Combined fungal and bacterial infection in deep burns of the lower limb – a case report

Introduction

Fungal infections are caused by microscopic fungi. These microorganisms are widespread both in the environment and on the skin of the humans and animals [1]. They are eukaryotic organisms, formerly being part of the fungal kingdom; however, they currently form a separate entity. Fungi differ from plants in the absence of chlorophyll. It also differs from plants in the structure of the cell wall that contains complex sugars, especially chitin, but also chitosan, mannan, and glucan. Some dyes specifically bind to these substances and therefore they are important for the diagnosis of micromycetes in clinical material [2]. The vast majority of medically important micromycetes are not primary pathogens in most cases and they do not attack a healthy macroorganism, but they are opportunistic pathogens. Accordingly, it is necessary to assess the individual findings of fungi in the clinical material in the context of the patient's health. Superficial mycoses affect the skin and visible mucous membranes. Deep mycoses include organ and systemic forms. The incidence of these diseases is increasing due to the use of broad-spectrum antibiotics, corticosteroids and cytostatics. The following patients are most at risk: the patients with long-term treatment in intensive care units, patients after transplants with subsequent immunosuppression, patients with oncological diseases, patients after complicated injuries and extensive burns, and patients with HIV. Serious fungal infections are often complicated by a combination of multiple pathogens – other mycoses and bacteria. The course of mycoses often tends to be chronic and allergic. Their wall is very antigenic for the macro-organism and very difficult to remove due to the lack of effective enzymes. Fungal infections occur mostly sporadically, the epidemic occurrence is not typical for them. Mycotoxin production plays an important role in the pathogenicity of some micromycetes. Producers of these toxins might not damage the macro-organism by themselves. The disease caused by the ingestion of mycotoxins is called mycotoxicosis [3].

Burned patients suffer from a higher risk of fungal infection compared to other hospitalized patients. Although infections caused by Candida spp., Aspergillus spp. and by other opportunistic fungi become a major cause of delayed morbidity and mortality, they are often underestimated and late diagnosed. The main risk factor for the development of a fungal infection in burn patients is the overall extent of the burn, immune disorders associated with severe burn trauma. The occurrence of fungal infections is also adversely affected with the frequent use of antibiotics in burn patients; at this occasion, the patient’s natural microbial flora is disrupted (Tab. 1).

The diagnosis of fungal infections is possible in several ways: microscopic detection of hyphae in a sample from wound exudate, bronchoalveolar lavage or sputum; cultivation of fungal colonies from smear from the wounds, sputum or bronchoalveolar lavage [4]; histological evidence of fungal cells in a tissue sample taken at biopsy from a burned area [5]; serological detection of fungal infection by detection of antigen or antibodies. The serological tests used include latex agglutination, ELISA, G-test and complement fixation reaction [6]. Molecular biological diagnostics of DNA and RNA of fungi by polymerase chain reaction (PCR) is a very sensitive method for the detection of mycosis [7].

The treatment of mycoses has undergone rapid development in recent decades. The first antifungals were synthesized in the 1950s, and the development of new systemic antifungals has been still ongoing. Antifungals are divided according to their chemical structure (poly­enes, azoles, echinocandins, antimetabolites). It is further divided according to the method of administration into systemic and local. The mechanism of action of antifungals is also different. In terms of toxicity, it is necessary to ensure in therapy that the toxicity of the drug is always higher for the pathogenic cell than for the patient's cells (Tab. 2) [8].

Case report

A 62-years-old male patient was hospitalized at the Department of Burns and Plastic Surgery, University Hospital Brno, with extensive burns over 35% total body surface area (TBSA), predominantly in the area of both lower extremities. The depth of burns was of 3rd degree (in the full thickness of the skin) in most areas; on the fingers, it reached up to 4th degree (affecting deeper structures, i.e. subcutaneous tissue, muscles). The man was injured when his shoes and clothes caught fire while he was burning leaves in the garden. The patient was not seriously ill before the injury and was without chronical medication. The primary treatment was performed in the operating theatre under general anaesthesia. The burned areas on the lower limbs were deep and circular, so it was necessary to perform escharotomies to prevent compartment syndrome that can occur due to massive soft tissue swelling in deep circular burns. As early as during the primary treatment, the patient showed mummification on the toes of the right lower limb extending to the Chopart joint (Fig. 1, 2). Only the distal toe joints were mummified in the left lower limb (Fig. 3). The patient was hospitalized in the intensive care unit. There was further progression of necrosis during his hospitalization, probably also due to massive circulation support with noradrenaline (norepinephrine). Necrotic soft tissues of the distal half of the shin, including muscles, were found on the right lower limb during dressing changes. On 16th day of hospitalization, local situation with progression of the necrosis to the deeper layers resulted in a below knee amputation on the right. The soft tissues and muscles of the left lower limb were less affected and amputation was necessary only for the distal joints of the 1st–3rd toe. In several stages, a combined surgical (fascial and tangential) and chemical necrectomy (with 40% benzoic acid) was performed. Subsequently, the areas after necrectomies were covered with split-thickness skin grafts (STSGs). Donor sites were localized on the both thighs, buttocks, hips and abdomen. In total, 26% TBSA was transplanted. Swabs and imprints for bacterial and fungal testing from the affected areas were taken for microbiological analysis regularly every 2 days. During microbiological surveillance, several bacterial pathogens were cultured from the burned areas, of which Klebsiella pneumoniae dominated, firstly wild type, then ESBL+ (extended spectrum beta-lactamases) bacterial strains and also gram-positive cocci. Targeted antibiotic therapy was promptly applied as the response to bacterial infection. According to microbiological cultivation results, several antibiotics and chemotherapeutics were used gradually – sulfamethoxazole/trimethoprim, piperacillin/tazobactam, metronidazole, vancomycin, meropenem, tigecycline. On 17th day of hospitalization, at the phase of progression of necrosis, several species of micromycetes were also cultured from burn-wounds in the lower extremities. It was a combination of filamentous fungi (zygomycetes) – Lichtheimia corymbifera, Mucor circinelloides, Rhizomucor sp. and yeast (Candida catenulata). The pan-fungal test was borderline positive. Amphotericin B (Abelcet lipid complex) was therefore introduced into therapy at a usual dose of 5 mg/kg (450 mg per day). After 8 days of application of amphotericin B, it was de-escalated to posaconazole (Noxafil) at a dose of 300 mg per day. No specific topical therapy was used. After this therapy, further cultures were no longer found in the micromycetes and there was a significant improvement in the local finding and the patient’s overall condition. After 72 days of hospitalization and 32 surgeries under general anaesthesia, the patient was transferred to a surgery ward at his place of residence.

