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Once upon a time, there was a little girl named Goldilocks. She went for a drive in the city. Pretty soon, she came upon three roadways. Goldilocks was worried about [...]

Roadway lighting offers significant safety benefits but also represents a substantial share of the operating budgets of agencies tasked with maintaining the lighting infrastructure. Standard practice requires that roadway lighting [...]

Whether you call them aerial lifts, cherry pickers or long scissoring arms with a person basket at the end, bucket trucks are vital to the installation and maintenance of an [...]

Even though drivers disregarding a stop sign is widely considered a major contributing factor for crashes at unsignalized intersections, an equally important problem that leads to severe crashes at such locations is misjudgment of gaps. This paper presents the results of an effort to fully understand gap acceptance behavior at unsignalized intersections using SHPR2 Naturalistic Driving Study data. The paper focuses on the findings of two research activities: the identification of critical gaps for common traffic/roadway scenarios at unsignalized intersections, and the investigation of significant factors affecting driver gap acceptance behaviors at such intersections. The study used multiple statistical and machine learning methods, allowing a comprehensive understanding of gap acceptance behavior while demonstrating the advantages of each method. Overall, the study showed an average critical gap of 5.25 s for right-turn and 6.19 s for left-turn movements. Although a variety of factors affected gap acceptance behaviors, gap size, wait time, major-road traffic volume, and how frequently the driver drives annually were examples of the most significant.

Crashes involving roadway objects can cause severe injuries and property damage. Utilizing data from the Second Strategic Highway Research Program (SHRP 2) naturalistic driving study (NDS), this study investigated crashes involving roadway objects and their implications for the potential of machine vision-based driving systems in preventing such crashes. A comprehensive statistical and machine learning analysis was first conducted to identify major factors affecting the occurrence and severity of such events. Machine vision performance metrics (based on the SHRP 2 NDS cameras) and human driving decisions were then analyzed to identify opportunities where machine vision systems could particularly mitigate risk factors. The results suggest that driver behaviors/errors, speed, reaction time, and object characteristics played the most significant role in the occurrence and severity outcome of the SHRP 2 events. The average object detection distance based on the SHRP 2 cameras was approximately 20 m for all objects. The average reaction time provided by the SHRP 2 cameras was 1.5 s for all events but 1.1 s for events involving animals and roadway debris. In general, the machine vision reaction time was longer than the driver reaction time for approximately 95% of all analyzed events and 75% of the events in which drivers reacted before collisions. Drivers were able to make safe evasive maneuvers in 56% of all analyzed events and 72% events involving roadway debris and animals. Based on these results, the paper discusses in detail when and how machine vision systems could assist in preventing crashes involving roadway objects.

ABSTRACTLight levels recommended for parking facilities should be backed by empirical research that accounts for all users. In the current study, pedestrians’ and drivers’ visual performance and their perceptions of safety, comfort, and visibility were evaluated at a parking garage and at parking lots with asphalt and concrete pavements under three light source types (high-pressure sodium luminaire, 3000 K light emitting diode [LED] luminaire, and 5000 K LED luminaire) and at multiple light levels. Visual performance involved facial and hand recognition, wheel stop detection, detection of a side-facing pedestrian, and detection of a vehicle backing up from a parking spot. Perceptions of safety, comfort, and visibility were assessed by means of a questionnaire. Results showed that in the parking garage, an increase in light level beyond 10 lux of average horizontal pavement illuminance did not result in a statistically significant increase in visual performance or perceptions of safety, comfort, and visibility. For parking lots of asphalt and concrete pavements, this plateauing was observed at the 2 lux light level. No statistical differences were observed between the light source types for the visual performance tasks, but the perceptions of safety, comfort, and visibility were highest for the 5000 K LED luminaires.

