Blood-Modified Carbapenem Inactivation Method: a Phenotypic Method for Detecting Carbapenemase-Producing Enterobacteriaceae Directly from Positive Blood Culture Broths

Abstract

A variant of the modified carbapenem inactivation method (mCIM) was developed to detect carbapenemase activity directly from positive blood culture broths. The method, termed “Blood-mCIM,” was evaluated using Bactec blood culture bottles (Becton, Dickinson and Company, Franklin Lakes, NJ) inoculated with 27 different carbapenemase-producing Enterobacteriaceae (CPE) isolates and 34 different non-CPE isolates. The assay was positive for all blood culture broths inoculated with CPE isolates and negative for all blood culture broths inoculated with non-CPE isolates, corresponding to a diagnostic sensitivity and specificity of 100%, respectively. This assay is inexpensive using “off the shelf” reagents, does not require centrifugation or mechanical lysis, and can be readily implemented in any clinical microbiology laboratory. The Blood-mCIM should facilitate expedient administration of antimicrobial therapy targeted toward CPE bloodstream infections and assist infection control and public health surveillance.

Variability in Zinc Concentration among Mueller-Hinton Broth Brands: Impact on Antimicrobial Susceptibility Testing of Metallo-β-Lactamase-Producing Enterobacteriaceae

“…The importance of these host factors cannot be overemphasized, as demonstrated in direct-from-blood-culture carbapenemase detection assays, where zinc has to be added to blood to improve MBL detection, further reinforcing the evidence that free zinc concentrations are low in vivo (32). Unsurprisingly, in the blood-modified carbapenem inactivation method assay, zinc supplementation is not required, given the extra dilution step in tryptic soy broth (33). Undoubtedly, reducing supraphysiologic zinc concentrations in media to match free physiologic concentrations will result in clinically relevant MBL AST results.…”

Modern Blood Culture

“…Overall, both colorimetric and mCIM-based methods demonstrate high specificities (≥90%) and sensitivities (80%–100%) for the detection of β-lactamase and/or carbapenemase-producing Enterobacterales extracted directly from aerobic blood culture bottles. 71 , 72 , 73 , 74 Resulting times between 20 minutes to 6.5 hours have been reported for colorimetric methods, and between 8 to 24 hours for mCIM-based methods. Although these early results are generally promising, more studies must be done to standardize methodology and result interpretation before clinical use.…”

“…Because these assays are relatively cheap and simple, many have explored their use directly on positive blood cultures to test for the presence of β-lactamase and/or carbapenemase-producing gram-negative bacteria, which are of great clinical concern internationally. 71 , 72 , 73 , 74 Colorimetric methods usually start with microbial extraction from positive blood cultures using lysis centrifugation or a short subculture on solid media. The ideal choice of hemolytic agent varies depending on the assay.…”

“…Variations of CLSI’s modified carbapenem inactivation method (mCIM) have also been used for bacteria with ESBL and carbapenemase activity directly from positive blood cultures. 71 , 73 , 74 Briefly, bacteria are extracted from blood cultures and incubated with either a meropenem or a cephalosporin disk at 35°C to 37°C for approximately 2 hours. Zinc supplementation can be used for metallo-β-lactamase activity detection.…”

Hindsight Is 2019—the Year in Clinical Microbiology

“…MBLs require zinc for activity, and zinc is chelated by EDTA; this distinction is important due to differences in therapeutic options [19]. Several studies evaluated using modified carbapenem (or other β-lactam) inactivation assays directly from blood culture bottles with good results [20][21][22][23].…”