Send to

Choose Destination
BMC Microbiol. 2009 May 26;9:106. doi: 10.1186/1471-2180-9-106.

Isothermal micro calorimetry--a new method for MIC determinations: results for 12 antibiotics and reference strains of E. coli and S. aureus.

Author information

Research Station Agroscope Liebefeld-Posieux ALP, Bern, Switzerland.



Antimicrobial susceptibility testing of microorganisms is performed by either disc diffusion or broth dilution tests. In clinical use, the tests are often still performed manually although automated systems exist. Most systems, however, are based on turbidometric methods which have well-known drawbacks.


In this study we evaluated isothermal micro calorimetry (IMC) for the determination of minimal inhibitory concentrations (MICs) of 12 antibiotics for five micro-organisms. Here we present the data for the 12 antibiotics and two representative microorganisms E. coli (a Gram-) and S. aureus (a Gram+). IMC was able to determine the MICs correctly according to CLSI values. Since MICs require 24 hours, time was not reduced. However, IMC provided new additional data - a continuous record of heat-producing bacterial activity (e.g. growth) in calorimetry ampoules at subinhibitory antibiotic concentrations. Key features of the heatflow (P) and aggregate heat (Q) vs. time curves were identified (t delay and Delta Q/Delta t respectively). Antibiotics with similar modes of action proved to have similar effects on t delay and/or Delta Q/Delta t.


IMC can be a powerful tool for determining the effects of antibiotics on microorganisms in vitro. It easily provides accurate MICs - plus a potential means for analyzing and comparing the modes of action of antibiotics at subinhibitory concentrations. Also IMC is completely passive, so after evaluation, ampoule contents (media, bacteria, etc.) can be analyzed by any other method desired.

[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for BioMed Central Icon for PubMed Central
Loading ...
Support Center