THE COLORIMETRIC DETERMINATION OF HYDROGEN ION CONCENTRATION AND ITS APPLICATIONS IN BACTERIOLOGY PART III

Evidence-based guidelines for controlling pH in mammalian live-cell culture systems

A fundamental variable in culture medium is its pH, which must be controlled by an appropriately formulated buffering regime, since biological processes are exquisitely sensitive to acid-base chemistry. Although awareness of the importance of pH is fostered early in the training of researchers, there are no consensus guidelines for best practice in managing pH in cell cultures, and reporting standards relating to pH are typically inadequate. Furthermore, many laboratories adopt bespoke approaches to controlling pH, some of which inadvertently produce artefacts that increase noise, compromise reproducibility or lead to the misinterpretation of data. Here, we use real-time measurements of medium pH and intracellular pH under live-cell culture conditions to describe the effects of various buffering regimes, including physiological CO2/HCO3- and non-volatile buffers (e.g. HEPES). We highlight those cases that result in poor control, non-intuitive outcomes and erroneous inferences. To improve data reproducibility, we propose guidelines for controlling pH in culture systems.

HYDROGEN ION CONCENTRATION OF CULTURES OF PNEUMOCOCCI OF THE DIFFERENT TYPES IN CARBOHYDRATE MEDIA

1. The optimum hydrogen ion concentration for growth of pneumococcus is pH 7.8. 2. In broth cultures growth of pneumococcus continues until a final hydrogen ion concentration of about pH 5.0 is reached, if sufficient fermentable carbohydrate' (above 0.4 per cent) is present. Apparently this acidity is sufficient in itself to stop growth. 3. If less carbohydrate is present in the medium growth ceases at a lower hydrogen ion concentration, apparently because of exhaustion of carbohydrate. If no carbohydrate is present save that extracted from the meat of which the broth is made (plain broth medium), growth initiated at pH 7.8 (optimum reaction) ceases at about pH 7.0. 4. If bacteria-free filtrates of plain broth cultures in which growth has ceased are readjusted to pH 7.8 and reinoculated with pneumococcus, no growth occurs unless carbohydrate is added. However, if bacteria-free filtrates of dextrose broth cultures in which growth has ceased (pH 5) are readjusted to pH 7.8 and reinoculated with pneumococcus growth occurs. 5. Cultures of pneumococcus with all the carbohydrates which were fermentable under the conditions used, namely maltose, saccharose, lactose, galactose, raffinose, dextrose, and inulin, gave identical results in the rate of reaction change, and final hydrogen ion concentration (pH 5.0) attained. 6. The different immunological types of pneumococcus, for the limited number of strains studied, behaved alike in fermenting the carbohydrates mentioned above.

THE AMPHOTERIC PROPERTIES OF SOME AMINO-ACIDS AND PEPTIDES

The titration curves of solutions of glycine, alanine, α-ammo-butyric acid, leucine, glycyl-glycine, alanyl-glycine, alanyl-alanine, acetone, acetamide, urea, acetic acid, and aceturic acid were determined and some of the relations as dependent upon the chemical structures discussed. The isoelectric points of some of the amphoteric electrolytes were found experimentally. The definition of isoelectric point, its theoretical significance, and method of calculation were considered in some detail.

THE RELATIVE REACTION WITHIN LIVING MAMMALIAN TISSUES : III. INDICATED DIFFERENCES IN THE REACTION OF THE BLOOD AND TISSUES ON VITAL STAINING WITH PHTHALEINS

