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C Allison

Publications and source records attributed to C Allison.

At least 37 records · Page 2Linked to original sources
PubMed1998

Role of Fusobacterium nucleatum and coaggregation in anaerobe survival in planktonic and biofilm oral microbial communities during aeration.

Coaggregation is a well-characterized phenomenon by which specific pairs of oral bacteria interact physically. The aim of this study was to examine the patterns of coaggregation between obligately anaerobic and oxygen-tolerant species that coexist in a model oral microbial community. Obligate anaerobes other than Fusobacterium nucleatum coaggregated only poorly with oxygen-tolerant species. In contrast, F. nucleatum was able to coaggregate not only with both oxygen-tolerant and other obligately anaerobic species but also with otherwise-noncoaggregating obligate anaerobe-oxygen-tolerant species pairs. The effects of the presence or absence of F. nucleatum on anaerobe survival in both the biofilm and planktonic phases of a complex community of oral bacteria grown in an aerated (gas phase, 200 ml of 5% CO2 in air x min-1) chemostat system were then investigated. In the presence of F. nucleatum, anaerobes persisted in high numbers (>10(7) x ml-1 in the planktonic phase and >10(7) x cm-2 in 4-day biofilms). In an equivalent culture in the absence of F. nucleatum, the numbers of black-pigmented anaerobes (Porphyromonas gingivalis and Prevotella nigrescens) were significantly reduced (P </= 0.001) in both the planktonic phase and in 4-day biofilms, while the numbers of facultatively anaerobic bacteria increased in these communities. Coaggregation-mediated interactions between F. nucleatum and other species facilitated the survival of obligate anaerobes in aerated environments.

Actinomyces↗
PubMed1997

Methods for microscopic characterization of oral biofilms: analysis of colonization, microstructure, and molecular transport phenomena.

Assessment of the role of biofilm microstructure in biofilm-specific activities requires non-destructive measurement techniques for parameterization of structural characteristics in parallel with relevant biochemical and physiological data. This paper briefly reviews some current methods for biofilm structural analysis, with emphasis on new developments in optical imaging and mathematical modeling methods. Fluorescence imaging studies of bacterial colonization events occurring on exposed model tooth surfaces indicated that bacterial adhesion to sessile organisms was of central importance to the early colonization process and that this occurred in a non-random manner. Structural studies of mature biofilms by confocal microscopy demonstrated the spatial distribution of individual species using fluorescent antibodies. Biofilms grown under different physiological conditions exhibited differences in structure, and methods were developed for parameterizing the spatial orientations of the bacteria. Diffusive processes within biofilm microstructures were studied using a random walk model in both 2-D and 3-D. Modeling of convective flow within biofilm microstructures was achieved by application of lattice Boltzmann methodology.

Bacteriological Techniques↗
PubMed1995

Growth, incidence and activities of dissimilatory sulfate-reducing bacteria in the human oral cavity.

Viable counts and activities of sulfate-reducing bacteria were determined in the oral cavities of 12 healthy volunteers. Of these, 10 harboured viable sulfate-reducing bacteria populations. Six separate sites were sampled: the posterior tongue, anterior tongue, mid buccal mucosa, vestibular mucosa, supragingival plaque and subgingival plaque. Sulfate-reducing bacteria occurred in all areas, with the highest incidence in supragingival plaque. Viable counts and sulfate-reducing activities in each of the regions varied from 0 to 10(8) cfu (g wet weight)-1 and from 0 to 50 nmol (g wet weight)-1 h-1, respectively. As sulfate-reducing bacteria can be detected in the oral cavity, they may potentially be involved in terminal oxidative processes carried out by the microflora of the mouth.

Adult↗
PubMed1995

Requirement for FlhA in flagella assembly and swarm-cell differentiation by Proteus mirabilis.

Swarming by Proteus mirabilis is characterized by cycles of rapid population migration across surfaces, following differentiation of typical rods into long, aseptate swarm cells that overexpress flagella and virulence factors, particularly haemolysin. A non-swarming Tn5phoA mutant was unable to synthesize flagella, to fully elongate or to induce high levels of the toxin. The mutation lay within a 2091 bp gene encoding a homologue of the Escherichia coli FlhA belonging to a family of proteins that are required for assembly of flagella or virulence proteins and that are suggested to act either directly in membrane translocation and/or in regulating synthesis of the export apparatus. In trans expression of multicopy flhA restored cell elongation and migration and generated differentiation-specific hyperexpression of flagellin and toxin genes to levels above those seen in the wild-type strain. Transcription of flhA was strongly induced during differentiation, from its own putative sigma 28 promoter. The results suggest a mechanistic coupling of flagella assembly and swarm-cell differentiation.

