[Biorhythms of antibiotic resistance of microorganisms].

AIM: To study of circadian dynamics of antibiotic susceptibility and resistance of Gram-positive and Gram-negative microorganisms. MATERIALS AND METHODS: Circadian dynamics of antibiotic susceptibility was studied on clinical strains of enterobacteria, non-fermenting Gram-negative bacteria, and staphylococci which were isolated and identified by common methods. During a day, with 3-hours intervals, studied strains were tested on susceptibility to ampicillin, oxacillin, ceftriaxone, meropenem, gentamycin, and ciprofloxacin using method of serial dilutions in agar. RESULTS: Circadian biorhythms of resistance to antibiotics in studied microorganisms were revealed. Along with common patterns, differences in temporal changes of microrganisms' susceptibility to antibacterial drugs were noted. Chronobiologic approach allowed to reveal significant amplitude of changes of minimal inhibitoryconcentration (MIC) of antibiotics versus resistant Gram-positive cocci reflecting presence of susceptibility periods, whereas in susceptible Gram-negative bacteria peaks of resistance were observed. Circadian dynamics of MIC of majority of antibiotics versus resistant Gram-negative bacteria and susceptible Gram-positive cocci was characterized by lower amplitude of changes without shifts from antibiotic resistance to susceptibility and vice versa. CONCLUSION: Obtained data open perspective of using biorhythmological approach in study of susceptibility of microorganisms to antibiotics during the elucidation of mechanisms of pathogens adaptation to environmental conditions and creation of new strategies of control for antibiotic resistance strains.

[Modification of bacterial population structure on anti-lysozyme activity under the influence of hexylresorcinol].

AIM: To investigate the modifying effect of hexylresorcinol chemical analog on anti-lysozyme activity of bacteria. MATERIALS AND METHODS: Influence of hexylresorcinol on anti-lysozyme activity (ALA) of bacteriawas studied on the examples of such strains as Bacillus cereus 279, Klebsiella pneumoniae 278, Escherichia coli 101, which are able to inactivate lysozyme. As a chemical analog of microbial regulators, C6-alkyloxybenzol (C6-AOB) was used, which was introduced in growth medium containing microorganisms, which than were cultivated until entering in the stationary growth phase. Isolation of clones was carried out by seeding the 24-hours broth culture on solid growth medium followed by measurement of ALA with photometric method. RESULTS: Modifying effect of chemical analog of extracellular microbial regulators (C6-AOB) on population structure of bacteria on the sign of anti-lysozyme activity was revealed. Maximal effect was observed at C6-AOB concentrations 1 and 10 mcg/ml. Clonal redistribution on ALA manifested by decrease of proportion of clones with high and intermediate values of ALA and increase of proportion of clones with low ALA or its absence. CONCLUSION: Obtained data are perspective for development of measures for control of persisting pathogenic microorganisms by modification of persistence factors with microbial autoregulators.

[Influence of chemical analogue of extracellular microbial autoregulators on antilysozyme activity of bacteria].

Modifying action of C7-alkyloxybenzol (methylresorcin) on the antilysozyme activity (ALA) of opportunistic microorganisms (Bacillus cereus, Klebsiella pneumoniae, and Escherichia coli) was studied. C7-alkyloxybenzol (C7-AOB, methylrezorcin), which was used as chemical analogue of microbial autoregulators, was added to growth medium containing microorganisms, which were cultivated until entered stationary phase. Isolation of clones was performed by seeding of 24-hours broth culture on solid growth medium, and then ALA was measured using photometric method. Modifying action of C7-AOB on ALA characteristic-based population structure of B.cereus, K. pneumoniae, and E. coli was revealed. Maximal effect was detected when the concentration of C7-AOB was in range 1-10 mcg/ml. Decrease of mean ALA level caused by C7-AOB was linked to decrease of proportion of clones with high and intermediate ALA level, increase of proportion of clones with low level of lysozyme inhibitor, and emergence of clones lacking ALA in the population.