Biomedical subjects

M I Williamson

Publications and source records attributed to M I Williamson.

7 recordsLinked to original sources

PubMed1987

Comparison of Sabouraud dextrose and Pagano-Levin agar media for detection and isolation of yeasts from oral samples.

The sensitivities of Sabouraud dextrose agar and modified Pagano-Levin agar for the primary isolation of yeasts and the recovery of multiple yeast species from single clinical samples were compared by using oral-rinse samples. Although there was a highly significant positive correlation between the numbers of yeasts recovered from both media, modified Pagano-Levin agar was far superior in detecting multiple yeast species in a single sample. Of 150 oral samples containing yeasts, 23 (15.3%) contained more than one yeast species. The most frequent combination of different yeasts was Candida albicans and Torulopsis glabrata.

Candida↗

PubMed1987

A new simple method for biotyping Candida albicans.

A simple method which allows rapid, reproducible biotyping of Candida albicans isolates, and is suitable for use in any diagnostic medical microbiology laboratory is described. This system comprises three tests, the API ZYM system, the API 20C system, and a plate test for resistance to boric acid. The system differentiated a possible 234 biotypes, of which 33 were found amongst the 130 isolates of C. albicans taken from oral, genital and skin sites. Major biotypes found amongst oral and non-oral isolates were similar, although differences were found amongst minor biotypes. The new system was found to be reproducible, discriminatory, reasonably fast (48 h), easy to perform, and had no requirement for specialised equipment. Hence this biotyping system is suitable for use in diagnostic microbiology laboratories for epidemiological investigations of C. albicans infections.

Boric Acids↗

PubMed1986

Biotypes of oral Candida albicans and Candida tropicalis isolates.

213 oral isolates of Candida albicans and 62 isolates of C. tropicalis were tested for their hydrolytic enzyme profiles with the API ZYM system. One major biotype accounted for more than 50% of the isolates and a number of minor biotypes was recognized in both Candida species. The enzyme profiles of the major biotypes were identical and one quarter of the C. tropicalis isolates possessed a beta-glucosidase which has not been previously described.

Candida↗

PubMed1986

Phospholipase activity as a criterion for biotyping Candida albicans.

The phospholipase activity of 100 oral isolates of Candida albicans was determined by a plate assay. 94% of the C. albicans isolates were phospholipase producers with varying degrees of activity ranging from Pz values of 0.3 to 0.9. As variations in the degree of phospholipase activity on repeat testing of isolates was high it is concluded that the latter criterion cannot be usefully incorporated into a biotyping system of C. albicans.

Candida albicans↗

PubMed1984

Evidence that glucose and sucrose uptake in oral streptococcal bacteria involves independent phosphotransferase and proton-motive force-mediated mechanisms.

Sugar transport and glycolysis in Streptococcus sanguis NCTC 7865, Streptococcus mitis ATCC 903, Streptococcus salivarius NCTC 8606 and several strains of Streptococcus mutans were investigated by following the rate of acid production by washed bacteria at a constant pH of 7.0. The phosphoenolpyruvate-phosphotransferase system (PTS) was inhibited by low concentrations of chlorhexidine. When this PTS-inhibitory concentration of chlorhexidine was added to cells washed and re-suspended in KCl, glucose uptake and glycolysis continued at a greatly-reduced rate. Chlorhexidine abolished glucose and sucrose uptake and metabolism in bacteria washed and incubated in saline. The Na+-inhibition was reproduced in KCl-washed bacteria using the cyclic peptide ionophores, valinomycin and gramicidin, to dissipate K+ and H+ gradients across the cell membrane. Glucose metabolism by Strep. mutans B13 was more resistant to chlorhexidine than that of Strep. mutans NCTC 10449 or Strep. sanguis but was more sensitive to the ionophores. Valinomycin had a greater inhibitory effect on strain B13 than the other two. That ion gradients are important in the chlorhexidine-resistant glucose-uptake mechanism was confirmed using the classical uncoupling agents, carbonylcyanide-m-chlorophenylhydrazone, 2,4-dinitrophenol and KSCN. Glucose metabolism was inhibited in the presence of both the uncouplers and the PTS-inhibitory concentration of chlorhexidine and significant inhibition was also observed in the absence of the PTS inhibitor. Lactate or the ATPase inhibitor, dicyclohexyl carbodiimide (DCCD), had similar inhibitory effects on the non-PTS uptake system.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗

