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.

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 ...

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 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 ...

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 ...

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 ...

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.

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.