Mice can be vitally stained with many of the phthalein indicators. The staining is diffuse, appearing to interfere not at all with health in the case of the majority of the dyes. The color phenomena show that these retain the character of indicators. A special technique has been evolved for the determination of the hues of the various organs, which are readily modified by extraneous influences. The ability to recognize that the pH has thus been altered is a signal advantage of the indicator method. Phthaleins of slightly alkaline range or one that trenches slightly on acidity have been employed for the work here reported. Cresol red, phenol red, and brom phenol red have proved especially useful. The observations with the three agree closely in pointing to the existence of notable differences between the reaction of the blood and that within the tissues generally. The hue of blood plasma from the right heart is such as to suggest that its reaction lies at about pH 7.38 ordinarily, whereas that of the most alkaline of the tissues, judging from its color, the connective tissue, would appear to have a pH of 7.2 or slightly less. The tendons seem to be nearly but not quite so alkaline. The other stained tissues without exception, are of a hue which would indicate that the reaction lies beyond the range of phenol red on the acid side, that is to say is at least as acid as pH 6.6. In a subsequent paper observations which accord with these findings, carried out with indicators of frankly acid range, will be described. On the exposure of tissues to air, without disturbance of the circulation, some of them become alkaline. In the case of connective tissue, at least, the change is a consequence of the escape of carbon dioxide. The gas passes readily in and out, exerting a practically immediate influence on the color of the tissue bared by eversion of a skin flap; and so much may be absorbed on exposure to pure carbon dioxide, when the surface is large, that a general acidosis results. The precise interpretation of the color changes in terms of pH waits necessarily upon further work.

THE CULTURAL DIFFERENTIATION OF BETA HEMOLYTIC STREPTOCOCCI OF HUMAN AND BOVINE ORIGIN

None of the procedures described serves by itself to differentiate streptococci of human and bovine origin with certainty, though each of them serves as a strong presumptive test. Most strains fall easily into the human or bovine group by all the tests. Eliminating these from consideration we have left certain irregular strains listed in Table VII. See PDF for Structure Taking all characters into consideration we are inclined to regard Strains J-E7, Cheese 1, and Cheese 2 as undoubtedly of bovine origin. Strain J-MJ also is representative of a group of streptococci which Jones has found in milk and which is being further studied by him. There remains Strain J-C65 which for the present must be regarded as of doubtful origin.

A STUDY OF BACILLUS PYOGENES

Bacillus pyogenes is probably quite common in this country, as it is known to be in Europe. A careful study of twelve strains from cattle and one from a hog has disclosed the following characteristics which have not been reported or have been in dispute. Bacillus pyogenes is Gram-positive and pleomorphic, producing forms ranging from short chains of streptococcoid elements to branching filaments. It is hemolytic, producing the beta type of hemolysis in blood agar. It is not hemoglobinophilic, though its growth is greatly favored by some higher protein material such as egg albumin, serum, or blood. It ferments xylose in addition to the substances previously reported. The coagulation of milk by Bacillus pyogenes is primarily an enzyme coagulation and the subsequent digestion of the curd takes place in an acid medium. The intravenous injection of rabbits was invariably fatal. The lesions most commonly developed were those of the bones. Paralysis was frequently produced, and in each case was caused by lesions in the vertebrae exerting pressure against the ventral columns of the spinal cord. Muscle abscesses were also frequently produced. The authors regard the organism as belonging to the Corynebacteria rather than to the influenza group.

THE USE OF PHENOL RED AND BROM-CRESOL PURPLE AS INDICATORS IN THE BACTERIOLOGICAL EXAMINATION OF STOOLS

1. Either phenol red or brom-cresol purple may be used as indicators in the preparation of lactose agar plates for the isolation of members of the typhoid-dysentery group of bacteria from stools. Of the two, brom-cresol purple gives sharper differentiation and is to be preferred. 2. These indicators exercise no restraining influence upon the growth of cultures of the typhoid bacillus or paratyphoid bacillus freshly isolated from the human body, or of laboratory cultures of Bacillus dysenteria. 3. Both indicators may be successfully employed with brilliant green in the isolation of the typhoid-paratyphoid group from stools without sacrificing the restraining activity of the brilliant green upon other bacteria.

DIFFERENTIAL STAINING OF SPECIALIZED CELLS IN BEGONIA WITH INDICATORS

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On Rope (and Sourness) in Bread: Together with a Method of estimating Heat-resistant Spores in Flour

The skins of grains, all flours and all bread contain bacteria belonging to the group B. mesentericus. The cultural characters of six types of B. mesenteriucus isolated from grains and flour are given. Five of these were also obtained from ropy (or sour) bread. None of these five types can be identified as corresponding to the organisms isolated by earlier workers on rope. Rope, or sourness, does not result from the presence of these bacteria unless conditions are such as to allow of great development. The factors determining development of rope in bread are (1) degree of infection, (2) moisture, (3) temperature, ? (4) reaction, and (5) composition of the flour. A method of estimating the degree of infection of flours is given.