The utility of Gram stains and culture in the management of limb ulcers in persons with diabetes

In Tanzania, limited laboratory services often preclude routine identification of microorganisms that cause infections in persons with diabetes. Thus, we carried out this study to determine the utility of a Gram stain alone versus culture in guiding appropriate antimicrobial therapy. During February 2006 to December 2007 (study period), deep tissue biopsies were obtained from persons with diabetes presenting to the Muhimbili National Hospital (MNH) with infected limb ulcers. Specimens were Gram-stained then cultured for bacteria and fungi. Biopsies were obtained from 128 patients. Of 128 cultures, 118 (92%) yielded bacterial or fungal growth; 59 (50%) of these 118 cultures yielded mixed growth (80% included Gram-negative organisms); 38 (32%) and 20 (17%) yielded Gram-negative and Gram-positive organisms alone, respectively. The predictive value positive of a Gram stain for bacterial growth was 93% (110/118); a Gram-positive stain was 75% (15/20) predictive of growth of Gram-positive organisms whereas a Gram-negative stain was 82% (31/38) predictive of growth of Gram-negative organisms. In regions with limited resources, a Gram stain of an ulcer biopsy that is carefully procured is largely predictive of the type of microorganism causing infection. Gram staining of deep tissue biopsies might have a potential role to play in the management of infected diabetic limb ulcers.