A systems-level approach to intersection lighting design has shown that illuminating the intersection box increases drivers’ nighttime visual performance. However, for an intersection lighting design to be effective and accepted, it should not only maximize visual performance but also enhance perceived visibility and minimize glare. The goals of this study were to assess the effects of different intersection lighting designs on these two outcomes. Visibility was assessed with respect to a pedestrian, several targets, and an intersection. Perceptions of visibility and glare were measured using Likert scales, with participants exposed to multiple lighting designs on a realistic intersection. Twenty-four participants completed the study, with an equal number of younger (18–35 years) and older (65+) drivers. The lighting design that illuminated the intersection box had the highest levels of perceived target and intersection visibility and the lowest ratings of glare. For the same lighting configuration, a strong positive correlation was also found between perceived target visibility and previous results on target detection distances. In this configuration, perceived visibility plateaued between 7 and 10 lux of mean intersection illuminance. Increased levels of perceived visibility in different conditions were likely a result of size and contrast differences, and the distribution of the luminaires used. These results suggest that illuminating the intersection box has multiple benefits, in that it not only increases visual performance but also increases perceived visibility and reduces glare.

Portable light towers are a significant source of glare to motorists entering a work zone. Although existing research has evaluated the effect of light tower orientation on visibility and glare, the effects of factors like mounting height, offset distance from the roadway, and number of light towers in the work zone, on visual performance and discomfort glare is not known. Understanding these relationships can help in developing illuminating guidelines for work zones that can reduce glare for drivers. The goal of this paper is to understand the effect of mounting height, offset distance to the roadway, and number of light towers in the work zone on drivers’ visual performance and discomfort glare. Participants drove through a realistic work zone and evaluated portable light towers in varying mounting heights, offset distances, and number of light towers in the work zone. Results showed that the mounting height and offset distances play a critical role in affecting the driver’s visual performance and discomfort glare rating. Portable light towers, irrespective of wattage and lumen output, at lower than a mounting height of 20 ft and closer to the roadway result in decreasing driver visual performance and increasing their discomfort glare. Portable light towers should be mounted at a height of at least 20 ft and balloon light towers with higher wattage (4,000 W and greater) and lumen output (400,000 lumens and greater) should be located at an offset distance of at least 10 ft from the roadway.

Virtual reality (VR) can be a very effective tool to evaluate built environment to support improvement of pedestrian and other vulnerable road user safety. However, in order to draw actionable conclusions from VR it is important to understand the degree to which pedestrians’ perceptions and behaviors match across real and virtual environments. In this study, participants experienced equivalent real and virtual environments and performed similar tasks in each. Tasks included pedestrian’ intention to cross, estimation of speed and distance of an approaching vehicle, and the perceived safety and risk of crossing a road. Pedestrians’ presence was also measured in all environments. Result showed that there were no differences between the real and virtual environments for most of the tasks. Significant differences between real and virtual environments were observed in the estimation of speed and measures of presence. These results have important implications for using VR as tool to evaluate pedestrian safety in built environments.

ABSTRACTNighttime crashes at intersections present a major traffic safety issue in the United States. Existing approaches to intersection lighting design do not account for a driver’s visual performance or the potential interactive effects of vehicle headlamps and roadway lighting. For effective design lighting at intersections, empirical research is required to evaluate the effects of lighting configuration (part of the intersection illuminated) and lighting levels on nighttime driver visual performance. The current study had two goals: First, to quantify visual performance in three lighting configurations (illuminating the intersection box, approach, or both) and second, to determine what lighting levels within each lighting configuration support the best visual performance. The study involved a target detection task completed at night on a realistic roadway intersection. Illuminating the intersection box led to superior visual performance, as indicated by longer target detection distances, fewer missed targets, and more targets identified within a safe stopping distance. For this lighting configuration, visual performance plateaued between 7 and 10 lx of mean intersection illuminance. These results have important implications for the design of intersection lighting at isolated/rural intersections, specifically that illuminating the intersection box is an effective strategy to increase nighttime visual performance for a wider range of driver ages and could also be an energy-efficient solution.

Nighttime crashes at work zones are major concerns for construction workers and motorists. Although in a majority of the U.S. states, department of transportation specifications for work zone lighting mention that contractors should reduce glare for workers and drivers, only two states advocate detailed specifications like light positions, orientation, and light levels. Although some studies have examined the impact of glare from work zone lights on workers and others have calculated veiling luminance levels for drivers in the work zone, the effect of work zone lighting on drivers’ visual performance and glare perception has never been studied in a realistic setting. The goal of this study was to understand the impact of commercially available portable light towers (metal halide, LED, and balloon) and their orientation on drivers’ visual performance and their perceptions of glare. Participants drove through a realistic work zone simulated on the Virginia Smart Road. Visual performance was assessed by a detection task and perception of visibility and glare were assessed by questionnaires. Results indicated that the type of light tower and its orientation affect visual performance and perceptions of visibility and glare. Light towers aimed toward the driver resulted in lowering drivers’ visual performance, both objectively and subjectively. When the light towers were aimed away from or perpendicular to the driver, the visual performance was higher and the differences in visual performance between the types of light towers were minimal. These findings indicate that these orientations should be preferred for work zone light towers.

