Candida biofilms and oral candidosis: treatment and prevention

In recent years, there has been a significant increase in the incidence of human fungal infections (60). A number of factors have been implicated with this increase, but it is generally accepted that the main influences relate to the more widespread provision of new medical practices, such as immunosuppressive therapy and use of broad spectrum antibiotics, and invasive surgical procedures such as solid organ or bone marrow transplantation. Infections may either be superficial, affecting the skin, hair, nails and mucosal membranes, or systemic, involving major body organs (95). The risk of systemic infection appears to be enhanced in cases where the individual is already colonized by Candida (71). With regard to superficial mucosal infections, the continued spread of HIV infection (29) and the more extensive use of inhaled steroids (36) have also played significant roles. Of the fungi regarded as human pathogens, members of the genus Candida are amongst the most frequently recovered from disease. The Candida genus is a taxomomic grouping that was originally used to define yeast-like organisms that were not considered to have a sexual reproductive life cycle. Candida contains over 350 heterogeneous species, but only a minority of these have been implicated in human disease (Table 1). Infections caused by Candida are collectively referred to in the plural as candidoses (singular candidosis) or candidiases (singular candidiasis). Both terms are used in the literature although candidosis is preferred to candidiasis by many due to the -osis part of the word being consistent with the nomenclature used for other fungal infections. Of the Candida species isolated from humans, Candida albicans is the most prevalent in both health and disease. It is generally accepted that commensal carriage of this species occurs in approximately 50% of individuals (81, 107), although figures do vary depending on the population examined. Mycological studies have shown that C. albicans represents over 80% of isolates from all forms of human candidosis (85). However, the so-called non-Candida albicans Candida species are increasingly recognized as important agents of human infection (41, 46, 55, 72). The apparently increased involvement of non-Candida albicans Candida species in human candidoses may partly relate to improvements in diagnostic methods, such as the use of primary agars with the ability to differentiate species, and the introduction of molecular techniques in the routine diagnosis of fungaemia (64). However, the increased prevalence of non-Candida albicans Candida species in disease could also be a reflection of the inherently higher level of antifungal drug resistance in some nonCandida albicans Candida species (39) compared with C. albicans, as this would promote their persistence, possibly to the detriment of C. albicans, in mixed-species infections treated with traditional antifungal agents. Candidoses have been recognized throughout human history and are often described as being diseases of the diseased , reflecting the opportunistic pathogenic nature of Candida. Whilst Candida species are generally regarded as harmless members of the healthy commensal microflora of humans, infection can arise if a colonized individual becomes immunocompromised. Candida species have been encountered in a wide spectrum of diseases, and almost all human body organs can become infected (79). Systemic infections are rare, but are serious when they do occur, with