Detection of Brucella spp. in the Sheep and Goats Milks from Southeastern Iran Using Culture and PCR

Brucellosis is a zoonotic disease caused by the members of the genus Brucella. This bacterium is transmitted to humans through exposure to infected animals or via consumption of contaminated dairy products. Cultivation of the bacteria or amplification of its DNA using polymerase chain reaction (PCR) are conventional diagnostic approaches for definitive identification of Brucella in raw milk.
We collected 530 milk samples from 485 healthy animals, and 45 animals with a history of abortion from Kerman province, southeast Iran. The specimens were first cultured in Eugon broth and then were subcultured on Brucella agar. Gram smears from colonies for characterization of the bacteria were prepared. Also, DNA extraction and PCR amplification of IS711 fragment were performed to detect Brucella DNA in the milk samples.
The culture method detected Brucella Spp. in 10 milk samples including two samples from apparently healthy animals (1 sheep sample, and 1 goat sample) as well as eight samples from animals with abortion history (6 sheep samples, and 2 goat samples). PCR identified Brucella DNA in 43 samples including those from healthy sheep (n=4) and goats (n=9), as well as animals milk with abortion history (7 sheep, and 23 goats). The proportion of positive samples detected by PCR method was significantly higher than culture method (P=0.014).
The PCR assay turned to be a convenient method for detection of Brucella contamination of raw milk and can be used as a reliable tool for surveillance and screening of contaminated milk.