The limited information in traditional safety data makes exploration of the complex interaction between characteristics of roadway lighting and crash risks and driver behavior difficult, yet this knowledge is needed by transportation agencies that want to reduce energy consumption while maintaining safety. Data from the SHRP 2 Naturalistic Driving Study (NDS) have provided researchers a powerful tool for safety analysis. In addition, the availability of a massive adaptive lighting database (ALD) has made it possible to evaluate and improve the use of roadway lighting as a safety countermeasure. This paper integrates ALD and NDS data and provides insight into how other spatially related data can be integrated with the NDS data to cater to the needs of safety studies. The ALD includes detailed in situ roadway lighting measurements for more than 2,000 mi of major roads in seven states. This paper fills a gap in NDS-related documentation by detailing the NDS database structure and elements. An efficient spatial approach for integrating NDS data with ALD or other large roadway-related data sets in a similar format is presented. The approach uses a combination of existing and custom geographic information system tools, including a hybrid tool that uses attributes to perform the ArcGIS Near function.

Almost all existing research about intersection lighting indicates that the presence of lighting reduces nighttime crashes. This study aimed to quantify the effect of lighting level and lighting quality on the night-to-day (ND) crash ratios at rural intersections. Illuminance measurements were collected from 99 lighted and unlighted rural intersections in Virginia. The measurements were then combined with the crash data, obtained from the Virginia Department of Transportation, for each of the intersections. A negative binomial regression was used to model the crash and lighting data. Results indicated that lighting level (average horizontal illuminance) significantly affected the ND crash ratios at rural intersections. A 1 lux (lx) increase in the average horizontal illuminance at all rural intersections in Virginia corresponded to a 7% decrease in the ND crash ratio. For the lighted intersections, a 1 lx increase in average horizontal illuminance corresponded to a 9% decrease in the ND crash ratio. The largest decrease in the ND crash ratio was for unlighted intersections, where a 1 lx increase in the average horizontal illuminance corresponded to a 21% decrease. Stop-controlled intersections had smaller ND crash ratios than signalized intersections. Intersections with a posted speed limit of less than or equal to 40 mph had lower ND crash ratios than intersections with a posted speed limit of greater than 40 mph. Each of the results is discussed with respect to the impacts of the lighting measurements on nighttime driving safety and overall visibility.

Adaptive lighting is an approach to lighting design that proposes to change the light level on a roadway on the basis of the needs of drivers. A review of the literature and building the connection between crashes and light level allowed the development of a system to select roadway luminance levels and then modify these levels on the basis of the needs of the driver. This adaptive lighting system uses parameters such as traffic volume, ambient light levels, pavement marking quality, intersection density, and, most important, the presence of pedestrians to allow lighting design criteria to be selected through a weighting system. As these parameters (such as traffic volume) change, a new light requirement is determined, and the lighting system can be adjusted with controllable luminaires and a master control system. Guidelines for the implementation of this system and an example are provided.

This paper describes the visibility experiment conducted as part of a research effort to establish the durability of pavement markings in an on-road installation. Six marking technologies were installed on a portion of Route 460 in Blacksburg, Virginia. A human factors experiment in natural rain conditions was performed to establish the visibility needs of the driver. The retroreflectivity of the markings was measured at intervals of 2 to 5 months, with six measurements over the course of 23 months (these data are discussed in a separate paper). Previous research suggested that a minimum retroreflectivity of 150 mcd/m2/lx should be maintained to meet drivers' visibility needs. As part of this research, a human factors experiment was conducted to test the validity of this recommendation. The distance at which participants could detect the end of a pavement marking was measured as well as the retroreflectivity of the marking at those points. The relationship of detection distance and retroreflectivity found in this study suggests that as retroreflectivity increases beyond 150 mcd/m2/lx, there are diminishing returns on detection distance. This finding suggests that the recommended minimum is appropriate for providing increased visibility for drivers, while keeping retroreflectivity requirements at a reasonable level for marking manufacturers.