Discussion

Patients with deep and extensive burns are confronted with numerous microbiological pathogens on a daily basis. Thus, combating infectious complications is one of the greatest challenges in the treatment of thermal trauma. In deep burns, the most common infectious agent is bacteria, causing 70% of infectious complications in burn patients. Another common agent is fungi, causing 20% of infectious complications. Viral infections are the least common in deep burns (10%) [9]. Complications associated with bacterial or fungal infection are very closely related to the incidence of late morbidity and mortality in burn patients [10,11]. The risk of infection in patients after thermal trauma is primarily increased by the loss of skin cover and thus by the barrier function of the skin. Furthermore, the incidence of infections increases down-regulation of the immune system (specific immunosupression), invasive vascular access, and permanent urinary catheters [12]. Significant advances in the treatment of burns in the second half of the 20th century, fluid resuscitation, such as early necrectomy, wound bed preparation, and especially STSGs application, have significantly increased patients' chances of survival after severe thermal trauma [13]. The massive use of broad-spectrum antibiotics has gradually become part of modern treatment of burns. This led to a significant reduction in the incidence of bacterial infections, but at the same time it also caused an increased incidence of fungal infections [14,15]. Since the 1960s, we have seen an up to ten-fold increase in the prevalence of fungal infections in burns [16].

Mycoses are often part of polymicrobial infections of burned areas. Risk ­factors for mycosis in burn patients include age, depth and extent of burns (above 30% TBSA), inhalation injury, delayed burn necrectomy, antibiotic therapy, corticosteroid therapy, hyperglycaemic episodes, central venous catheter and mechanical ventilation. Early and effective diagnosis and subsequent targeted treatment can be life-saving for a patient with many fungal infections. The diagnosis of fungal infections can be performed in several ways, depending on the severity of the infection. Microscopic methods are the standard for the detection of mycosis. Fungi can be observed either directly in the exudate, or cultured in colonies, or observed in biopsy material within incisional biopsy. More modern methods in the diagnosis of fungi use serological tests or a very sensitive molecular biological method for the detection of nucleic acids (DNA, RNA) by PCR.

If yeasts and/or moulds are detected in the region of the burn-wound, it is necessary to strictly distinguish between fungal wound colonization (FWC) and fungal wound infection (FWI). FWC is defined as the identification of fungal elements in the burn necrosis not penetrating deeper into the deeper viable tissue. FWI, on the other hand, is defined as a fungal invasion into the viable tissue [17].

Treatment options for fungal infections have improved significantly in recent years. The first antibiotics were synthesized in the mid-twentieth century, and since then a number of effective drugs have been developed and new ones are still being developed. The goal of developing new antifungals is to maxi­mize antifungal efficiency with the lowest possible toxicity to users.

Conclusion

The case report in this article points to the severity of fungal infections in severely burned patients. In the described case, a dangerous infection of fibrous fungi was diagnosed in time due to regular and especially frequent, microbiological examination. This early-recognized fungal infection was cured within a few days thanks to adequately guided therapy. As a result, the infection did not endanger the patient's life or worsen the local findings in the affected areas.

Roles of authors: All authors contributed equally to this work.

Disclosure: The authors have no conflicts of interest to disclose. The authors declare that this study has received no financial support. All procedures performed in this study involving human participant were in accordance with ethical standards of the institutional and/or national research committee and with the Helsinki declaration and its later amendments or comparable ethical standards.

Iva Tresnerová, M.D.

Department of Burns and Plastic Surgery

University Hospital Brno

Jihlavská 20, 625 00 Brno

Czech Republic

tresnerova.iva@fnbrno.cz cz

Submitted: 8.7.2021

Accepted: 29.10.2021