For most clinically significant strains of bacteria, the biofilm form of life is the most common which guarantees optimal conditions for the release of pathogenic and colonization potential. Moreover, it contributes to the preservation of a metabolically inactive part of the population with a very low sensitivity to the effects of most antibiotics. The current strategy of antibacterial treatment is based on preliminary determination of the sensitivity of the etiological factor to chemotherapeutic agents. The most widespread methods of research nowadays are the definition of antibiotic susceptibility of microorganisms in planktonic form. The purpose of the study was to compare the susceptibility to representatives of β-lactam antibiotics and fluoroquinolones of circulating Pseudomonas aeruginosa and Escherichia coli strains in different forms of existence, such as planktonic form, the state of biofilm formation and the state of formed mature biofilm. Material and methods. The study involved 3 circulating strains of both Pseudomonas aeruginosa and Escherichia coli as test strains isolated from the clinical material from patients hospitalized with firstly diagnosed and confirmed etiological role of these bacteria. Susceptibility to β-lactam antibiotics and fluoroquinolones primarily established by the disc diffusion method was the criterion for test strain selection. Results and discussion. The results of the comparative determination of susceptibility of circulating Pseudomonas aeruginosa and Escherichia coli strains in various forms of existence such as: planktonic form, state of biofilm formation and state of formed mature biofilm, to representatives of β-lactam antibiotics and fluoroquinolones are presented. It has been established that the “minimum inhibitory concentration” of antibiotics in relation to bacteria in the state of biofilm formation was increased by 8-16 times in comparison with the minimum inhibitory concentration determined for planktonic forms of test strains. Thus, 100% inhibition of the growth of the test strains of Pseudomonas aeruginosa required 8 times greater concentration of ceftriaxone or ciprofloxacin and 16 times greater concentration of meropenem (p <0.05). Minimum inhibitory concentration of antibiotics for test strains of Echerichia coli was elevated 8 times for ceftriaxone or ciprofloxacin and 32 times for meropenem (p <0.05). In no case was it possible to provide 100% inhibition of growth of test strains in the state of the formed biofilm after the effect of 256 µg / ml ciprofloxacin and 512 µg / ml ceftrіaxone or meropenem. Concentration of ceftriaxone, meropenem or ciprofloxacin in this case exceeded the MIC for Pseudomonas aeruginosa in planktonic form by 128, 256 and 1024 times, respectively (p <0.00). For the strains of the Echerichia coli these indices exceeded 2000 times. Conclusions. Signs of destruction of the formed biofilms of Pseudomonas aeruginosa were determined by the concentration of antibiotics that exceeded the therapeutically acceptable levels. In the case of Echerichia coli, excess of the limit values was established for ciprofloxacin.
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