Gram staining is one way scientists can identify bacteria. Gram-positive bacteria, such as Staphylococcus, appear blue or purple under a microscope when scientists apply a stain. Conversely, Gram ...

First, gram-negative bacteria have a thin cell wall that is about 1.5 to 10 nanometers across, whereas gram-positive bacteria have a thick cell wall measuring about 20 to 80 nanometers.

Using Gram stain diagnosis of bacterial vaginosis as the standard, Pap smear and vaginal culture test results had sensitivity of 43.1 and 77.8%, specificity of 93.6 and 97.7%, positive predictive ...