Thermus thermophilus is responsible for the pink discolouration defect in cheese

High-throughput, culture-independent DNA sequencing-based strategies have revolutionised our understanding of the composition of microbial populations, including those in foods. While many are descriptive studies, there are studies linking particular microorganisms with specific desirable/undesirable impacts being revealed. Here we apply such a strategy to study pink discolouration of cheese, a spoilage defect that affects the associated industry worldwide. Despite efforts over many decades, the basis for this phenomenon has remained elusive with traditional approaches having failed to reveal a microbial basis for this problem. The bacterial composition problematic cheeses were assessed by DNA sequencing. This revealed the presence of bacteria from the genus Thermus, at higher levels in defect, relative to control, cheeses. This observation was particularly notable in light of the fact that, Thermus, which are non-pathogenic, thermophilic bacteria which do not readily grow on the media employed to culture dairy microorganisms, have previously been associated with pink discolouration problems in the paper industry. Prompted by this finding, a target-specific culture-based approach was employed and Thermus thermophilus was successfully cultured from defect cheeses. Furthermore, qPCR revealed the species to be present at 103 cfu g-1 in the aforementioned defect-containing cheeses but to be absent or present at low levels only (101 cfu g-1) in the equivalent control cheeses. The link between Thermus and the pinking phenomenon was further investigated through the production and analysis of cheeses into which Thermus was spiked and of control cheeses. Crucially, the defect was reconstructed only in test cheeses containing the cheese-derived T. thermophilus.