Wild-type distributions of minimum inhibitory concentrations and epidemiological cut-off values-laboratory and clinical utility.

The characterization of wild-type minimum inhibitory concentration (MIC) and zone diameter distributions with the setting of epidemiological cut-off values (ECOFFs or ECVs) provides a reference for the otherwise relative MIC values in the international system for antimicrobial susceptibility testing. Distributions of MIC values for a species and an agent follow a log-normal distribution, which in the absence of resistance mechanisms is monomodal and designated wild type (WT). The upper end of the WT distribution, the ECOFF, can be identified with statistical methods. In the presence of phenotypically detectable resistance, the distribution has at least one more mode (the non-WT), but despite this, the WT is most often identifiable using the same methods. The ECOFF provides the most sensitive measure of resistance development in a species against an agent. The WT and non-WT modes are independent of the organism´s response to treatment, but when the European Committee on Antimicrobial Susceptibility Testing (EUCAST) determines the clinical breakpoints, the committee avoids breakpoints that split WT distributions of target species. This is to avoid the poorer reproducibility of susceptibility categorization when breakpoints split major populations but also because the EUCAST has failed to identify different clinical outcomes for isolates with different MIC values inside the wild-type distribution. In laboratory practice, the ECOFF is used to screen for and exclude resistance and allows the comparison of resistance between systems with different breakpoints from different breakpoint organizations, breakpoints evolving over time, and different breakpoints between human and animal medicine. The EUCAST actively encourages colleagues to question MIC distributions as presented on the website (https://www.eucast.org/mic_and_zone_distributions_and_ecoffs) and to contribute MIC and inhibition zone diameter data.

Vibrio species: development of EUCAST susceptibility testing methods and MIC and zone diameter distributions on which to determine clinical breakpoints.

OBJECTIVES: Most human infections caused by Vibrio spp. do not warrant antimicrobial treatment but in severe cases, targeted antimicrobial treatment can be lifesaving. For Vibrio spp., standardized antimicrobial susceptibility testing (AST) guidelines with EUCAST methodology are lacking. In this study, we aimed to produce data suitable for EUCAST to establish clinical MIC breakpoints and zone diameter correlates for Vibrio spp. METHODS: An intercontinental collection (N = 524) comprising five important Vibrio spp. (V. alginolyticus, V. cholerae, V. fluvialis, V. parahaemolyticus and V. vulnificus) was organized. All isolates were subjected to broth microdilution (BMD) against 11 antimicrobial agents according to ISO 20776-1 using unsupplemented Mueller-Hinton broth on freeze-dried Sensititre panels (Thermo Scientific, UK), and most isolates (n = 371) were also tested with disc diffusion according to EUCAST methodology for non-fastidious organisms. RESULTS: Aggregated results were used to generate MIC and zone diameter distributions and to prepare graphs of MIC-zone diameter correlation. Based on these results, the EUCAST Steering Committee determined clinical susceptible (S) and resistant (R) MIC (mg/L) breakpoints (S≤/R>) for the five Vibrio spp. for piperacillin/tazobactam (1/1), cefotaxime (0.25/0.25), ceftazidime (1/1), meropenem (0.5/0.5), ciprofloxacin (0.25/0.25), levofloxacin (0.25/0.25), azithromycin (4/4), doxycycline (0.5/0.5) and trimethoprim/sulfamethoxazole (0.25/0.25). The corresponding zone diameter breakpoints were identified. CONCLUSIONS: We demonstrated the validity of using standard BMD and EUCAST disc diffusion methodology for AST of five Vibrio spp., and generated suitable data to allow EUCAST to determine clinical MIC and zone diameter breakpoints for five pathogenic Vibrio spp., including both non-toxigenic and toxigenic V. cholerae.

Corynebacterium diphtheriae and Corynebacterium ulcerans: development of EUCAST methods and generation of data on which to determine breakpoints.

