Colistin-resistance and phage sensitivity of clinical gram-negative bacterial strains

Treatment of bacterial infections has become a serious problem all over the world, due to the increasing antibiotic resistance developed by microorganisms. Clinicians are being forced to intervene with either less effective backup drugs or ones with substantial side-effects. Among such drugs is the antibiotic colistin, which despite its adverse side effects (nephrotoxicity and neurotoxicity) is used for treatment of infections caused by multi-drug resistant gram-negative bacteria. However, in the last few years there has been an increase in resistance to colistin worldwide, both in E.coli strains and among bacterial strains, synthesizing carbapenemase enzymes. Consequently, the effectiveness of antibiotic therapy further reduced. As the area of action of antibiotics decreases, there is a growing interest in alternative ways of treating bacterial infections. At present, the practical use of the antimicrobial properties of virulent bacteriophages is considered as an alternative to antibiotic therapy. The aim of our study was to detect colistin-resistant clinical gram-negative bacterial strains; Detection of plasmids and MCR-gene – the major determinant of colistin-resistance; Determination of susceptibility of colistin-resistant strains to a wide range of antibiotics; Also, selection of bacteriophages active against colistin-resistant clinical strains. The resistance of 292 gram-negative bacterial strain (including E.coli hemolytic strains) to colistin, isolated from different clinical materials in 2018-2020, was studied using the Minimum Inhibitory Concentration (MIC) method. As a result, colistin-resistance was identified in 6 strains: 5 E.coli, 1 K.pneumoniae. The content of plasmids in 3 of them was studied and shown. The specific nucleotide sequence of the MCR gene using the PCR method has been confirmed in 5 colistin-resistant bacteria. The susceptibility of colistin-resistant strains to a wide range of antibiotics was studied using a double disc-diffusion method, also several virulent bacteriophages of antimicrobial activity were selected for 5 of the 6 colistin-resistant strains using the “Spot test” method.

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