Assessing the antimicrobial efficacy of nonthermal plasma treatment on filamentous fungi spores and biofilms

With the increasing resistance of biofilms to existing products and their predominantly negative impact on the environment, efforts are being made to find new alternatives to suppress microbial growth. One of them involves the use of a nonthermal plasma (NTP). This physical method of eradicating microbial growth has been well studied in terms of its application to bacteria and yeasts, while the effect of NTP on microscopic filamentous fungi has been neglected. However, NTP could serve as a viable alternative to existing disinfectants within food industry production facilities to eliminate the development of fungal contamination. This study investigates the effect of a NTP on the metabolic activity of spores regrowth and biofilms of filamentous fungi as well as on the morphological changes of microbial cultures after exposure to NTP. The morphological changes have been imaged using the scanning electron microscopy (SEM). It has been shown that high quality SEM images of the fungal spores can be obtained without a conductive coating, but in case of the fungal biofilms the use of the coating was necessary. In all examined microorganisms, the NTP treatment led to a reduction in the extracellular matrix of the biofilm and inflicted damage to the hyphae. Untreated samples displayed a layered biofilm structure, while post-treatment, the structure transitioned to a sparse, monolayered form. Particularly notable morphological alterations in the biofilm, as evidenced by SEM microscopy, were observed in Alternaria alternata. These changes align with the observed decrease in metabolic activity following NTP treatment, which was most prominent in this strain.