BACKGROUND: Evidence-based clinical susceptibility breakpoints have been lacking for antimicrobial agents used for diphtheria. OBJECTIVES: We aimed to evaluate broth microdilution and disc diffusion methods and create a dataset of MIC values and inhibition zone diameters (ZDs) from which breakpoints could be determined. METHODS: We included 400 recent clinical isolates equally distributed by species (Corynebacterium diphtheriae and Corynebacterium ulcerans) and by national surveillance programmes (France and Germany). Non-duplicate toxigenic and non-toxigenic isolates were chosen to enable the inclusion of a diversity of susceptibility levels for the 13 agents tested. Broth microdilution and disc diffusion, using EUCAST methodology for fastidious organisms, were used. RESULTS: The distributions of MIC and ZD values were largely in agreement among methods and countries. Breakpoints to allow categorization of WT isolates as susceptible, i.e. susceptible (S) or susceptible, increased exposure (I) were determined for 12 agents. The data supported a breakpoint for benzylpenicillin and amoxicillin of resistant (R) > 1 mg/L since WT isolates were inhibited by 1 mg/L or less. WT isolates were categorized as I (S ≤ 0.001 mg/L) for benzylpenicillin, emphasizing the need for increased exposure, and S (S ≤ 1 mg/L) for amoxicillin. Erythromycin breakpoints were set at S ≤ 0.06 mg/L and R > 0.06 mg/L. The corresponding ZD breakpoints were determined for all agents except amoxicillin, for which categorization was based on benzylpenicillin results. CONCLUSIONS: This work provided a large set of antimicrobial susceptibility data for C. diphtheriae and C. ulcerans, using a harmonized methodology. The dataset allowed EUCAST and experts in the diphtheria field to develop evidence-based breakpoints in January 2023.

Evaluation of prolonged incubation time of 16-20 h with the EUCAST rapid antimicrobial susceptibility disc diffusion testing method.

OBJECTIVES: Antimicrobial resistance rates are continuously increasing, driving the need for rapid antimicrobial susceptibility testing (RAST) results, especially in the treatment of bloodstream infections. The EUCAST RAST method performed directly from positive blood cultures with incubation times from 4 to 8 h was developed in 2018 and is now used in many laboratories. To increase the practicality of the method, an extended incubation time of 16 and 20 h was evaluated in this study. METHOD: Blood culture bottles were spiked with clinical isolates (n = 325) of the seven most important sepsis pathogens. The EUCAST RAST method was performed, extending the incubation time to 16 and 20 h. Broth microdilution (BMD) was used as a reference, except for screening tests where standard disc diffusion or presence of resistance genes was used. RESULTS: Inhibition zones were possible to read for all species-agent combinations. For 16 and 20 h, the MIC zone diameter correlations were sufficiently similar to allow establishment of common breakpoints for the time interval of 16-20 h. The proportion of isolates in the area of technical uncertainty was, on average, 6% for all species and the number of errors were low, with <1% false-resistant and <0.5% false-susceptible results. CONCLUSIONS: This study shows that, for EUCAST RAST, prolonging the recommended incubation to 16-20 h is possible and can be used as a complement when the intended shorter incubation is not possible to achieve. The introduction of the prolonged incubation will increase the usefulness of the EUCAST RAST method in clinical laboratories with limited opening hours.

Assessing the quality of the anaerobic environment - a method developed to support EUCAST disk diffusion of anaerobic bacteria.

The purpose of this study is to establish a method for assessing the anaerobic environment for EUCAST disk diffusion antimicrobial susceptibility testing (AST) of anaerobic bacteria on fastidious anaerobe agar with 5% mechanically defibrinated horse blood (FAA-HB). The method utilizes the association between a decrease in the metronidazole disk zone diameter and increasing oxygen levels with an aerotolerant Clostridium perfringens strain DSM 25589 (CCUG 75076 and NCTC 14679). The C. perfringens strain was tested on FAA-HB with a McFarland 1 inoculum and a metronidazole 5 µg disk. FAA-HB was incubated for 16-20 h at 35-37°C. The association between oxygen levels (0, 0.16, 1, 2, and 4% oxygen) and the metronidazole zone diameter was determined. Reproducibility at 0% oxygen was investigated as part of a European multi-centre study of disk diffusion of anaerobic bacteria. The median zone diameters (n=12) at each oxygen level were 29 mm (0%), 21 mm (0.16%), 16 mm (1%), 15 mm (2%), and 15 mm (4%). The metronidazole zone diameters at 0% oxygen from the multi-centre reproducibility-study had a median of 29 mm and a 95%-percentile range of 25-33 mm (n=236). Only one reading was below 25 mm. Based on our results, a zone diameter of ≥25 mm using a metronidazole 5 µg disk and the C. perfringens strain, tested with EUCAST recommendations, can be used to indicate that the anaerobic environment is of sufficient quality for culture and disk diffusion AST. EUCAST has included the method as part of the quality control for AST of anaerobic bacteria.

