A Gram stain is a vaginal testing method used to help identify bacteria in a sample.
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‘Gram stain’ can also be used as an additional descriptor for a bacteria. While Evvy does not do gram stain testing, gram stain is a property of the bacteria that doctors are familiar with (hence why it’s listed on our expanded report!). If a sample is being examined under a microscope, a stain is added to highlight bacteria - cells with thicker cell walls are gram stain positive, while a thinner cell wall indicates a gram stain negative microbe. As an example, Prevotella bivia is an anaerobic bacteria, and it appears negative on a gram stain - both “anaerobic” and “gram stain negative” are just ways to describe this microbe!

On an Evvy Expanded Panel PCR report, the gram stain for each microbe is reported as gram-negative (—), gram-positive (+), unknown (U), or not applicable (N/A). Stains reported for each microbe are based on published scientific literature.
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You may see “N/A” listed next to some bacteria - this is common when the microbe lacks a cell wall, or if there is inconsistency in how it stains. There’s room for variability, which is another reason why NGS sequencing is more comprehensive than Gram stains alone to identify a bacteria!