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Keywords:

  • Antimicrobial susceptibility breakpoints;
  • bacterial drug resistance;
  • CLSI;
  • Escherichia coli;
  • EUCAST;
  • surveillance;
  • trends

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Transparency Declaration
  9. References
  10. Appendix

Clin Microbiol Infect 2012; 18: E466–E472

Abstract

Dutch laboratories are currently changing their breakpoint criteria from mostly Clinical Laboratory and Standards Institute (CLSI) breakpoints to European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints. To evaluate the impact of these changes, we studied antimicrobial resistance trends of Escherichia coli in blood specimens from January 2008 to January 2012 using CLSI and EUCAST breakpoints and compared them with the antimicrobial susceptibility test (AST) interpretations reported by Dutch laboratories participating in the Infectious Disease Surveillance Information System for Antibiotic Resistance (ISIS-AR). ISIS-AR collects AST interpretations, including underlying minimal inhibitory concentrations (MICs) of routinely cultured bacterial species on a monthly basis from Dutch laboratories. MICs of Etests or automated systems were reinterpreted according to the CLSI 2009 and EUCAST 2010 guidelines. Trends in non-susceptibility (i.e. intermediate resistant and resistant) over time were analysed by the Cochran–Armitage test for trend. The effects of the change from CLSI to EUCAST breakpoints on non-susceptibility were small. There were no differences in non-susceptibility to amoxicillin, amoxicillin/clavulanic acid, cefuroxim, gentamicin and co-trimoxazol and only small differences (1–1.5%) for ciprofloxacin between AST interpretations by CLSI or EUCAST. However, for ceftazidime, and cefotaxime/ceftriaxone the proportion of non-susceptibility was substantially higher when EUCAST breakpoints were used (2–3%). The effects on time trends of the change in guidelines were limited, with only substantial differences for the oxymino-cephalosporins. Our study shows that the implementation of EUCAST breakpoints has a limited effect on the proportion of non-susceptible isolates and time trends in E. coli for most, but not all, antimicrobial agents.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Transparency Declaration
  9. References
  10. Appendix

Antimicrobial surveillance is an important tool to monitor the emergence and impact of resistant organisms. Additionally, surveillance guides the empirical treatment choices of clinicians [1]. The value of surveillance systems, especially on-site laboratory based surveillance systems, depends on the comparability of the applied methodology and the quality assurance of the participating laboratories [2]. Standardization of interpretation criteria and the use of internationally accepted techniques for antimicrobial susceptibility testing (AST) are therefore essential in surveillance systems based on routinely generated data.

Both the Clinical and Laboratory Standards Institute (CLSI) and the European Committee for Antimicrobial Susceptibility Testing (EUCAST) provide reference methods and breakpoints for classifying organisms as susceptible or resistant to antimicrobial agents. EUCAST was initiated by the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) to harmonize minimum inhibitory concentration (MIC) breakpoints across Europe [3]. EUCAST in general recommends lower MIC breakpoints defining resistance than CLSI and both EUCAST and CLSI have changed their recommendations regarding the interpretation of susceptibility results for certain antimicrobial agents in Enterobacteriaceae over time (http://www.eucast.org) [4]; EUCAST established susceptibility breakpoints for cefotaxime and ceftazidime at ≤1 mg/L in 2006/2007 [5], while CLSI changed the breakpoint for cefotaxime from ≤8 to ≤1 mg/L and for ceftazidime from ≤8 to ≤4 mg/L in 2010 (Table 1) [4]. Another important change in the CLSI 2010 guideline has been the reporting of AST data for cephalosporins as found, irrespective of the presence of extended-spectrum-β-lactamases (ESBLs), while previous editions recommended that ESBL-producers should be reported as resistant to cephalosporins, irrespective of the MIC [4,6]. A similar recommendation was previously made by EUCAST in 2009 [7–9].

Table 1.   EUCAST 2010 (v1.1) and 2011 (v1.3) and CLSI 2009, 2010 and 2011 MIC clinical breakpoint recommendations in mg/L (http://www.eucast.org) [4,6,11,13]
Antimicrobial agentEUCAST 2010EUCAST 2011CLSI 2009CLSI 2010CLSI 2011
S≤R>S≤R>S≤R>S≤R>S≤R>
  1. aFor this study a susceptibility MIC breakpoint of ≤8 was used, categorizing all wild-type Escherichia coli isolates as susceptible.

