Evaluation of the rapid carbapenem inactivation method (rCIM): a phenotypic screening test for carbapenemase-producing Enterobacteriaceae.

Objectives: Fast and accurate diagnostic tests to identify carbapenemase-producing Enterobacteriaceae (CPE) are mandatory for proper antimicrobial therapy and implementing infection control measures. Here, we have developed a rapid Carbapenem Inactivation Method (rCIM) for CPE detection. Methods: The rCIM consists of the incubation of a potential carbapenemase producer with meropenem discs and use of the resulting supernatant to challenge a susceptible indicator strain. Growth of the indicator strain is monitored using a nephelometer. The performances of the rCIM were compared with the CIM and Carba NP tests using a collection of 113 well-characterized carbapenem-resistant enterobacterial isolates, including 85 carbapenemase producers and 28 non-carbapenemase producers. In addition, rCIM was compared with the Carba NP test and PCR sequencing in a prospective analysis of 101 carbapenem-resistant enterobacterial isolates addressed to the French National Reference Center for Antimicrobial Resistance in July 2017. Results and discussion: The rCIM correctly identified 84/85 carbapenemase producers and 28/28 non-carbapenemase producers, yielding a sensitivity of 99% and a specificity of 100%, slightly higher than the CIM and Carba NP test. In the prospective validation study, the rCIM showed a sensitivity and specificity of 97% and 95%, respectively. Two cephalosporinase-hyperproducing Enterobacter cloacae gave false-positive results, whereas an IMI-17-producing Enterobacter asburiae gave a false-negative result. The result was, however, positive when the isolate was grown on selective antibiotic-containing media. Conclusions: The rCIM is a rapid (less than 3 h), cheap and accurate test for the detection of CPEs, which can be implemented in low-resource settings, making it a useful tool for microbiology laboratories.

Calcineurin inhibitors impair neutrophil activity against Aspergillus fumigatus in allogeneic hematopoietic stem cell transplant recipients.

BACKGROUND: Neutrophils are key effectors against the widely distributed mold Aspergillus fumigatus, which is a major threat for immunocompromised patients, including allogeneic hematopoietic stem cell transplant (HSCT) recipients. Yet little is known about neutrophil activity over time after cell transplantation, especially regarding A fumigatus. OBJECTIVE: We aimed at assessing the activity of neutrophils on A fumigatus in allogeneic HSCT recipients at different posttransplantation time points. METHODS: We performed a longitudinal study involving 37 patients undergoing HSCT, drawing blood samples at engraftment and at 2, 6, and 10 months after the HSCT. Posttransplantation neutrophil activity in the recipients was compared with that of the respective donors. Neutrophil/A fumigatus coculture, flow cytometry, and video microscopy were used to assess neutrophil inhibition of fungal growth, cell/fungus interactions, reactive oxygen species production, major surface molecule expression, and neutrophil extracellular trap (NET) formation. RESULTS: The ability of neutrophils to interfere with Aspergillus species hyphal growth was impaired after HSCT. The administration of calcineurin inhibitors appeared to play an important role in this impairment. We also observed that post-HSCT neutrophils produced less NETs, which was correlated with increased fungal growth. Tapering immunosuppression led to the recuperation of inhibition capacity 10 months after HSCT. CONCLUSION: In HSCT recipients neutrophil-driven innate immunity to fungi is altered in the early posttransplantation period (between recovery from neutropenia and up to 6 months). This alteration is at least partly related to administration of calcineurin inhibitors and diminution of NETs production.