Amino Acid Sequence↗
PubMed1994

The role of swarm cell differentiation and multicellular migration in the uropathogenicity of Proteus mirabilis.

The uropathogenic bacterium Proteus mirabilis displays a form of multicellular behavior called swarming, in which typical vegetative rods differentiate into long hyperflagellate swarm cells that undergo rapid and coordinated population migration across surfaces. Such behavior might inherently assist ascending colonization of the urinary tract, and it has also been shown that swarming differentiation in vitro is central to the expression of conventional virulence factors. This study provides support for a role of swarming in vivo. Mortality rates of mice inoculated intravenously with 2.5 x 10(8) vegetative cells were lower than rates for those inoculated with wild type strains in the case of motile transposon mutants either completely unable to swarm (< 1%) or able to undergo only aberrant swarming migration (< 40%, P < .001). Histologic analysis of renal tissues from mice infected by wild type Proteus strains showed that long differentiated cells were the major cell type, whereas the extracellular inflammatory exudate contained primarily short vegetative cells. Following intravesical (bladder) inoculation with 2.0 x 10(7) vegetative cells, kidney infection was not established by any of the three motile swarm-defective mutants; indeed, the nonswarming mutant was not retained in the bladder. In contrast, the wild type strain and a normally swarming but nonhemolytic mutant achieved a high incidence of ascending infection to the kidney.

Animals↗
PubMed1994

Screening for coronary heart disease risk factors in retail pharmacies in Sheffield, 1992.

OBJECTIVE: To investigate the current and likely future provision of screening services for risk factors for coronary heart disease in retail pharmacies in Sheffield. DESIGN: This was a questionnaire survey asking about screening tests currently offered, price charged per test, likely future provision of screening tests, the action respondents would take upon finding an abnormal test result, whether the pharmacy was owner-run, franchised, or part of a commercial chain, and inviting open comments from respondents. SETTING: All retail pharmacy premises on the Sheffield Family Health Services Authority list. RESULTS: Seventy seven responses were obtained to 102 questionnaires distributed. Only nine of these currently offered any screening test other than pregnancy testing, although 37 indicated that they might offer tests in the future. Thirty nine were not offering screening and had no plans to do so. Pharmacies offering or likely to offer screening tests were mainly owner-run. All pharmacists who replied to the question asking about their action upon finding abnormal result (33) reported that they would advise the patient to see a doctor. The most frequent comments made by pharmacists were about the commercial viability of screening in pharmacies and the lack of space available to ensure patient privacy and confidentiality during screening. CONCLUSIONS: Screening in retail pharmacies would probably be a commercial failure unless doctors were able to contract for screening services from pharmacies. Evidence from this study and others, however, leads us to question the desirability of this option.

Attitude of Health Personnel↗
PubMed1993

Cell differentiation of Proteus mirabilis is initiated by glutamine, a specific chemoattractant for swarming cells.

Swarming by Proteus mirabilis involves differentiation of typical short vegetative rods into filamentous hyperflagellated swarm cells which undergo cycles of rapid and co-ordinated population migration across surfaces and exhibit high levels of virulence gene expression. By supplementing a minimal growth medium (MGM) unable to support swarming migration we identified a single amino acid, glutamine, as sufficient to signal initiation of cell differentiation and migration. Bacteria isolated from the migrating edge of colonies grown for 8 h with glutamine as the only amino acid were filamentous and synthesized the characteristic high levels of flagellin and haemolysin. In contrast, addition of the other 19 common amino acids (excluding glutamine) individually or in combination did not initiate differentiation even after 24 h, cells remaining typical vegetative rods with basal levels of haemolysin and flagellin. The glutamine analogue gamma-glutamyl hydroxamate (GH) inhibited swarming but not growth of P. mirabilis on glutamine MGM and transposon mutants defective in glutamine uptake retained their response to glutamine signalling and its inhibition by GH, suggesting that differentiation signalling by glutamine may be transduced independently of the cellular glutamine transport system. Levels of mRNA transcribed from the haemolysin (hpmA) and flagellin (fliC) genes were low in vegetative cells grown on MGM without glutamine or with glutamine and GH, but were specifically increased c. 40-fold during glutamine-dependent differentiation. In liquid glutamine-MGM cultures, differentiation to filamentous hyper-flagellated hyper-haemolytic swarm cells occurred early in the exponential phase of growth, and increased concomitantly with the concentration of glutamine from a 0.1 mM threshold up to 10 mM.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1993

Prosol-chlorhexidine irrigation reduces the incidence of bacteremia during ultrasonic scaling with the Cavi-Med: a pilot investigation.