Amoxicillina 8 8816816816
Amoxicillin/clavulanic acida 8 8816816816
Cefuroxim8888816816816
Ceftazidime14148164848
Ceftriaxone12128321212
Cefotaxime12128321212
Gentamicin2424484848
Ciprofloxacin0.510.51121212
Co-trimoxazole2424222222

The adoption of new guidelines or changes in breakpoints can have a substantial effect on the outcome and implications of antimicrobial resistance surveillance [10]. Currently, laboratories in Europe are encouraged to adopt EUCAST guidelines to facilitate comparability of AST results. In 2010, Dutch laboratories started the implementation of EUCAST guidelines for AST as recommended by the Dutch Society for Medical Microbiology (NVMM). Previously, breakpoints as recommended by CLSI or by the Dutch Breakpoint Committee (CRG) were used. To evaluate the impact of the adoption of EUCAST on surveillance, we compared resistance trends among Escherichia coli using CLSI and EUCAST breakpoints and the AST results reported by Dutch laboratories participating in the Infectious Disease Surveillance Information System for Antibiotic Resistance (ISIS-AR).

Material and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Transparency Declaration
  9. References
  10. Appendix

ISIS-AR

ISIS-AR started in 2008 and is coordinated by the Centre for Infectious Disease Control, National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands. Currently, 29 laboratories, located in various regions of the Netherlands, submit AST results (i.e. susceptible, intermediate and resistant), including underlying MICs of Etest or automated susceptibility testing systems and patient data (i.e. age, gender, hospital department, specimen site), of routinely cultured bacterial species on a monthly basis. Participating laboratories serve tertiary referral centres, teaching and community hospitals, outpatient clinics, long-term care facilities, and general practitioners. ISIS-AR covers approximately 50% of the Dutch population and is, due to the wide geographical distribution and diversity of sampling sites, considered representative for clinical AST data in the Netherlands. Data quality is assured by structural quality control, which includes monthly feedback to the laboratories of absolute numbers of isolates submitted, susceptibility patterns of specific organisms such as Staphylococcus aureus and E. coli, absolute number of highly resistant organisms, and isolates with impossible and exceptional phenotypes according to the EUCAST expert rules [8]. Exceptional phenotypes are included in the ISIS-AR database only when confirmed by a secondary susceptibility test. In addition, most laboratories are regularly audited by independent external experts of the Dutch institute for the promotion of quality in laboratory research and for the accreditation of laboratories in the health care sector (CCKL [http://www.cckl.nl/]).

Isolates

We included all blood cultures with E. coli from January 2008 to January 2012. To avoid over-representation of multiple isolates from individual patients we only included the first isolate per patient per year. For all isolates, MICs for amoxicillin or ampicillin (AMO), amoxicillin/clavulanic acid (AMC), cefuroxim (CFX), ceftazidime (CAZ), cefotaxime (CTX), ceftriaxone (CRO), gentamicin (GEN), ciprofloxacin (CIP) and co-trimoxazole (SXT) were reinterpreted as susceptible or non-susceptible (i.e. intermediate susceptible or resistant) using the CLSI 2009 and the EUCAST 2010 (v1.1) breakpoints (Table 1) [6,11]. MICs from Etests were given priority over MICs from automated systems. AST data for CRO and CTX were combined (i.e. if an isolate was non-susceptible to either CRO or CTX, the isolate was considered to be non-susceptible).

Statistical analysis

We determined the proportion of isolates non-susceptible as recommended for surveillance purposes by CLSI [12], for the AST interpretations reported by the laboratories and for the MIC reinterpretations according to the CLSI 2009 and EUCAST 2010 breakpoints. Additionally, we performed a similar analysis in which laboratories were simulated to use CLSI 2009 breakpoints in 2008 and 2009 and EUCAST 2010 breakpoints in 2010 and 2011, providing information on the effect of the adoption of EUCAST guidelines on antimicrobial resistance (i.e. guideline switch). Trends over time were analysed by the Cochran–Armitage test for trend using SAS software version 9.2 (SAS Institute Inc., Cary, NC, USA).

