MINIMUM INHIBITORY CONCENTRATION FOR DETERMINING ANTIMICROBIAL RESISTANCE IN ENTEROBACTERIA

ESBL (extended spectrum β-lactamases) are enzymes capable for spliting penicillins, cephalosporins and monobactams and not hydrolyzing cephamycins and carbapenems. The most common ESBL producers are Escherichia coli and Klebsiella pneumoniae.

Antibiotic susceptibility testing by serial dilution determines the effective dosage of antibiotics.

The aim of the work is to study the minimum inhibitory concentration of various antibiotics and determine the production of β-lactamase for the bacteria Klebsiella pneumoniae and Escherichia coli using the Sensititre ESB1F tablet.

In the course of the work, two Sensititre ESB1F plates were used, the wells of which contained dry antimicrobials at certain concentrations, saline, Mueller-Hinton broth, an automatic pipette for 10 and 50 µl with disposable tips, McFarland standard 0.5 units, blood agar plates to control the purity of cultures.

The results were recorded visually, registering growth by cloudiness of the medium, formation of a film or sediment at the bottom of the plate in comparison with the control wells.

To account for the results of the test confirming the presence of ESBL, the MIC obtained for ceftazidime, cefotaxime and the MIC obtained for the combination of these antibiotics with clavulanic acid (ceftazidime/clavulanic acid and cefotaxime/ clavulanic acid) were compared. The test result was considered positive if the difference in MIC was more than two dilutions.

For E. coli, the MICs of ceftazidime and ceftazidime/clavulanic acid were 8 and 0.25/4, respectively, i.e. the difference in dilutions was 7; for cefotaxime, the MIC corresponds to 1 mg/l, with respect to cefotaxime/clavulanic acid, the studied E. coli turned out to be sensitive at all concentrations studied. For Kl. pneumoniae MIC of ceftazidime was 16, ceftazidime/clavulanic acid was 0.5 (difference of 6 dilutions); cefotaxime - 2 and cefotaxime / clavulanic acid - 0.25 (3 dilution difference). It follows from this that both studied microorganisms produce extended spectrum β lactamases.

A conclusion was made about the expedient use of Sensititre ESB1F tablets, which make it possible to determine and confirm the presence of ESBL enzymes in representatives of the Enterobacteriaceae family.

The results of assessing the level of betalactamase activity will reduce the unreasonable use of antibacterial drugs from the group of betalactams.

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