities to CHX. After each CHX pulse, the numbers of bacteria fell markedly. Again, L. casei was least affected, while A. viscosus, B. intermedius, and F. nucleatum were temporarily undetectable but returned to their original levels within 2-4 generation times. Counts of S. mutans were affected more by CHX than those of S. sanguis or S. mitior. The effect of successive pulses of CHX on the viability of some bacteria and on acid production (as measured by pH-fall experiments) decreased, suggesting that adaptation to CHX had occurred. The fact that the in vitro observations paralleled previous clinical findings suggests that the mixed-culture system could be used as a predictive model of the probable effect on the oral flora of new anti-microbial agents prior to expensive trials in animals or human volunteers.

Protonmotive force driven 6-deoxyglucose uptake by the oral pathogen, Streptococcus mutans Ingbritt.

Streptococcus mutans Ingbritt was grown in glucose-excess continuous culture to repress the glucose phosphoenolpyruvate phosphotransferase system (PTS) and allow investigation of the alternative glucose process using the non-PTS substrate, (3H) 6-deoxyglucose. After correcting for non-specific adsorption to inactivated cells, the radiolabelled glucose analogue was found to be concentrated approximately 4.3-fold intracellularly by bacteria incubated in 100 mM Tris-citrate buffer, pH 7.0. Mercaptoethanol or KCl enhanced 6-deoxyglucose uptake, enabling it to be concentrated internally by at least 8-fold, but NaCl was inhibitory to its transport. Initial uptake was antagonised by glucose but not 2-deoxyglucose. Evidence that 6-deoxyglucose transport was driven by protonmotive force (delta p) was obtained by inhibiting its uptake with the protonophores, 2,4-dinitrophenol, carbonylcyanide m-chlorophenylhydrazine, gramicidin and nigericin, and the electrical potential difference (delta psi) dissipator, KSCN. The membrane ATPase inhibitor, N,N1-dicyclohexyl carbodiimide, also reduced 6-deoxyglucose uptake as did 100 mM lactate. In combination, these two inhibitors completely abolished 6-deoxyglucose transport. This suggests that the driving force for 6-deoxyglucose uptake is electrogenic, involving both the transmembrane pH gradient (delta pH) and delta psi. ATP hydrolysis, catalysed by the ATPase, and lactate excretion might be important contributors to delta pH.

The effect of lowering the pH on the composition and metabolism of a community of nine oral bacteria grown in a chemostat.

Nine oral bacteria, associated with both healthy and diseased sites in the mouth, were grown at D = 0.05 h-1 (mean generation time 13.9 h) in a glucose-limited chemostat. After an initial period of steady-state growth at pH 7.0, pH control was discontinued. The pH then decreased until it stabilized at pH 4.1 after 9 d (16 generations), while the Eh rose from -165 mV to +160 mV. The lowering in pH resulted in the composition and metabolism of the flora being altered and in increased bacterial aggregation. At pH 7.0, 'Streptococcus mitior', Veillonella alcalescens and S. sanguis were most numerous while at pH 4.1 the counts of all bacteria fell except for Lactobacillus casei, which became predominant. The proportions of S. mutans within the community also increased while S. sanguis was recovered only occasionally and Bacteroides intermedius was not detected below pH 4.6. The survival at pH 4.1 of several other species would not have been predicted from earlier pure culture studies. Relative to pH 7.0, the community growing at pH 4.1 produced more lactic acid, washed cells had a greater glycolytic activity over a wider pH range but amino acid metabolism decreased. In general, when pH control was restored, so were the original patterns of metabolism and bacterial counts, except for B. intermedius, which was still not detected. The inverse relationship between S. sanguis and S. mutans, and the increase in proportions of L. casei and S. mutans during growth in a low pH environment parallel observations made in vivo and suggest that the chemostat can be used as a model for microbial behaviour in dental plaque.

Effect of hemin on the physiology and virulence of Bacteroides gingivalis W50.

