Epicoccum sp. as the causative agent of a reddish-brown spot defect on the surface of a hard cheese made of raw ewe milk

Colour defects can affect the appearance of cheese, its flavour, the safety of its consumption, and the price it can demand. This work reports the identification of five fungal isolates from a dairy plant where the surface of most cheeses was affected by patent, reddish-to-brown stains. One of these isolates was obtained from cheese, two from brine, and two from a bulk tank containing ewe milk. Molecular identification by partial amplification, sequencing, and database comparison of the concatenated sequence of the genes coding for the largest subunit of RNA polymerase II (RPB2), beta-tubulin (beta-TUB), and the large subunit of the rRNA molecule (LSU), plus the in-ternal transcribed sequence (ITS) regions, assigned the isolates to Epicoccum layuense, Epicoccum italicum, and Epicoccum mezzettii. Features of the growth of these different species on different agar-based media, and of the morphology of their conidia following sporulation, are also reported. The strain isolated from cheese, E. layuense IPLA 35011, was able to recreate the reddish-brown stains on slices of Gouda-like cheese, which linked the fungus with the colour defect. In addition, two other strains, E. italicum IPLA 35013 from brine and E. italicum IPLA 35014 from milk, also produced stains on cheese slices. Epicoccum species are widely recognized as plant pathogens but have seldom been reported in the dairy setting, and never as human or animal pathogens.

Automated summary

Colour defects can impact the appearance, flavor, safety, and price of cheese. This study identified and characterized five fungal isolates from a dairy plant that caused reddish-to-brown stains on the surface of most cheeses. The isolates were classified as Epicoccum layuense, Epicoccum italicum, and Epicoccum mezzettii through molecular identification and analysis of their gene sequences. The study also investigated the growth characteristics and conidial morphology of these fungi. The findings highlight the presence of Epicoccum species in the dairy setting, which are typically known as plant pathogens and not human or animal pathogens.