Differences between AST results using CLSI 2009 breakpoints and EUCAST 2010 breakpoints for each antimicrobial agent were determined by calculating the proportion of isolates that were differently interpreted (i.e. susceptible vs. non-susceptible) by the two test methods. For analysis purposes, isolates that were interpreted as susceptible by CLSI breakpoints but non-susceptible by EUCAST breakpoints were given the value 1, and isolates that were interpreted to be similar were given the value 0. Subsequently, we used the Cochran–Armitage test for trend to evaluate the change in the proportion of isolates differently interpreted over time. A significant increasing trend will suggest that isolates are significantly more often interpreted as non-susceptible over time when using EUCAST breakpoints in comparison to CLSI breakpoints (i.e. a significant time trend towards more resistance with EUCAST). Furthermore, we performed a similar analysis for AST results by the guideline switch (i.e. CLSI 2009 to EUCAST 2010) and AST results reported by the laboratories to evaluate the impact of the implementation of EUCAST breakpoints on reported resistance levels. Finally, the same analysis was performed for AST results by EUCAST 2010 breakpoints and AST results reported by Dutch laboratories to evaluate the reliability of a surveillance system based on on-site laboratory AST interpretations. For the last two analyses, isolates that were interpreted as non-susceptible by CLSI/EUCAST breakpoints but susceptible by the laboratory were given the value 1, isolates that were interpreted to be similar were given the value 0, and isolates that were interpreted as susceptible by CLSI/EUCAST breakpoints but non-susceptible by the laboratory were given the value −1. We defined statistical significance as p < 0.05.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Transparency Declaration
  9. References
  10. Appendix

A total of 17 486 E. coli isolates were included. Reinterpretation of MIC values with CLSI and EUCAST breakpoints was possible for AMC, CIP, GEN and SXT in 90% of isolates (Table 2). For all other agents reinterpretation of MIC values was possible for over 70% of isolates and was similar for CLSI and EUCAST breakpoints. Not all participating laboratories submit MIC values for all agents, explaining most of the isolates for which an MIC reinterpretation was not possible (Table 2). We therefore assumed that these isolates were randomly distributed among susceptible and non-susceptible phenotypes, limiting selection bias.

Table 2.   Percentage of E. coli isolates in blood specimens with data available on antimicrobial susceptibility test interpretations reported by laboratories (SIR), MIC value and with a MIC value that was reinterpretable by CLSI 2009 and EUCAST 2010 (v1.1) breakpoints, the Netherlands 2008–2012 (n = 17 486)
Antimicrobial agentSIR %MIC value %CLSI 2009 %EUCAST 2010 %
Amoxicillin99818181
Amoxicillin/clavulanic acid98909090
Cefuroxim93858585
Ceftazidime96878786
Ceftriaxone/Cefotaxime95878787
Gentamicin98909090
Ciprofloxacin99909090
Co-trimoxazole99909090

Time trends

Except for CIP and SXT, the proportion of non-susceptible isolates was highest when the AST interpretations reported by the laboratories were used (Table 3). For all four AST interpretation methods, there was no increase in the proportion of isolates non-susceptible to AMO and SXT over time, while the proportion of isolates non-susceptible to CFX, CAZ, GEN and CIP increased significantly since January 2008 (Table 3). For AMC the proportion of non-susceptible isolates showed a significant increase from 22.2% in 2008 to 25.8% in 2011 for the AST results reported by the laboratories. However, there was no increase in AMC non-susceptibility when MICs were reinterpreted according to the EUCAST and CLSI breakpoints (19.8% in 2008 and 19.3% in 2011). For CRO/CTX there was a significant increase in non-susceptibility over time when analysing AST interpretations according to the laboratories and EUCAST 2010 breakpoints, and when switching in 2010 from CLSI 2009 to EUCAST 2010 breakpoints, while there was no increase when analysing AST interpretations according to CLSI 2009 breakpoints (Table 3).

Table 3.   Percentage of non-susceptible (NS) E. coli isolates (n = 17 486) in blood specimens per year according to the antimicrobial susceptibility test interpretations reported by laboratories (SIR), CLSI 2009 breakpoints (CLSI 2009) and EUCAST 2010 (v1.1) breakpoints (EUCAST 2010) and according to the use of CLSI 2009 breakpoints in 2008 and 2009 and EUCAST 2010 breakpoints in 2010 and 2011 (CLSI/EUCAST), the Netherlands 2008–2012
Antimicrobial agent% NS 2008% NS 2009% NS 2010% NS 2011p-value trendb
  1. aIn the case of the same susceptibility breakpoint for CLSI 2009 and EUCAST 2010, results for EUCAST 2010 are presented because the percentage of isolates that are non-susceptible will be the same irrespective of the guideline used.