The purpose of this pilot investigation was to determine whether the incidence of bacteremia following subgingival ultrasonic scaling and root planing could be reduced by the use, pre- and intraoperatively, of an irrigant containing 0.12 per cent chlorhexidine (CHX); Prosol. Individuals having evidence of significant periodontal disease (minimum of seven sites per quadrant 4.0 mm and bleeding on probing) were entered into this study. By use of a random number table, patients were assigned to either the experimental or control groups. The procedures, as described below, were carried out in a double blind fashion so that neither the investigator nor the patient was aware of whether Prosol or placebo was being used. The placebo solution was flavored to make it indistinguishable from Prosol. Patients were first anesthetized. Their gingival crevices were then irrigated using the Cavi-Med ultrasonic scaler. At this point, the ultrasonic action was not activated. Ten minutes later, ultrasonic scaling and root planing with the Cavi-Med unit were begun with a continuous flow of either the placebo or control solutions. Blood samples were taken preoperatively, while postoperative samples were taken one minute after completing the scaling of each quadrant and then 10 minutes after scaling the second quadrant. Routine aerobic and anaerobic bacterial culture methods were used to identify viable blood-borne bacteria. The results show that there was no difference in the distribution or presentation of periodontal disease between the experimental and control quadrants.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Co-ordinate expression of virulence genes during swarm-cell differentiation and population migration of Proteus mirabilis.

The uropathogenic Gram-negative bacterium Proteus mirabilis exhibits a form of multicellular behaviour termed swarming, which involves cyclical differentiation of typical vegetative cells into filamentous, multinucleate, hyperflagellate swarm cells capable of rapid and co-ordinated population migration across surfaces. We observed that differentiation into swarm cells was accompanied by substantial increases in the activities of intracellular urease and extracellular haemolysin and metalloprotease, which are believed to be central to the pathogenicity of P. mirabilis. In addition, the ability of P. mirabilis to invade human urothelial cells in vitro was primarily a characteristic of differentiated swarm cells, not vegetative cells. These virulence factor activities fell back as the cells underwent cyclical reversion to the vegetative form (consolidation), in parallel with the diagnostic modulation of flagellin levels on the cell surface. Control cellular alkaline phosphatase activities did not increase during differentiation or consolidation. Non-flagellated, nonmotile transposon insertion mutants were unable to invade urothelial cells and they generated only low-level activities of haemolysin, urease and protease (0-10% of wild type). Motile mutants unable to differentiate into swarm cells were comparably reduced in their haemolytic, ureolytic and invasive phenotypes and generated threefold less protease activity. Mutants that were able to form swarm cells but exhibited various aberrant patterns of swarming migration produced wild-type activities of haemolysin, urease and protease, but their ability to enter urothelial cells was three- to 10-fold lower.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1992

Ability of Proteus mirabilis to invade human urothelial cells is coupled to motility and swarming differentiation.

Proteus mirabilis causes serious kidney infections which can involve invasion of host urothelial cells. We present data showing that the ability to invade host urothelial cells is closely coupled to swarming, a form of cyclical multicellular behavior in which vegetative bacteria differentiate into hyperflagellated, filamentous swarm cells capable of coordinated and rapid population migration. Entry into the human urothelial cell line EJ/28 by P. mirabilis U6450 isolated at different stages throughout the swarming cycle was measured by the antibiotic protection assay method and confirmed by electron microscopy. Differentiated filaments entered urothelial cells within 30 min and were 15-fold more invasive (ca. 0.18% entry in 2 h) than an equivalent dry weight of vegetative cells isolated before differentiation, which attained only ca. 0.012% entry in the 2-h assay. The invasive ability of P. mirabilis was modulated in parallel with flagellin levels throughout two cycles of swarming. Septation and division of intracellular swarm cells produced between 50 and 300 vegetative bacteria per human cell, compared with 4 to 12 intracellular bacteria after incubation with vegetative cells. Transposon (Tn5) mutants of P. mirabilis with specific defects in motility and multicellular behavior were compared with the wild-type for the ability to invade. Mutants which lacked flagella (nonmotile nonswarming) were entirely noninvasive, and those which were motile but defective in swarm cell formation (motile nonswarming) were 25-fold less invasive than wild-type vegetative cells. Mutants with defects in the coordination of multicellular migration and the temporal control of consolidation (cyclical reversion of swarm cells to vegetative cells) were reduced ca. 3- to 12-fold in the ability to enter urothelial cells. In contrast, a nonhemolytic transposon mutant which swarmed normally retained over 80% of wild-type invasive ability. Swarm cells and early consolidation cells were at least 10-fold more cytolytic than vegetative cells as a result of their high-level production of hemolysin.