This paper includes a review of the current methodologies used in the design of sag vertical curves, a review of the changes in headlamp technologies, the results of a survey of practitioners and two visibility experiments, and conclusions. The review of the headlamp technology shows that, over time, headlamp technologies have increasingly limited the amount of light emitted above the horizontal axis of the headlamp. In addition to the regulatory impact, headlamp technologies such as visually optically aligned systems also limit the upward divergence of the light beam from the longitudinal axis of the vehicle (uplight). The practitioner survey found that very few deviations from AASHTO design methodologies were used. On the basis of the practitioner review, the potential to modify current methodologies is limited to the manipulation of the vehicle speed, deceleration, and change in angle of curvature. The results of the visibility experiments showed that participants detected objects at distances that were significantly shorter than the stopping sight distance (SSD), not only in sag vertical curves but also on flat roadway. This finding indicated that even if sag vertical curves were redesigned, visibility distance would still be shorter than SSD because the headlamps would be the limiting factor. A review of the potential modifications to the design of sag vertical curves (which were suggested in the responses to the practitioner survey) found that these changes would be inadequate to make up the difference between visibility distance and SSD.

More than half of the pedestrian fatalities occur at night. It is important to understand the factors that lead to pedestrian detection for designing and implementing effective countermeasures in order to reduce pedes-trian fatalities. Research has shown that expectancy, motion and overhead lighting affect pedestrian visibil-ity. This goal of this study is to understand the combined effect of these three factors on nighttime visibil-ity. Twenty four participants were recruited to drive on a test track under different conditions of expectancy and overhead lighting. The participants were asked to identify static and moving objects. The results showed that as the level of expectancy increases the detection distances also increase. Moving objects were detected from farther than static objects and presence of overhead lighting also increased the detection dis-tances. Motion tends to draw more attention than expectancy when detecting new objects. These results have implications in the areas of pedestrian safety, novice driver training and work zone safety. They also reiterate the safety benefits of providing overhead lighting at high pedestrian-vehicle conflict areas.

Driving is often considered a visually oriented task. This visual task is constrained when drivers drive at night. Visibility is reduced because visual cues available during the day are not present at night. This study attempted to develop a link between driver safety and the nighttime visual environment. This research required creating and integrating new technology, observing and collecting data, and developing a model framework called the Dynamic Driver Visual Model (DDVM). Conceptually, a DDVM is a system of rules, statistics, and expectations that can be used to define how a driver collects visual information from the environment. Several information sources were investigated, and several dependent variables were identified. Data were collected on how information from signage, objects, lighting, pavement markings, and other vehicles moderates a driver's visual search of the roadway environment. Several logistic regression analyses were performed on the collected data to identify common characteristics to be implemented in the DDVM. These variables included age, lighting, vehicle headlamps, several different objects, glance time, target luminance, and contrast information. The results suggest that a number of target and visibility elements have nonlinear effects on a driver's detection performance at a variety of detection distances. This paper discusses the implications of these findings and the initial framework of the DDVM. Future research and additional data requirements are also discussed.

The purpose of this project was to develop a specification for the minimum retroreflectivity of pavement markings in wet nighttime conditions. For this specification to be established, the performance of four retroreflective pavement marking materials in wet night conditions was evaluated. The performance of the pavement markings was evaluated by driver participants under simulated rain conditions with a protocol similar to that of studies that had already been performed at the Virginia Tech Transportation Institute, Virginia Polytechnic Institute and State University. The performance of the markings was verified on the basis of the participants' ability to detect the end points of the markings in both rainy and clear conditions. This investigation reached the following conclusions: (a) The materials developed over recent years showed an improved performance over those tested previously. (b) The log-linear relationship found previously was functional for the data provided. Two models were developed. The model with no intercept provided a more constrictive boundary at low levels of retroreflectivity. (c) A retroreflectivity value above 250 millicandelas per square meter per lux (mcd/m2/lx) provided limited return in terms of detection distance. (d) A specification limit of 150 mcd/m2/lx provided adequate visibility for 55 mph in dry conditions and 40 mph in wet conditions with standard dry retroreflectivity measurements and 1 in./h measurements for wet conditions. This value should be the minimum maintained over the life of the marking. (e) The retroreflectivity specifications for a white and a yellow material should be equal. (f) The rumble stripe showed a significant recovery time improvement over the other tested materials. A minimum retroreflectivity of 150 mcd/m2/lx for white and yellow pavement markings in both dry and wet nighttime conditions is recommended.

