Evaluation of the EDTA-Modified Carbapenem Inactivation Method for Detecting Metallo-β-Lactamase-Producing Pseudomonas aeruginosa

Abstract

The prevalence of carbapenem-resistant Pseudomonas aeruginosa is increasing. Identification of carbapenemase-producing P. aeruginosa will have therapeutic, epidemiological, and infection control implications. This study evaluated the performance of the EDTA-modified carbapenem inactivation method (eCIM) in tandem with the modified carbapenem inactivation method (mCIM) against a large collection of clinical P. aeruginosa isolates (n = 103) to provide clinicians a phenotypic test that not only identifies carbapenemase production but also distinguishes between metallo-β-lactamase and serine-carbapenemase production in P. aeruginosa. The mCIM test was performed according to Clinical and Laboratory Standards Institute guidelines, while the eCIM was conducted as previously described for Enterobacteriaceae. Test performance was compared to the genotypic profile as the reference. mCIM testing successfully categorized 91% (112/123) of P. aeruginosa isolates as carbapenemases or non-carbapenemase producers, with discordant isolates being primarily Guiana extended-spectrum (GES)-type producers. To increase the sensitivity of the mCIM for GES-harboring isolates, a double inoculum, prolonged incubation, or both was evaluated, with each modification improving sensitivity to 100% (12/12). Upon eCIM testing, all Verona integrin-encoded metallo-β-lactamases (VIM; n = 27) and New Delhi metallo-β-lactamases (NDM; n = 13) tested had 100% concordance to their genotypic profiles, whereas all Klebsiella pneumoniae carbapenemase (KPC; n = 8) and GES (n = 12) isolates tested negative, as expected, in the presence of EDTA. The eCIM failed to identify all imipenemase (IMP)-producing (n = 22) and Sao Paulo metallo-β-lactamase (SPM)-producing (n = 14) isolates. KPC-, VIM-, and NDM-producing P. aeruginosa were well defined by the conventional mCIM and eCIM testing methods; additional modifications appear required to differentiate GES-, IMP-, and SPM-producing isolates.

The ERACE-PA Global Surveillance Program: Ceftolozane/tazobactam and Ceftazidime/avibactam in vitro Activity against a Global Collection of Carbapenem-resistant Pseudomonas aeruginosa

“…Additional CarbaR NxG testing was conducted on ceftolozane/tazobactam-resistant isolates that tested mCIM negative to evaluate for GES-harboring isolates as this enzymology has previously been described as testing falsely negative [ 15 , 16 ].…”

EDTA-modified carbapenem inactivation method (eCIM) for detecting IMP Metallo-β-lactamase–producing Pseudomonas aeruginosa: an assessment of increasing EDTA concentrations

“…A recent study assessing the utility of tandem mCIM/ eCIM against a variety of clinical metallo-β-lactamase (MBL)-producing P. aeruginosa isolates demonstrated high eCIM sensitivity for NDMs and VIMs but not for IMP-producers [6]. The poor sensitivity in differentiating IMP-harboring P. aeruginosa isolates as metallo-based enzymes mirrors similar findings among IMP-harboring Enterobacterales [7].…”

Treatment options for K. pneumoniae, P. aeruginosa and A. baumannii co-resistant to carbapenems, aminoglycosides, polymyxins and tigecycline: an approach based on the mechanisms of resistance to carbapenems

“…However, considering the limitations of some rapid diagnostic methods regarding the detection of rare or novel β-lactamase variants [23,[25][26][27], susceptibility to the selected treatment regimen should always be confirmed with traditional growth-based methods. Pending such confirmation (and taking into consideration local epidemiological data), it may be reasonable to use combination empirical therapy for severely ill patients at risk for carbapenem-resistant infections [17].…”

“…1 Several rapid methods are available or under development that can detect both the production and the type of carbapenemases [20][21][22][23]. Because rare or novel β-lactamase variants may not be detectable by some methods [23,[25][26][27], susceptibility should always be confirmed with traditional growth-based methods and combination therapy may be reasonable pending such confirmation, especially in severe infections [17]. 2 CAZ/AVI is active against both Class A and some Class D carbapenemases [59] and is less affected by outer membrane permeability changes (porin mutations or efflux pumps) [85,86].…”

“…MBL are the predominant carbapenemases in P. aeruginosa, but GES carbapenemases are increasingly being reported [45][46][47] Neither IMI/REL nor CAZ/ AVI or C/T is active against MBL-producing P. aeruginosa [55,59,76], while GES carbapenemases may inactivate IMI/REL [46,47] and C/T [45,111] but not CAZ/AVI [45,111]. Because rare or novel β-lactamase variants may not be detectable by some rapid methods [23,[25][26][27], susceptibility should always be confirmed with traditional growth-based methods and combination therapy may be reasonable pending such confirmation, especially in severe infections [17]. 2 Both CAZ/AVI and C/T are unaffected by the most common mechanism of resistance in P. aeruginosa (OprD porin mutations, overexpression of efflux pumps, overexpression of AmpC) [101,102].…”