Animals↗
PubMed1991

Closely linked genetic loci required for swarm cell differentiation and multicellular migration by Proteus mirabilis.

The pathogenic bacterium Proteus mirabilis exhibits a form of multicellular behaviour called swarming migration. This involves the differentiation of vegetative cells at the colony margin into swarm cells which are long, aseptate, multinucleate, hyper-flagellated filaments able to undergo repeated cycles of co-ordinated population migration and consolidation (reversion to vegetative cells). Transposon mutagenesis of uropathogenic P. mirabilis strain U6450 with Tn5 generated 4860 chromosomal insertions and, of these, 75 (1.6%) caused visibly abnormal swarming behaviour, indicating that at least 45 genes are involved in directing motility, cell differentiation and multicellular behaviour. While about one fifth of the swarm-defective mutants lacked flagella and were non-motile non-swarming (NMNS) the majority were normally flagellated and motile but were unable to form swarm cells (motile non-swarming, MNS), or were motile and able to form swarm cells but displayed aberrant patterns of multicellular migration (dendritic swarming, DS) or consolidation (frequent and infrequent consolidation, FC and IC). Restriction enzyme mapping of representative mutant DNAs by Southern hybridization with transposon DNA probes identified eight different mutated genetic loci within the five phenotypic classes. Subsequent Southern analysis of large restriction fragments separated by pulsed-field electrophoresis showed that these eight mutated loci required for motility, cell differentiation and multicellular migration were clustered on a region of DNA spanning approximately 8% of the 4.2 mbp P. mirabilis chromosome. Further linkage analysis showed that the DS locus involved in the ordered migration of the swarm cell population mapped separately from two main clusters of swarm loci, one cluster containing, within 112 kbp, genetic determinants of motility (NMNS) and also differentiation into swarm cells (MNS1, MNS2), and a second within a neighbouring 95 kbp DNA sequence containing three loci involved in the control of consolidation (FC, IC1, IC2).

Base Sequence↗
PubMed1991

Bacterial swarming: an example of prokaryotic differentiation and multicellular behaviour.

Bacterial swarming involves the differentiation of vegetative cells into hyperflagellated swarm cells which undergo cycles of rapid and coordinated population migration across solid surfaces. Species capable of this simple form of developmental behaviour lie on the boundary between unicellular and multicellular organisms and provide processes for study which are not only of intrinsic interest but which are analogous to components of more complex eukaryotic systems. This review attempts to place current knowledge of bacterial swarming within the framework provided by more extensively studied forms of prokaryotic multicellular behaviour. It discusses the potential of swarming as a readily accessible model of differentiation and multicellular behaviour and describes evidence indicating that swarming differentiation plays an important role in bacterial virulence.

Bacterial Adhesion↗
PubMed1990

Regulation of protease production in Clostridium sporogenes.

The physiological and nutritional factors that regulate protease synthesis in Clostridium sporogenes C25 were studied in batch and continuous cultures. Formation of extracellular proteases occurred at the end of active growth and during the stationary phase in batch cultures. Protease production was inversely related to growth rate in glucose-excess and glucose-limited chemostats over the range D = 0.05 to 0.70 h-1. In pulse experiments, glucose, ammonia, phosphate, and some amino acids (tryptophan, proline, tyrosine, and isoleucine) strongly repressed protease synthesis. This repression was not relieved by addition of 4 mM cyclic AMP, cyclic GMP, or dibutyryl cyclic AMP. Protease formation was markedly inhibited by 4 mM ATP and ADP, but GTP and GDP had little effect on the process. It is concluded that protease production by C. sporogenes is strongly influenced by the amount of energy available to the cells, with the highest levels of protease synthesis occurring under energy-limiting conditions.

Adenine Nucleotides↗
PubMed1990

Alternative pathways for hydrogen disposal during fermentation in the human colon.

