Both EUCAST and CLSI recommend broth microdilution (BMD) for antimicrobial susceptibility testing of colistin, but BMD is rarely used in routine microbiology laboratories. The objective of this study ...was to evaluate five commercially available BMD products and two brands of gradient tests for colistin MIC determination using BMD according to ISO standard 20776-1 as reference.
Colistin MIC determination was performed according to the manufacturer's instructions on five commercially available BMD products (Sensititre, MICRONAUT-S, MICRONAUT MIC-Strip, SensiTest, and UMIC) and two gradient tests (Etest and MIC Test Strip). Colistin reference MICs were determined using frozen panels according to ISO standard 20776-1. An international collection of Gram-negative bacteria (n=75) with varying levels of colistin susceptibility was tested.
The colistin BMD products correlated well with reference tests, in particular for Sensititre and the two MICRONAUT products (essential agreement ≥96%: 66/69 (96%, CI 88–99%), 72/75 (96%, CI 88–99%) and 74/75 (99%, CI 92–100%)). The results were somewhat poorer for the BMD products SensiTest and UMIC: EA 88% (51/58, CI 77–95%) and 82% (61/74, CI 72–89%), respectively), and considerably poorer for the gradient tests (EA 43–71% depending on gradient test and Mueller-Hinton agar manufacturer). The gradient tests generally underestimated colistin MICs, resulting in a significant number of false susceptible results (9–18 of total 75 tests, compared with 1–3 for the BMD products).
Based on the results of this study, we advise laboratories not to trust gradient tests for colistin susceptibility testing and to use broth microdilution methods for this purpose. There are several commercial broth microdilution tests available and in principle they perform well.
The ECO.SENS study is the first international survey to investigate the prevalence and susceptibility of pathogens causing community-acquired acute uncomplicated urinary tract infections (UTIs). ...Midstream urine samples were taken for culture and for testing for the presence of leucocytes from 4734 women not older than 65 years presenting with symptoms of acute UTI at 252 community health care centres in 17 countries. Recognized urinary tract pathogens were identified and the susceptibility to 12 antimicrobials determined. Pathogens were present in 3278 (69.2%) patients, Escherichia coli accounting for 77.0% of isolates. In E. coli, 42% of the isolates were resistant to one or more of the 12 antimicrobial drugs investigated. Resistance was most common to ampicillin (29.8%) and sulfamethoxazole (29.1%), followed by trimethoprim (14.8%), trimethoprim/sulfamethoxazole (14.1%) and nalidixic acid (5.4%). Resistance in E. coli to co-amoxiclav, mecillinam, cefadroxil, nitrofurantoin, fosfomycin, gentamicin and ciprofloxacin was <3%. However, co-amoxiclav resistance was apparent in Portugal (9.3%) as was resistance to the quinolones, nalidixic acid and ciprofloxacin, in Portugal (11.6% and 5.8%, respectively) and Spain (26.7% and 14.7%, respectively). Overall, Proteus mirabilis were less resistant to ampicillin (16.1%) and more resistant to trimethoprim (25.5%) than E. coli, whereas Klebsiella spp. were more resistant to ampicillin (83.5%) and fosfomycin (56.7%). 'Other Enterobacteriaceae' were more resistant to the broad spectrum beta-lactams (ampicillin 45.9%, co-amoxiclav 21.3% and cefadroxil 24.6%), nitrofurantoin (40.2%) and fosfomycin (15.6%). In Staphylococcus saprophyticus resistance development was rare. Overall, antimicrobial resistance was lowest in the Nordic countries and Austria and highest in Portugal and Spain.
EUCAST has revised the definition of the susceptibility category I from ‘Intermediate’ to ‘Susceptible, Increased exposure’. This implies that I can be used where the drug concentration at the site ...of infection is high, either because of dose escalation or through other means to ensure efficacy. Consequently, I is no longer used as a buffer zone to prevent technical factors from causing misclassifications and discrepancies in interpretations. Instead, an Area of Technical Uncertainty (ATU) has been introduced for MICs that cannot be categorized without additional information as a warning to the laboratory that decision on how to act has to be made. To implement these changes, the EUCAST-AFST (Subcommittee on Antifungal Susceptibility Testing) reviewed all, and revised some, clinical antifungal breakpoints.
