A Gram stain and culture of the material from an infected site are the most commonly performed microbiology tests used to identify the cause of an infection. Often, determining whether an infection is caused by an organism that is Gram positive or Gram negative will be sufficient to allow a doctor to prescribe treatment with an appropriate antibiotic while waiting for more specific tests to be completed. Absence or presence of white blood cells in the Gram stain can determine the adequacy of the specimen.

A Gram stain is done with a bacterial culture when a bacterial infection is suspected.

Determining the Gram status of an organism allows the doctor to select an appropriate antibiotic before culture results are available. Gram stains cannot confirm the organism’s identity or susceptibility to antibiotics. Only a culture of the material can supply this information.

Bacterial infections should not be ignored, even if the symptoms are mild. You should consult your doctor so treatment, if necessary, can begin promptly, and the spread and severity of the disease can be limited. If left untreated, bacterial infections can migrate throughout the body and cause tissue and organ damage.