Automated Gram staining increases reliability and safety

June 1, 2010

Despite recent advances in automated laboratory systems, most microbiology laboratories continue to rely on manual Gram stain methods for testing patient samples. Most have accepted manual Gram staining as a standard operating procedure, with only high-volume microbiology laboratories adopting automated methods. Manual Gram staining can pose a unique set of problems for microbiologists. It is sometimes cumbersome and time consuming, includes numerous steps that must be performed in a specific sequence with precise timing, and exposes laboratory personnel to toxic chemicals. Additionally, the quality of the stain often is directly related to the microbiologist’s experience and technique. Manually prepared slides are less reproducible compared with automated Gram-staining methods that eliminate manual steps and increase efficiency, standardization, and productivity.

Current automated Gram-staining instruments utilize various methods for staining slides. One method involves automatically dunking slides into staining baths. This type of system increases the potential for contamination as slides are in direct contact with each other and are exposed to the same aliquot of staining solution. The dunking method also exposes laboratory personnel to toxic chemicals. A modification of this system uses special adapters that minimize contact among slides, thus reducing the risk for cross contamination. Other automated Gram-stain instruments use a closed system for storing chemical reagents and waste products, minimizing technician exposure to toxic chemicals. These systems apply the stain by spraying the slides as they spin in a rotor. This method uses only 10% of the volume of reagents typically used in manual staining procedures. This reduction results in lower reagent costs and less waste.

Automated Gram-stainer systems increase the number of slides that a microbiologist can stain at one time. In the time it takes a microbiologist to stain and dry one slide, an automated Gram-staining instrument can stain multiple slides simultaneously. Some instruments can process and stain up to 30 slides in about five minutes using varying rotor heads with the flexibility to fix samples on the slide or to use an off-line fixation process. Some systems may also provide cytocentrifuge capabilities to sediment cells from liquid suspensions.

Automated Gram-staining instruments eliminate manual manipulations and processing, and detect Gram-positive and Gram-negative strains with equal clarity. Some utilize less reagents and produce less waste while providing consistent and reliable results that reduce the potential for errors or repeat testing. More importantly, some automated Gram-stain instruments reduce reagent use, waste volumes, and reduce the time required to stain slides, freeing microbiologists to perform other tests. After all, the skilled technologist is the most important asset of all in the microbiology laboratory.

Kathleen Shelton is marketing manager for
the Full Microbiology Laboratory Automation,
PREVI Color Gram from bioM’erieux Inc., located
in Durham, NC.