The aim was to present an overview of the current antifungal breakpoints and supporting evidence behind the changes.
This document is based on the ten recently updated EUCAST rationale documents, clinical breakpoint and breakpoint ECOFF documents.
The following breakpoints (in mg/L) have been revised or established for Candida species: micafungin against C. albicans (ATU = 0.03); amphotericin B (S ≤/> R = 1/1), fluconazole (S ≤/> R = 2/4), itraconazole (S ≤/> R = 0.06/0.06), posaconazole (S ≤/> R = 0.06/0.06) and voriconazole (S ≤/> R = 0.06/0.25) against C. dubliniensis; fluconazole against C. glabrata (S ≤/> R = 0.001/16); and anidulafungin (S ≤/> R = 4/4) and micafungin (S ≤/> R = 2/2) against C. parapsilosis. For Aspergillus, new or revised breakpoints include itraconazole (ATU = 2) and isavuconazole against A. flavus (S ≤/> R = 1/2, ATU = 2); amphotericin B (S ≤/> R = 1/1), isavuconazole (S ≤ /> R = 1/2, ATU = 2), itraconazole (S ≤/> R = 1/1, ATU = 2), posaconazole (ATU = 0.25) and voriconazole (S ≤/> R = 1/1, ATU = 2) against A. fumigatus; itraconazole (S ≤/> R = 1/1, ATU = 2) and voriconazole (S ≤/> R = 1/1, ATU = 2) against A. nidulans; amphotericin B against A. niger (S ≤/> R = 1/1); and itraconazole (S ≤/> R = 1/1, ATU = 2) and posaconazole (ATU = 0.25) against A. terreus.
EUCAST-AFST has released ten new documents summarizing existing and new breakpoints and MIC ranges for control strains. A failure to adopt the breakpoint changes may lead to misclassifications and suboptimal or inappropriate therapy of patients with fungal infections.
With the support of ESCMID and European countries, EUCAST has developed a disk diffusion test with zone diameter breakpoints correlated with the EUCAST clinical MIC breakpoints. The development of ...the EUCAST disk diffusion method and quality control criteria are described, together with guidance on quality control and implementation of the method in clinical microbiology laboratories. The method includes the use of Mueller–Hinton agar without supplements for non-fastidious organisms and with 5% mechanically defibrinated horse blood and 20 mg/L β-NAD for fastidious organisms, a standardized inoculum resulting in confluent growth, an incubation time of 16–20 h, a reading guide on how to read zone diameters on individual species-agent combinations and zone diameter breakpoints calibrated to the EUCAST clinical MIC breakpoints. EUCAST recommendations are described in detail and updated regularly on the EUCAST website (http://www.eucast.org).
Healthcare-associated infections due to multidrug-resistant Gram-negative bacteria (MDR-GNB) are a leading cause of morbidity and mortality worldwide. These evidence-based guidelines have been ...produced after a systematic review of published studies on infection prevention and control interventions aimed at reducing the transmission of MDR-GNB. The recommendations are stratified by type of infection prevention and control intervention and species of MDR-GNB and are presented in the form of ‘basic’ practices, recommended for all acute care facilities, and ‘additional special approaches’ to be considered when there is still clinical and/or epidemiological and/or molecular evidence of ongoing transmission, despite the application of the basic measures. The level of evidence for and strength of each recommendation, were defined according to the GRADE approach.
Whole genome sequencing (WGS) offers the potential to predict antimicrobial susceptibility from a single assay. The European Committee on Antimicrobial Susceptibility Testing established a ...subcommittee to review the current development status of WGS for bacterial antimicrobial susceptibility testing (AST).