Antimicrobial susceptibility testing of Bacteroides species by disk diffusion: The NordicAST Bacteroides study.

OBJECTIVES: Antimicrobial susceptibility testing (AST) of anaerobic bacteria has until recently been done by MIC methods. We have carried out a multi-centre evaluation of the newly validated EUCAST disk diffusion method for AST of Bacteroides spp. METHODS: A panel of 30 Bacteroides strains was assembled based on reference agar dilution MICs, resistance gene detection and quantification of cfiA carbapenemase gene expression. Nordic clinical microbiology laboratories (n = 45) performed disk diffusion on Fastidious Anaerobe Agar with 5% mechanically defibrinated horse blood (FAA-HB) for piperacillin-tazobactam, meropenem and metronidazole. RESULTS: A total of 43/45 (95.6%) laboratories carried out disk diffusion per protocol. Intraclass correlation coefficients were 0.87 (0.80-0.93) for piperacillin-tazobactam, 0.95 (0.91-0.97) for meropenem and 0.89 (0.83-0.94) for metronidazole. For metronidazole, one media lot yielded smaller zones and higher variability than another. Piperacillin-tazobactam and meropenem zone diameters correlated negatively with cfiA expression. A meropenem zone diameter of <28 mm in B. fragilis indicated presence of cfiA. Piperacillin-tazobactam had the most false susceptible results. Categorical errors for this antimicrobial were particularly prevalent in cfiA-positive strains, and piperacillin-tazobactam had the highest number of comments describing zone reading difficulties. CONCLUSIONS: Inter-laboratory agreement by disk diffusion was good or very good. The main challenges were media-related variability for metronidazole and categorical disagreement with the reference method for piperacillin-tazobactam in some cfiA-positive strains. An area of technical uncertainty specific for such strains may be warranted.

Update from the European Committee on Antimicrobial Susceptibility Testing (EUCAST).

The European Committee on Antimicrobial Susceptibility Testing (EUCAST) is an international susceptibility testing committee, organized by the European Society for Clinical Microbiology and Infectious Diseases (ESCMID) and functioning as the breakpoint advisory committee of the European Medicines Agency (EMA). The original remit of EUCAST was to harmonize European clinical breakpoints, but very soon, the activities expanded beyond the borders of Europe and included newly licensed agents in Europe. Among the milestones were the aggregating of large numbers of MIC distributions, creating software to display these distributions, the EUCAST concept of identifying epidemiological cutoff values (ECOFF), and the development of a EUCAST disk diffusion method. The EUCAST Development Laboratory has played a critical role in the development of antimicrobial susceptibility testing (AST) methodology, including development work for novel antimicrobial agents and for rapid AST directly from blood culture bottles. EUCAST has several standing subcommittees, including for AST in fungi (AFST) and mycobacteria (AMST) and for microorganisms of veterinary interest (VetCAST), and ad hoc subcommittees on subjects such as anaerobic bacteria, MIC and zone diameter distributions and epidemiological cutoff values, the relationship between phenotypic and genotypic resistance, and expert rules and methods for the detection of resistance mechanisms. All EUCAST decisions are subjected to the EUCAST public consultation process, the only exception being breakpoints of novel antimicrobial agents where confidentiality agreements during the licensing process prevent public participation. EUCAST has recently revised the definitions of clinical susceptibility interpretive categories S, I, and R, acknowledging the intimate relationship between drug exposure and susceptibility reporting.

Cefiderocol: EUCAST criteria for disc diffusion and broth microdilution for antimicrobial susceptibility testing.