A preliminary field test assessed the impact of splash and spray on road users. The test was part of a larger project sponsored by FHWA to develop a model that could characterize a highway's propensity to generate splash and spray during rainfall and the impact of this on road users. "Splash and spray" refers to water thrown into the air when a vehicle tire crosses a wet surface. For the experiment, participants observed videos recorded from the driver position of a vehicle as it traveled behind another vehicle in rain conditions. The videos were recorded on the Virginia Smart Road, and the rain conditions were created with a weather-making system. The full factorial design used two levels for each of the five variables: driver vehicle, spray vehicle, maneuver, rain rate, and speed. Participants rated each video for five categories: obstruction, concentration, confidence, control, and risk. In addition, an objective measure of visual obstruction, the occlusion factor, was recorded. Several factors and interactions were found to be significant for the subjective ratings, but significance varied depending on the category being rated. The occlusion factor was found to have a strong correlation with each of the ratings, and the lowest R2 value was .75. This correlation result suggests that the occlusion factor could be used to predict user perceptions of splash and spray.

Twenty-six participants evaluated a series of crosswalk lighting designs by visually detecting objects at each crosswalk location while traveling in a moving vehicle. The research was performed on a closed test track under nighttime conditions while the participants were driving an SUV with regular halogen headlamps. The conditions included several vertical illuminance levels (6, 10, 20, and 30 lux), varied luminaire types [highpressure sodium (HPS) and metal halide (MH)], and various target object types (pedestrian and surrogate objects). Only one age group of participants (66 years and older) was used for the study, with equal representation of males and females. The participants were asked to detect objects at each crosswalk location when they were confident an object was present. The results indicated that object detection distances changed on the basis of vertical illuminance level, luminaire type, and object type. Object detection distance for HPS was greatest at 30 vertical lux and for MH at 20 vertical lux. However, these results were moderated by the clothing color of the target object. When object color was considered, pedestrians in white clothing were identified earlier under the HPS lighting condition at 20 lux. Under the MH configuration, denim-clothed objects were detected earlier than black-clothed objects, especially at the 20-lux lighting level. The results suggest that a vertical illuminance level of 20 lux at crosswalk locations provides adequate levels for target object detection. In addition to benefiting from vertical illuminance, target objects that wore white clothing had detection distances superior to other object types of different clothing colors. Recommendations for crosswalk lighting configurations are further discussed.

Fifty-three participants evaluated the visibility of four different pavement marking materials under a simulated rain system operating at 0.8 in. (20 mm) of rain per hour at night while driving a vehicle on a closed test track. The conditions tested include a variable lighting condition, glare, pavement types, and two different vehicle types. The evaluation consisted of determining the detection distance of a start or an end point of a white 4-in. edge line. Results showed that lighting improved visibility and mitigated the effects of glare. Results also showed that the wet retroreflective tape provided the longest visibility distance, followed by equivalent performance of profile thermoplastic; large glass beads with standard paint provided the shortest visibility distance. The detection distance was compared with the retroreflective performance of the pavement marking technology. It was found that a log-linear relationship exists between the retroreflectivity and the detection distance. It was also found that the level of retroreflectivity provided by the materials tested did not provide adequate visibility distance for a sedan with a 2-s visibility time at speeds greater than 45 mph.

