Phenotypic and molecular identification of carbapenemase-producing Enterobacteriaceae - challenges in diagnosis and treatment

Carbapenem resistance determinants in Klebsiella pneumoniae strains isolated from blood cultures-comparative analysis of molecular and phenotypic methods

Introduction: This study provides data on carbapenemases identified in carbapenem-resistant Klebsiella pneumoniae (CR-KP) isolated from blood-cultures by the multiplex molecular method.

Material and method: Between October 2016 and September 2017, 47 non-duplicate Klebsiella pneumoniae (KP) were isolated from blood cultures, from hospitalized patients in the Regional Institute of Gastroenterology and Hepathology, Cluj-Napoca, Romania. Identification and antimicrobial susceptibility tests (AST) were performed by Vitek 2 Compact. The combination disks test (CDT) was used for phenotypic analysis and the LightCycler® Multiplex DNA assay was used to detect and identify the carbapenemases by the LightCycler®z 480 Instrument. The following targets were chosen: blaKPC, blaNDM, blaGES, blaIMP and blaOXA-48 genes and the Cobas® 4800 software variant 2.2.0 was used for the results interpretation.

Results: Taking into consideration the meropenem minimum inhibitory concentration (MIC), 29 KP were susceptible and 18 were not-susceptible (MIC≥0.5 µg ml-1). In the CR-KP group, the CDT identified OXA-48 (10/18) and KPC (7/18) producers. One isolate showed a noninterpretable profile. The multiplex molecular analyses confirmed the carbapenemases production as: 9 CR-KP were KPC and OXA-48 co-producers, 8 were OXA-48 and one was KPC producing strains. In CR-KP group, we found a significant correlation between the CDT and RT-PCR tests results, concerning KPC (p = 0.671). Eight phenotypic results were confirmed by molecular Light-Cycler® Multiplex DNA assay. For CR-KP co-producers (KPC and OXA-48), the CDT could indicate only one carbapenem-hydrolyzing enzyme.

Conclusion: This study highlights the CR-KP co-producers (OXA-48 and KPC). OXA-48-like is more frequently encountered in our area than other carbapenemases.

Municipal Wastewaters Carry Important Carbapenemase Genes Independent of Hospital Input and Can Mirror Clinical Resistance Patterns

The spatiotemporal variation of several carbapenemase-encoding genes (CRGs) was investigated in the influent and effluent of municipal WWTPs, with or without hospital sewage input. Correlations among gene abundances, bacterial community composition, and wastewater quality parameters were tested to identify possible predictors of CRGs presence. Also, the possible role of wastewaters in mirroring clinical resistance is discussed. The taxonomic groups and gene abundances showed an even distribution among wastewater types, meaning that hospital sewage does not influence the microbial diversity and the CRG pool. The bacterial community was composed mainly of Proteobacteria, Firmicutes, Actinobacteria, Patescibacteria, and Bacteroidetes. Acinetobacter spp. was the most abundant group and had the majority of operational taxonomic units (OTUs) positively correlated with CRGs. This agrees with recent reports on clinical data. The influent samples were dominated by blaKPC, as opposed to effluent, where blaIMP was dominant. Also, blaIMP was the most frequent CRG family observed to correlate with bacterial taxa, especially with the Mycobacterium genus in effluent samples. Bacterial load, blaNDM, blaKPC, and blaOXA-48 abundances were positively correlated with BOD5, TSS, HEM, Cr, Cu, and Fe concentrations in wastewaters. When influent gene abundance values were converted into population equivalent (PE) data, the highest copies/1 PE were identified for blaKPC and blaOXA-48, agreeing with previous studies regarding clinical isolates. Both hospital and non-hospital-type samples followed a similar temporal trend of CRG incidence, but with differences among gene groups. Colder seasons favored the presence of blaNDM, blaKPC and blaOXA-48, whereas warmer temperatures show increased PE values for blaVIM and blaIMP. IMPORTANCE Wastewater-based epidemiology has recently been recognized as a valuable, cost-effective tool for antimicrobial resistance surveillance. It can help gain insights into the characteristics and distribution of antibiotic resistance elements at a local, national, and even global scale. In this study, we investigated the possible use of municipal wastewaters in the surveillance of clinically relevant carbapenemase-encoding genes (CRGs), seen as critical antibiotic resistance determinants. In this matter, our results highlight positive correlations among CRGs, microbial diversity, and wastewater physical and chemical parameters. Identified predictors can provide valuable data regarding the level of raw and treated wastewater contamination with these important antibiotic resistance genes. Also, wastewater-based gene abundances were used for the first time to observe possible spatiotemporal trends of CRGs incidence in the general population. Therefore, possible hot spots of carbapenem resistance could be easily identified at the community level, surpassing the limitations of health care-associated settings.