OBJECTIVES: The reproducibility of cefiderocol MIC determination using broth microdilution (BMD) in iron-depleted CAMHB (ID-CAMHB) was investigated, and the EUCAST disc diffusion (DD) method for cefiderocol susceptibility testing was developed and validated against reference BMD. METHODS: Cefiderocol values were determined for wild-type (WT) and non-WT isolates using BMD plates with ID-CAMHB (Thermo Scientific, Oakwood, USA) per EUCAST guidelines. DD was performed using standard EUCAST methodology on unsupplemented Mueller-Hinton agar with cefiderocol 30 µg discs. Control agents were included in all tests. MICs were correlated with zone diameters (ZD), and ZD breakpoints (BP) best corresponding to the MIC BPs were determined. Areas of technical uncertainty (ATU) were included where appropriate. External laboratory validation of cefiderocol DD was performed per the EUCAST SOP 9.2. RESULTS: MIC and ZD distributions for cefiderocol against WT isolates were established. Cefiderocol ZD BPs were set at susceptible ≥22 mm, resistant <22 mm for Enterobacterales and Pseudomonas aeruginosa and ATUs were decided. For Acinetobacter baumannii and Stenotrophomonas maltophilia, ZD cut-off values of ≥17 mm and ≥20 mm corresponded to MIC values of ≤2 and ≤0.5 mg/L, respectively. Cefiderocol ZDs for Escherichia coli ATCC 25922 (target 27 mm) and P. aeruginosa ATCC 27853 (target 26 mm) were within ±3 mm of the target values. For DD, there was no problematic variation between discs, media or laboratories. CONCLUSIONS: DD is a robust and easy-to-perform method for cefiderocol susceptibility testing. For isolates with results in the ATU, an MIC test should be performed to confirm the results.

Pivmecillinam, the paradigm of an antibiotic with low resistance rates in Escherichia coli urine isolates despite high consumption.

OBJECTIVES: Pivmecillinam, the oral version of mecillinam, represents one of the major recommended and used antibiotics for empiric and targeted treatment of urinary tract infections in primary care in Denmark, Norway and Sweden. Mecillinam resistant mutants in Escherichia coli develop easily in vitro, but their fitness cost has been shown to be high. METHODS: We revisited the resistance and consumption data from the monitoring programmes in the three countries and compared pivmecillinam with ciprofloxacin from 2010 to 2020. RESULTS: Mecillinam resistance rates in Escherichia coli remained around 6% in Denmark and Norway relative to a constant consumption in Norway of 1.6-1.8 DID (defined daily doses per 1000 inhabitants per day), and even increasing in Denmark from 1.6 to 2.3 DID. In Sweden resistance was significantly lower at 4% related to the lower consumption of 0.5 DID. For ciprofloxacin, resistance rates fluctuated around 6%-12%, highest in Sweden with the highest consumption (0.8-0.6 DID) and lowest in Denmark (0.55-0.35 DID) and Norway (0.7-0.3 DID), although consumption declined significantly in all three countries. CONCLUSIONS: Pivmecillinam is an example of an antibiotic, which easily develops resistance in vitro, but apparently can be used broadly in primary care without increase in resistance rates.

Determination of norvancomycin epidemiological cut-off values (ECOFFs) for Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus haemolyticus and Staphylococcus hominis.

OBJECTIVES: To determine the epidemiological cut-off values (ECOFFs) of norvancomycin for Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus haemolyticus and Staphylococcus hominis. METHODS: We collected 1199 clinical isolates of Staphylococcus species from five laboratories located in four cities in China. MICs and inhibitory zone diameters of norvancomycin were determined by broth microdilution and the disc diffusion method, separately. ECOFFs of norvancomycin for four species were calculated by ECOFFinder software following EUCAST principles. Methicillin and vancomycin resistance genes (mecA/mecC and vanA/vanB/vanC/vanD/vanE) were screened for by PCR in all isolates. Pearson correlation and χ2 test were used to calculate the correlation of MICs and inhibition zone diameters, and MICs and resistance genes, respectively. RESULTS: MICs of norvancomycin for all strains from five laboratories fell in the range of 0.12-2 mg/L. ECOFFs of norvancomycin were determined to be 2 mg/L for S. epidermidis and S. haemolyticus and 1 mg/L for S. aureus and S. hominis. A weak correlation was observed between MIC values and zone diameters for S. haemolyticus (r = -0.36) and S. hominis (r = -0.26), while no correlation was found for S. epidermidis and S. aureus. The mecA gene was detected in 63.1% of Staphylococcus, whereas no isolate carried mecC, vanA, vanB, vanC, vanD or vanE. ECOFFs of norvancomycin were not correlated with mecA gene carriage in Staphylococcus species. CONCLUSIONS: ECOFFs of norvancomycin for four Staphylococcus species were determined, which will be helpful to differentiate WT strains. The correlation of MICs and zone diameters of norvancomycin was weak in Staphylococcus species.

