Microbial profiles, resistance patterns, and clinical outcomes in diabetic foot ulcers: a prospective cohort study using the WIfI classification

The microbiological profile of infected diabetic foot ulcers varies by region and its relation to the WIfI (Wound, Ischemia and foot Infection) classification has not been examined. This study assessed the association between the microorganisms isolated from deep tissue cultures and the WIfI foot infection grade and amputation risk stage, and with major amputation and in-hospital death. This prospective cohort study was conducted at a tertiary hospital in Belo Horizonte, Brazil, between February 2017 and March 2019. Adults with diabetes admitted with a foot ulcer and WIfI foot infection grade 1 to 3 were enrolled consecutively, and 100 infected limbs from 98 patients were included. Species were analysed at the isolate level and resistance phenotypes and outcomes at the limb level. Associations were estimated by Firth penalised logistic regression. Of the 133 isolates, 54.1% were Gram-negative, 43.6% Gram-positive and 2.3% fungi; Staphylococcus aureus was the most frequent species (23.3%). Cultures were monomicrobial in 71 limbs (71.0%). Proteus mirabilis (OR 15.00; 95% CI 1.98 to 112.03; p = 0.011), Klebsiella pneumoniae and Klebsiella aerogenes (OR 16.78; p = 0.039 for both) were more frequent in grade 3 than in grade 2 infection. Enterobacterales rose from 13.6% of the isolates in the very low risk stage to 40.5% in the high risk stage, and Enterococcus faecalis fell from 31.8% to 7.1%. Carbapenem-resistant organisms were isolated from 25.7% of the limbs with grade 1 infection, 8.3% with grade 2 and 40.0% with grade 3; in grade 1, eight of the nine were non-fermenting Gram-negative bacilli. Major amputation occurred in 15 limbs (15.0%) and rose from 0.0% to 32.4% across the amputation risk stages (test for trend, p = 0.003). Two patients (2.0%) died in hospital. Enterobacterales became more frequent and Enterococcus faecalis less frequent as the WIfI amputation risk stage increased, while the fall in Gram-positive bacteria did not reach significance. Carbapenem resistance in mild infection was carried almost entirely by non-fermenting Gram-negative bacilli and does not indicate greater infection severity. Major amputation increased across the same stages, and the number of in-hospital deaths was too small to allow any conclusion about mortality. Clinical trial number: not applicable.