Bacteroides gingivalis W50 was grown in a chemostat under steady-state conditions at pH 7.5 +/- 0.2 and a constant growth rate of 6.9 h for periods of up to 6 weeks (146 bacterial generations) in a complex medium. Hemin was capable of limiting the growth of cells up to a concentration of approximately 0.5 micrograms/ml since higher concentrations of hemin did not increase cell yields; cells grew in the absence of exogenously added vitamin K1. Only a limited number of amino acids was metabolized during growth, but because none of these was totally depleted, the limiting nutrient under hemin excess conditions was probably a peptide. A range of fermentation products was produced under all conditions of growth; higher concentrations of cytotoxic metabolites such as propionate and butyrate were formed under hemin excess conditions, although more ammonia was released under hemin limitation. When viewed by electron microscopy, cells grown under hemin limitation appeared to be either coccobacillary or short rods and possessed few fimbriae per cell, but large numbers of extracellular vesicles could be seen both surrounding the cell surface and free in the environment. In contrast, cells grown under hemin excess conditions were more commonly coccus shaped and were more heavily fimbriated but had fewer extracellular vesicles. Marked differences were found in the susceptibility of mice to infection with cells grown under different concentrations of hemin. Cells transferred to media without any added hemin were avirulent, whereas those grown under conditions of hemin limitation (0.33 and 0.40 micrograms/ml) produced a 20 and 50% mortality in mice, respectively. In contrast cells grown under hemin excess always caused 100% mortality in mice, although this virulence was dose dependent. When virulent, the bacteria caused an extensive, spreading infection with necrosis of the skin and subcutaneous tissues. Collagen disintegration was seen histologically, implying a role for collagenase production in the pathogenicity of these bacteria.

Environmental regulation of carbohydrate metabolism by Streptococcus sanguis NCTC 7865 grown in a chemostat.

Carbohydrate metabolism by the oral bacterium Streptococcus sanguis NCTC 7865 was studied using cells grown in a chemostat at pH 7.0 under glucose or amino acid limitation (glucose excess) over a range of growth rates (D = 0.05 h-1-0.4 h-1). A mixed pattern of fermentation products was always produced although higher concentrations of lactate were formed under amino acid limitation. Analysis of culture filtrates showed that arginine was depleted from the medium under all conditions of growth; a further supplement of 10 mM-arginine was also consumed but did not affect cell yields, suggesting that it was not limiting growth. Except at the slowest growth rate (D = 0.05 h-1) under glucose limitation, the activity of the glucose phosphotransferase (PTS) system was insufficient to account for the glucose consumed during growth, emphasizing the importance of an alternative method of hexose transport in the metabolism of oral streptococci. The PTS for a number of sugars was constitutive in S. sanguis NCTC 7865 and, even though the cells were grown in the presence of glucose, the activity of the sucrose-PTS was highest. The glycolytic activity of cells harvested from the chemostat was affected by the substrate, the pH of the environment, and their original conditions of growth. Glucose-limited cells produced more acid than those grown under conditions of glucose excess; at slow growth rates, in particular, greater activities were obtained with sucrose compared with glucose or fructose. Maximum rates of glycolytic activity were obtained at pH 8.0 (except for cells grown at D = 0.4 h-1 where values were highest at pH 7.0), while slow-growing, amino acid-limited cells could not metabolize at pH 5.0. These results are discussed in terms of their possible significance in the ecology of dental plaque and the possible involvement of these bacteria in the initiation but not the clinical progression of a carious lesion.

The establishment of reproducible, complex communities of oral bacteria in the chemostat using defined inocula.

Nine commonly isolated oral bacterial populations were inoculated into a glucose-limited and a glucose-excess (amino acid-limited) chemostat maintained at a constant pH 7.0 and a mean community generation time of 13.9 h. The bacterial populations were Streptococcus mutans ATCC 2-27351, Strep. sanguis NCTC 7865, Strep. mitior EF 186, Actinomyces viscosus WVU 627, Lactobacillus casei AC 413, Neisseria sp. A1078, Veillonella alkalescens ATCC 17745, Bacteroides intermedius T 588 and Fusobacterium nucleatum NCTC 10593. All nine populations became established in the glucose-limited chemostat although Strep. sanguis and Neisseria sp. were present only after a second and third inoculation, respectively. In contrast, even following repeated inoculations, Strep. mutans, B. intermedius and Neisseria sp. could not be maintained under glucose-excess conditions. A more extensive pattern of fermentation products and amino acid catabolism occurred under glucose-limited growth; this simultaneous utilization of mixed substrates also contributed to the higher yields (Y molar glucose) and greater species diversity of these communities. Microscopic and biochemical evidence suggested that cell-to-cell interactions and food chains were occurring among community members. To compare the reproductibility of this system, communities were established on three occasions under glucose-limitation and twice under glucose-excess conditions. The bacterial composition of the steady-state communities and their metabolic behaviour were similar when grown under identical conditions but varied in a consistent manner according to the nutrient responsible for limiting growth. Although a direct simulation of the oral cavity was not attempted, the results show that the chemostat could be used as an environmentally-related model to grow complex but reproducible communities of oral bacteria for long periods from a defined inoculum.