[Role of yeasts in diabetic foot ulcer infection]

Abstract

Aims: The aim was to assess the incidence of isolation of individual fungal species and interpret the meaning of fungal isolates from foot ulcers of 509 diabetic outpatients using mycologic and histopathologic methods. Another aim was to explore risk factors for the development of fungal infections in foot ulcer.

Methods: Fungus isolation was made on selective media and their identification by standard mycologic methods. Histopathologic diagnosis of fungal ulcer infections was made on PAS-stained histopathologic preparations and imprint preparations (PAS and Papanicolaou staining) of foot wound biopsy specimens.

Results: Fungal and mixed foot ulcer infections were found in 14.9% of diabetic patients. In 33.8% of patients, these infections were confirmed by a finding of fungal elements in histopathologic preparations of ulcer biopsy specimens, as follows: in 16.9% of patients, by finding fungal elements in imprint preparations of ulcer biopsy specimens and by isolation fungus from the swab of the same ulcer; in 2.3% by fungus isolation from ulcer biopsy specimens; in 36.9% by fungus isolation from ulcer swabs in pure culture and/or in a large number of colonies and/or from several ulcers on the foot of the same patient. More than 89% of patients had a single foot ulcer with fungal or mixed infection, big toe and the plantar-metatarsal region in one foot or both feet being the most common sites of ulcer. Fifteen species from the genera Candida, Cryptococcus, Trichosporon and Rhodotorula were the causative agents of fungal and mixed foot ulcer infections. C. parapsilosis (in 61.5% of patients), and C. albicans and C. tropicalis (in 10.8% of patients each) were the most common causes of these infections. The presence of yeasts and/or dermatophytes in the toe web of the same or other foot, or of both feet, did not influence the incidence of fungal and mixed foot ulcer infections. Patient sex and age, type and length of diabetes, or clinical picture of diabetic foot did not affect it either. In IDDM patients, the risk factor for the development of fungal and mixed foot ulcer infections was ulcer infection lasting for more than 13 weeks, whereas in NIDDM patients the length of ulcer infection did not contribute to the incidence of fungal and mixed foot ulcer infection.

Discussion: Our results and other reports suggest that Candida species are the most common fungal isolates (between 93.2% and 100% of all fungal isolates) from diabetic foot ulcer, with C. parapsilosis being the most common causative agent of fungal and mixed infection. From diabetic foot ulcer, bacterial isolation was 5 times as common as that of yeasts (327 vs. 65 patients). Nevertheless, this investigation showed fungal isolates, originating not only from a primarily sterile ulcer sample (biopsy specimen) but also from foot ulcer swabs to be the causative agents (not ulcer colonizers or contaminants) of the foot ulcer infection. The pathogen c effect of yeasts in foot ulcer is indicated by the severity of clinical finding, chronic course of infection, and infection progression despite antibiotic therapy. Equally indicative are microbiologic diagnostic parameters (isolation in pure culture, and/or isolation in a large number of colonies, and/or isolation from several ulcers in the foot of the same patient).

Conclusions: In diabetic patients at highest risk of developing fungal and mixed foot ulcer infections (IDDM patients with ulcer infection persisting for more than 13 weeks, and NIDDM patients with the clinical picture of deep ulcer and abscess in the plantar region, irrespective of the duration of ulcer infection), routine bacteriologic diagnosis should be supplemented with targeted mycologic and histopathologic methods.