Cystic fibrosis (CF) is an autosomal recessive genetic disease caused by a mutation in the gene coding for the protein CFTR (Cystic Fibrosis Transmembrane Conductance Regulator). This mutation leads to excessive mucus production and defective mucociliary clearance, resulting in chronic bacterial infections and respiratory failure, which are the main causes of morbidity and mortality [1,2].

Approximately 80% of microbial infections in CF are related to biofilms [3]. CF infections often involve polymicrobial biofilms that are difficult to eradicate with antimicrobial treatment [4]. Candida albicans is capable of forming polymicrobial biofilms with both Gram-positive and Gram-negative bacteria. C. albicans and Staphylococcus species have been co-isolated from various diseases associated with biofilms, including CF [5].

Due to the frequent and persistent bacterial infections in CF patients, fungal infections are commonly encountered in the lungs of patients who are concurrently colonized with bacteria. The extensive use of antibiotics, as well as inhaled and oral steroids, can potentially predispose CF patients to colonization by Candida spp. [6].

Biofilms formed by Candida species are known for their role in intrinsic resistance against antifungal drugs and immune defenses [7] posing a significant threat in clinical settings and contributing to the pathogenicity of Candida-related infections as well as high mortality rates associated with these infections [8], [9], [10], [11].

C. albicans has long been recognized as the most common Candida species [12], [13], [14], [15], [16] associated with oral and systemic candidiasis. However, there has been a notable increase in non-albicans Candida infections, exceeding C. albicans in both frequency and associated mortality [16], [17], [18], [19], [20], [21], [22], [23]. Despite C. albicans remaining predominant in respiratory cultures among CF patients, other non-albicans species have emerged, albeit less frequently [24]. Understanding the implications of these infections, especially in vulnerable populations like CF patients, is crucial for effective management and treatment [25].

In this context, and as the first study of its kind in Algeria, we aimed to investigate the polymicrobial interaction between Candida spp. and S. aureus co-isolated from the same sputum of CF patients admitted to the pediatric unit to evaluate their ability to form mixed-species biofilms.