Comparison of Six Phenotypic Assays with Reference Methods for Assessing Colistin Resistance in Clinical Isolates of Carbapenemase-Producing Enterobacterales: Challenges and Opportunities

The global escalation of severe infections due to carbapenemase-producing Enterobacterales (CPE) isolates has prompted increased usage of parenteral colistin. Considering the reported difficulties in assessing their susceptibility to colistin, the purpose of the study was to perform a comparative evaluation of six phenotypic assays—the colistin broth disc elution (CBDE), Vitek 2 Compact (bioMérieux SA, Marcy l’Etoile, France), the Micronaut MIC-Strip Colistin (Merlin Diagnostika GMBH, Bornheim-Hensel, Germany), the gradient diffusion strip Etest (bioMérieux SA, Marcy l’Etoile, France), ChromID Colistin R Agar (COLR) (bioMérieux SA, Marcy l’Etoile, France), and the Rapid Polymyxin NP Test (ELITechGroup, Signes, France)—versus the reference method of broth microdilution (BMD). All false resistance results were further assessed using population analysis profiling (PAP). Ninety-two nonrepetitive clinical CPE strains collected from two hospitals were evaluated. The BMD confirmed 36 (39.13%) isolates susceptible to colistin. According to the BMD, the Micronaut MIC-Strip Colistin, the CBDE, and the COLR medium exhibited category agreement (CA) of 100%. In comparison with the BMD, the highest very major discrepancy (VMD) was noted for Etest (n = 15), and the only false resistance results were recorded for the Rapid Polymyxin NP Test (n = 3). Only the PAP method and the Rapid Polymyxin NP Test were able to detect heteroresistant isolates (n = 2). Thus, there is an urgent need to further optimize the diagnosis strategies for colistin resistance.

Multiplex lateral flow immunochromatographic assay is an effective method to detect carbapenemases without risk of OXA-48-like cross reactivity

BACKGROUND

It is essential to detect carriers of carbapenemase-producing Enterobacterales in order to implement infection control measures. The objectives of this study was to evaluate the NG-Test® CARBA 5 (CARBA 5) assay for detection of five carbapenemases and to assess the cross reactivity of other OXA-type carbapenemases with the OXA-48-like specific antibodies.

METHODS

A total of 197 Enterobacterales isolates were tested. To evaluate the cross reactivity, 73 carbapenem-resistant A. baumannii, harboring OXA-type variants, were tested. Polymerase chain reaction (PCR) served as gold standard for carbapenemase identification.

RESULTS

Excellent agreement was found between PCR and CARBA 5, for all but one isolate. The single false positive result (a blaSME positive S. marcescens isolate) was incorrectly positive for blaOXA-48 by CARBA 5. No cross reactivity was observed. The sensitivity and specificity were 100.0% and 98.0%, respectively.

CONCLUSIONS

The CARBA 5 assay is highly sensitive and specific and is recommended as a tool for the detection of the main carbapenemases of interest in clinical microbiology laboratories.

Difficult to Treat Proteeae strains in high risk Romanian hospital departments

Introduction: Resistance to first-line antibiotics of the Proteeae strains within the difficult-to-treat (DTR) phenotype is a cause of limitation of therapeutic options. The study aimed to characterize these strains, to identify the factors that influence their acquisition and the predictive factors for the patient’s evolution.

Material and methods: Between July 2017 and January 2019, 400 of Proteeae strains were isolated from samples of patients admitted to intensive care units (ICUs) and surgical wards of a university hospital in Romania. The identification and testing of antibiotic sensitivity was performed using the Vitek 2 Compact system. The DTR phenotype was defined as the resistance (or intermediate resistance) to all categories of β-lactams, carbapenems and fluoroquinolones.