This project investigated the lighting levels required for crosswalk illumination. The current European methods for lighting suggest a crosswalk lighting level of 40 vertical lux for ensured safety. Two major questions were studied: the required vertical illuminance level for adequate pedestrian visibility and the selection of an object that could act as a surrogate for the pedestrian. The vertical illuminance was determined from an experiment that measured the visibility of pedestrians at lighting levels of 5, 20, 40, and 60 vertical lux. During the experiment, a crosswalk scene was presented to the participants and the time taken for identification of an object was measured. In addition to the lighting level, the conditions used in the experiment were lamp type (metal halide versus high-pressure sodium), the presence of glare, the use of overhead lighting, and the type of pedestrian clothing (white, black, and denim). The study found that a lighting design level of 20 vertical lux is likely adequate for proper pedestrian visibility. Except in selected cases, the lamp type was not significant. The impact of glare was not influenced by the lighting design. Three surrogate objects were developed for the experiment and were tested in the same manner as the pedestrians. The surrogates used were an extruded octagon, a cylinder, and a cylinder with a ball on top. These surrogates were selected to allow easy lighting design calculations while best representing a pedestrian. The experiment found that all surrogates performed equally well and that the surrogate can be chosen on the basis of the ease of calculation. It is recommended that a cylinder be used as a pedestrian surrogate.

Thirty-three participants, all 60 years of age and older, evaluated the visibility of six different pavement marking materials under a simulated rain system operating at 0.8 in. (20 mm) of rain per h at night. Evaluation consisted of counting the number of skip lines visible from both a sedan and truck tractor, under headlight illumination only. Participants also evaluated markings from the sedan under dry conditions at night. Visual observations were compared with measured retroreflectivity of pavement marking materials, measured luminance of pavement marking materials at 30 m, and calculated retroreflectivity at 30 m, on the basis of measured luminance and illuminance provided by vehicle headlights. Data showed a high degree of correlation between the visibility distance of a marking material and the log of both the measured retroreflectivity and the calculated retroreflectivity. A definitive level of retroreflectivity required to meet drivers’ needs in wet night conditions was not found in the investigation and is now the subject of further study. There was also a high degree of correlation between measured and calculated values of retroreflectivity under simulated rain and measurements with the use of two current ASTM test methods, E2176 and E2177. In a second experiment, six original participants evaluated the visibility of the pavement marking materials for a 10-min interval following cessation of simulated rain. Results of the second experiment indicated significant differences in the time required for the visual performance of a pavement marking material to recover from rain for paint and bead products versus that of other pavement marking materials under evaluation.

This investigation examined the ability of cells of Bacteroides melaninogenicussubsp. asaccharolyticus381 to adhere to surfaces that might be important for its initial colonization of the mouth and its subsequent colonization in periodontal pockets. Of 48 asaccharolytic strains of B. melaninogenicus, 47 agglutinated human erythrocytes, whereas none of 20 fermentative strains, which included reference cultures of the subspecies intermediusand melaninogenicus, were active. Electron microscopy indicated that both asaccharolytic and fermentative strains possessed pili; hence, the presence of pili did not correlate with the hemagglutinating activities of B. melaninogenicusstrains. Both asaccharolytic and fermentative B. melaninogenicusstrains suspended in phosphate-buffered saline adhered in high numbers to buccal epithelial cells and to the surfaces of several gram-positive bacteria tested, including Actinomyces viscosus, A. naeslundii, A. israelii, Streptococcus sanguis, and S. mitis. B. melaninogenicussubsp. asaccharolyticus381 also attached, but in comparatively low numbers, to untreated and to saliva-treated hydroxyapatite. Addition of clarified whole saliva to suspensions of strain 381 almost completely eliminated adherence to buccal epithelial cells and to hydroxyapatite surfaces, but saliva had no detectable effect on attachment to gram-positive plaque bacteria. Both fermentative and nonfermentative strains of B. melaninogenicusalso attached in high numbers to crevicular epithelial cells derived from human periodontal pockets, but normal human serum strongly inhibited attachment. Serum also inhibited attachment of strain 381 to saliva- and serum-treated hydroxyapatite, but it had little effect upon attachment to gram-positive bacteria. These observations suggested that salivary and serum components would strongly inhibit the attachment of B. melaninogenicuscells to several oral surfaces, but not to the surfaces of certain gram-positive bacteria commonly present in human dental plaque. This was confirmed by an in vivo experiment in which streptomycin-labeled cells of B. melaninogenicus381-R were introduced into the mouths of two volunteers. After 10 min, several hundred-fold higher numbers of the organism were recovered from preformed bacterial plaque present on teeth than from clean tooth surfaces or from the buccal mucosa and tongue dorsum. High numbers of B. melaninogenicuscells were also recovered from preformed plaque after 150 min, but virtually no cells of the organism were recovered from the other surfaces studied. These data suggest that the presence of dental plaque containing Actinomycesand other gram-positive bacteria may be essential for the attachment and colonization of B. melaninogenicuscells after their initial introduction into the mouth. Similarly, the presence of subgingival plaque containing gram-positive bacteria may be necessary for its secondary colonization in periodontal pockets.

