Effects of Microplate Type and Broth Additives on Microdilution MIC Susceptibility Assays

The determination of antibiotic potency against bacterial strains by assessment of their minimum inhibitory concentration normally uses a standardized broth microdilution assay procedure developed more than 50 years ago. However, certain antibiotics require modified assay conditions in order to obse...

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Bibliographic Details
Published in:Antimicrobial agents and chemotherapy Vol. 63; no. 1
Main Authors: Kavanagh, Angela, Ramu, Soumya, Gong, Yujing, Cooper, Matthew A, Blaskovich, Mark A T
Format: Journal Article
Language:English
Published: United States 01.01.2019
Subjects:
Aminoglycosides - chemistry
Aminoglycosides - pharmacology
Anti-Bacterial Agents - chemistry
Anti-Bacterial Agents - pharmacology
Calcium - pharmacology
Ciprofloxacin - chemistry
Ciprofloxacin - pharmacology
Colistin - chemistry
Colistin - pharmacology
Culture Media - chemistry
Culture Media - pharmacology
Depsipeptides - chemistry
Depsipeptides - pharmacology
Escherichia coli - drug effects
Escherichia coli - growth & development
Escherichia coli - metabolism
Factor Analysis, Statistical
Lipoglycopeptides - chemistry
Lipoglycopeptides - pharmacology
Methicillin-Resistant Staphylococcus aureus - drug effects
Methicillin-Resistant Staphylococcus aureus - growth & development
Methicillin-Resistant Staphylococcus aureus - metabolism
Microbial Sensitivity Tests - instrumentation
Oxacillin - chemistry
Oxacillin - pharmacology
Penicillin G - chemistry
Penicillin G - pharmacology
Plastics - chemistry
Polymyxin B - chemistry
Polymyxin B - pharmacology
Polysorbates - pharmacology
Rifampin - chemistry
Rifampin - pharmacology
Teicoplanin - analogs & derivatives
Teicoplanin - chemistry
Teicoplanin - pharmacology
Trimethoprim - chemistry
Trimethoprim - pharmacology
Vancomycin - chemistry
Vancomycin - pharmacology
broth microdilution assay
additive effects
microtiter plate effects
MIC
ISSN:1098-6596, 1098-6596
Online Access:Get more information
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Summary:The determination of antibiotic potency against bacterial strains by assessment of their minimum inhibitory concentration normally uses a standardized broth microdilution assay procedure developed more than 50 years ago. However, certain antibiotics require modified assay conditions in order to observe optimal activity. For example, daptomycin requires medium supplemented with Ca , and the lipoglycopeptides dalbavancin and oritavancin require Tween 80 to be added to the growth medium to prevent the depletion of free drug via adsorption to the plastic microplate. In this report, we examine systematically the effects of several different plate types on microdilution broth MIC values for a set of antibiotics against Gram-positive and Gram-negative bacteria, both in medium alone and in medium supplemented with the commonly used additives Tween 80, lysed horse blood, and 50% human serum. We observed very significant differences in measured MICs (up to 100-fold) for some lipophilic antibiotics, such as the Gram-positive lipoglycopeptide dalbavancin and the Gram-negative lipopeptide polymyxins, and found that nonspecific binding plates can replace the need for surfactant additives. Microtiter plate types and any additives should be specified when reporting broth dilution MIC values, as results can vary dramatically for some classes of antibiotics.
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ISSN:1098-6596
1098-6596
DOI:10.1128/AAC.01760-18