The cytolytic capacity of Enterococcus faecalis isolates from cheese, yogurt, and curd

Food safety is an important issue that concerns scientific and commercial communities worldwide for its direct impact on people’s health. The current study used conventional methods to isolate Enterococcus faecalis from dairy products. The study was also evaluated its pathogenicity (cytolysin) and detected the genes responsible for the production of cytolysin (cylM, cylB, asa, cylA, and cylLs) using polymerase chain reaction (PCR). Here, the study was first started with collecting of 72 dairy product samples (21 cheese, 31 yogurts, and 20 curd samples). The samples were subjected to conventional cultivation, cytotoxicity, and PCR methods. The results of the cultivation revealed the presence of the E. faecalis in 43/72 (59.7%) samples, which is distributed over 20/21 (95.2%) cheese, 14/31 (45.2%) yogurt, and 9/20 (45%) curd samples. The findings of the hemolysis analysis demonstrated that the hemolytic capability of the isolated bacteria of types (γ, α, and β) differed, depending on the type of blood agar (BA) employed (human (Hn), sheep (S), and horse (Hs)). On HnBA plates, 17 isolates (39.5%) exhibited γ hemolytic action; however, 21 isolates (48.8%) exhibited β hemolytic activity. The cytotoxic activity on Vero cells showed various rates of dead cells and ranged from 0.2% (for the control) to 50.1% for specific isolates. The result of the PCR revealed the amplification of the examined genes in the bacterial isolates of dairy products. The current data demonstrate the presence of Enterococcus faecalis in dairy products with the indications of its pathogenicity due to the presence of cytolysin-coding genes and the cytotoxic activity of this protein on Vero cells.