The Growth of the Bacillus tuberculosis and other Micro-Organisms in Varying Percentages of Oxygen

The Effect on the Virulence of Bact. aertrycke of Cultivation in Atmospheres containing Varying Proportions of Oxygen

1. A given strain ofBact. aertryckewas sub-cultured daily, except on Sundays, in 5–7 c.c. of casein broth,pH 7·4–7·6, under different partial pressures of oxygen. Most experiments were continued till about ninety sub cultures had been made. Virulence determinations were made from time to time by intraperitoneal inoculation of twenty mice with about 100 living organisms, the control and the experimental cultures generally being tested simultaneously. The results showed that under anaerobic conditions there was no appreciable change in virulence. Under the usual aerobic conditions, and in partial pressures of oxygen varying from 1 to 21 per cent., the virulence declined, the extent and rapidity of the fall increasing with the pressure of oxygen supplied. In high partial pressures of oxygen, varying from 40 to 100 per cent., there was a slight increase in virulence, the increase being greatest in cultures incubated in pure oxygen.

2. Some of the literature dealing with incitants to microbic dissociation is discussed, particularly that dealing with variations in oxygen pressure.

3. In explanation of the experimental results obtained, a tentative hypothesis is put forward with reference to the dissociation ofBact. aertrycke. It is suggested that under aerobic conditions, and under low partial pressures of oxygen generally, substances are formed in the medium, as the result of growth, which favour dissociation, and lead to the appearance of weakly virulent or completely avirulent variants. Under anaerobic conditions these substances either are not formed at all, or appear in amounts too small to be of significance. In cultures incubated in high partial pressures of oxygen, these substances are formed, probably in large quantity, but owing to the high alkalinity of the medium and the abundant oxygen present, they undergo rapid destruction. This explanation is based on the fact that many protein degradation products, particularly those with a phenolic grouping, prove markedly unstable in an alkaline medium in the presence of free oxygen.

As an alternative hypothesis it is suggested that the maintenance of the organisms in the virulent state depends on the intracellularpH. Under anaerobic conditions it is supposed that the metabolism is such as to lead to no marked change in the H-ion concentration within the cell. In the presence of air and of low pressures of oxygen generally, owing to the breakdown of the protein in the medium and the production of ammonia, the intracellular reaction becomes more alkaline; whereas in high pressures of oxygen the increased amount of CO2produced is sufficient to compensate for the production of ammonia, and the intracellularpH remains more or less at its original value. This hypothesis rests on the observation of Stephenson and Whetham (1924) that in high pressures of oxygenBact. colimay produce considerably larger quantities of CO2from lactic acid than under ordinary aerobic conditions; and on the demonstration by Jacobs (1920b) that, owing to the ease with which CO2is able to penetrate the living cell, the intracellularpH may differ markedly from that of the medium to which the cell is exposed.

4. It is of interest to note thatBact. aertrycke, when incubated under partial pressures of 40 to 75 per cent. of oxygen, rapidly passed into the nonmotile O form.

The Action of Dysentery Bacilli on Nitrites and Nitrates

(1) Dysentery strains from various sources have been examined with respect to their power of reducing nitrates to nitrites and of further destroying nitrites. All the strains with one exception (B. Neisser Ac.) reduced nitrates to nitrites. None of the strains which fail to ferment mannite (Shiga type) destroyed nitrites. Those dysentery strains which form acid from mannite differ amongst themselves in regard to their action on sugars and also in their effect on nitrites. Of the eight mannite-fermenting strains examined, two (B. dysenteriae Jürgens and B. Neisser Nc.) failed to destroy nitrites.

(2) B. dysenteriae Jürgens, although closely related to B. dysenteriae Flexner, differs from it both in its action on litmus-whey and in failing to destroy nitrite. It must therefore be considered a different strain. B. dysenteriae Jürgens is remarkable as being the only one of the strains examined which forms indol and at the same time fails to destory nitrites. It is consequently the only one which gives the cholera-red reaction.

(3) The addition of glucose (i.e. of a carbohydrate from which acid can be formed) enables Shiga strains to destroy nitrite.

(4) In the presence of an abundant supply of oxygen all the strains fail to destroy nitrites and nitrates.

(5) In glucose-containing media the inhibitory effect of oxygen is less marked.

(6) Under anaerobic conditions Shiga strains and B. dysenteriae Jiirgens still fail to destroy nitrites.

Effect of total and partial pressure (oxygen and carbon dioxide) on aerobic microbial processes

In industrial bioreactors, levels and gradients of total and partial pressures are considerably higher than on the laboratory scale. In the relevant range (in general up to 2 or 3 bar, maximum approx. 10 bar), effects of total pressure on aerobic cultures are negligibly small. CO2 partial pressures of more than approx. 100 mbar may have inhibitory effects on aerobic cultures. Growth of aerobic cultures can be enhanced by O2 partial pressures higher than 210 mbar (corresponding to air at 1 bar), if oxygen transfer is limited. In many cases, however, increased O2 partial pressure (higher than approx. 1 bar) is toxic to aerobic cultures and inhibits microbial growth and product formation. Stepwise and cyclic variations of O2 partial pressure may have positive or negative effects, depending on strain of microorganism, culturing conditions, and range of dissolved oxygen concentration. Knowledge of these effects is required in process development and bioreactor scale-up.

OXYGEN INHIBITION OF GROWTH OF MYCOBACTERIUM TUBERCULOSIS

Gottlieb, S. F. (Linde Division, Union Carbide Corporation, Tonawanda, N.Y.), Noel R. Rose, Jerome Maurizi, and Edward H. Lanphier. Oxygen inhibition of growth of Mycobacterium tuberculosis. J. Bacteriol. 87:838-843. 1964.-Continuous or intermittent exposure to 3 atm of oxygen in the presence or absence of 40 mm of Hg CO(2) resulted in marked delay or inhibition of growth of Mycobacterium tuberculosis. This inhibition was more pronounced with newly inoculated cultures, as compared to young, actively growing cultures. Oxygen inhibition of growth was observed on both Lowenstein-Jensen and blood agar media. Bacteriostatic effects of oxygen are a direct function of exposure time. A more marked effect of oxygen was observed in the presence of isoniazid, streptomycin, or p-aminosalicyclic acid.