Prevalence of Brucella spp. in raw milk and artisanal cheese tested via real-time qPCR and culture assay

Brucellosis is one of the most prevalent zoonotic diseases with worldwide distribution. Although the incidence of brucellosis varies widely in different regions, it is a major concern for public health around the world. This study aimed to determine the prevalence and quantity of Brucella spp. in sheep and goat raw milk, as well as artisanal cheeses produced in the North-west of Iran. To evaluate the intrinsic parameters that may affect the survival of Brucella spp., some of the cheese properties (e.g., pH, salt, moisture, and storage time before selling) were also assessed. A total of 572 samples consisting in 214 sheep raw milk, 92 goat raw milk, and 266 local artisanal cheese samples were collected. The artisanal cheeses were manufactured from a mixture of raw sheep and goat milk. According to the results, using quantitative real-time PCR (qPCR), 17.29%, 15.22%, and 22.93% of the sheep raw milk, goat raw milk, and artisanal cheese samples were found positive for Brucella spp., respectively. In comparison with culture assay, qPCR was 3.5 to 5 times (p < 0.05) more sensitive in the detection of Brucella spp. The results also revealed that the mean values of Brucella spp. load in sheep and goat raw milk and artisanal cheeses were 1.22, 1.55, and 1.43 log cell/ml or g, respectively. A positive correlation was found between Brucella load and successful detection of Brucella spp. by culture assay. Data also suggested a correlation (p < 0.01) between the load of Brucella spp. estimated by qPCR and pH value, salt content, and storage period of the cheese samples. However, Brucella spp. load did not correlate significantly with the moisture content. Based on the results, in any of the cheese samples with a pH value less than 4.5 and a storage period more than five months, no contamination with Brucella spp. was detected.