STUDIES ON VIRULENCE : II. THE INCREASE IN VIRULENCE IN VITRO OF A STRAIN OF PNEUMOCOCCUS

THE INTERCONVERTIBILITY OF "R" AND "S" FORMS OF PNEUMOCOCCUS

1. Single cell cultures of "R" pneumococci may revert in all respects to the "S" type. 2. In all instances in which reversion has occurred the "R" forms have invariably reverted to the same specific type from which they were originally derived. 3. The transformation "R" to "S" may be effected in vitro by growth in anti-"R" sera, as well as in vivo by the method of animal passage. 4. Reversion from "R" to "S" whether effected in vivo or in vitro, is always accompanied by the acquisition of maximal virulence.

STUDIES ON VIRULENCE : III. INFLUENCE OF HYDROGEN ION CONCENTRATION AND OF INGREDIENTS OF PLAIN BROTH ON THE VIRULENCE OF PNEUMOCOCCI

1. A highly virulent strain of pneumococcus, Type I, Neufeld, when grown in an automatic transferring device at 2 hour intervals on different lots of plain broth adjusted respectively to pH = 6.5, 7, 7.5, or 7.8, lost its virulence at a rate in direct ratio to the H ion concentration of the media-the more acid the media, the more rapid the decrease. 2. Growth of a virulent pneumococcus upon plain broth of an H ion concentration changing gradually either to the acid or the alkaline side of neutrality was accompanied by an initial rise in virulence with a subsequent fall, the change being more rapid in the alkaline than in the acid medium. The organism under these conditions underwent an alteration in its behavior toward agglutinating sera; although still specific, its agglutinability became much greater than that of the original organism. This change was more pronounced in the alkaline than in the acid medium. 3. The virulence of a relatively virulent culture of a pneumococcus grown on plain broth underwent different alterations when the organism was transferred at intervals of 1, 2, 4, or 8 hours. With the 1 hour interval, there occurred seemingly an immediate decrease in virulence, while at intervals of 2, 4, and 8 hours, there occurred first a rise and then a fall, the rise being greatest with the 8 hour interval of transfer and least with the 2 hour. 4. Meat infusion adjusted to various H ion concentrations-pH = 7, 7.3, and 7.7-and made with different amounts of meat furnished conditions which caused a decrease in virulence, the unfavorable action varying in inverse proportion to the concentration of the infusion. Dextrose added to both plain broth and to meat infusion neutralized to a marked degree the unfavorable action of these media. 5. The growth of pneumococci on the different ingredients of plain broth, with plain broth made from the same supply as a control, revealed the fact that peptone in 2 per cent solution maintained and even increased the virulence of the strain of pneumococcus studied, while meat infusion caused the usual decrease. The rate of decrease with plain broth was slower than with meat infusion, showing that the 2 per cent peptone neutralized to some extent the unfavorable action of the infusion.

STUDIES ON VIRULENCE : IV. INFLUENCE ON VIRULENCE OF PNEUMOCOCCI OF GROWTH ON VARIOUS MEDIA

FROM THE STUDY OF DIFFERENT TISSUE EXTRACTS AS MEDIA FOR THE GROWTH OF PNEUMOCOCCI USED IN AN AUTOMATIC TRANSFER DEVICE, CERTAIN INFERENCES ARE WARRANTED: 1. Media made from calf lung or heart, or from horse skeletal muscle maintain virulence over a long period of time. Conversely, media made from calf spleen lead to a decrease in virulence. 2. Lung medium causes an increase in virulence of seven strains of pneumococci. 3. Virulence is maintained in normal horse serum; but, it rapidly decreases in immune serum, or in pneumococcus antibody solution, a finding which confirms the work of Stryker. Immune serum freed from protective antibody gives results similar to normal serum. 4. Rabbit medium made from the entire animal apparently is less suitable for the maintenance of virulence of pneumococci than medium made in the same way from guinea pig.

CULTURE CONDITIONS AND THE DEVELOPMENT OF THE PHOTOSYNTHETIC MECHANISM : II. AN APPARATUS FOR THE CONTINUOUS CULTURE OF CHLORELLA

1. An apparatus has been developed which maintains a constant density of population of Chlorella by automatic dilution of the growing culture with fresh medium. 2. Cells harvested from the apparatus in daily samples are highly uniform in rate of growth and rate of photosynthesis measured under arbitrarily chosen conditions.

Observations on the Growth of Meningococci in vitro in Relation to Virulence: A Report to the Medical Research Council on Work Carried out at the University of Cambridge Pathological Laboratory and Field Laboratories

Every bacteriologist is only too well aware of the many problems presented by the preparation of culture media for the growth of bacteriain vitro.

Increased mutation rate of E. coli K12 lambda cultures maintained in continuous logarithmic growth

Continuous logarithmic growth of E. coli K12 lambda in an automatic culture cell resulted in marked increases in the proportion of several mutants. The P1 phage-resistant cells increased 10 to 3000 times, the T2 phage-resistant cells 1 to 1000 times, the neomycin-resistant cells 1 to 10 times, and the virus-producing cells 30 to 70 times. No change occurred in the penicillin-resistant cells. Calculation of the growth curves and direct determination of the mutation rates by the null fraction method showed that the increases in the proportion of mutants were due to increases in the mutation rates.