Certified Surgical Technologist (CST) Practice Exam

Which laboratory test determines bacterial identification?

1. Gram stain

2. Manual count

3. Gel electrophoresis

4. Prothrombin time

The correct answer is: Gram stain

The Gram stain is a critical laboratory test for bacterial identification because it provides valuable information about the structure of the bacterial cell wall. This test categorizes bacteria into two primary groups: Gram-positive and Gram-negative, based on how they absorb the dye used during the staining process. Gram-positive bacteria retain the dye and appear purple under microscope examination, while Gram-negative bacteria do not retain the dye and take on a pink color after a counterstain is applied. This fundamental distinction not only helps in identifying the type of bacteria present but also guides healthcare professionals in choosing appropriate antibiotic treatments, as the structure of the cell wall influences a bacterium's sensitivity to antimicrobial agents. The other options listed do not serve the purpose of bacterial identification in the same way. Manual count refers to the quantification of cells but does not provide specific information regarding bacterial species or classification. Gel electrophoresis is primarily utilized for the separation and analysis of DNA or proteins, which may assist in identifying genetic sequences but is not a standard test for bacterial identification. Prothrombin time is a test measuring blood coagulation and is unrelated to microbiological assessments. Therefore, the Gram stain's ability to differentiate bacteria based on their cell wall characteristics makes it the correct choice for determining bacterial identification.