Aerobes

AEROBES (from Greek aer — air, and bios — life), microbes requiring free oxygen for their development, are divided into obligate, i.e., absolute aerobes, and facultative, i.e., those that under certain conditions can also develop in the absence of oxygen. The life of microbes, like the life of any organism, is accompanied by a continuous expenditure of energy. The restoration of expended energy reserves occurs through chemical reactions accompanied by the release of heat. This act of heat release is the essence of the respiration of living creatures. A number of microbes do not bring the oxidation process to end products, but form other organic compounds. An example of such incomplete oxidation can be acetic acid fermentation, in which ethyl alcohol is oxidized by acetic acid microbes into acetic acid. But if acetic acid is subjected to the further action of these microbes until the alcohol is completely exhausted, the oxidation process goes to completion and ends with the release of carbon dioxide and water. Most pathogenic microbes belong to facultative aerobes; obligate aerobes include a large number of microbes (among them B. pestis, B. influenzae, B. mallei, B. diphtheriae, Diplococcus pneumoniae, B. subtilis, and others), many saprophytes, fungi, and Protozoa. Aerobes also include sulfur bacteria, which oxidize hydrogen sulfide into sulfuric acid; nitrifying bacteria, which oxidize ammonia into nitrous and further into nitric acid; iron bacteria and hydrogen bacteria, which oxidize hydrogen; all of them release a significant amount of thermal energy during the respiration process. Luminous microbes, or photobacteria, also belong to aerobes; under the influence of oxidative processes occurring within them, they release energy not in the form of heat, but in the form of light, and with an increase in the oxygen supply, the luminescence becomes brighter. Pigmented, or colored microbes also belong to aerobes and form pigment only in the presence of oxygen. Among other oxidation processes occurring under the influence of aerobic microbes, mention should also be made of the decomposition of manure, which is accompanied by strong exothermicity. The oxygen concentration necessary for the development of various aerobes is far from identical, which is why for each microbe there is its own minimum, optimum, and maximum. Porodko showed that the boundaries between the minimum and maximum oxygen concentrations are very wide. Thus, for B. prodigiosus, the maximum oxygen concentration is 5.45–6.32 oxygen atmospheres (where the unit of oxygen atmosphere is understood as the pressure of a column of pure oxygen at 760 mm), and for B. proteus 3.63–4.25 oxygen atmospheres, which corresponds to an oxygen content in the surrounding air of approximately 20–30 air atmospheres. However, these microbes do not lose the ability to live at the very minimal concentration of oxygen and even almost at its complete exclusion. An increase in the oxygen concentration beyond the limit of its maximum leads to the complete cessation of microbial life. The fact that pressure as such plays no role is proved by the experiments of Sabrazès and Bazin: these authors took cultures of B. typhi, B. coli, B. pyocyaneus and subjected them to the action of carbon dioxide pressure of 60 atmospheres for 6–10 hours, and such high pressure had no effect on the indicated microbes. Khlopin and Taman showed that bacteria, yeasts, and molds tolerate a pressure of 3,000 atmospheres without any harm to them. Thus, it follows that exclusively the partial pressure of oxygen has an effect. [The stray text fragment 'ЛІТОГИЕНІТОНКУМ Печень' appears to be an OCR artifact/misprint in the source material and is omitted from translation].

The transition from the maximum to the optimum oxygen concentration, if it occurs gradually, is tolerated well by aerobes. However, a rapid decrease in the oxygen content acts very detrimentally on microorganisms; first, individual functions begin to drop out, for example, motility, the ability to secrete pigment, enzymes, the ability to form spores, and then more important functions, which leads to the complete death of the microbe. An increase in oxygen concentration beyond the limits of the optimum acts harmfully on obligate microbes, delaying their development; this is seen from experiments with diphtheria bacilli, the growth of which under the influence of pure oxygen is sharply delayed. For some microbes, the optimum oxygen concentration lies below its normal content in the air; thus, this was proved by Lorentz in relation to gonococci, and by Oliver and Perkins in relation to streptococci. Many aerobes, especially labile forms, such as gonococci, meningococci, and others, are better and longer preserved when isolated from the influence of atmospheric oxygen. Observations by Ungermann, Lumière, and Chevrotier show that in liquid nutrient media—liquid serum—cultures of the gonococcus or meningococcus remain alive and virulent for 16 months after primary inoculation, under conditions of isolation from the influence of free oxygen. Animal cells belong to facultative aerobes: inside tissues they receive the oxygen necessary for their life from a loose compound of oxygen with hemoglobin; in cultures in vitro they grow with access to free oxygen.

Ya. Libershtein. AEROGENIC (from Greek aer — air, and genesis — origin), originating from the air; a term used in relation to diseases transmitted through the air, and most often to tuberculosis.