Toxigenic Genes of Coagulase-Negative/Positive Staphylococcus aureus from Milk and Dairy

Abstract

This study was performed to determine the prevalence of toxin-related genes and methicillin-resistance genes in coagulase-positive/negative Staphylococcus aureus isolated from raw milk and dairy products. The incidence of Staphylococcus aureus in tested 260 raw milk and 755 dairy samples was highest with ice cream (15.7%) followed by raw milk (11.2%), cheese (10.1%), and butter (2.7%) samples. The distribution of coagulase-positive and negative Staphylococcus aureus was 3.2% (33 isolates) and 5.3% (54 isolates) respectively. The average counts of Staphylococcus aureus among the dairy, positive samples were 3.46 and 3.16 log CFU/ml-g for coagulase-positive and negative isolates respectively. According to the results of Polymerase Chain Reaction, the enterotoxin gene sea (6.9%) was detected in milk and 5 cheese, seb (2.3%) in 2 cheese, see (1.1%) in a cheese isolate of coagulase-positive Staphylococcus aureus. One coagulase-negative Staphylococcus aureus isolated from milk possessed both tss and etb genes. None of the isolates had the sec, sed enterotoxin, pvl, eta virulence, and mecA methicillin resistance genes. As a result, enterotoxin genes were determined among coagulase-positive Staphylococcus aureus isolated from dairy products, while toxin genes associated with human infections were assigned in coagulase-negative Staphylococcus aureus isolates. Coagulase-negative Staphylococcus aureus strains are not considered in standard food surveillance analysis. These strains carrying toxigenic genes can be ingested with food and colonized in the gastrointestinal tract, and they can transfer their pathogenic genes to other strains and/or bacteria. Thus, it should be considered in terms of public health that staphylococci harboring toxin genes. Our work demonstrated the pathogenic potential of neglected bacteria coagulase-negative staphylococci carrying virulence genes. More research is needed about this bacteria implemented in the food matrix, and clinical isolates. In the future, surveillance of coagulase-negative Staphylococcus aureus in foods and human infections may be included food legislation rules.