TY - JOUR
T1 - Combining diagnostic methods for antimicrobial susceptibility testing – A comparative approach
AU - Klodzinska, Sylvia Natalie
AU - Priemel, Petra Alexandra
AU - Rades, Thomas
AU - Nielsen, Hanne Mørck
PY - 2018/1
Y1 - 2018/1
N2 - Background The minimum inhibitory concentration (MIC) is a measure of antimicrobial susceptibility testing (AST) of a given antibiotic but provides insufficient information when bacterial killing is crucial, e.g., when treating immunocompromised patients. In these cases, the minimum bactericidal concentration (MBC) is a more reliable measure of antibiotic activity. Here, we aim to demonstrate and recommend combinations of methods for MIC and MBC measurements. We also aim to emphasize the importance of uniform protocols for these procedures including the time point for reading MIC results, which the authors suggest to be 20 h. Methods To address the challenges with obtaining fast and reliable readouts on MIC as well as the kinetic and end-point effects of antibiotics, the broth micro dilution method, a calorimetric method and a microscopy-based screening system (MBSS) were evaluated in this study. For MBC determination, fluorophore staining with SYTO9 and propidium iodide was compared to the broth regrowth method. Results Three scenarios for combining the MIC and MBC methods depending on the investigators' primary concern (time, cost or sensitivity) are presented. Further, as the MBSS and the isothermal microcalorimetry method detected delayed bacterial growth up to 18 h after initiation of experiments, the importance of reading MIC testing after a full 20 h is emphasized. A one-fold change in MIC values can be observed when comparing data obtained at 16 h and 20 h of incubation. Conclusion The authors suggest that combining MIC and MBC determinations will provide more detailed understanding of the bacteria susceptibility to antibiotic drugs and result in more clinically relevant data and optimized therapies. Furthermore, establishing 20 h as a time point for reading MIC results will provide more uniform data across laboratories.
AB - Background The minimum inhibitory concentration (MIC) is a measure of antimicrobial susceptibility testing (AST) of a given antibiotic but provides insufficient information when bacterial killing is crucial, e.g., when treating immunocompromised patients. In these cases, the minimum bactericidal concentration (MBC) is a more reliable measure of antibiotic activity. Here, we aim to demonstrate and recommend combinations of methods for MIC and MBC measurements. We also aim to emphasize the importance of uniform protocols for these procedures including the time point for reading MIC results, which the authors suggest to be 20 h. Methods To address the challenges with obtaining fast and reliable readouts on MIC as well as the kinetic and end-point effects of antibiotics, the broth micro dilution method, a calorimetric method and a microscopy-based screening system (MBSS) were evaluated in this study. For MBC determination, fluorophore staining with SYTO9 and propidium iodide was compared to the broth regrowth method. Results Three scenarios for combining the MIC and MBC methods depending on the investigators' primary concern (time, cost or sensitivity) are presented. Further, as the MBSS and the isothermal microcalorimetry method detected delayed bacterial growth up to 18 h after initiation of experiments, the importance of reading MIC testing after a full 20 h is emphasized. A one-fold change in MIC values can be observed when comparing data obtained at 16 h and 20 h of incubation. Conclusion The authors suggest that combining MIC and MBC determinations will provide more detailed understanding of the bacteria susceptibility to antibiotic drugs and result in more clinically relevant data and optimized therapies. Furthermore, establishing 20 h as a time point for reading MIC results will provide more uniform data across laboratories.
U2 - 10.1016/j.mimet.2017.11.010
DO - 10.1016/j.mimet.2017.11.010
M3 - Journal article
C2 - 29154899
SN - 0167-7012
VL - 144
SP - 177
EP - 185
JO - Journal of Microbiological Methods
JF - Journal of Microbiological Methods
ER -