Detection of Brucella melitensis by BACTEC NR660 blood culture system

Data on the performance of modern blood culture systems for the detection of Brucella spp. are insufficient. To evaluate the performance of the BACTEC NR660 blood culture system for the detection of Brucella melitensis within the routine 1-week blood culture protocol, a prospective 24-month study was conducted in an area endemic for B. melitensis in southern Israel. Blood samples obtained from patients with suspected brucellosis were monitored and blindly subcultured once per week for 4 weeks, and the fraction of blood cultures positive for B. melitensis detected by the BACTEC NR660 instrument within the first week was determined. During the study period, a total of 373 blood cultures were obtained from patients in whom brucellosis was suspected, and 27 (7.2%) of them, drawn from 21 different patients, were positive for B. melitensis. Twenty-one (78.8%) of these positive cultures were detected by the BACTEC instrument within 7 days, and six positive cultures were detected by subculture after 2 or 3 weeks of incubation. It is concluded that the BACTEC NR660 blood culture system detects the majority of B. melitensis isolates within the routine 1-week blood culture schedule. To maximize the recovery of the organism, however, prolonged incubation and periodic performance of blind subcultures are still required.