Staphylococcus aureus bloodstream infections: diverging trends of meticillin-resistant and meticillin-susceptible isolates, EU/EEA, 2005 to 2018.

BackgroundInvasive infections caused by Staphylococcus aureus have high clinical and epidemiological relevance. It is therefore important to monitor the S. aureus trends using suitable methods.AimThe study aimed to describe the trends of bloodstream infections (BSI) caused by meticillin-resistant S. aureus (MRSA) and meticillin-susceptible S. aureus (MSSA) in the European Union (EU) and the European Economic Area (EEA).MethodsAnnual data on S. aureus BSI from 2005 to 2018 were obtained from the European Antimicrobial Resistance Surveillance Network (EARS-Net). Trends of BSI were assessed at the EU/EEA level by adjusting for blood culture set rate (number of blood culture sets per 1,000 days of hospitalisation) and stratification by patient characteristics.ResultsConsidering a fixed cohort of laboratories consistently reporting data over the entire study period, MRSA percentages among S. aureus BSI decreased from 30.2% in 2005 to 16.3% in 2018. Concurrently, the total number of BSI caused by S. aureus increased by 57%, MSSA BSI increased by 84% and MRSA BSI decreased by 31%. All these trends were statistically significant (p < 0.001).ConclusionsThe results indicate an increasing health burden of MSSA BSI in the EU/EEA despite a significant decrease in the MRSA percentage. These findings highlight the importance of monitoring antimicrobial resistance trends by assessing not only resistance percentages but also the incidence of infections. Further research is needed on the factors associated with the observed trends and on their attributable risk.

Clinical and Laboratory Standards Institute and European Committee on Antimicrobial Susceptibility Testing Position Statements on Polymyxin B and Colistin Clinical Breakpoints.

Recent data on polymyxin pharmacokinetics, pharmacodynamics, toxicity, and clinical outcomes suggest these agents have limited clinical utility. Pharmacokinetics-pharmacodynamics data show a steady-state concentration of 2 µg/mL is required for killing bacteria with colistin minimum inhibitory concentrations of 2 µg/mL. Less than 50% of patients with normal renal function achieve this exposure, and it is associated with high risk of nephrotoxicity. This exposure does not achieve bacterial stasis in pneumonia models. Randomized and observational studies consistently demonstrate increased mortality for polymyxins compared with alternative agents. The Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) are 2 global organizations that establish interpretive criteria for in vitro susceptibility data. CLSI has recently taken the step to eliminate the "susceptible" interpretive category for the polymyxins, whereas EUCAST maintains this interpretive category. This viewpoint describes the opinions of these organizations and the data that were used to inform their perspectives.

The EUCAST rapid disc diffusion method for antimicrobial susceptibility testing directly from positive blood culture bottles.

OBJECTIVES: With increasing antimicrobial resistance, rapid antimicrobial susceptibility testing (RAST) becomes important, especially in patients with bloodstream infections. EUCAST decided to develop a standardized rapid method, based on EUCAST disc diffusion, to offer susceptibility reports within 4-8 h of a positive blood culture (BC). METHODS: BC bottles were spiked with clinical isolates (n = 332) of the seven most relevant sepsis pathogens with a variety of resistance mechanisms. RAST was performed directly from the bottle and zones read after 4, 6 and 8 h. Several variables were investigated, including the effect of using different BC bottles and of a 0-18 h delay between a positive signal and the performance of RAST. RESULTS: For five species, most inhibition zones could be read after 4 h. The proportion of results that could be interpreted increased from 75% at 4 h to 84% after 8 h. Categorical agreement against the reference method was good, with error rates of false susceptibility of 0.2%, 0.2% and 0.2% at 4, 6 and 8 h and false resistance of 1.2%, 0.2% and 0.1% at 4, 6 and 8 h, respectively. CONCLUSIONS: With the EUCAST RAST method, reliable AST results can be delivered within 4-8 h of positivity of BC bottles for seven important bloodstream infection pathogens. To reduce the occurrence of errors and to absorb the variability caused by using a non-standardized inoculum, material from different manufacturers and workflow-related delays, we have introduced an area in which interpretation is not permitted, the Area of Technical Uncertainty.

