Distribution of MIC values of antibacterial drugs for Flavobacteriales isolated from respiratory samples in Russian patients with cystic fibrosis
Authors: Kondratenko Olga V. , Zubova K.V. 
Published: September 2023

Objective.
Analysis of the distribution of the values of the minimum inhibitory concentrations (MIC) of a number of antibacterial drugs in relation to representatives of the order Flavobacteriales isolated from respiratory samples from patients with cystic fibrosis of the Russian Federation by the method of double serial dilutions.

Materials and Methods.
The distribution of the values of MIC of a number of antibacterial drugs was evaluated in relation to 100 strains of bacteria, representatives of the order Flavobacteriales, isolated from respiratory samples from patients with cystic fibrosis from 60 regions of the Russian Federation as part of a routine microbiological examination. Of these, 75 representatives of Chryseobacterium spp., among which C. arthrospherae – 28, C. formosense – 1, C. gambrini – 3, C. gleum – 10, C. indologenes – 20, C. joostei – 1, C. oraniemense – 10, C. shandongense – 2 strains, 4 strains of Elizabethkingia spp., among which 2 – E. miricola, and one strain of E. meningoseptica and E. anopheles, respectively, as well as 21 strains of E. falsenii. Identification of all isolated cultures was carried out using MALDI-ToF mass spectrometry (Bruker, Germany). The MIC values were determined for 17 antimicrobial drugs: amikacin, amoxicillin/clavulanate, aztreonam, cefotaxime, ceftazidime, ceftazidime/avibactam, ceftolozane/ tazobactam, ciprofloxacin, colistin, ertapenem, gentamicin, imipenem, meropenem, piperacillin/ tazobactam, tigecycline, tobramycin and trimethoprim/sulfamethoxazole using Sensititre kits DKMGN.

Results.
The MIC values of colistin, cefotaxime and tobramycin more than 8 µg/ml, as well as more than 2 µg/ml with respect to ertapenem was demonstrated for 100% of isolates. For most strains, the MIC values of imipenem and meropenem were more than 4 µg/ml. MIC of ceftazidime against 20% of Chryseobacterium spp. strains was up to 2 µg/ml. Indicators of MIC of amikacin in relation to Elizabethkingia spp. strains were 32 µg/ml or more. For 38% of the strains of Chryseobacterium spp. and E.falsenii, this value did not exceed 8 µg/ml. As in the case of amikacin, all Elizabethkingia spp. strains demonstrated high levels of gentamicin MIC – 8 µg/ml (25% of strains) and more (75% of strains). For 20% of all tested strains, the MIC value was in the range of ≤ 2 µg/ml. In relation to half of the tested isolates, the MIC values for ceftazidime/avibactam, as well as ceftolozane/tazobactam were at the level of up to 2⁄4 µg/ml inclusive. More than a third of the strains had a level of MIC ciprofloxacin up to 0.25 µg/ml inclusive. For 25% of strains, the level of MIC of tigecycline was up to 0.5 µg/ml, inclusive, the lowest MIC indicators for the tested group of strains were demonstrated for trimethoprim/sulfamethoxazole: for 88% of strains, the MIC value was ≤ 1⁄19 µg/ml, for another 9% of strains, this indicator was 2⁄38 µg/ml.

Conclusions.
Representatives of the order Flavobacteriales are a group of microorganisms characterized by multiple antibiotic resistance. Most strains isolated from patients with cystic fibrosis in the Russian Federation retain low MIC values for trimethoprim/sulfamethoxazole.