Hydrogen gas, which is produced during fermentation in the human colon, is either excreted in breath or metabolised by gut bacteria through a variety of pathways. These may include methanogenesis, dissimilatory sulphate reduction, and acetogenesis. To determine which of these routes predominates in the large intestine, stools were taken from 30 healthy subjects and incubated as 5% (w/v) slurries with Lintner's starch. In 23 of 30 subjects, methane production was the main method of hydrogen disposal. In the remaining seven, high rates of sulphate reduction were recorded together with raised production of H2S. All samples showed relatively low rates of hydrogen evolution and of acetate formation from CO2 and H2. Sulphate reduction and methanogenesis seem to be mutually exclusive in the colon and this is probably linked to sulphate availability. Sulphate reduction, methanogenesis, and acetogenesis were strongly influenced by pH. Sulphate reduction was optimal at alkaline pH values whereas methane production was maximal at a neutral pH and acetogenesis favoured acidic conditions. Faecal H2S values were related to carriage of sulphate reducing bacteria. These data show that a number of competing pathways for hydrogen disposal are possible in the large gut and that a variety of factors such as colonic pH and sulphate availability can determine which of these mechanisms predominates.

Acetates↗
PubMed1989

Influence of pH, nutrient availability, and growth rate on amine production by Bacteroides fragilis and Clostridium perfringens.

Dimethylamine, methylamine, propylamine, and pyrrolidine were the major amines formed by Bacteroides fragilis NCDO 2217 during the active phase of growth in batch culture. Production of these metabolites was strongly pH dependent and was optimal under acidic conditions (pH 6.0). Low pH also favored the formation of pyrrolidine, cadaverine, and dimethylamine by Clostridium perfringens C523, but the reverse was the case with putrescine, butylamine, and propylamine, where production was maximal at neutral pH. B. fragilis was grown in continuous culture under either starch or casein limitation. Amine formation was influenced by carbohydrate availability and was greatest when the bacteria were grown at high growth rates (dilution rate, 0.20/h) under starch limitation, where they constituted about 18% of the total fermentation products measured. Amine production was optimal and increased concomitantly with growth rate when C. perfringens was grown in glucose-limited continuous culture. Under conditions of high growth rate and glucose limitation, amines accounted for approximately 27% of the fermentation products measured. When glucose in the feed medium was increased from 5 to 15 g/liter, amine production was repressed, and under these nutritional conditions the growth rate had little effect on the process.

Amines↗
PubMed1989

Dissimilatory nitrate reduction by Propionibacterium acnes.

Propionibacterium acnes P13 was isolated from human feces. The bacterium produced a particulate nitrate reductase and a soluble nitrite reductase when grown with nitrate or nitrite. Reduced viologen dyes were the preferred electron donors for both enzymes. Nitrous oxide reductase was never detected. Specific growth rates were increased by nitrate during growth in batch culture. Culture pH strongly influenced the products of dissimilatory nitrate reduction. Nitrate was principally converted to nitrite at alkaline pH, whereas nitrous oxide was the major product of nitrate reduction when the bacteria were grown at pH 6.0. Growth yields were increased by nitrate in electron acceptor-limited chemostats, where nitrate was reduced to nitrite, showing that dissimilatory nitrate reduction was an energetically favorable process in P. acnes. Nitrate had little effect on the amounts of fermentation products formed, but molar ratios of acetate to propionate were higher in the nitrate chemostats. Low concentrations of nitrite (ca. 0.2 mM) inhibited growth of P. acnes in batch culture. The nitrite was slowly reduced to nitrous oxide, enabling growth to occur, suggesting that denitrification functions as a detoxification mechanism.

Feces↗
PubMed1989

Studies on mixed populations of human intestinal bacteria grown in single-stage and multistage continuous culture systems.

Mixed intestinal bacteria were grown for 336 h in two identical single-stage chemostats at low growth rates in a carbohydrate-limited medium. Complex bacterial populations were maintained and anaerobes always outnumbered aerobes. The predominant organisms belonged to the genera Bacteroides, Bifidobacterium, Lactobacillus, Clostridium, Eubacterium, Propionbacterium, Peptococcus, and Peptostreptococcus. Bacteroides species predominated in both fermentors, particularly B. ovatus and B. thetaiotaomicron. A high degree of reproducibility of bacteriological and fermentation product data was obtained in these experiments. When gut contents were inoculated into a five-stage continuous culture system (retention time of 79 or 38 h) containing soya bran, the medium flow rate had little quantitative effect on the formation of acidic fermentation products; however, more oxidized fermentation acids were produced at the higher retention time. Diverse bacterial populations were maintained in every vessel at each flow rate. Bacteroides fragilis group organisms, especially B. ovatus, were numerically the most important. The viability of bacteria decreased through the system, especially at a retention time of 79 h, when the bacteria were growing under severely nutrient-limited conditions.

Bacteria↗