EUCAST rapid antimicrobial susceptibility testing (RAST) in blood cultures: validation in 55 European laboratories.

OBJECTIVES: When bloodstream infections are caused by resistant bacteria, rapid antimicrobial susceptibility testing (RAST) is important for adjustment of therapy. The EUCAST RAST method, directly from positive blood cultures, was validated in a multi-laboratory study in Europe. METHODS: RAST was performed in 40 laboratories in northern Europe (NE) and 15 in southern Europe (SE) from clinical blood cultures positive for Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus or Streptococcus pneumoniae. Categorical results at 4, 6 and 8 h of incubation were compared with results for EUCAST standard 16-20 h disc diffusion. The method, preliminary breakpoints and the performance of the laboratories were evaluated. RESULTS: The total number of isolates was 833/318 in NE/SE. The number of zone diameters that could be read (88%, 96% and 99%) and interpreted (70%, 81% and 85%) increased with incubation time (4, 6 and 8 h). The categorical agreement was acceptable, with total error rates in NE/SE of 2.4%/4.9% at 4 h, 1.1%/3.5% at 6 h and 1.1%/3.3% at 8 h. False susceptibility at 4, 6 and 8 h of incubation was below 0.3% and 1.1% in NE and SE, respectively, and the corresponding percentages for false resistance were below 1.9% and 2.8%. After fine-tuning breakpoints, more zones could be interpreted (73%, 89% and 93%), with only marginally affected error rates. CONCLUSIONS: The EUCAST RAST method can be implemented in routine laboratories without major investments. It provides reliable antimicrobial susceptibility testing results for relevant bloodstream infection pathogens after 4-6 h of incubation.

Antimicrobial susceptibility of Corynebacterium diphtheriae and Corynebacterium ulcerans in Germany 2011-17.

BACKGROUND: Diphtheria is mainly caused by diphtheria-toxin-producing strains of Corynebacterium diphtheriae and Corynebacterium ulcerans. The recommended first-line antibiotic is penicillin or erythromycin, but reliable susceptibility data are scarce. OBJECTIVES: To define WT MIC distributions of 12 antimicrobial agents and provide data for the determination of tentative epidemiological cut-off values (TECOFFs) for potentially toxigenic corynebacteria and to evaluate the potential usefulness of a gradient test (Etest) for susceptibility testing of penicillin, erythromycin and clindamycin. METHODS: For the 421 human or veterinary isolates from the period 2011-17, MICs of 12 antimicrobial agents were determined. Etest performance was evaluated for penicillin, erythromycin and clindamycin. RESULTS: MIC distributions were characterized and TECOFFs could be set for 11 out of 24 antibiotic/species combinations. The current EUCAST clinical breakpoints, predominantly determined for Corynebacterium species other than C. diphtheriae and C. ulcerans, divide the WT MIC distributions of penicillin and clindamycin, thereby making reproducible susceptibility testing of C. diphtheriae and C. ulcerans difficult. For erythromycin, 4% of C. diphtheriae and 2% of C. ulcerans had MICs higher than those for WT isolates. Phenotypically detectable resistance to other antibiotics was rare. Etest underestimated MICs of penicillin and lower concentrations needed to be included for erythromycin, while for clindamycin the Etest was not a good surrogate method. CONCLUSIONS: MIC distributions based on reference broth microdilution for potentially toxigenic Corynebacterium spp. were developed. For five and six agents, TECOFFs were suggested for C. diphtheriae and C. ulcerans, respectively, but for Corynebacterium pseudotuberculosis the number of isolates was too low.

Linking antimicrobial resistance surveillance to antibiotic policy in healthcare settings: the COMBACTE-Magnet EPI-Net COACH project.

