Burkholderia pseudomallei multi-centre study to establish EUCAST MIC and zone diameter distributions and epidemiological cut-off values

Abstract

Objectives: Melioidosis, caused by Burkholderia pseudomallei, requires intensive antimicrobial treatment. However, standardized antimicrobial susceptibility testing (AST) methodology based on modern principles for determining breakpoints and ascertaining performance of methods are lacking for B. pseudomallei. This study aimed to establish MIC and zone diameter distributions on which to set epidemiological cut-off (ECOFF) values for B. pseudomallei using standard EUCAST methodology for nonfastidious organisms. Methods: Non-consecutive, non-duplicate clinical B. pseudomallei isolates (9e70 per centre) were tested at eight study centres against eight antimicrobials by broth microdilution (BMD) and the EUCAST disc diffusion method. Isolates without and with suspected resistance mechanisms were deliberately selected. The EUCAST Development Laboratory ensured the quality of study materials, and provided guidance on performance of the tests and interpretation of results. Aggregated results were analysed according to EUCAST recommendations to determine ECOFFs. Results: MIC and zone diameter distributions were generated using BMD and disc diffusion results obtained for 361 B. pseudomallei isolates. MIC and zone diameter ECOFFs (mg/L; mm) were determined for amoxicillin-clavulanic acid (8; 22), ceftazidime (8; 22), imipenem (2; 29), meropenem (2; 26), doxycycline (2; none), tetracycline (8; 23), chloramphenicol (8; 22) and trimethoprim-sulfamethoxazole (4; 28). Conclusions: We have validated the use of standard BMD and disc diffusion methodology for AST of B. pseudomallei. The MIC and zone diameter distributions generated in this study allowed us to establish MIC and zone diameter ECOFFs for the antimicrobials studied. These ECOFFs served as background data for EUCAST to set clinical MIC and zone diameter breakpoints for B. pseudomallei.

Epidemiological and Clinical Characteristics of Melioidosis Caused by Gentamicin-SusceptibleBurkholderia pseudomalleiin Sarawak, Malaysia

“…Second, for antibiotic susceptibility, an adaptive interpretation of the CLSI guidelines was used, as CLSI does not provide specific criteria for interpreting disk diffusion tests for Bp . Recently the European Committee on Antimicrobial Susceptibility Testing has defined specific disk diffusion zone diameter distributions and epidemiological cutoff values for Bp [ 39 , 40 ]. Nevertheless, the specific interpretation of gentamicin susceptibility for Bp isolates from our study remains valid, given the clear separation of susceptible and resistant isolates on both Etest and disk diffusion.…”

How to: ECOFFs—the why, the how, and the don'ts of EUCAST epidemiological cutoff values

“…It is therefore important that investigators, journal editors and reviewers understand the concepts of defining wild type distributions and ECOFFs and what data are required to establish ECOFFs. There are investigators that have designed studies with the explicit purpose of creating an MIC database suitable for the purpose [14,15]. This should be encouraged by editors and reviewers whereas publishing ECOFFs based on less than three distributions [16][17][18] should be discouraged.…”

Melioidosis: A Neglected Infection in Bangladesh

“…Rectal swabs should also be cultured using selective media. It is recommended that cultures are repeated for any culture-negative patient whose symptoms are strongly suggestive of melioidosis 27,28 .…”