Colistin resistance of carbapenem-resistant Klebsiella pneumoniae strains: molecular mechanisms and bacterial fitness

The increasing use of colistin in the clinic has led to the emergence and spread of colistin resistance. According to the literature, antibiotic resistance can have a metabolic cost, resulting in poor adaptation and survival, i.e. reduced bacterial fitness. The aim of this study was to investigate molecular mechanisms underlying resistance to colistin and their effect on the bacterial fitness of carbapenem-resistant (carba-R) strains of K. pneumoniae isolated from the patients of Moscow hospitals in 2012–2017. Of 159 analyzed carba-R isolates, 71 (45%) were resistant to colistin (minimum inhibitory concentration over 2 mg/L). By conducting Sanger sequencing, we were able to identify the mechanisms underlying colistin resistance in 26 (37%) isolates. Growth curves were constructed by measuring optical density at 600 nm wavelength for 15 hours. The competitive growth of colistin-resistant (col-R) K. pneumoniae isolates was assessed relative to the colistin-susceptible (col-S) isolate. Col-R and col-S cultures harvested in the exponential phase were combined at the ratio of 1:1, incubated in the Luria-Bertani medium and plated onto Luria-Bertani agar plates with 10 mg/L colistin and without it. The competition index was calculated as the ratio of grown col-R and col-S colonies. Resistance to colistin did not affect the growth kinetics of K. pneumoniae, but did reduce the competitive ability of the bacteria as compared to the col-S isolates. However, some col-R isolates were more competitive than the col-S strains of the same sequence type. Further research is needed to elucidate the effects of colistin resistance on bacterial fitness.

[The mass-spectrometric evaluation of сarbapenemase activity of Pseudomonas aeruginosa.]

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.

[The comparison of methods for determination of colistin susceptibility in carbapenem-resistant Klebsiella pneumoniae.]

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.

[SPECTRUM OF ANTIBIOTIC RESISTANCE AND PREVALENCE OF OXA-CARBAPENEMASES AMONG ACINETOBACTER BAUMANNII STRAINS, ISOLATED FROM PATIENTS OF SURGICAL AND REANIMATION DEPARTMENTS IN MOSCOW]

AIM

Characterize spectrum of antibiotics resistance of Acinetobacter baumannii strains, isolated from patients of 8 surgical and reanimation departments of 3 medical institution of Moscow, and determine molecular-genetic mechanisms of stability of their carbapenem-resistant forms.

MATERIALS AND METHODS

95 strains of A. baumannii, isolated from patients of reanimation and surgical departments of Moscow in 2012-2014, were studied. Sensitivity of strains to antibiotics was tested phenotypically according to recommendations of EUCAST. The presence of VIM, IMP, OXA-23, OXA-40, OXA-48, OXA-58 and NDM genes in the studied strains was determined by polymerase chain reaction in real time.

RESULTS

86.3% of strains turnedout to be non-sensitive to carbapenems, sensitive--13.7%. 80.0% of strains were non-sensitive to gentamicin, 80.0% of strains--to netilmicin, 94.7% of strains--to ciprofloxacin 2.1%--to colistin. 91.6% of isolates have shown non-sensitivity to members of 2 and more classes of antibiotics, 78.9% of strains--to members of 3 classes. 2 strains were panresistant, 4.2% (4/95) of the isolates were sensitive to all the classes of antibiotics. Metallo-β-lactamases were not detected. Genes of carbapenemases (OXA-23 and/or OXA-40) were detected in 85.3% (81/95) of strains, characterized phenotypically as non-sensitive to carbapenems.

CONCLUSION

The results obtained shown an increase of resistance to carbapenems and multiple resistance in clinically significant strains of A. baumannii. Resistance to carbapenems is associated with OXA-23 and OXA-40 genes. The conclusions allow to justify perspectives of introduction of technologies of molecular-genetic testing of antibiotics resistance.

[Monitoring and antibiotic resistance profile of tracheal aspirate microbiota in ICU children with severe craniocerebral trauma]

Nosocomial infections and their rational antibiotic treatment represent a major challenge for the healthcare nowadays. In this context, gramnegative bacteria including Pseudomonas aeruginosa, Acinetobacter baumanii and Enterobacteriaceae spp. are etiologically important and characterized by a significant level of antibiotic resistance. To examine dynamics of the respiratory tract colonization by hospital flora, tracheal aspirates obtained at three time points from 69 children with severe craniocerebral trauma during their stay in ICU were analysed. Colonization was observed on the 4th day of the ICU stay with predomination of K. pneumoniae (45%) and A. baumanii (27-37%). P. aeruginosa was detected after the 8th day of the ICU stay with the isolation rate of 33%. Substantial proportions of P. aeruginosa (61%), A. baumanii (78%) and K. pneumoniae (25%) were resistant to carbapenems. In 65 carbapemen resistant isolates, the presence of carbapenemases was examined using PCRs. OXA-48 carbapenemase was detected in 11 out of 14 (78%) K. pneumoniae isolates. Among the A. baumanii isolates, 30/31 (97%) carried OXA-40 and 1/31 (3%) had OXA-23 carbapenemases. None of the examined A. baumanii and K. pneumoniae isolates produced metallo-betalactamases (MBL). In contrast, all 20 carbapenem resistant P. aeruginosa isolates produced a MBL, and in 12 out of 20 (60%) of theme VIM-2 was detected. Thus, gramnegative nosocomial microflora rapidly colonizes ICU patients and has a high level of resistance to antibiotics, including carbapenems.