Pseudomonas aeruginosa and Escherichia coli are known to be involved in mixed communities in diverse niches. In this study we examined the influence of the predominant form of cell existence of and the exometabolite production by P. aeruginosa strains on interspecies interactions, in vitro. Bacterial numbers of P. aeruginosa and E. coli in mixed plankton cultures and biofilms compared with their numbers in single plankton cultures and biofilms changed in a different way, but were in accordance with the form of P. aeruginosa cell existence. The mass of a mixed-species biofilm was greater than the mass of a single-species biofilm. Among the mixed biofilms, the one with the "planktonic" P. aeruginosa strain had the least biomass. The total pyocyanin and pyoverdin levels were found to be lower in all mixed plankton cultures. Despite this, clinical P. aeruginosa strains irrespective of the predominant form of existence ("biofilm" or "planktonic") had a higher total concentration of exometabolites than did the reference strain in 12-24 h mixed cultures. The metabolism of E. coli, according to its bioluminescence, was reduced in mixed cultures, and the decrease was by 20- to 100-fold greater with the clinical Pseudomonas strains than the reference Pseudomonas strain. Thus, both the predominant form of existence of and the exometabolite production by distinct P. aeruginosa strains should be considered to fully understand the interspecies relationship and bacteria survival in natural communities.

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Nowadays, in the presence of wide diagnostic possibilities, laboratory diagnostics of microecological disorders of vaginal biotope are often limited to clinical data, microscopic examination results and the use of a culture method. However, with such a complex it is impossible to get an answer about the functional activity of microorganisms. The aim of investigation was to evaluate the information content of a combined study of growth parameters and the ability to produce lactic acid by clinical strains of Lactobacillus spp. to characterize the state of the microecology of the cervical-vaginal biotope. Materials and methods. Studied the growth kinetics of strains of lactobacilli isolated from the detachable posterior vaginal fornix. The concentration of lactic acid in the medium was determined using the “Lactic Acid - Olvex” kit (Russia). Samples were taken every 12 hours of cultivation. Statistical analysis of the results was performed using the methods of descriptive statistics, Student’s t-test. Results. It has been shown that 44% of Lactobacillus spp. to 72 hours of cultivation did not reach the phase of exponential growth. The remaining strains from 12-24 hours passed into the phase of exponential growth. In the production of lactic acid, the strains that are in the lag-phase did not differ from each other, since they practically did not synthesize this metabolite. Among the remaining strains that are in the phase of exponential growth, some did not produce lactic acid, others increased their lactate production every hour. Part of the strains reached the peak of acid production by 36 hours and by 72 hours some decrease in synthetic activity was observed. Conclusion. It has been shown that for most vaginal strains of Lactobacillus spp. characteristic variability of the duration of the adaptation period and the level of functional activity. In addition, only a small number of clinical strains produced lactic acid 24 hours after the start of cultivation. Therefore, to adequately assess the microecological status of the vaginal biotope, microscopic examination of both native material and cultures isolated on special nutrient media is not enough. It seems that, along with the use of modern methods of genetic analysis, the determination of in vitro growth characteristics, primarily lag-phase duration, and lactate production by lactic acid bacteria strains can clarify many issues related to the formation of dysbiotic states, in particular, in the vaginal biotope, and will also serve to increase the effectiveness of the prescribed treatment.

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