If your gram stain is negative for disease-causing bacteria, your doctor may order other tests to learn what’s causing your symptoms. How we reviewed this article: Sources ...

Gram-positive bacteria are bacteria with thick cell walls. In a Gram stain test, these organisms yield a positive result. Here’s why knowing whether the result is positive or negative is important.

Gram-positive bacteria show blue or purple after Gram-staining in a laboratory test. They have thick cell walls. Gram-negative bacteria show pink or red on staining and have thin walls.

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 ...

With delicate hues of purple and pink, a lab technique called gram staining has reliably characterized bacteria for more than a century. Yet many scientists are mistaken about why the vivid method ...

The color of gram positive and gram negative bacteria at each stage of Gram staining. Credit: Technology Networks Gram stain procedure - Preparing a sample. Label a clean glass microscope slide with ...

More information: Çağatay Işıl et al, Virtual Gram staining of label-free bacteria using dark-field microscopy and deep learning, Science Advances (2025). DOI: 10.1126/sciadv.ads2757.

The Gram staining was first developed by a Danish scientist, Christian Gram, in 1884 and it has been used so far as the golden standard to classify bacteria. However, it has several obstructions.

The sensitivity and specificity of Gram stain for "many" bacteria were 51.3% and 91.0%, respectively, with an accuracy of 76.8%. Gram stain showed a positive predictive value ...