The ability of M-protein-positive (M+) and M-protein-negative (M-) strains (including an M- mutant lacking the structural gene for M-protein) ofStreptococcus pyogenes to attach to human pharyngeal, buccal, and tongue epithelial cells was compared. We observed that M+ strains ofS. pyogenes attached in significantly higher numbers to human pharyngeal epithelial cells than to human buccal or tongue cells. M- strains did not exhibit high-level binding to any type of epithelial cell. Also, the adhesion of an M+ and an M- strain ofS. pyogenes was low to all types of rat epithelial cells tested. The apparent differences in the surface components between human pharyngeal and buccal epithelial cells were confirmed by studies utilizing radiolabeled lectins.Ulex europaeus lectin with a specificity for fucosyl residues, andTriticum vulgaris lectin with a specificity for N-acetyl glucosamine and N-acetyl neuraminic acid residues, bound in higher amounts to human pharyngeal cells than to buccal cells. Pretreatment of pharyngeal epithelial cells with microgram quantities of highly purified type 6 M-protein or miligram quantities of lipoteichoic acid (LTA) derived fromS. pyogenes decreased the subsequent attachment of the organism. However, the binding specificities of3H-LTA were different from those of intact streptococci;3H-LTA bound comparably to human pharyngeal, buccal, and tongue epithelial cells, and it bound in higher quantities to rat epithelial cells. Also, although the adsorption ofS. pyogenes cells to pharyngeal cells was inhibited by the presence of fucose and galactose, these sugars had little effect on the binding of3H-LTA to epithelial cells. In contrast, the high adhesion of M+ strains but not M- mutants to pharyngeal cells suggested that M-protein may play an important role. This possibility was supported by the observation that3H-labeled purified type 6 M-protein bound in higher concentrations to human pharyngeal epithelial cells than to human buccal cells. Furthermore, human pharyngeal epithelial cells were estimated to contain larger numbers of binding sites for M-protein than buccal cells, whereas the affinity of M-protein was similar to both cell types. These adsorption parameters are similar to those previously established for intact streptococcal cells.

A new assay was used to study the adhesion ofStreptococcus pyogenes strains to epithelial cells. [3H]thymidine-labeled bacteria were incubated with standardized preparations of epithelial cells collected from oral-pharyngeal surfaces of human volunteers. The mixtures were then centrifuged in 50% Percoll to form a density gradient. Epithelial cells with attached bacteria formed a band near the top of the tube, whereas unattached bacteria were located near the bottom. The epithelial cells were collected on membrane filters, and the number of adherent bacteria was then determined by scintillation counting.

Virulent M protein-containing strains of Streptococcus pyogeneswere found to adhere well to human pharyngeal cells in vitro. In contrast, an avirulent M - strain and an enteropathogenic Escherichia colistrain adhered feebly. When various rat tissues were exposed to mixtures of a virulent S. pyogenesstrain and an enteropathogenic E. colistrain, the relative proportions of the two pathogenic strains recovered from mucosal surfaces differed among the sites studied. S. pyogenescells were found to adhere in higher proportions than enteropathogenic E. colicells to the mucosal surfaces of rat tongues, whereas on surfaces of the urinary bladder, their affinities were reversed. The data indicate that bacterial adherence is influenced by the specificity of both the bacterial and epithelial surfaces, and they suggest that adherence may influence the tissue tropisms of pathogens. Early stationary-phase cells of S. pyogenesattached better to epithelial cells than did bacteria in other growth phases. The adherence of S. pyogenescells was impaired by pretreatment with trypsin, wheat germ lipase, Tween 80, Triton X-100, sodium lauryl sulfate, heat at 56 C, anti-group A antiserum, the presence of phospholipids, and preincubation of the epithelial cells with Streptococcus salivariuscell walls. Altering the pH or treatment with ethylenediaminetetraacetic acid had no effect on the ability of S. pyogenescells to adhere.

