Bromothymol blue and carbohydrate-sensitive plating media.
(9/21)
A new plating medium using bromothymol blue (BTB) indicator is described and compared with eosin-methylene blue (EMB), MacConkey, and Endo media. These media were tested with L-arabinose by plating fermenting and nonfermenting mutant strains of Escherichia coli. The minimum concentrations of L-arabinose that permitted differentiation of these strains were determined. Different concentrations were required for differentiating confluent patches of cells, isolated colonies, and closely spaced or adjacent colonies. L-Arabinose, L-rhamnose, D-lactose, and D-galactose were tested with modified enteric media and with BTB medium, again to determine minimum usable concentrations. BTB media and reformulated conventional media allowed detection of acidification, aerobically, at one-fifth to one-hundredth the (1%, wt/vol) concentration of carbohydrate used in standard indicator plates. (+info)
Short prereduced anaerobically sterilized (PRAS) biochemical scheme for identification of clinical isolates of bile-resistant Bacteroides species.
(10/21)
The rapid identification of isolates of bile-resistant Bacteroides species has clinical and therapeutic relevance because of differences in their patterns of susceptibility and virulence. Five hundred twenty-one strains of bile-resistant Bacteroides species that were previously identified by conventional biochemical methods were reexamined to determine the minimum essential parameters necessary for correct identification. Rapid tests for bile resistance, indole production, and catalase were combined with a novel scheme for biochemical determination of saccharolytic activity on arabinose, trehalose, rhamnose, and/or xylan that included the postincubation addition of bromthymol blue for visual pH determination. Organisms were inoculated into prereduced anaerobically sterilized (PRAS) carbohydrates directly from plates, and identification was complete within 24 h of obtaining a pure culture. Ninety-three percent of bile-resistant Bacteroides species from routine clinical specimens were identified correctly by this scheme; a small number of other indole-positive strains, B. splanchnicus, B. eggerthii, and B. stercoris, were misidentified as B. uniformis. (+info)
Inhibition of Escherichia coli serotype O157:H7 by bromthymol blue.
(11/21)
Bromthymol blue, at a concentration of 0.1% in tryptose-glucose broth, inhibited growth of 98.4% of Escherichia coli serotype O157:H7 isolates but only 0.8% of E. coli non-O157:H7 isolates after an overnight incubation at 44.5 degrees C, but not 35 degrees C. The inhibition was dependent on temperature, density of inoculum, bromthymol blue concentration, time of incubation, and composition of the medium. Compared with serologic typing, the inhibition had sensitivity, specificity, predictive values of the positive and negative tests, and overall agreement between the two tests of 98.4, 99.2, 98.4, 99.2, and 98.9%, respectively. The inhibition could be useful as a presumptive test to identify E. coli isolates of serotype O157:H7, especially in laboratories that do not have serotyping capabilities. (+info)
Five methods for determining urinary calcium compared.
(12/21)
We compared frequently used methods for calcium in urine with respect to linearity, analytical recovery, within- and between-batch imprecision, bias, and practicability. We assayed serum, lyophilized urine, native urine, and an aqueous reference solution of calcium carbonate. We found that atomic absorption spectrometry and the Corning 940 Analyzer have the widest ranges of linearity; the methylthymol blue method has the poorest analytical recovery. All methods--the aforementioned three plus the Du Pont aca and Technicon RA-1000 methods--had acceptable precision, although random errors were found with the methylthymol blue method, and, except for one type of commercial lyophilized urine assayed by the Technicon method, there were no matrix problems or difficulties with bias. We cannot recommend the methylthymol blue method, but evidently urinary calcium assays can be adequately done with many currently available methods. Intralaboratory attention to methodology should give improved performance in assessment programs. (+info)
An oxygenation-linked dye binding to Limulus polyphemus hemocyanin.
(13/21)
The reaction of Limulus polyphemus hemocyanin with a dye, bromthymol blue, was examined by equilibrium dialysis, spectrophotometric titration and stopped-flow methods. Oxy-hemocyanin contained one binding site per hexamer unit. The dye binding was linked to oxygenation, and the affinity of the dye for the oxy form was about 10 times as high as that for the deoxy form. Conversely, the dye increased the O2 affinity of hemocyanin. Hemocyanin showed a simple hyperbolic binding curve in the bromthymol blue titration, whereas the time course of the reaction was generally biphasic. It was inferred from the kinetic analyses that the reaction proceeds in two steps. The first bimolecular step is characterized by an increase in the apparent pKa of the bound dye, while the second unimolecular step by a red shift of the absorption band of the unionized dye. The dye binding to partially oxygenated hemocyanin was examined spectrophotometrically; the fractional change in the binding was found to be ahead of the increase in the average degree of O2 saturation. It was concluded that the structural changes in hemocyanin which lead to the increased dye affinity take place at an early stage of the ligand binding sequence. (+info)
Chemically defined antimicrobial susceptibility test medium for Pseudomonas aeruginosa.