  2. bCochran–Armitage test for trend.

Amoxicillin
 EUCAST 2010a48.047.347.847.80.99
 SIR48.848.149.050.60.09
Amoxicillin/clavulanic acid
 EUCAST 2010a19.818.422.819.30.34
 SIR22.221.926.525.8<0.001
Cefuroxim
 EUCAST 2010a9.29.510.811.4<0.001
 SIR10.510.912.612.00.02
Ceftazidime
 CLSI 20091.71.82.42.20.05
 EUCAST 20103.53.34.34.7<0.001
 CLSI/EUCAST1.71.84.34.7<0.001
 SIR3.63.94.75.4<0.001
Cefotaxime/Ceftriaxone
 CLSI 20093.03.43.62.80.84
 EUCAST 20103.54.05.35.9<0.001
 CLSI/EUCAST3.03.45.35.9<0.001
 SIR3.74.15.15.7<0.001
Gentamicin
 CLSI 20094.14.75.06.1<0.001
 EUCAST 20104.85.96.26.6<0.001
 CLSI/EUCAST4.14.76.26.6<0.001
 SIR4.76.66.97.5<0.001
Ciprofloxacin
 CLSI 200912.412.613.914.00.01
 EUCAST 201013.814.215.115.50.02
 CLSI/EUCAST12.412.615.115.5<0.001
 SIR12.512.714.214.30.006
Co-trimoxazole
 EUCAST 2010a30.728.928.730.50.99
 SIR30.628.828.529.90.99

To evaluate the effect of the application of a specific guideline (i.e. CLSI or EUCAST) on antimicrobial resistance trends, we determined the proportion of isolates differently interpreted for each antimicrobial agent by EUCAST 2010 and CLSI 2009 breakpoints as described in the methods section. This analysis showed a significant increase over time in the proportion of isolates that were interpreted as non-susceptible to CAZ and CRO/CTX with EUCAST breakpoints, but that were interpreted as susceptible with CLSI breakpoints. This finding suggests a larger rise in non-susceptibility to the oxymino-cephalosporins when the EUCAST breakpoints are used.

Furthermore, to assess the impact of a guideline change on resistance trends, we determined the proportion of isolates differently interpreted by the simulated guideline switch and the AST results of the laboratories. Surprisingly, despite the fact that the same susceptibility breakpoints are used by CLSI and EUCAST for AMO and AMC (Table 1), there was a significant increase over time in the proportion of isolates that were interpreted as non-susceptible by the laboratories, but were interpreted as susceptible by the simulated guideline switch, suggesting a larger rise in non-susceptibility when laboratory AST results are used. A similar finding was found for GEN. For CFX, the susceptibility breakpoints for EUCAST and CLSI are the same as well. However, there was a significant decrease over time in the proportion of isolates that were interpreted as non-susceptible by the laboratories, but were interpreted as susceptible by the simulated guideline switch, suggesting a larger rise in non-susceptibility to CFX with the simulated guideline switch. A similar finding was found for CIP.

Finally, we determined the proportion of isolates differently interpreted by EUCAST 2010 breakpoints and the AST results of the laboratories to evaluate the reliability of a surveillance system based on on-site laboratory AST interpretations in comparison to a surveillance system based on MICs. Results found were the same as described above for the simulated guideline switch with respect to AMO, AMC and CFX, suggesting a larger rise in non-susceptibility to AMO and AMC when laboratory AST interpretations are used, and a larger rise in non-susceptibility to CFX when EUCAST breakpoints are used.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Transparency Declaration
  9. References
  10. Appendix

In 2011, 45% of the laboratories participating in ISIS-AR used EUCAST breakpoints for AST vs. none in 2008. One of the concerns regarding the change from CLSI to EUCAST recommendations is the anticipated increase in resistance because EUCAST recommends lower MIC breakpoints defining resistance for most antimicrobial agents than CLSI (Table 1) [13]. However, the effects of the implementation of EUCAST breakpoints on antimicrobial non-susceptibility in E. coli were small based on AST results of Dutch laboratories. For most antimicrobial agents there were either no differences in non-susceptibility (AMO, AMC, CFX, GEN and SXT) or only small differences (CIP). For CAZ and CRO/CTX, the proportion of non-susceptibility was, however, substantially higher when EUCAST breakpoints were used (2–3%) and there was a substantial difference in resistance trends for the oxymino-cephalosporins when CLSI or EUCAST breakpoints were used. Additionally, there was a significant increase in the proportion of isolates over time that were interpreted as non-susceptible to CAZ and CRO/CTX with EUCAST 2010 breakpoints, but that were interpreted as susceptible with CLSI 2009 breakpoints, providing evidence for a rise of isolates with an MIC between 1 and 8 mg/L and a true increase in resistance only detected with the lower MIC susceptibility breakpoints used by EUCAST. It is important to mention that CLSI has lowered its susceptibility breakpoints for the oxymino-cephalosporins in 2010 and that for CRO and CTX the breakpoints currently used by CLSI and EUCAST are the same (Table 1) [4].

