Performance evaluation of the UMIC® Cefiderocol to determine MIC in Gram-negative bacteria.

BACKGROUND: Cefiderocol is a catechol-substituted cephalosporin with potent in vitro activity against carbapenem-resistant (CR) Gram-negative bacteria (GNB). Cefiderocol susceptibility testing is complex because iron concentrations need to be taken into consideration. Here, we assessed the clinical performance of Bruker's UMIC® Cefiderocol and corresponding iron-depleted CAMHB to determine MIC by broth microdilution (BMD) for clinically relevant GNB. METHODS: MICs of cefiderocol for 283 GN clinical isolates were determined by BMD using iron-depleted CAMHB. Frozen panels were used as a reference. The concentration range of cefiderocol was 0.03-32 mg/L. The isolates, with different degrees of susceptibility to cefiderocol, included Enterobacterales (n = 180), Pseudomonas aeruginosa (n = 49), Acinetobacter baumannii (n = 44) and Stenotrophomonas maltophilia (n = 10). RESULTS: The rates of categorical agreement (CA), essential agreement (EA) and bias were calculated to evaluate the performance of the UMIC® Cefiderocol, as compared with the reference method. Overall, the UMIC® Cefiderocol showed 90.8% EA (95% CI: 86.9%-93.7%) with a bias of -14.5% and a CA of 90.1% (95% CI: 86.1%-93.1%). For Enterobacterales, the UMIC® Cefiderocol showed 91.7% EA (95% CI: 86.7%-94.9%) with a bias of -25.0% and a CA of 87.8% (95% CI: 82.2%-91.8%). For non-fermenters, the UMIC® Cefiderocol showed 89.3% EA (95% CI: 81.9%-93.9%) (not significantly different from 90.0%, Student t-test) with a bias of -3.9% and a CA of 94.2% (95% CI: 87.7%-97.3%). CONCLUSIONS: UMIC® Cefiderocol is a valid method for the determination of cefiderocol MICs even if higher than expected discrepancies were observed with NDM-producing Enterobacterales, which presented in most cases MIC values close to the breakpoint.

Evaluation and readout optimization of the rapid polymyxin NP test for the detection of colistin-resistant Enterobacteriaceae.

PURPOSE: In an increasing number of cases the last therapeutic option for treatment of carbapenem-resistant Enterobacteriaceae is colistin. As the detection of colistin resistance is problematic and time-consuming, it is desirable to find a rapid and reliable test. The rapid polymyxin NP test developed by Nordmann et al. addresses this problem and has a sensitivity of 99.3  % and a specificity of 95.4  %, as described by the authors. METHODS: In this study, we aimed to evaluate the NP test and tested the effect of measuring the absorbance of the test with an enzyme-linked immunosorbent assay (ELISA) reader at 430 nm as an alternative objectified readout. We performed a study with 120 carbapenemase-producing Enterobacteriaceae isolates, including 40 colistin-resistant and 23 colistin-susceptible Klebsiella pneumoniae, 4 resistant and 23 susceptible Escherichia coli, and 20 susceptible and 10 resistant Enterobacter species, respectively. RESULTS: Our data showed lower values for sensitivity and specificity than previously, namely only 91  % and 70 %, respectively, due to visual inspection. Furthermore, the results revealed a weakness in the correct detection of colistin-susceptible Enterobacter species. With the measurement of the absorbance we optimized the results to prevent misinterpretations of weak or inconclusive colour changes and enhanced the accuracy and objectivity of the rapid polymyxin NP test results. CONCLUSION: We reinforced the rapid polymyxin NP test as a rapid and valuable tool for detecting colistin-resistant K. pneumoniae isolates, although false-positive results were obtained for several colistin-susceptible Enterobacter spp. By using the optimized method, we were able to increase the sensitivity and specificity values to 94  % and 95  %, respectively.

Evaluation of the automated BD Phoenix CPO Detect panel in combination with the ß-CARBA assay for detection and classification of carbapenemase-producing Enterobacterales.

Recently, the CPO Detect panel for the detection of carbapenemase-producing, Gram-negative bacteria was introduced for the Phoenix semi-automated antimicrobial susceptibility testing system. The CPO Detect assay aims to detect carbapenemase activity (P/N test) and to type carbapenemase producers according to the Ambler classification (Ambler test). The P/N test-based detection of carbapenemase producers was 100% sensitive and 55.3% specific in the assessment of 57 carbapenemase-producing and 38 non-carbapenemase-producing Enterobacterales. False-positive test isolates in the P/N test arose from carbapenemase-non-producing, but carbapenem-non-susceptible isolates. In contrast, using the Ambler test-based approach for carbapenemase detection resulted in a specificity of 100% and a sensitivity of 79%. In order to improve the overall performance, we established an algorithm that additionally included the colorimetric ß-CARBA assay as downstream test for P/N test-positive isolates, which remained un-typed in the Ambler test. This algorithm displayed an overall sensitivity and specificity of 98.3% and 100%, respectively. Our data demonstrate that the combination of the CPO Detect assay with the ß-CARBA test allows for rapid detection and classification of carbapenemase-producing Enterobacterales.

Complete Nucleotide Sequence of a Citrobacter freundii Plasmid Carrying KPC-2 in a Unique Genetic Environment.

The complete and annotated nucleotide sequence of a 54,036-bp plasmid harboring a blaKPC-2 gene that is clonally present in Citrobacter isolates from different species is presented. The plasmid belongs to incompatibility group N (IncN) and harbors the class A carbapenemase KPC-2 in a unique genetic environment.

Fbl is not involved in the invasion of eukaryotic epithelial and endothelial cells by Staphylococcus lugdunensis.

For several Staphylococci, such as Staphylococcus aureus, Staphylococcus saprophyticus, and Staphylococcus epidermidis, invasion of eukaryotic cells has been described and this mechanism has been considered an important part of the infection process. The fibrinogen-binding protein (Fbl) of Staphylococcus lugdunensis, a homolog of the clumping factor A of S. aureus, has been described as fibrinogen-binding adhesin and might promote invasion of cells. We therefore characterized several clinical strains of S. lugdunensis in terms of whole cell fibrinogen and fibronectin binding and correlated these results with the invasion of epithelial and endothelial cells by S. lugdunensis. We described for the first time invasion of cells by S. lugdunensis. As invasion of cells by S. lugdunensis was only partly inhibited by cytochalasin D in contrast to a complete inhibition of invasion of cells by S. aureus, further invasion mechanisms are likely to be present in S. lugdunensis. In addition, the Fbl of S. lugdunensis is not involved in the invasion of cells as ruled out by an isogenic fbl mutant.