(14/21)
A chemically defined growth medium containing physiological concentrations of magnesium and calcium ions was utilized in a microdilution procedure for antimicrobial drug susceptibility testing of Pseudomonas aeruginosa. Determinations of growth end points were simplified by use of sodium citrate as a sole carbon source and bromothymol blue as a pH indicator. Growth of the test organisms was detectable by a change in the indicator color from green to blue after alkalinization of the medium due to citrate utilization. Minimal inhibitory concentrations of amikacin, carbenicillin, gentamicin, and tobramycin were determined on 100 recent clinical isolates of Pseudomonas. Parallel determinations using the microdilution procedure and a conventional tube-broth dilution technique incorporating Mueller-Hinton broth with identical magnesium and calcium content generally agreed within one twofold dilution. Modal minimal inhibitory concentrations for susceptible strains using the microdilution method were: amikacin, 6 mug/ml; carbenicillin, 50 mug/ml; gentamicin, 1.5 mug/ml; tobramycin, 1.5 mug/ml. This modified microdilution technique allowed rapid, definitive minimal inhibitory concentration determinations, using growth end points defined by a color indicator change. (+info)
Hydrophilic region of lecithin membranes studied by bromothymol blue and effects of an inhalation anesthetic, enflurane.
(15/21)
A pH-indicator dye, bromothymol blue, was used to probe the hydrophilic surface of dimyristoyl-, dipalmitoyl-, and distearoylphosphatidylcholine bilayer vesicles. The apparent pK of the surface-adsorbed dye was larger than the bulk pK value. The contribution of the choline positive charge on the dissociation constant of the dye adsorbed on the vesicle surface was estimated by screening the charge interaction with 2 M KCl. The effective surface potentials interacting with the dye were thus estimated to be 33.2, 45.6, and 46.8 mV, respectively, for the dimyristoyl-, dipalmitoyl-, and distearoylphosphatidylcholine vesicles. From the differences between the obtained effective potentials and the calculated surface potentials of the charge-determining plane of the choline head, the distances between the prototropic part of the dye and the choline charge-determining plane were estimated to be 10.5, 8.0, and 7.8 A, respectively. These values were obtained at 25 degrees C; the dimyristoylphosphatidylcholine membrane was in the liquid-crystalline phase and the other two were in the solid gel phase. Addition of an inhalation anesthetic, enflurane, decreased the distance in the dimyristoylphosphatidylcholine vesicles and increased the distance in the dipalmitoyl- and distearoylphosphatidylcholine vesicles. The increase of precessional motion of choline head by the inhalation anesthetic is apparently responsible for the changes. (+info)
Bromothymol blue broth: improved medium for detection of Ureaplasma urealyticum (T-strain mycoplasma).
(16/21)
Bromothymol blue (B) broth for the cultivation, detection, and identification of Ureaplasma urealyticum is described. In this medium, strains Cook and 960 had shorter generation times (60 min or less) and reached higher populations (over 10(8)) than have yet been reported for this species. Furthermore, the indicator changes color before the end of logarithmic growth, and the cultures retain viability for at least 1 day thereafter, greatly simplifying the handling of the organism. When the populations in cultures of these two strains and seven new isolates were determined, growth was detected earlier and proceeded to higher final titers in B broth than in urease test color medium (U-9 broth). The inclusion of antibiotics in B broth for use in clinical laboratories (B/NL broth) made the medium selective, specific, and more sensitive for the isolation of U. urealyticum. Comparison of B/NL broth with genital mycoplasma (GM) agar and U-9 broth for the primary isolation of U. urealyticum was made with 183 urethral swabs. All 70 isolates were detected on B/NL broth, but only 66 and 63 isolates were detected on GM agar and in U-9 broth, respectively. Moreover, the cultures in B/NL broth were pure and at titers that generally showed good correlation with colony counts on GM agar. (+info)