Swab cultures accurately identify bacterial pathogens in diabetic foot wounds not involving bone

Current clinical practice assumes swab cultures from wounds are unreliable. However, this assumption is based upon data culled only from wounds in which osteomyelitis and/or gangrene were present. This study aimed to re-evaluate the accuracy of swab cultures vs. deep tissue cultures in diabetic wounds of varying depth and severity.

A total of 60 infected diabetic foot wounds were cultured. Two specimens were taken from each wound: superficial swab before debridement and deep tissue specimen towards the end of surgical debridement.

In 37 wounds (62%), the micro-organisms isolated from the swab specimen and those isolated from the deep tissue specimen were identical. In another 12 wounds (20%), the swab culture contained all micro-organisms isolated from the deep tissue culture, but also contained additional micro-organisms. Analysis according to the depth of the wound, demonstrated that swabs identified all micro-organisms isolated from the deep tissue specimens in 36/40 wounds (90%) that did not extend to bone as opposed to 13/20 wounds (65%) that extended to bone.

Swab cultures are valuable in identifying pathogens in diabetic foot wounds when bone is not involved. When surgical debridement is contraindicated or delayed, swab cultures can be used to select appropriate antibiotic therapy.