Novel Antibiofilm Non-Biocidal Strategies

Abstract

Subaerial biofilm (SAB) formation on cultural heritage objects is often considered an undesirable process in which microorganisms and their by-products, e.g., enzymes and pigments, cause damage or alteration to a surface. Since biofilms are widespread phenomena, there has been a high demand for preventive and control strategies that resist their formation or reduce their negative effects once formed. Up to date, the main strategy to control biofilms has been the use of biocides. Because of their intrinsic properties, biocidal products can pose risks to humans, animals, and the environment. In this chapter, the authors call “green” only those alternative strategies to biocides able to prevent/control biofilms but that do not kill microorganisms, i.e., irrespective of the use of natural compounds. Here, we describe some of the methods that are most commonly used to test the effectiveness of antibiofilm compounds with multiple-species biofilm model systems. A unified terminology and well described protocols and guidelines are still required to compare and test the effectiveness of traditional or novel compounds against biofilms retrieved on heritage surfaces.

Characterization of the Community of Black Meristematic Fungi Inhabiting the External White Marble of the Florence Cathedral

“…Among natural products considered against biodeterioration of stone heritage, EOs have gained recognition as potential biocides due to their strong antimicrobial activity, and their experimental use has become increasingly popular as an alternative to conventional biocides [ 33 , 47 ]. The commonly used broad-spectrum commercial biocides can cause cross-resistance in microorganisms, and their use on stone materials may cause the drastic removal of competitors, favoring the development of more resistant microorganisms, also, in the surrounding environment [ 21 , 32 ]. Thus, traditional biocides are often used in sub-inhibitory concentrations, which, in the long run, could cause a decreasing sensitivity of the microorganisms to biocides and lead the polyextreme tolerant fungi towards an even greater resistance [ 48 ].…”

“…Commercial biocides commonly used in conservation are very often toxic for human health and the environment and might be aggressive for materials, too. Moreover, they are nonspecific, so they could increase bioreceptivity [ 32 ]. For these reasons, innovative green methods have been tested for biodeterioration control.…”

Essential oils to contrast biodeterioration of the external marble of Florence Cathedral

“…The most widely used strategy to contrast biodeterioration on cultural heritage so far has been the application of synthetic biocides (Pinna, 2017). However, because of their intrinsic properties, commercial large-spectrum and aggressive biocides are toxic and potentially have a high environmental and health impact (Pinna, 2017;Cappitelli and Villa, 2021), even if the risk they pose depends on their toxicity level and the exposure conditions (Pinna, 2022). Many are poorly biodegradable and lead to long-term soil and water pollution (Romani et al, 2022).…”

“…Many are poorly biodegradable and lead to long-term soil and water pollution (Romani et al, 2022). Moreover, biocides harm non-target populations of the surrounding environment and they carry a risk of the development of resistance to themselves as well as cross-resistance to antibiotics (Cappitelli and Villa, 2021). The ecotoxicity of biocides is a significant factor associated with their use on outdoor building materials and, according to Romani et al (2022), the costs of the fight against biodeterioration will include in the future "also the costs associated with their application in safe conditions for customers and likely the costs associated with their environmental impact".…”