Search

The Pseudomonas aeruginosa is among number of leading opportunistic pathogens. The evaluation of sensitivity of hospital isolates of P. aeruginosa to antibiotics is an important stage in the struggle with Pseudomonas sepsis pathology. The purpose of study is to confirm diagnostic efficiency of mass spectrometry approach in evaluation of сarbapenemase activity in clinical isolates of P. aeruginosa. The study was targeted to detection of сarbapenemases in 50 clinical isolates of P. aeruginosa, non-sensitive to сarbapenemas (control group - 9 isolates of P. aeruginosa sensitive to сarbapenemas). The comparative analysis was implemented concerning the results obtained using laser desorption ionization time-of-flight mass spectrometry and using such common techniques as phenotype detection of presence of metallo-beta-lactamase using E-tests and detection of presence of genes of carbapenemases (VIM, IMP, NDM) using polymerase chain reaction in real-time. The metallo-beta-lactamase activity was established in 14 (28%) out of 50 non-sensitive to сarbapenemas strains. All of them had genes of carbapenemases VIM-type. No IMP and NDM genes were detected in any strain. The VIM genes were detected only in metallo-beta-lactamase positive strains and metallo-beta-lactamase activity was registered only in carriers of VIM genes. According data of MALDI-TOF, all metallo-beta-lactamase and VIM positive strains demonstrated increased capacity of hydrolyzing meropenem. The percentage of hydrolysis under testing of the given strains made up to from 7.6 to 59.3. The absence of carbapenemase activity was demonstrated by 36 (72%) out of 50 strains non-sensitive to сarbapenemases with percentage of hydrolysis from 0 to 4. None of 9 control isolates sensitive to сarbapenemases had metallo-beta-lactamase activity, carried analyzed genes of сarbapenemas and hydrolyzed meropenem. The MALDI-TOF mass spectrometry is a perspective technique to be applied in practice of clinical microbiology for detect isolates of P. aeruginosa, producing сarbapenemases., Competing Interests: The authors declare no conflict of interest.

In recent years, because of carbapenemase spreading in Klebsiella pneumoniae strains, the antibiotic of reserve group, colistin, is increasingly prescribed. In vitro testing of colistin susceptibility in everyday practice has a number of difficulties due to the cationic properties of molecule and weak diffusion into agar. Therefore it is recommended to use the reference Broth Microdilution Method (BMD) for determination of the Minimum Inhibitory Concentration (MIC) for colistin. The purpose of the study was to determine susceptibility to colistin in 119 carbapenem-resistant K. pneumoniae (CRKp) which were isolated from the patients at three hospitals in Moscow in 2012-2016 by the broth microdilution method (BMD) and to compare these data with the ones obtained by epsilometer test (E-test) and VITEK 2 Compact. The proportion of resistant isolates (MIC>2 mg/L) was 52%, 39%, 35% respectively. Both commercial methods demonstrated a high level of the very major error (VME) that was 26% for the E-test method and 34% for the VITEK 2 Compact. The values of categorical agreement and essential agreement (CA, EA) were less than 90%. A single major error (ME) was detected for the VITEK 2 Compact. In conclusion, results of both commercial tests for determination of MIC for colistin showed differences with the results of the reference BMD. It is necessary for clinical laboratories to be aware about this discrepancy and to use E-tests and VITEK 2 Compact with caution to determine colistin susceptibility., Competing Interests: The authors declare no conflict of interest.