Detection of carbapenemase-producing Pseudomonas aeruginosa: Evaluation of the carbapenem inactivation method (CIM)

Molecular epidemiology of carbapenem-resistant gram-negative bacilli in Ecuador

INTRODUCTION

Carbapenem-resistant gram-negative bacilli are a worldwide concern because of high morbidity and mortality rates. Additionally, the increasing prevalence of these bacteria is dangerous. To investigate the extent of antimicrobial resistance and prioritize the utility of novel drugs, we evaluated the molecular characteristics and antimicrobial susceptibility profiles of carbapenem-resistant Enterobacterales, Pseudomonas aeruginosa and Acinetobacter baumannii in Ecuador in 2022.

METHODS

Ninety-five clinical isolates of carbapenem non-susceptible gram-negative bacilli were collected from six hospitals in Ecuador. Carbapenem resistance was confirmed with meropenem disk diffusion assays following Clinical Laboratory Standard Institute guidelines. Carbapenemase production was tested using a modified carbapenemase inactivation method. Antimicrobial susceptibility was tested with a disk diffusion assay, the Vitek 2 System, and gradient diffusion strips. Broth microdilution assays were used to assess colistin susceptibility. All the isolates were screened for the blaKPC, blaNDM, blaOXA-48, blaVIM and blaIMP genes. In addition, A. baumannii isolates were screened for the blaOXA-23, blaOXA-58 and blaOXA-24/40 genes.

RESULTS

Carbapenemase production was observed in 96.84% of the isolates. The blaKPC, blaNDM and blaOXA-48 genes were detected in Enterobacterales, with blaKPC being predominant. The blaVIM gene was detected in P. aeruginosa, and blaOXA-24/40 predominated in A. baumannii. Most of the isolates showed co-resistance to aminoglycosides, fluoroquinolones, and trimethoprim/sulfamethoxazole. Both ceftazidime/avibactam and meropenem/vaborbactam were active against carbapenem-resistant gram-negative bacilli that produce serin-carbapenemases.

CONCLUSION

The epidemiology of carbapenem resistance in Ecuador is dominated by carbapenemase-producing K. pneumoniae harbouring blaKPC. Extensively drug resistant (XDR) P. aeruginosa and A. baumannii were identified, and their identification revealed the urgent need to implement strategies to reduce the dissemination of these strains.

Uncovering the Resistance Mechanisms in Extended-Drug-Resistant Pseudomonas aeruginosa Clinical Isolates: Insights from Gene Expression and Phenotypic Tests

(1) Background: The purpose of the study was to describe the activity of mex efflux pumps in Multidrug-Resistant (MDR) clinical isolates of Pseudomonas aeruginosa and to compare the carbapenem-resistance identification tests with PCR; (2) Methods: Sixty MDR P. aeruginosa were analyzed for detection of carbapenemase by disk diffusion inhibitory method, carbapenem inactivation method and Modified Hodge Test. Endpoint PCR was used to detect 7 carbapenemase genes (blaKPC, blaOXA48-like, blaNDM, blaGES-2, blaSPM, blaIMP, blaVIM) and mcr-1 for colistin resistance. The expression of mexA, mexB, mexC, mexE and mexX genes corresponding to the four main efflux pumps was also evaluated; (3) Results: From the tested strains, 71.66% presented at least one carbapenemase gene, with blaGES-2 as the most occurring gene (63.3%). Compared with the PCR, the accuracy of phenotypic tests did not exceed 25% for P. aeruginosa. The efflux pump genes were present in all strains except one. In 85% of the isolates, an overactivity of mexA, mexB and mostly mexC was detected. Previous treatment with ceftriaxone increased the activity of mexC by more than 160 times; (4) Conclusions: In our MDR P. aeruginosa clinical isolates, the carbapenem resistance is not accurately detected by phenotypic tests, due to the overexpression of mex efflux pumps and in a lesser amount, due to carbapenemase production.

The Revolution of Lateral Flow Assay in the Field of AMR Detection

The global spread of antimicrobial resistant (AMR) bacteria represents a considerable public health concern, yet their detection and identification of their resistance mechanisms remain challenging. Optimal diagnostic tests should provide rapid results at low cost to enable implementation in any microbiology laboratory. Lateral flow assays (LFA) meet these requirements and have become essential tools to combat AMR. This review presents the versatility of LFA developed for the AMR detection field, with particular attention to those directly triggering β-lactamases, their performances, and specific limitations. It considers how LFA can be modified by detecting not only the enzyme, but also its β-lactamase activity for a broader clinical sensitivity. Moreover, although LFA allow a short time-to-result, they are generally only implemented after fastidious and time-consuming techniques. We present a sample processing device that shortens and simplifies the handling of clinical samples before the use of LFA. Finally, the capacity of LFA to detect amplified genetic determinants of AMR by isothermal PCR will be discussed. LFA are inexpensive, rapid, and efficient tools that are easy to implement in the routine workflow of laboratories as new first-line tests against AMR with bacterial colonies, and in the near future directly with biological media.

