Multicenter Evaluation of the Modified Carbapenem Inactivation Method and the Carba NP for Detection of Carbapenemase-Producing Pseudomonas aeruginosa and Acinetobacter baumannii

Abstract

The purpose of this study was to develop the modified carbapenem inactivation method (mCIM) for the detection of carbapenemase-producing (CP-PA) and carbapenemase-producing (CP-AB) and perform a multicenter evaluation of the mCIM and Carba NP tests for these nonfermenters. Thirty and 30 isolates previously characterized by whole-genome sequencing from the CDC-FDA Antibiotic Resistance Isolate Bank were evaluated, including CP isolates (Ambler class A, B, and D), non-carbapenemase-producing (non-CP) carbapenem-resistant isolates, and carbapenem-susceptible isolates. Initial comparison of a 1-μl versus 10-μl loop inoculum for the mCIM was performed by two testing sites and showed that 10 μl was required for reliable detection of carbapenemase production among and Ten testing sites then evaluated the mCIM using a 10-μl loop inoculum. Overall, the mean sensitivity and specificity of the mCIM for detection of CP-PA across all 10 sites were 98.0% (95% confidence interval [CI], 94.3 to 99.6; range, 86.7 to 100) and 95% (95% CI, 89.8 to 97.7; range, 93.3 to 100), whereas the mean sensitivity and specificity among CP-AB were 79.8% (95% CI, 74.0 to 84.9; range, 36.3 to 95.7) and 52.9% (95% CI, 40.6 to 64.9; range, 28.6 to 100), respectively. At three sites that evaluated the performance of the Carba NP test using the same set of isolates, the mean sensitivity and specificity of the Carba NP test were 97.8% (95% CI, 88.2 to 99.9; range, 93.3 to 100) and 97.8% (95% CI, 88.2 to 99.9; range, 93.3 to 100) for and 18.8% (95% CI, 10.4 to 30.1; range, 8.7 to 26.1) and 100% (95% CI, 83.9 to 100; range, 100) for Overall, we found both the mCIM and the Carba NP test to be accurate for detection of carbapenemase production among isolates and less reliable for use with isolates.

NDM Metallo-β-Lactamases and Their Bacterial Producers in Health Care Settings

“…The CNP test is based on the in vitro hydrolysis of imipenem and has been extensively evaluated for detecting carbapenemases in Enterobacteriaceae (140) and Pseudomonas (151). The test has both excellent specificity (84% to 100%) and sensitivity (93.3% to 100%) for detecting carbapenemases, including NDM in Enterobacteriaceae (152)(153)(154) and P. aeruginosa (155). However, CNP is relatively labor-intensive, as reagents need to be prepared in-house, and some have short shelf lives (e.g., 72 h) (156).…”

“…A multisite evaluation found that the mCIM is accurate for detection of carbapenemases in P. aeruginosa, with 86.7% to 100% sensitivity and 93.3% to 100% specificity. Detection of carbapenemase-producing Acinetobacter with this method is more problematic, with 36.3% to 95.7% sensitivity and 28.6% to 100% specificity (155). Another study has shown mCIM to have low sensitivity (45.1%) for the detection of carbapenemases in Acinetobacter and Pseudomonas (174).…”

Bulgecins as β-Lactam Enhancers Against Multidrug Resistant (MDR) Pseudomonas aeruginosa

“…Given that 15-33% of P. aeruginosa isolates are multidrug resistant (have at least one resistance mechanism) [16,17] and that resistance is associated with up to fivefold greater mortality [18,19], choosing the right antibiotic combinations have a tremendous impact on patient outcomes. Advances in the rapid diagnosis of P. aeruginosa, and use of both rapid phenotypic tests such as CARBA NP [20] or rapid molecular diagnostics to identify specific ESBL and carbapenemase enzymes, have enhanced the clinician's ability to get patients on the right therapy sooner. Identification of patient risk factors, including prior antibiotic exposure, and knowledge of local trends in resistance patterns are useful in selection of empiric antibiotics, until antimicrobial susceptibilities and genotypic results are available for guidance.…”

Biographical Feature: Stephen G. Jenkins, Ph.D., D(ABMM), F(AAM)

“…He has studied the emergence and spread of antibiotic-resistant organisms (9)(10)(11)(12)(13)(14) as well as the methods for and utility of detecting such organisms in the microbiota (15)(16)(17)(18). Dr. Jenkins has published on methods of susceptibility testing throughout his career, most recently on detection of carbapenem resistance in Gram-negative bacilli (19)(20)(21). His interest in rapid diagnostic testing has been driven by a desire to improve patient care by providing timely results, with his research including studies of molecular and phenotypic tests to detect the spread of clonal organisms in the hospital setting, resistant organisms, and respiratory virus infections (22)(23)(24)(25)(26).…”