[Changes in the phase variant spectra in the populations of lactic acid bacteria under antibiotic treatment].

Effect of the antibiotics kanamycin and ampicillin on growth and phase variation of the populations of four strains of lactic acid bacteria (Lactobacillus sp. M67AT, L. casei MB, Enterococcus faecium M, and E. faecium M3185) was studied. The presence of antibiotics in the medium resulted in a dose-dependent decrease in viable cell numbers and in partial or complete substitution of the dominant S variant with the minor Sm and Sb variants. The variants differed in colony morphology, as well as in some physiological, biochemical, biotechnological, and probiotic characteristics. The Sm type variants of all strains exhibited the highest resistance to antibiotics. High production of exopolysaccharides was found in Sb variants of lactobacilli and in S variants of enterococci. The highest antibacterial activity was found in Sm variants of lactobacilli, especially in Lactobacillus sp. M76AT The latter is biotechnologically the most promising strain, since all variants fermented milk yielding the products with uniformly pronounced functional and organoleptic properties. These patterns are of importance for the understanding of the mechanisms of antibiotic resistance and for selection of the variants with desired properties, as well as for quality control of the lactic acid bacteria starter cultures.

[Divergence in the level of DNA hybridization and formation of sibling species in the lactic acid bacteria Streptococcus thermophilus]. / Divergentsiia po urovniu gibridizatsii DNK i obrazovanie vidov-dvoinikov u molochnokislykh bakteri Streptococcus thermophilus.

Previously, five distinct groups with 80-90% intragroup DNA homology values were revealed among 19 lactic acid-producing bacterial strains. The study of 39 new strains of thermophilic streptococci in the present work allowed us to reveal the sixth DNA homology group. The nine strains of this group are similar, at 55-70% DNA homology levels, to the type strain S. thermophilus ATCC 19258. Group VI showed a low level of DNA-DNA reassociation (20-30%) with the DNA homology groups I, II, III, and V. The intergroup DNA-DNA reassociation values determined from DNA renaturation rates varied from 20 to 50%. These data were interpreted as indicative of the existence of at least four sibling species among the thermophilic streptococci studied.

Specific immune responses in changed gaseous environments.

The capacity of lymphoid cells to participate in immunity reactions was evaluated by blast transformation of lymphocytes under the influence of phytohemagglutinin. Blast transformation was measured by cytologic analysis and autoradiographic investigation of the rate of RNA synthesis in cells (tritiated uridin used as label). An analysis of the material taken from the three test subjects during the year-long experiment showed that various situations affected significantly the blast transformation level of lymphocytes. The reaction was substantially reduced 10 days after a simulated emergency situation which involved a change in the atmosphere, increase of physical load, etc. The level of blast transformation increased 1.5 to 2 months after the simulation, exceeding the average value, then to be normalized. Atmospheric variations appear to be one of the factors that may change the activity of lymphoid cells. A parallel experiment was performed in which three subjects lived 10 days in a hyperoxic enclosed environment (53% O2). They showed a considerable intensification of blast transformation (by 2.2-2.6 times) and pronounced activation of the RNA synthesis. Investigations give evidence that a long-term enclosure exerts an effect on the reactivity of the systems involved in the development of basic immune reactions.