Comparison of testing methods assessing the in vitro efficacy of the combination of aztreonam with avibactam on multidrug-resistant Gram-negative bacilli.

BACKGROUND: Aztreonam-avibactam (ATM-AVI) combination shows promising effectiveness on most carbapenemase-producing Gram-negatives, yet standardized antibiotic susceptibility testing (AST) methods for evaluating the combination in clinical laboratories is lacking. We aimed to evaluate different ATM-AVI AST approaches. METHODS: 96 characterized carbapenem-resistant clinical isolates belonging to 9 Enterobacterales (EB; n = 80) and P. aeruginosa (PA; n = 16) species, including 90 carbapenemase producers and 72 strains resistant to both CAZ-AVI and ATM, were tested. Paper disk elution (DE; Bio-Rad) and E-test gradient strips stacking (SS; bioMérieux) were performed for the ATM + CAZ-AVI combination. MIC Test Strip (MTS; Liofilchem) was evaluated for ATM-AVI MIC determination. Results were interpreted applying ATM clinical breakpoints of the EUCAST guidelines and compared to the broth microdilution method (Sensititre, Thermofisher). RESULTS: According to broth microdilution method, 93% of EB and 69% of PA were tested susceptible to ATM-AVI. The synergistic effect of ATM-AVI was of 95% for EB, but of only 17% for PA. The MTS method yielded higher categorical and essential agreement (CA/EA) rates for both EB (89%/91%) and PA (94%/94%) compared to SS, where the rates were 87%/83% for EB and 81%/81% for PA. MTS and SS yielded 2 and 3 major discrepancies, respectively, while 3 very major discrepancies each were observed for both methods. Concerning the DE method, CA reached 91% for EB and 81% for PA, but high number of very major discrepancies were observed for EB (n = 6; 8%) and for PA (n = 3; 19%). CONCLUSIONS: The ATM-AVI association displayed excellent in vitro activity against highly resistant clinical Enterobacterales strains. MTS method offers accurate ATM-AVI AST results, while the SS method might serve as better alternative then DE method in assessing the efficacy of ATM + CAZ-AVI combination. However, further investigation is needed to confirm the methods' ability to detect ATM-AVI resistance.

Helicobacter pylori resistance to antibiotics in Europe in 2018 and its relationship to antibiotic consumption in the community.

OBJECTIVE: Our aim was to prospectively assess the antibiotic resistance rates in Helicobacter pylori strains in Europe in 2018 and to study the link between antibiotic consumption in the community and H. pylori resistance levels in the different countries. DESIGN: The proportion of primary antibiotic resistance cases of H. pylori and their corresponding risk factors were investigated in 24 centres from 18 European countries according to a standardised protocol. Data on antibiotic consumption in the community were collected for the period 2008-2017. The link between antibiotic consumption and resistance data was assessed using generalised linear mixed models. The model with the best fit was selected by means of the Akaike Information Criterion. RESULTS: H. pylori resistance rates for the 1211 adult patients included were 21.4% for clarithromycin, 15.8% for levofloxacin and 38.9% for metronidazole and were significantly higher in Central/Western and Southern than in the Northern European countries.The best model fit was obtained for the Poisson distribution using 2013 consumption data. A significant association was found between H. pylori clarithromycin resistance and consumption in the community of macrolides (p=0.0003) and intermediate-acting macrolides (p=0.005), and between levofloxacin resistance and consumption of quinolones (p=0.0002) and second-generation quinolones (p=0.0003). CONCLUSION: This study confirms the positive correlation between macrolide and quinolone consumption in the community and corresponding H. pylori resistance in European countries. Hence, H. pylori treatment with clarithromycin and levofloxacin should not be started without susceptibility testing in most European countries.

Multicenter study of automated systems for colistin susceptibility testing.

PURPOSE: Broth microdilution (BMD) stays as the reference testing method for determination of antimicrobial susceptibility testing (AST) to colistin and is considered essential for patient management and for monitoring of colistin resistance. This multicenter study aimed to evaluate the performance of automated systems for colistin AST among Enterobacterales as an alternative for BMD since the majority of laboratories use automated systems as first-line method. METHODS: Twenty colistin resistant (COL-R) including 10 MCR producers and 10 colistin-susceptible (COL-S) Enterobacterales isolates were blindly tested for colistin susceptibility with the routine automated AST systems used by 8 laboratories (3 with BD Phoenix, 3 with Vitek2 and 2 with MicroScan). Additionally, 3 reference strains (E. coli ATCC 25922, E. coli NCTC 13846, and one COL-R mcr-negative K. pneumoniae M/14750) were tested in triplicate by each laboratory. RESULTS AND CONCLUSION: Results were compared with BMD performed at the reference laboratory. BD Phoenix and MicroScan automated AST systems provide accurate and reproducible categorical results for the testing of colistin in Enterobacterales. However, Vitek2 system showed poor performance for the detection of COL-R isolates especially those with MICs close to the susceptibility breakpoint (categorical agreement of 88% and precision categorical agreement of 81%).