Loesche, WalterJ. (Forsyth Dental Center and Harvard School of Dental Medicine, Boston, Mass.), Ronald J. Gibbons, and Sigmund S. Socransky. Biochemical characteristics of Vibrio sputorumand relationship to Vibrio bubulusand Vibrio fetus. J. Bacteriol. 89:1109–1116. 1965.—Twenty-seven strains of Vibrio sputorumwere isolated from human gingival debris. All strains reduced nitrate beyond nitrite, and all produced H2S. None produced catalase, indole, or acetylmethylcarbinol. Carbohydrates were not fermented, and acid end products or volatile neutral products could not be detected. Motility was observed infrequently, although 14-hr cultures usually had a few cells which displayed darting motility. Shadowed electron microscopic preparations demonstrated that most cells in a given culture were nonflagellated, although some cells with a single terminal or subterminal flagellum were always observed. V. sputorumwas demonstrated not to be a strict anaerobe as previously described, but rather a microaerophile. Addition of nitrate to culture media markedly enhanced growth. V. sputorumwas found to be closely related to the animal microaerophilic vibrios, V. bubulusand V. fetus. V. sputorumdiffered from V. fetusby being capable of anaerobic growth, producing H2S, and failing to produce catalase or to grow in 10% O2. Antigens of V. sputorumcross-reacted in low titer with antisera to V. fetusserotypes I, II, III, and V. V. sputorumdiffered from V. bubulusby being inhibited by 3.5% NaCl and by qualitative differences in growth in the presence of 1% glycine and 10% O2. These differences do not appear sufficient to recognize two distinct species, and it is proposed that both species be recognized as V. sputorum, which has priority. Strains unable to grow in 3.5% NaCl would be considered V. sputorumvar. sputorum, whereas strains capable of growth in 3.5% NaCl would be V. sputorumvar. bubulum.

Lactobacilli were found in saliva, on teeth, and on the dorsum of the tongue, the vestibular mucosa, and the hard palate in humans. Their proportions in saliva, expressed as percentage of the anaerobically cultivable flora, were 10- to 100-fold higher than those on the tooth surface, but were comparable to those on the epithelial surfaces. The adherence of Lactobacillus caseiand L. fermentito oral surfaces was compared with that of streptomycin-labeled Streptococcus sanguisand S. salivariusby using in vitro-cultivated cells. The affinity of both Lactobacillusspecies for the tooth surface was very low compared with that of S. sanguisbut was somewhat higher than that of S. salivarius.The lactobacilli and both Streptococcusspecies adhered to a similar extent to the dorsum of the tongue, whereas the affinity of the lactobacilli and S. salivariusfor the vestibular mucosa was about one-half of that of S. sanguis.The results suggest that the affinity of lactobacilli for oral surfaces significantly influences their proportional distribution in the mouth. The relatively low affinity of lactobacilli for the tooth surface suggests that their recognized association with carious lesions and mechanical appliances under certain conditions may be due primarily to mechanical retention rather than unique growth conditions.

A naphthoquinone-dependent strain of Bacteroides melaninogenicushas been used in a microbiological assay to survey bacteria for compounds of the vitamin K group. Organisms known to contain vitamin K, as well as several bacteria that are obligate anaerobes, produced substances which satisfied the naphthoquinone requirement of the assay organism. Vitamin K was chemically isolated from strains of Bacteroides melaninogenicus, Bacteroides fragilis, and Veillonella alcalescens.

The adhesion-promoting proteins (APP) (molecular mass approx. 300 kDa), which promote adhesion of Streptococcus mutans. JBF (serotype c) to hydroxyapatite, were isolated from human submandidular-sublingual (SMSL) saliva by gel filtration on a Trisacryl GP2000 M column. The effects of hexoses, pentoses, methyl-pentoses, hexosamines, N-acetylhexosamines, a basic amino acid, polyamines and ammonium chloride on the bacterial adhesion-promoting activity of the APP were examined. Galactosamine, mannosamine, l-lysine, spermine, putrescine, and ammonium chloride inhibited the adhesion-promoting activities of the APP. The other sugars, including the N-acetylhexosamines, were without effect. Thus, compounds containing a primary amino-group appear to have a specific inhibitory effect on adhesion of S. mutans JBP to APP adsorbed onto hydroxyapatite, an activity which is lost if the amino-group is acetylated.