Microorganisms should be cultured under conditions that best support their growth including atmosphere, temperature, and duration of incubation. For example, incubation of bacteria on non-selective media for 18-48 hours, in an ambient or CO2 atmosphere, incubated at 33-37° C generally yield optimal spectra. Note that studies have shown that after appropriate incubation, accurate identification can be achieved when plates are held at room temperature (RT) for up to 12 hours. This includes obligate anaerobic organisms.
We have noted a couple of exceptions:
- Campylobacter: Cultivation can be prolonged to 72 hours (+12 hours storage at RT)
- Streptococcus pneumoniae: Cultivation should not be longer than 24 hours (+12 hours storage at RT)
Some organisms can still give acceptable spectra after up to three days of non-refrigerated storage, but for reliable identification, if testing is not performed within 12 hours the isolate should be sub-cultured prior to testing on the MALDI-TOF MS. Refrigerated isolates should be sub-cultured, as refrigeration may adversely affect the quality of the spectra.