OBJECTIVES: To systematically summarize the evidence on how to collect, analyse and report antimicrobial resistance (AMR) surveillance data to inform antimicrobial stewardship (AMS) teams providing guidance on empirical antibiotic treatment in healthcare settings. METHODS: The research group identified 10 key questions about the link between AMR surveillance and AMS using a checklist of 9 elements for good practice in health research priority settings and a modified 3D combined approach matrix, and conducted a systematic review of published original studies and guidelines on the link between AMR surveillance and AMS. RESULTS: The questions identified focused on AMS team composition; minimum infrastructure requirements for AMR surveillance; organisms, samples and susceptibility patterns to report; data stratification strategies; reporting frequency; resistance thresholds to drive empirical therapy; surveillance in high-risk hospital units, long-term care, outpatient and veterinary settings; and surveillance data from other countries. Twenty guidelines and seven original studies on the implementation of AMR surveillance as part of an AMS programme were included in the literature review. CONCLUSIONS: The evidence summarized in this review provides a useful basis for a more integrated process of developing procedures to report AMR surveillance data to drive AMS interventions. These procedures should be extended to settings outside the acute-care institutions, such as long-term care, outpatient and veterinary. Without proper AMR surveillance, implementation of AMS policies cannot contribute effectively to the fight against MDR pathogens and may even worsen the burden of adverse events from such interventions.

Point-Counterpoint: Differences between the European Committee on Antimicrobial Susceptibility Testing and Clinical and Laboratory Standards Institute Recommendations for Reporting Antimicrobial Susceptibility Results.

INTRODUCTIONAntibiotic susceptibility test results are among the most important results issued by clinical microbiology laboratories because they routinely guide critical treatment decisions. Interpretations of MIC or disk diffusion test results, such as "susceptible" or "resistant," are easily understood. Clinical laboratories also need to determine whether and how their reports will reflect more complex situations. Such situations include, first, whether there is need to administer higher or more frequent doses of antibiotic than usual for clinical efficacy; second, whether an antimicrobial is likely to be effective at a body site where it concentrates; and third, whether there is some uncertainty in the test results due to technical variability that cannot be eliminated. Two leading organizations that set standards for antimicrobial susceptibility testing, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) and the Clinical and Laboratory Standards Institute (CLSI), have taken different strategies to deal with these challenges. In this Point-Counterpoint, Gunnar Kahlmeter and Christian Giske discuss how EUCAST is addressing these issues, and Thomas Kirn and Susan Sharp discuss the CLSI approach.

Strong correlation between the rates of intrinsically antibiotic-resistant species and the rates of acquired resistance in Gram-negative species causing bacteraemia, EU/EEA, 2016.

BackgroundAntibiotic resistance, either intrinsic or acquired, is a major obstacle for treating bacterial infections.AimOur objective was to compare the country-specific species distribution of the four Gram-negative species Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter species and the proportions of selected acquired resistance traits within these species.MethodWe used data reported for 2016 to the European Antimicrobial Resistance Surveillance Network (EARS-Net) by 30 countries in the European Union and European Economic Area.ResultsThe country-specific species distribution varied considerably. While E. coli accounted for 31.9% to 81.0% (median: 69.0%) of all reported isolates, the two most common intrinsically resistant species P. aeruginosa and Acinetobacter spp. combined (PSEACI) accounted for 5.5% to 39.2% of isolates (median: 10.1%). Similarly, large national differences were noted for the percentages of acquired non-susceptibility to third-generation cephalosporins, carbapenems and fluoroquinolones. There was a strong positive rank correlation between the country-specific percentages of PSEACI and the percentages of non-susceptibility to the above antibiotics in all four species (rho > 0.75 for 10 of the 11 pairs of variables tested).ConclusionCountries with the highest proportion of P. aeruginosa and Acinetobacter spp. were also those where the rates of acquired non-susceptibility in all four studied species were highest. The differences are probably related to national differences in antibiotic consumption and infection prevention and control routines.

Capsule Typing of Haemophilus influenzae by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry.

Encapsulated Haemophilus influenzae strains belong to type-specific genetic lineages. Reliable capsule typing requires PCR, but a more efficient method would be useful. We evaluated capsule typing by using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Isolates of all capsule types (a-f and nontypeable; n = 258) and isogenic capsule transformants (types a-d) were investigated. Principal component and biomarker analyses of mass spectra showed clustering, and mass peaks correlated with capsule type-specific genetic lineages. We used 31 selected isolates to construct a capsule typing database. Validation with the remaining isolates (n = 227) showed 100% sensitivity and 92.2% specificity for encapsulated strains (a-f; n = 61). Blinded validation of a supplemented database (n = 50) using clinical isolates (n = 126) showed 100% sensitivity and 100% specificity for encapsulated strains (b, e, and f; n = 28). MALDI-TOF mass spectrometry is an accurate method for capsule typing of H. influenzae.