The minimum inhibitory concentration (MIC) is one of the most important values in the clinical bacteriology. The lowest concentration of a specific antibiotic that inhibits growth after overnight incubation determines whether an organism is reported susceptible or resistant. Researchers from the department of Biomedical Engineering, University of Wisconsin-Madison, published about a portable self-loading technology for determining MIC values in journal Lab on a Chip this week. The device is kept as simple as possible and requires only a single user pipetting step to introduce the sample.
The device consists of chambers molded in polydimethylsiloxane (PDMS), a silicone like material often used in microfluidic platforms because of its flow characteristics. The chambers are preloaded with different antibiotics and vacuum sealed to a second layer. The new vacuum approach developed by this research group made it possible to automatically fill the dead-end microfluidic chambers that normally require valves and actuators. Because the gas is absorbed by the PDMS, the sample fluid will flow towards the chambers and dissolve the antibiotic without cross contamination. An added colorimetric pH indicator will visualize the growth of bacteria.
In the paper Nate Cira et al compared the MIC values of vancomycin, tetracycline, and kanamycin against E. faecalis, P. mirabilis, K. pneumoniae and E. coli with standard liquid broth dilution measurements. In all cases these results matched the off chip data within one, two-fold dilution.
In the end the authors speculate on some other options like using a fluorescence growth indicator instead of colorimetric pH for faster automated detection. More chambers with different concentrations or different combinations of antibiotics makes it possible to get a higher resolution and gain more test results in parallel. They even suggest this technique can be used for other applications as long as the reagents can be dispensed, dried and stored under vacuum.
Abstract in Lab on a Chip: A self-loading microfluidic device for determining the minimum inhibitory concentration of antibiotics