The published evidence for using WGS as a tool to infer antimicrobial susceptibility accurately is currently either poor or non-existent and the evidence / knowledge base requires significant expansion. The primary comparators for assessing genotypic–phenotypic concordance from WGS data should be changed to epidemiological cut-off values in order to improve differentiation of wild-type from non-wild-type isolates (harbouring an acquired resistance). Clinical breakpoints should be a secondary comparator. This assessment will reveal whether genetic predictions could also be used to guide clinical decision making. Internationally agreed principles and quality control (QC) metrics will facilitate early harmonization of analytical approaches and interpretive criteria for WGS-based predictive AST. Only data sets that pass agreed QC metrics should be used in AST predictions. Minimum performance standards should exist and comparative accuracies across different WGS laboratories and processes should be measured. To facilitate comparisons, a single public database of all known resistance loci should be established, regularly updated and strictly curated using minimum standards for the inclusion of resistance loci. For most bacterial species the major limitations to widespread adoption for WGS-based AST in clinical laboratories remain the current high-cost and limited speed of inferring antimicrobial susceptibility from WGS data as well as the dependency on previous culture because analysis directly on specimens remains challenging.
For most bacterial species there is currently insufficient evidence to support the use of WGS-inferred AST to guide clinical decision making. WGS-AST should be a funding priority if it is to become a rival to phenotypic AST. This report will be updated as the available evidence increases.
It has long been acknowledged that the cephalosporin breakpoints used in most European countries and the USA fail to detect many or most extended spectrum β-lactamases (ESBLs) in Enterobacteriaceae ...and that all ESBLs are clinically significant. Therefore, microbiological laboratories have undertaken not only regular cephalosporin susceptibility tests based on breakpoints, but also special tests to detect all ESBLs. An increasing accumulation of clinical data implies that the clinical success of third generation cephalosporin therapy is related more to the minimum inhibitory concentration (MIC) than to the presence or absence of an ESBL. However, the breakpoints must be lower than those previously recommended by many breakpoint committees. In Europe, this adjustment has been achieved by EUCAST (European Committee on Antimicrobial Susceptibility Testing) through the ongoing process of harmonising European breakpoints. In the USA, the CLSI recently voted to adopt similar guidelines but are waiting to implement these while revising other β-lactam breakpoints. As Enterobacteriaceae are becoming increasingly resistant, a less ‘diehard’ interpretation of the relationship among MICs, ESBLs and clinical outcome may provide therapeutic alternatives in difficult situations.
Mueller–Hinton (MH) agar is recommended by EUCAST and CLSI for disc diffusion antimicrobial susceptibility testing. Using EUCAST methodology, we evaluated the performance of 21 internationally ...available brands of dehydrated MH agar from 17 manufacturers.
MH plates were prepared in-house and evaluated against four quality control (QC) strains tested in triplicate, using EUCAST disc diffusion methodology. This resulted in 30 disc–QC strain combinations and 90 readings per MH brand. All brands were tested blindly and in parallel. Results were evaluated against targets and ranges in the EUCAST QC tables. The agar depth, pH and concentration of five cations were measured for all brands.
Six brands of MH agar (Bio-Rad, Biolife, Oxoid, Sigma MH 2, BD BBL MH II and CRITERION) demonstrated excellent performance, with ≥99% of zone diameter readings within QC ranges and ≥70% on target ±1 mm. The poorest performance was seen for Biolab and Merck MH, with 10% (9/90) and 23% (21/90) of readings outside the QC ranges, respectively. Of all readings, 4.9% (93/1890) were out of range, mainly related to trimethoprim sulfamethoxazole (n = 25), aminoglycosides (n = 25) and fluoroquinolones (n = 15). The cation content differed considerably between the agars, and for four brands pH values were outside the acceptable range 7.2–7.4.
This study evaluated the performance and content of 21 brands of MH dehydrated media. Six brands showed excellent performance with all investigated antimicrobial classes. Others exhibited problems with one or more classes of agents. This could partly be explained by differences in concentration of specific chemical components and pH.
PDF
