What are the limitations of gram staining technique?

Gram staining is a key laboratory procedure for detecting the presence of bacteria and differentiating between gram-positive and gram-negative bacteria. It is simple and cost effective and yields quick results when examining infections. Despite its many advantages, there are also a few limitations associated with this technique.  

Gram staining only provides preliminary information regarding bacterial infection. It is necessary to perform additional procedures such as culture to confirm the findings suggested by gram stain. False negative results may occur in case of any errors while performing the procedure or if there are low numbers of organisms present in the sample. Additionally, certain organisms such as Legionella or mycobacteria (TB) do not stain well with Gram stain, potentially yielding inaccurate results. There are several factors that could potentially interfere with the interpretation. These include age of the isolate, background material, samples collected from patients taking antibiotics, or cultures transferred from media that contain antibiotics. 

Obtaining blood samples for gram staining could have side effects such as bruising in the area where the blood is drawn. Performing gram staining on tissue samples carries risks such as infection or excessive bleeding associated with removing the tissue.