# Airborne Fungi in Show Caves from Southern Spain
## 4 Discussion
### Fungal Hazard in Show Caves  
[PERSON] et al. [7] established a classification or index of fungal hazard in European show caves with rock art, based on the concentration of spores in the cave air. Five categories were established, from \(<\)50 CFU/m\({}^{3}\) to \(>\)1000 CFU/m\({}^{3}\). The application of this index to the Andalusian caves revealed that Cueva de Ardales was the least contaminated, which agrees with the fact that it is the cave with the lowest number of visits. This cavity corresponded to a category 2 (between 50 and 150 CFU/m\({}^{3}\), which represents an alarm signal and some periodic controls and studies are required to disclose the problem). However, CFU/m\({}^{3}\) can increase on specific occasions, for example after group visits, as [PERSON] et al. [6] pointed out, particularly in Galeria del Calvario, which reached 1010 CFU/m\({}^{3}\) and is the most sensitive area to visits.  
Gruta de las Maravillas, despite the high number of visitors that it receives, had relatively low fungal concentrations, being higher in Sala de las Conchas and in the exit passage, which are the areas closest to the entrance. This cavity must be classified as category 3, as a cave threatened by fungi, reaching between 150 and 500 CFU/m\({}^{3}\) and for which a different cave management (visits, air currents, closure of doors, etc.) and controls are necessary. However, in Gruta de las Maravillas two factors intervene to cause the fungal concentrations to not be very high, considering the number of visitors/year; on the one hand, the large volume of the rooms and, on the other, periodic maintenance and cleaning tasks.  
The minimum values of CFU/m\({}^{3}\) recorded in Cueva del Tesoro were equivalent to the maximums in the other two caves. The factors that can influence the high concentrations are: two connections with the exterior, relatively small dimensions of its rooms and galleries, and the abundant presence of phototrophic communities on the speleothems and walls [14]. This cave would be in a category 5 (caves that suffer irreversible ecological damage and potentially harmful to the conservation of paintings, with concentrations of fungi higher than 1000 CFU/m\({}^{3}\) of air). However, the phototrophic biofilms were removed and the speleothems and walls were cleaned in 2014 [14], after this study, which probably at the present time has reduced the number of fungal spores in the air.  
Regarding the potential danger to human health, the most abundant fungi recorded in the caves have been considered opportunistic pathogens. They encompass _Cladosporium cladosporiades_[42], _Beauveria bassiana_[43], _Parengyodontium album_[44], _Schycophyllum commune_[45], _Aspergillus nidulans_[46], _Penicillium chrysogenum_[47], in addition to basidiomycetous yeasts [48; 49; 50]. [PERSON] et al. [51] reviewed the role of pathogenic and opportunistic microorganisms in caves and concluded that \"the most-frequent diseases produced by cave microorganisms are located in the respiratory system and, therefore, it is recommended that visitors should, at the least, wear protective masks\".  
Another important aspect is the biodeterioration caused by fungi thriving in caves. The most recurrent species isolated from rocks and speleothems and reported as producing deterioration are _Cladosporium cladosporiades, Parengyodontium album_ and _Penicillium chrysogenum_[52; 53; 54; 55]. Fungal deterioration can be evidenced by observation of structural and chemical changes using microscopic and spectroscopic techniques [56; 57].