Gram staining is one of the most common identification methods in bacteriology. It is a differen-tial staining process, which divides bacteria into two categories; gram negative and gram posi-tive. NordLab Kemi area laboratory owns a Previ®Color gram staining device manufactured by Biomerieux. This automated device does all the gram staining stages automatically, which leaves more time to analyse microbiological samples.

This paper reports a project study of Previ®Color gram staining device validation and staining parameter optimization. Assigner of this project was NordLab Kemi area laboratory in Länsi-Pohja Central Hospital.

Pretests were carried out with two different ATCC bacterial species and numerous patient sam-ples to find optimal staining parameters. After pretests validation stainings were done with new samples from ATCC bacterial species and patients. 10 copies were made out of each microbio-logical sample and stained separately to find out repeatability of the device and sample variation between stainings.

Results revealed that Previ®Color gram staining process is stable and can be used in daily basis at the laboratory. Optimal staining parameters give good contrast between gram positive and gram negative bacteria. Microbiology laboratory personnel were given instructions on how to use Previ®Color gram staining device and on different maintenance procedures.

These results and information of this report can be used in similar validation processes and stain-ing device introductions.