Comparison of disc diffusion, Etest and agar dilution for susceptibility testing of colistin against Enterobacteriaceae
- 23 September 2011
- journal article
- research article
- Published by Oxford University Press (OUP) in Letters in Applied Microbiology
- Vol. 53 (5), 546-551
- https://doi.org/10.1111/j.1472-765x.2011.03145.x
Abstract
Aims: In this study, we compared different methods of colistin susceptibility testing, disc diffusion, agar dilution and Etest using a set of Enterobacteriaceae isolates that included colistin‐resistant strains. Methods and results: Susceptibility of 200 clinical isolates of Enterobacteriaceae to colistin was tested to compare agar dilution (reference method), disc diffusion (50 and 10 μg) and Etest. MICs (minimum inhibitory concentrations) were interpreted using the criteria established by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Colistin exhibited excellent activity against Escherichia coli and E. cloacae (MIC90 = 0·5 mg l−1). In contrast, colistin was less active against Klebsiella pneumoniae (MIC90 = 16 mg l−1). Resistance rates varied from 0% in E. coli to 1·8% in E. cloacae and 13% in K. pneumoniae. High rates of very major errors were observed in the disc diffusion test using either the criteria of the Comité de l’antibiogramme de la Société Française de Microbiologie (CA‐SFM) or the criteria of the Clinical and Laboratory Standards Institute (CLSI), respectively, 3·5 and 2·5%. When the criteria of Gales et al. were applied, the number of very major errors was reduced to one (0·5%). The Etest showed good concordance with agar dilution method. Conclusion: Disc susceptibility testing methods are unreliable on detecting colistin resistance. MIC should be determined to confirm the susceptibility results by disc diffusion. Significance and Impact of the study: We recommend the determination of MIC by Etest for all multidrug‐resistant Enterobacteriaceae when colistin is required for the treatment.Keywords
This publication has 21 references indexed in Scilit:
- Resistance to polymyxins: Mechanisms, frequency and treatment optionsDrug Resistance Updates, 2010
- Nonclonal Emergence of Colistin-Resistant Klebsiella pneumoniae Isolates from Blood Samples in South KoreaAntimicrobial Agents and Chemotherapy, 2010
- Comparative Evaluation of the VITEK 2, Disk Diffusion, Etest, Broth Microdilution, and Agar Dilution Susceptibility Testing Methods for Colistin in Clinical Isolates, Including Heteroresistant Enterobacter cloacae and Acinetobacter baumannii StrainsAntimicrobial Agents and Chemotherapy, 2007
- Comparison of Etest, Vitek and agar dilution for susceptibility testing of colistinClinical Microbiology & Infection, 2007
- Colistin as a salvage therapy for nosocomial infections caused by multidrug-resistant bacteria in the ICUInternational Journal of Antimicrobial Agents, 2006
- Comparison of three standardized disc susceptibility testing methods for colistinJournal of Antimicrobial Chemotherapy, 2006
- Bacteraemia in cancer patients caused by colistin-resistant Gram-negative bacilli after previous exposure to ciprofloxacin and/or colistinClinical Microbiology & Infection, 2006
- Colistin: The Revival of Polymyxins for the Management of Multidrug-Resistant Gram-Negative Bacterial InfectionsClinical Infectious Diseases, 2005
- Successive Emergence of Enterobacter aerogenes Strains Resistant to Imipenem and Colistin in a PatientAntimicrobial Agents and Chemotherapy, 2005
- Evaluation of colistin as an agent against multi-resistant Gram-negative bacteriaInternational Journal of Antimicrobial Agents, 2004