Microbiology Education Series  

Specimen Collection for Microbiology Cultures

Wounds, tissues, fluids, and abscesses

Frequently the Microbiology Laboratory receives swabs for bacterial culture and the body site or specimen description will indicate tissue, body fluid, aspirate, abscess, etc.

The literature is quite clear that swabs are not an optimal specimen to yield the actual pathogen that is the cause of the infection.

The recommendations are:

1. Send the tissue that is infected, if possible.
2. Next best specimen is the fluid surrounding the tissue.
3. A swab of the tissue or the fluid is the least acceptable specimen.

Many organisms that are collected on a swab are in the vicinity of the infected tissue or fluid. The isolation of these organisms leads to treatment of either non-pathogen(s) or may lead to complicated antibiotic selection due to the multiple number of organisms that were isolated – not all of which may actually be pathogen(s).

Swabs also have the potential to bind bacteria to the fibers, and therefore when the swabs are plated on bacteriologic media all of the bacteria do not "come off" the swab readily. This would mean that a pathogen could be "missed".

Clearly tissues, fluids, and aspirates are superior to swabs. So whenever possible:

"Just Say No to Swabs"