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Proteus mirabilis - analysis of a concealed source of carbapenemases and development of a diagnostic algorithm for
Axel Hamprecht1, Janko Sattler2, Janina Noster3
1Institute for Medical Microbiology and Virology, University of Oldenburg and Klinikum Oldenburg, Oldenburg, Germany; Institute for Medical Microbiology, Immunology and Hygiene, University Hospital Cologne and Faculty of Medicine, University of Cologne, Cologne, Germany; DZIF (German Centre for Infection Research), Partner Site Bonn-Cologne, Cologne, Germany.
Objectives:
To analyse carbapenemases in Proteus mirabilis and assess the performance of carbapenemase detection assays.
Methods:
Eighty-one clinical P. mirabilis isolates with high-level resistance at least to ampicillin (>32 mg/L) or previous detection of carbapenemases were selected and investigated by three susceptibility testing methods (microdilution, automated susceptibility testing, and disk diffusion), six phenotypic carbapenemase assays (CARBA NP, modified carbapenemase inactivation method [CIM], modified zinc-supplemented CIM, simplified CIM, faropenem, and carbapenem-containing agar), two immunochromatographic assays, and whole-genome sequencing.
Results:
Carbapenemases were detected in 43 of 81 isolates (OXA-48-like [n = 13]; OXA-23 [n = 12]; OXA-58 [n = 12]; New Delhi metallo-β-lactamase (NDM) [n = 2]; Verona integron-encoded metallo-β-lactamase (VIM) [n = 2]; Imipenemase (IMP) [n = 1]; Klebsiella pneumoniae carbapenemase (KPC) [n = 1]). Carbapenemase-producing Proteus were frequently susceptible to ertapenem (26/43; 60%), meropenem (28/43; 65%), ceftazidime (33/43; 77%), and some even to piperacillin-tazobactam (9/43; 21%). Sensitivity/specificity of phenotypic tests were 30% (CI: 17-46%)/89% (CI: 75-97%) for CARBA NP, 74% (CI: 60-85%)/82% (CI: 67-91%) for faropenem, 91% (CI: 78-97%)/82% (CI: 66-92%) for simplified CIM, and 93% (CI: 81-99%)/100% (CI: 91-100%) for modified zinc-supplemented CIM. An algorithm for improved detection was developed, which demonstrated sensitivity/specificity of 100% (CI: 92-100%)/100% (CI: 91-100%) on the 81 isolates, and 100% (CI: 29-100%)/100% (CI: 96-100%) in a prospective analysis of additional 91 isolates. Interestingly, several OXA-23-producing isolates belonged to the same clonal lineage reported previously from France.
Discussion:
Current susceptibility testing methods and phenotypic tests frequently fail to detect carbapenemases in P. mirabilis, which could result in inadequate antibiotic treatment. In addition, the non-inclusion of blaOXA-23/OXA-58 in many molecular carbapenemase assays further impedes their detection. Therefore, the prevalence of carbapenemases in P. mirabilis is likely underestimated. With the herein proposed algorithm, carbapenemase-producing Proteus can be easily identified.
Insights
Standard tests often miss carbapenemases in Proteus mirabilis, leading to underestimation and potential treatment failures. A new algorithm accurately detects these carbapenemase-producing Proteus strains.
Area of Science:
- Clinical microbiology
- Antimicrobial resistance
- Molecular biology
Background:
- Proteus mirabilis is a common cause of healthcare-associated infections.
- Carbapenemase production in P. mirabilis is an emerging threat, complicating treatment options.
Purpose of the Study:
- To analyze carbapenemases in Proteus mirabilis isolates.
- To evaluate the performance of various carbapenemase detection assays.
Main Methods:
- Investigated 81 clinical P. mirabilis isolates using multiple susceptibility testing methods.
- Employed six phenotypic carbapenemase assays, two immunochromatographic assays, and whole-genome sequencing.
- Developed and validated a novel detection algorithm.
Main Results:
- Carbapenemases were identified in 43 of 81 isolates, including OXA-48-like, OXA-23, OXA-58, NDM, VIM, IMP, and KPC.
- Many carbapenemase-producing isolates remained susceptible to certain antibiotics like ertapenem and meropenem.
- The developed algorithm achieved 100% sensitivity and specificity in detecting carbapenemases.
Conclusions:
- Current susceptibility testing and phenotypic assays frequently fail to detect carbapenemases in P. mirabilis.
- The prevalence of carbapenemases in P. mirabilis is likely underestimated.
- The proposed algorithm offers an accurate and easy method for identifying carbapenemase-producing Proteus.