Increasing proportion of carbapenemase-producing Enterobacteriaceae and emergence of a MCR-1 producer through a multicentric study among hospital-based and private laboratories in Belgium from September to November 2015.

Carbapenemase-producing Enterobacteriaceae (CPE) strains have been increasingly reported in Belgium. We aimed to determine the proportion of CPE among Enterobacteriaceae isolated from hospitalised patients and community outpatients in Belgium in 2015. For the hospitalised patients, the results were compared to a previous similar survey performed in the same hospitals in 2012. Twenty-four hospital-based and 10 private laboratories collected prospectively 200 non-duplicated Enterobacteriaceae isolates from clinical specimens. All isolates were screened locally by carbapenem disk diffusion using European Committee on Antimicrobial Susceptibility Testing methodology. Putative CPE strains with inhibition zone diameters below the screening breakpoints were referred centrally for confirmation of carbapenemase production. From September to November 2015, we found a proportion of clinical CPE of 0.55% (26/4,705) and of 0.60% (12/1,991) among hospitalised patients and among ambulatory outpatients respectively. Klebsiella pneumoniae (26/38) and OXA-48-like carbapenemase (28/38) were the predominant species and enzyme among CPE. One OXA-48-producing Escherichia coli isolated from a hospital was found carrying plasmid-mediated MCR-1 colistin resistance. Compared with the 2012 survey, we found a significant increased proportion of clinical CPE (0.55% in 2015 vs 0.25% in 2012; p = 0.02) and an increased proportion of hospitals (13/24 in 2015 vs 8/24 in 2012) with at least one CPE detected. The study results confirmed the concerning spread of CPE including a colistin-resistant MCR-1 producer in hospitals and the establishment of CPE in the community in Belgium.

Comparative Evaluation of Four Phenotypic Tests for Detection of Carbapenemase-Producing Gram-Negative Bacteria.

Four screening assays aimed for rapid detection of carbapenemase production from Gram-negative bacterial isolates, i.e., the Neo-Rapid Carb kit (Rosco Diagnostica A/S), the Rapidec Carba NP test (bioMérieux SA), the ß Carba test (Bio-Rad Laboratories N.V.), and a homemade electrochemical assay (BYG Carba test) were evaluated against a panel comprising 328 clinical isolates (Enterobacteriaceae [n = 198] and nonfermentative Gram-negative bacilli [n = 130]) with previously characterized resistance mechanisms to carbapenems. Among Enterobacteriaceae isolates, the BYG Carba test and the ß Carba test showed excellent sensitivities (respectively, 100% and 97.3%) and specificities (respectively, 98.9% and 97.7%). The two other assays yielded poorer performances with sensitivity and specificity of 91.9% and 83.9% for the Rapidec Carba NP test and of 89.2% and 89.7% for the Neo-Rapid Carb kit, respectively. Among Pseudomonas spp., sensitivities and specificities ranged, respectively, from 87.3% to 92.7% and from 88.2% to 94.1%. Finally, all tests performed poorly against Acinetobacter spp., with sensitivities and specificities, respectively, ranging from 27.3% to 75.8% and from 75 to 100%. Among commercially available assays, the ß Carba test appeared to be the most convenient for routine use and showed the best overall performances, especially against OXA-48-like producers. The excellent performance of the BYG Carba test against Enterobacteriaceae was confirmed (100% sensitivity and 98.9% specificity).

Evaluation of a DNA microarray for rapid detection of the most prevalent extended-spectrum ß-lactamases, plasmid-mediated cephalosporinases and carbapenemases in Enterobacteriaceae, Pseudomonas and Acinetobacter.

The dissemination of Gram-negative bacteria (GNB) producing extended-spectrum ß-lactamases (ESBLs), plasmid-encoded cephalosporinases (pAmpCs) and carbapenemases is a matter of great clinical concern. In this study, we evaluated a new low-density DNA array 'Check-MDR CT103 XL' (Check-Points, Wageningen, The Netherlands) that identifies the most clinically relevant ß-lactamase genes of ESBLs (blaTEM, blaSHV, blaCTX-M, blaBEL, blaPER, blaGES and blaVEB), pAmpCs (blaCMY-2-like, blaDHA, blaFOX, blaACC-1, blaACT/MIR and blaCMY-1-like/MOX) and carbapenemases (blaKPC, blaOXA-48, blaVIM, blaIMP, blaNDM, blaGIM, blaSPM and blaOXA-23, -24 and -58) in cultured bacteria. In total, 223 GNB isolates with well-characterised resistance mechanisms to ß-lactams were analysed. A specificity and sensitivity of 100% were recorded for most bla genes, with a slightly lower signal observed for blaIMP. The Check-MDR CT103 XL array proved highly accurate for the identification of epidemiologically relevant ESBL, pAmpC and carbapenemase genes harboured in Enterobacteriaceae, Pseudomonas and Acinetobacter spp. The Check-MDR CT103 XL assay is a significant improvement compared with Check-MDR CT103 and it highlights the ability of this array to evolve rapidly to adjust to the current needs for the detection of resistance mechanisms to ß-lactam agents.