Comparison of culture and PCR for the detection of Brucella spp in goat and sheep milk samples in southeast Iran

Background: Brucellosis is a worldwide public health zoonotic disease caused by the genus Brucella, a bacterium that is easily transmitted to humans by exposure to infected animals or by ingestion of contaminated dairy products. Isolation of Brucella or detection of Brucella DNA by PCR is the only method that allows certainty of diagnosis.Materials and Methods: 580 hundred milk samples were collected from 515 healthy animals and 65 infected animals with history of abortion. Samples were inoculated on Brucella agar which contains antibiotic and inactivated horse serum and incubate for 5 days, then we prepared Gram smear from colonies which had blue shining under fluorescent light and biochemical test, was done as well. All samples were subjected to DNA extraction and PCR amplification targeting IS711(gene) region was performed to determine the presence of Brucella spp in milk samples.Results: The direct culture method detected Brucella orgnism in 10 milk samples and the PCR assay amplified Brucella DNA in 14 (5/93%) of sheep and 42 (12/2%) of goats milk samples. Of the 65 milk samples collected goats and sheep with history of abortion, 42 samples (9 form sheep and 33 form goats) were PCR positive for Brucella spp and the positive samples belonged to 14 (5 form sheep and 9 form goats) apparently healthy animals.Conclusion: The species-specific PCR assay detected a higher number of Brucella DNA both from milk samples than bacteriological culture methods. The milk PCR method is convenient to evaluate Brucella infection in raw milk samples, particularly used as a routine screening and surveillance tool to reduce brucellosis outbreaks.

Keywords:

Brucella , milk , PCR , culture , goats , sheep