Evaluation of phenotypic tests for detection of carbapenemases: New modifications with new interpretation

Antimicrobial and Diagnostic Stewardship of the Novel β-Lactam/β-Lactamase Inhibitors for Infections Due to Carbapenem-Resistant Enterobacterales Species and Pseudomonas aeruginosa

Carbapenem-resistant Gram-negative bacterial infections are a major public health threat due to the limited therapeutic options available. The introduction of the new β-lactam/β-lactamase inhibitors (BL/BLIs) has, however, altered the treatment options for such pathogens. Thus, four new BL/BLI combinations-namely, ceftazidime/avibactam, meropenem/vaborbactam, imipenem/relebactam, and ceftolozane/tazobactam-have been approved for infections attributed to carbapenem-resistant Enterobacterales species and Pseudomonas aeruginosa. Nevertheless, although these antimicrobials are increasingly being used in place of other drugs such as polymyxins, their optimal clinical use is still challenging. Furthermore, there is evidence that resistance to these agents might be increasing, so urgent measures should be taken to ensure their continued effectiveness. Therefore, clinical laboratories play an important role in the judicious use of these new antimicrobial combinations by detecting and characterizing carbapenem resistance, resolving the presence and type of carbapenemase production, and accurately determining the minimum inhibitor concentrations (MICs) for BL/BLIs. These three targets must be met to ensure optimal BL/BLIs use and prevent unnecessary exposure that could lead to the development of resistance. At the same time, laboratories must ensure that results are interpreted in a timely manner to avoid delays in appropriate treatment that might be detrimental to patient safety. Thus, we herein present an overview of the indications and current applications of the new antimicrobial combinations and explore the diagnostic limitations regarding both carbapenem resistance detection and the interpretation of MIC results. Moreover, we suggest the use of alternative narrower-spectrum antibiotics based on susceptibility testing and present data regarding the effect of synergies between BL/BLIs and other antimicrobials. Finally, in order to address the absence of a standardized approach to using the novel BL/BLIs, we propose a diagnostic and therapeutic algorithm, which can be modified based on local epidemiological criteria. This framework could also be expanded to incorporate other new antimicrobials, such as cefiderocol, or currently unavailable BL/BLIs such as aztreonam/avibactam and cefepime/taniborbactam.

Recombinase Polymerase Amplification Combined with Lateral Flow Strip for Rapid Detection of OXA-48-like Carbapenemase Genes in Enterobacterales

Carbapenem-resistant Enterobacterales (CRE) possessing various carbapenemases, particularly the OXA-48 group, are now rapidly spreading and becoming a major public health concern worldwide. Phenotypic detection of OXA-48-like carbapenemases is still suboptimal due to their weak carbapenemase activity, whereas highly sensitive and specific polymerase chain reaction (PCR)-based methods take at least 3–4 h. We, therefore, developed a recombinase polymerase amplification (RPA) combined with lateral flow (LF) strip assay for the rapid detection of bla_OXA-48-like in Enterobacterales. A total of 131 clinical isolates including 61 bla_OXA-48-like-carrying Enterobacterales isolates and 70 Gram-negative bacilli isolates containing other bla genes were subjected to the RPA method performed under isothermal conditions at 37 °C within 10 min and visually inspected by LF strip within 5 min. The RPA-LF assay provided 100% sensitivity (95% confidence interval, 92.6–100%) and 100% specificity (93.5–100%) for detecting bla_OXA-48-like genes from bacterial colonies. Its detection limit was 100 times less than that of the PCR method. This assay is rapid, easy to perform, and provides excellent performance without any special equipment. It may be applied for directly identifying the bla_OXA-48-like genes in Enterobacterales obtained from blood culture. Rapid identification of carbapenemase types is essential for selecting appropriate antimicrobial options, particularly the β-lactams combined with novel β-lactamase inhibitors.

In Vitro Activity of Plazomicin among Carbapenem-resistant Enterobacteriaceae

Background:  Carbapenem-resistant Enterobacteriaceae (CRE) have been disseminated worldwide and became a global threat. Due to limited therapeutic drugs plazomicin - a new semisynthetic aminoglycoside - have been suggested as an alternative option owing to its stability against aminoglycosides modifying enzymes (AMEs). This study aims to assess the in vitro activity of plazomicin against CRE isolates and to detect different types of carbapenemases among these isolates. Material and Methods: In this study, 102 CRE isolates were collected from different clinical samples at Cairo University hospitals and the presence of carbapenemases was detected by modified carbapenem inhibition method (mCIM) and multiplex PCR tests. Plazomicin susceptibility testing was done using E test. Results: The most frequently detected carbapenemase genes were blaNDM in 75 (73.5%) isolates, followed by blaOXA-48 in 57 (55.9%) and blaKPC in 16 (15.5%) isolates. Plazomicin was active against 32 (31.4%) isolates. Among the isolates carrying blaNDM gene only and those carrying blaOXA-48 gene only, 21% and 41% were sensitive to plazomicin, respectively. Plazomicin showed the highest sensitivity against CRE isolates compared to the other tested antibiotics. Conclusion: Plazomicin might be a good option for treatment of infections caused by CRE. In health care settings where blaNDM gene is prevalent, plazomicin may not be a good therapeutic option for CRE infections.