Despite the limited effects of the adoption of EUCAST breakpoints on non-susceptibility and surveillance, there is a potential effect on resistance levels, complicating therapy choices, due to the larger variations in resistance breakpoints than in susceptibility breakpoints between CLSI and EUCAST. These variations are explained by the intermediate category used by CLSI for certain agents, such as AMC and CFX, which is not used by EUCAST. For instance, resistance to AMC was 6.5% in 2011 when using CLSI breakpoints, compared with 19.3% when using EUCAST breakpoints. For CFX these numbers were 5.8% and 11.4%. For AMC there is an additional difference between CLSI and EUCAST; EUCAST recommends a fixed concentration of clavulanate of 2 mg/L, while CLSI recommends a fixed amoxicillin/clavulanate ratio (2:1) for susceptibility testing, which might influence resistance levels as well. Currently, most (25/29) of the laboratories participating in ISIS-AR use the VITEK automated system (bioMérieux Vitek Systems Inc., Hazelwood, MO, USA) and the fixed amoxicillin/clavulanate ratio for susceptibility testing.

Interestingly, the proportion of non-susceptible isolates was highest for the AST results of the Dutch laboratories. Additionally, there were substantially different time trends between AST interpretations of laboratories and AST reinterpretations by EUCAST breakpoints, in particular for AMC and CFX. EUCAST leaves it to the user to categorize wild-type E. coli as susceptible or intermediate for AMC depending on dosing, route of administration and whether the infection is systemic or affects the urinary tract only [11]. For this study we decided to categorize all wild-type E. coli (MIC ≤8 mg/L) as susceptible to AMC. The categorization of wild-type E. coli as intermediate will dramatically increase non-susceptibility levels when changing from CLSI to EUCAST breakpoints and explains approximately half of the higher proportion of non-susceptible isolates when AST results of the laboratories were used. For CFX, CLSI and EUCAST use the same breakpoint. Differences in non-susceptibility and time trends can therefore not be explained by the use of different guidelines and suggest the use of other MIC susceptibility breakpoints than the ones recommended by CLSI or EUCAST in Dutch laboratories. Other explanations for the differences found between AST results of the laboratories and AST reinterpretations with CLSI and/or EUCAST breakpoints are the use of expert-rules by automated testing systems, such as the editing of the AST results for certain beta-lactams if an ESBL-producing enzyme is present (explaining approximately 30% of the differences in AST interpretations), editing by the local clinical microbiologist, or errors in the laboratory information system.

We did not present data on imipenem, because no resistance was found. Furthermore, no data on piperacillin/tazobactam (PTZ) was presented because the significant >4% increase in PTZ non-susceptibility for all four AST interpretations that we found from 2009 to 2010 is likely to be explained by the switch in the reference method to validate the susceptibility results of the VITEK 2 automated system (bioMérieux Vitek Systems Inc., Hazelwood, MO, USA). Before 2009 VITEK 2 susceptibility data were validated against agar dilution, while since 2009 VITEK 2 susceptibility data have been validated against broth micro-dilution. In the four laboratories participating in ISIS-AR that are using the Phoenix automated system (BD, Franklin Lakes, NJ, USA) no significant increase was found in PTZ non-susceptibility.

The differences found between laboratory AST results and the reinterpretations of MICs by CLSI or EUCAST breakpoints demonstrate the importance of a uniform AST methodology for on-site surveillance systems. In a recent study by the European Antimicrobial Resistance Surveillance Network (EARS-net), resistance was determined by the guidelines used by the reporting countries because the MIC values were not systematically available for all participating laboratories [14]. Other surveillance systems, such as SENTRY and MYSTIC surveillance programs, use central laboratories for confirmation of speciation and susceptibility testing [15,16]. Centralized testing is a preferred method in surveillance due to the minimization of variation in techniques and control of the organism collection [2]. However, this is an expensive way of surveillance because all isolates have to be retested, which militates against the use of routinely generated data. A network in which participating laboratories are using the same AST methodology is a good alternative and compromise between feasibility and accuracy.