PubMed1983

Inhibition by the antimicrobial agent chlorhexidine of acid production and sugar transport in oral streptococcal bacteria.

Oral streptococci transport sugars via the phosphoenolpyruvate-phosphotransferase (PEP-PTS) system. In a specific assay of this system, low concentrations of chlorhexidine abolished the activity of the glucose and sucrose PTS in batch-grown cells of Streptococcus mutans Ingbritt and B13, Strep. sanguis NCTC 7865, Strep. mitis ATCC 903, Strep. milleri NCTC 10709 and Strep. salivarius NCTC 8606. Intact cells and cells made permeable to the assay reagents with toluene were used. Toluenized cells were more sensitive to chlorhexidine than intact cells (0.09 and 0.25 mM, respectively). This PTS-inhibitory concentration of chlorhexidine reduced acid production from glucose in pH fall experiments to values higher than are obtained solely from endogenous metabolism. The effect of chlorhexidine on rates of acid production was determined at pH 7.0 using cells washed with either 135 mM NaCl or 135 mM KCl. In general, faster rates of acid production from the metabolism of glucose and sucrose were obtained with potassium-treated cells. Addition of the PTS-inhibitory concentration of chlorhexidine markedly reduced or totally abolished acid production by NaCl-treated cells; a greater residual-activity was detected in the same cells washed with KCl (except with Strep. mutans B13 and Strep. mitis ATCC 903). The PTS-inhibitory concentration of chlorhexidine had little or no effect on the viability of cells. The results confirm the existence of sugar uptake systems in oral streptococci additional to the PTS and provide an explanation for the additive anti-caries effect of mouth-rinses containing both fluoride and chlorhexidine.

Acids↗

PubMed1982

Influence of sodium and potassium ions on acid production by washed cells of Streptococcus mutans ingbritt and Streptococcus sanguis NCTC 7865 grown in a chemostat.

A comparison was made of acid production by cells of Streptococcus mutans Ingbritt and S. sanguis NCTC 7865 that had been washed twice and incubated in different concentrations of sodium and potassium ions. Organisms were grown under defined conditions in a chemostat under both glucose limitation and glucose excess conditions at a dilution rate of 0.1 h(-1) (mean generation time, 6.9 h). Acid production after a pulse of glucose, sucrose, and fructose was measured by pH fall experiments and as a rate at pH 7.0. S. mutans produced more acid than S. sanguis as measured by either criterion, although statistically faster rates of acid production and lower terminal pH values were obtained when cells of both species were suspended in KCl rather than in NaCl, with 200 mM KCl resulting in the lowest terminal pH in pH fall experiments. Sodium ions inhibited acid production: 183 mM NaCl reduced the glycolytic rates of S. mutans and S. sanguis metabolizing glucose at pH 7.0 in 135 mM KCl by 39 and 33%, respectively. The most pronounced stimulatory effect of potassium on acid production was by washed cells of S. sanguis that had been grown under arginine and under phosphate limitation. The pH fell by a further 0.86 and 1.21 pH units, respectively, and to below the critical pH for enamel demineralization when these cells were metabolizing glucose in 135 mM KCl compared with the same concentration of NaCl. This enhancement of acid production was not due to potassium translocation, as had been suggested previously, because no movement of potassium ions across the cell membrane could be detected. An alternative explanation is proposed in which sodium ions are excluded from the cell at the expense of membrane energy, i.e., the proton motive force, which could otherwise be used for the transport of sugars.

Fructose↗