5.4 Use of susceptibility panels
Susceptibility panels are tests against multiple antimicrobials set up in parallel to look for particular patterns in resistance and sensitivity.
Susceptibility panels can be done as individual disk diffusion tests, but in practice they are mostly done using an automated system such as Vitek IITM, SensititreTM or PhoenixTM.
Figure 11 Susceptibility panel test from PhoenixTM
Show description|Hide descriptionImage A: The Phoenix automated system showing the test panels in place. Image B: An individual test panel. The wells on the test panel contain substrates which change colour due to bacterial action. The ones on the left are for biochemical reactions used to identify the species. The ones on the right determine the MIC to a range of antimicrobials. There are four different concentrations of antimicrobial for each and growth appears as a change from blue to pink. The machine detects this and analyses the resulting pattern to work out what the likely resistance mechanism is – for example β-lactamase, carbapenemase et cetera, as well as the MIC.