Evaluation of the rCIM for carbapenemase detection in Enterobacterales and Pseudomonas aeruginosa and description of the TSBrCIM, an optimized variant

OBJECTIVES

The rapid Carbapenem Inactivation Method (rCIM) was evaluated with a strain collection of 164 and 69 carbapenem-resistant Enterobacterales and Pseudomonas aeruginosa, respectively, that produced various carbapenemases. For an improved carbapenemase detection in Enterobacterales, an optimized variant of the rCIM named TSBrCIM was developed.

METHODS

Bacterial isolates were incubated with two meropenem disks in distilled water (rCIM) or tryptic soy broth (TSBrCIM). After centrifugation, the supernatant was incubated with a susceptible E. coli indicator strain in tryptic soy broth. Growth of the indicator strain implied carbapenemase activity in the test strain.

RESULTS

The rCIM detected 100/113 carbapenemase-producing Enterobacterales, resulting in a sensitivity of 88.5% and a specificity of 94.1%. For P. aeruginosa, sensitivity and specificity were 96.0% and 100%, respectively. The TSBrCIM was able to detect 105/113 carbapenemase-producing Enterobacterales, resulting in a sensitivity of 92.9% and a specificity of 96.1%.

CONCLUSION

This study shows that the TSBrCIM can be valuable tool for detection of carbapenemases in Enterobacterales in the clinical laboratory, while the rCIM showed the best results for carbapenemase detection in P. aeruginosa.

An Application of Imipenem Discs or P. aeruginosa ATCC 27853 Reference Strain Increases Sensitivity of Carbapenem Inactivation Method for Non-Fermenting Gram-Negative Bacteria

Non-fermenting Gram-negative rods are one of the most commonly isolated bacteria from human infections. These microorganisms are typically opportunistic pathogens that pose a serious threat to public health due to possibility of transmission in the human population. Resistance to beta-lactams, due to carbapenemases synthesis, is one of the most important antimicrobial resistance mechanisms amongst them. The aim of this study was to evaluate the usefulness of the Carbapenem Inactivation Method (CIM), and its modifications, for the detection of carbapenemase activity amongst non-fermenting Gram-negative rods. This research involved 81 strains of Gram-negative rods. Of the tested strains, 55 (67.9%) synthesized carbapenemases. For non-fermenting rods, 100% sensitivity and specificity was obtained in the version of the CIM test using imipenem discs and E. coli ATCC 25922 strain. The CIM test allows for differentiation of carbapenems resistance mechanisms resulting from carbapenemase synthesis from other resistance types. It is a reliable diagnostic method for the detection of carbapenemase activity amongst non-fermenting Gram-negative rods. Application of imipenem discs and P. aeruginosa ATCC 27853 reference strain increases CIM results sensitivity, while imipenem discs and E. coli ATCC 25922 strain use maintains full precision of the test for non-fermenting rods.

The Novel CarbaLux Test for Carbapenemases and Carbapenem Deactivating AmpC Beta-Lactamases

Objectives

To evaluate the rapid phenotypic CarbaLux test for routine diagnostics in the medical laboratory in a proof of concept study.

Methods

isolates of Gram-negative bacteria suspicious for carbapenem resistance including Enterobacterales (67), Pseudomonas (10), Acinetobacter (5), and Stenotrophomonas (1) species, collected between 2016 and 2018 from in-patients, were tested for carbapenemase activity using a novel fluorescent carbapenem. When subjected to extracted bacterial carbapenemases its fluorescence disappears. All bacteria to be tested were cultured on Columbia blood agar and few on other commercial media. MALDI TOF MS, molecular assays, automated MIC testing, and in part, agar diffusion tests served to characterize the isolates. For comparison, few selected bacteria were also investigated by prior phenotypic tests for carbapenemase detection.

Results

Under UV light, the CarbaLux test allowed a rapid detection of 39/39 carbapenemase-producing bacteria, including 15 isolates with OXA carbapenemases (e.g., OXA-23, OXA-24/40-like OXA-48-like or OXA-181). Several isolates had low MICs but still expressed carbapenemases. Among Enterobacter spp., it detected six strains with hyper-produced AmpC beta-lactamases, which deactivated carbapenems but were not detectable by prior rapid phenotypic assays. An unexpected high carbapenemase activity appeared with these enzymes. They were identified as AmpC variants by inhibition with cloxacillin.

Conclusion

Other than prior rapid phenotypic assessments for carbapenemases, which use secondary effects such as a change of pH, the inactivation of the fluorescent carbapenem substrate can be visualized directly under UV light. The new test works at 100 to 200-fold lower, therapy-like substrate concentrations. It takes advantage of the high substrate affinity to carbapenemases allowing also the detection of less reactive resistance enzymes via a trapping mechanism, even from bacteria, which might appear unsuspicious from initial antibiograms. The novel fluorescence method allows simple and safe handling, reliable readings, and documentation and is suitable for primary testing in the clinical laboratory.