Miniaturized oligonucleotide arrays: a new tool for discriminating colonization from infection due to Staphylococcus aureus in diabetic foot ulcers

Abstract

OBJECTIVE - To evaluate the use of oligonucleotide arrays to discriminate colonization from infection due to Staphylococcus aureus in diabetic foot ulcers.

RESEARCH DESIGN AND METHODS - We included diabetic patients hospitalized in a diabetic foot department for an episode of foot ulcer. Only patients who had no antibiotic treatment during the previous 6-month were included. At admission, ulcers were classified on clinical examination, according to the IDSA system. 72 patients with culture positive only for S. aureus as the sole pathogen were included. In individuals with a grade 1 ulcer, a second wound bacterial specimen was obtained one month later. Using oligonucleotide arrays, S. aureus resistance and virulence genes were compared between grade 1 and grade 2-4 ulcers.

RESULTS - S. aureus was initially isolated from 22 grade 1 and 50 grade 2-4 ulcers: 35 were methicillin-resistant and 37 methicillin-sensitive. In 20 grade 1 ulcers (92%), no virulence genes were identified whereas these genes were present in all but one grade 2-4 ulcers. During follow-up, the two grade 1 ulcers which infected with strains carrying virulence genes rapidly deteriored: the array technology showed unchanged genotype profiles. On the contrary, two grade 1 ulcers healed: the genotype profiles were different from those at inclusion but without appearance of virulence genes.

CONCLUSIONS - The DNA array appears as a promising technique, easy to perform. Our observational study suggests that it might help distinguish colonized grade 1 from infected grade 2 wounds, predict ulcer outcome and contribute to a more adequate use of antibiotics.