In this study, we used routinely collected MICs of Etests and automated testing systems to study resistance trends. Bias introduced by different breakpoints was therefore avoided. The results show that the implementation of EUCAST will have a limited effect on the proportion of non-susceptible isolates and time trends in E. coli for most, but not all, antimicrobial agents. Furthermore, our study shows that the reporting of MIC values is important for on-site laboratory-based surveillance systems and illustrates the importance of a uniform methodology for routine susceptibility data to effectively monitor antimicrobial resistance. The further implementation of EUCAST guidelines in Europe will therefore optimize comparability of routine AST results and will improve the reliability of current surveillance systems.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Transparency Declaration
  9. References
  10. Appendix

The authors thank Jose Ferreira, Department of IF/EMI, RIVM, for his statistical advice and comments on the manuscript. ISIS-AR is supported by the Dutch Ministry of Health. The results of this study were presented on 18 April 2012 at the Scientific Spring Meeting of the Dutch Society for Medical Microbiology (NVMM).

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Transparency Declaration
  9. References
  10. Appendix
  • 1
    O’Brien TF, Stelling J. Integrated multilevel surveillance of the world’s infecting microbes and their resistance to antimicrobial agents. Clin Microbiol Rev 2011; 24: 281295.
  • 2
    Jones RN, Masterton R. Determining the value of antimicrobial surveillance programs. Diagn Microbiol Infect Dis 2001; 41: 171175.
  • 3
    Kahlmeter G, Brown DF, Goldstein FW et al. European harmonization of MIC breakpoints for antimicrobial susceptibility testing of bacteria. J Antimicrob Chemother 2003; 52: 145148.
  • 4
    Clinical and Laboratory Standards Institute. 2010. Performance standards for antimicrobial susceptibility testing. Twentieth informational supplement. Document M100-S20. Wayne, PA: CLSI.
  • 5
    Kahlmeter G. Breakpoints for intravenously used cephalosporins in Enterobacteriaceae--EUCAST and CLSI breakpoints. Clin Microbiol Infect 2008; 14 (Suppl 1): 169174.
  • 6
    Clinical and Laboratory Standards Institute. 2009. Performance standards for antimicrobial susceptibility testing. Nineteenth informational supplement. Document M100-S19. Wayne, PA: CLSI.
  • 7
    Leclercq R, Canton R, Giske C et al. Expert rules in antimicrobial susceptibility testing. Version 1. Availble at: http://www.eucast.org. (last accessed 2 July 2012).
  • 8
    Leclercq R, Canton R, Brown DF et al. EUCAST expert rules in antimicrobial susceptibility testing. Clin Microbiol Infect 2011; Oct 2012. doi: 10.1111/j.1469-0691.2011.03703.x [Epub ahead of print].
  • 9
    European Committee on Antimicrobial Susceptibility Testing (EUCAST). EUCAST breakpoint table version 1.0. Availble at: http://www.eucast.org. (last accessed 2 July 2012).
  • 10
    Hombach M, Bloemberg GV, Bottger EC. Effects of clinical breakpoint changes in CLSI guidelines 2010/2011 and EUCAST guidelines 2011 on antibiotic susceptibility test reporting of Gram-negative bacilli. J Antimicrob Chemother 2012; 67: 622632.
  • 11
    European Committee on Antimicrobial Susceptibility Testing (EUCAST). EUCAST breakpoint table version 1.1. Available at: http://www.eucast.org. (last accessed 2 July 2012).
  • 12
    Hindler JF, Stelling J. Analysis and presentation of cumulative antibiograms: a new consensus guideline from the Clinical and Laboratory Standards Institute. Clin Infect Dis 2007; 44: 867873.
  • 13
    Clinical and Laboratory Standards Institute. 2011. Performance standards for antimicrobial susceptibility testing; Twenty-first informational supplement; M100-S21. Wayne, PA: Clinical and Laboratory Standards Institute.
  • 14
    Gagliotti C, Balode A, Baquero F et al. Escherichia coli and Staphylococcus aureus: bad news and good news from the European Antimicrobial Resistance Surveillance Network (EARS-Net, formerly EARSS), 2002 to 2009. Euro Surveill 2011; 16: [Epub ahead of print].
  • 15
    Jones RN. Global epidemiology of antimicrobial resistance among community-acquired and nosocomial pathogens: a five-year summary from the SENTRY Antimicrobial Surveillance Program (1997–2001). Semin Respir Crit Care Med 2003; 24: 121134.
  • 16
    Rhomberg PR, Jones RN. Summary trends for the Meropenem yearly susceptibility test information collection program: a 10-year experience in the United States (1999–2008). Diagn Microbiol Infect Dis 2009; 65: 414426.