Results: Out of 400 Proteeae strains, 21% were of the DTR type, most of them from the species Providencia stuartii and Proteus mirabilis, identified predominantly on the ICUs. The excess fatality in the DTR subsample compared to the non-DTR subsample was 16.37%. The multivariate analysis identified as independent risk factors: the number of antibiotics administered, the number of days of urinary catheterization, the presence of tracheostomy, nasogastric nutrition, respectively belonging to the species P. stuartii. The probabilities of survival were reduced by the presence of the central venous catheter (CVC), tracheostomy, by the increase of the number of hospitalization days respectively of the number of antibiotics administered.

Conclusion: The DTR phenotype in the case of Proteeae strains has been associated especially with the species P. stuartii, with invasive exogenous factors and with an increased fatality.

Molecular epidemiology and the clinical impact of carbapenemase-producing Enterobacterales isolates among adult patients: aspects from a Romanian non-teaching hospital

Introduction: A dramatic increase of infections induced by carbapenemase-producing Enterobacterales (CPE) has been registered worldwide. The aim of this study was to evaluate the molecular epidemiology and the clinical impact of CPE strains isolated from adult inpatients.

Material and methods: A one-year, single-center, retrospective observational study including 34 consecutive patients with 37 non-duplicate CPE strains recovered from clinical specimens was accomplished. The Vitek 2 Compact, M.I.C.Evaluator strips, the modified carbapenem inactivation method (mCIM), and the combination disks test (KPC, MBL, OXA-48 Confirm kit, Rosco Diagnostica) were applied as phenotypic tests. A multiplex polymerase chain reaction (PCR) assay was used for detection of blaKPC, blaNDM, and blaOXA-48-like genes. The clonality was assessed with pulsed-field gel electrophoresis (PFGE).

Results: Klebsiella pneumoniae (n=25) was the most frequent CPE encountered. The carbapenemase types were NDM (n=13), KPC (n=12), and OXA-48-like (n=12). Two distinct clonal clusters were identified among the 12 KPC positive strains. All CPE isolates exhibited non-susceptibility to carbapenems, cephalosporins, ciprofloxacin. Respiratory tract infections (n=16) and hospitalization in the intensive care unit (ICU) (n=14) were dominant. The most common comorbidity was congestive heart failure (n=11). Monotherapy was the main strategy adopted (n=15). Death occurred in 18 patients.

Conclusions: Our analysis underscores the scarcity of antibiotic solutions and high mortality. Monotherapy for urinary tract infections (UTIs) is beneficial. Inter- or intrahospital dissemination of successful epidemic clones is proved. The adequate CPE infections control programs and antimicrobial policies are essential..

Carbapenemase Producing Enterobacterales in Romania: Investigating the Origins

Carbapenemase-producing Enterobacterales (CPE) have emerged and spread in Romania since 2010. According to the reports of the EuSPACE (European survey of carbapenemase-producing Enterobacteriaceae) the epidemio-logical stage of the CPE expansion in Romania has shifted from sporadic occurrence in 2013 directly to inter-regional spread in 2014-2015. In this study we aimed to provide data from the timeframe when the dissemination of the carbapenemase genes in Romania began, by retrospectively analyzing CPE strains in a tertiary care university hospital. During the period of November 2012 – October 2013 we found 107 CPE (8.78%) out of 1219 non-duplicate Enterobacterales strains. 26 isolates of various Enterobacterales species carried blaNDM-1, 83 Klebsiella pneumoniae strains were positive for blaOXA-48-like and 2 of these co-harboured blaNDM-1. The increased incidence of OXA-48 producing K. pneumoniae was linked to a two-peaked hospital outbreak during February and May 2013. The percentage of 24.3% of NDM-1 producers was alarming due to the diversity of involved species and the higher resistance levels to carbapenems compared with blaOXA-48-like gene carriers. Plasmid replicon typing revealed a great diversity of plasmids in NDM-1-positive strains, belonging to incompatibility groups A/C, FII, FIIk, HI2, L and M. The strong connection between certain plasmid groups and host species suggests that the transfer of broad host-range plasmids through conjugation does not play the main role in the successful spread of blaNDM-1 among Enterobacterales species.