Isolation of bacteria from diabetic foot ulcers with special reference to anaerobe isolation by simple two-step combustion technique in candle jar

BACKGROUND & OBJECTIVES: Although polymicrobial infections involving both aerobic and anaerobic bacteria are very common in diabetic foot ulcers, in many centres of developing countries, anaerobes are rarely isolated due to technical difficulties. This can be overcome by using a new simple, innovative technique of a combination of candle combustion and use of acidified copper-coated steel wool, as reported here. METHODS: In-house developed method was used in a prospective clinico-microbiological study for anaerobes from randomly selected 43 patients with diabetic foot ulcers along with conventional method of anaerobic culture in GasPak system and aerobic culture by standard laboratory procedures. For primary isolation of anaerobes, Brucella blood agar supplemented with hemin (5 μg/ml) and menadione (1 μg/ml) was used. Antibiotic sensitivity tests were performed by the standard disc diffusion method for aerobes and E-test method for anaerobes. RESULTS: All the 43 samples were culture positive, of which aerobic Gram-negative bacteria (GNB) predominated, followed by Staphylococcus aureus, Enterococcus and diphtheroids. Anaerobes isolated from 21 samples were Peptostreptococcus, Bacteroides, Porphyromonas, Veillonella spp. and Clostridium perfringens by both GasPak and in-house developed and modified candle jar techniques. Imipenem and metronidazole were most sensitive while clindamycin, penicillin and cefoxitin were least sensitive drugs for anaerobes. Aerobic GNB were found to be multidrug resistant, especially to penicillin and cephalosporins. The most sensitive drug was piperacillin-tazobactam. INTERPRETATION & CONCLUSIONS: For isolation of anaerobes from clinical specimens such as diabetic foot ulcers, modified candle jar technique was found to be as reliable as GasPak system. This modified technique needs to be tested for many other clinical materials which are not yet evaluated.