Appendix

  1. Top of page
  2. Abstract
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Transparency Declaration
  9. References
  10. Appendix

Members of the ISIS-AR study group

Admiraal De Ruyter Hospital, Department of Medical Microbiology and Immunology, Goes (L.J.M. Sabbe); Albert Schweitzer Hospital, Department of Medical Microbiology, Dordrecht (H.M.E. Frénay, B. Maraha); Amphia Hospital, Department of Medical Microbiology, Breda (P.H.J. van Keulen, J.A.J.W. Kluytmans); St Antonius Hospital, Department of Medical Microbiology, Nieuwegein (B.M. de Jongh, B.J.M. Vlaminckx); Atrium MC Parkstad, Department of Medical Microbiology, Heerlen (E.I.G.B. de Brauwer, F.S. Stals); CBSL, Department of Medical Microbiology, Hilversum (L.J. Bakker, J.W. Dorigo-Zetsma); Deventer Hospital, Department of Medical Microbiology, Deventer (F.W. Sebens); Diagnostic Centre SSDZ, Department of Medical Microbiology, Delft (E.E. Mattsson); Diakonessenhuis, Laboratory of Medical Microbiology and Immunology, Utrecht (J.A. Kaan, S.F.T. Thijsen); St. Elisabeth Hospital, Department of Medical Microbiology, Tilburg (A.G.M. Buiting); Franciscus Hospital, Department of Medical Microbiology, Roosendaal (R.G.F. Wintermans); Gelre Hospitals, Department of Medical Microbiology, and Infection Prevention, Apeldoorn (B.C. van Hees); Haga Teaching Hospital, Department of Medical Microbiology, ‘s-Gravenhage (R.W. Brimicombe); Isala Clinics, Laboratory of Medical Microbiology and Infectious Diseases, Zwolle (G.J.H.M. Ruijs, M.J.H.M. Wolfhagen); Izore, Centre for Infectious Diseases Friesland, Leeuwarden (J.H. van Zeijl); Jeroen Bosch Hospital, Department of Medical Microbiology and Infection Control, ‘s-Hertogenbosch (N.H.M. Renders); Leiden University Medical Center, Department of Medical Microbiology, Leiden (A.T. Bernards); Lievensberg Hospital, Department of Medical Microbiology, Bergen op Zoom (R.G.F. Wintermans); Laboratory for Microbiology and Public Health, Enschede (F.G.C. Heilmann, T. Halaby); Laboratory for Infectious Diseases, Groningen (B.P. Overbeek, J.F.P. Schellekens); MCH Westeinde Hospital, Department of Medical Microbiology, ‘s-Gravenhage (C.L. Jansen); Medical Center Alkmaar, Department of Microbiology, Alkmaar (F. Vlaspolder); National Institute for Public Health and the Environment, Centre for Infectious Disease Control, Epidemiology and Surveillance, Bilthoven (J. Alblas, A.K. van der Bij, M. De Kraker, T. Leenstra, M. Leverstein-van Hall, J. Monen, J. Muilwijk, N. van de Sande-Bruinsma); PAMM, Department of Medical Microbiology, Veldhoven (H.T. Tjhie); Radboud University Nijmegen Medical Center, Department of Medical Microbiology, Nijmegen (P.D.J. Sturm); Regional Laboratory of Public Health, Haarlem (B.M.W. Diederen); Rijnstate Hospital, Laboratory for Medical Microbiology and Immunology, Velp (A.A. van Zwet); Saltro, Primary Health Care Laboratory, Department of Medical Microbiology, Utrecht (M.P.D. Deege); University Medical Center Utrecht, Department of Medical Microbiology, Utrecht (C.H.E. Boel, A.J.L. Weersink); ZorgSaam Hospital Zeeuws-Vlaanderen, Department of Medical Microbiology, Terneuzen (B.G.A. Hendrickx).