Comparison of culture and PCR for the detection of Brucella melitensis in blood and lymphoid tissues of serologically positive and negative slaughtered sheep.

AIMS To compare the culture and PCR methods for detection of Brucella melitensis in blood and lymphoid tissue samples obtained from slaughtered sheep (n = 162) testing positive/negative in serological tests (Rose Bengal test and serum agglutination test). METHODS AND RESULTS Of 162 sheep examined, 45 were positive and 117 negative in serological tests. A PCR assay based on a pair of Br. melitensis-specific primers was used to detect DNA in blood and lymphoid tissue. Brucella melitensis was isolated from 1.2% (2/162) and 17.2% (28/162) of the blood and lymphoid tissue samples respectively. Positive PCR products with a molecular size of 731 bp were obtained from 27.7% (45/162) of blood and 29.0% (47/162) of lymphoid tissue samples. CONCLUSIONS The species-specific PCR assay detected a higher number of Br. melitensis DNA both from serologically positive (P < 0.01 in blood PCR, P < 0.001 in tissue PCR) and serologically negative (P < 0.001 in both blood PCR and tissue PCR) sheep compared with classical bacteriological culture methods. SIGNIFICANCE AND IMPACT OF THE STUDY The results emphasize the importance of using more than one type of diagnostic technique for the detection of animals positive for brucellosis, especially with epidemiological purposes.