Abstract: Objective  To study practical value of synchronously screening the rifampin-dependent (R-dependent) M. tuberculosis (Mtb) strains during routine Mycobacterium culture, to early diagnose R-dependent infection in a clinical setting.  Methods Based on the typical growth conditions for R-dependent strains from clinical specimens in Lowenstein-Jensen medium (L-J) which contained rifampicin at concentration of 100μg/ml (L-J R100), a primary screening model was established. In routine BD960 fast liquid culture process, clinical specimens were also simultaneously inoculated in L-J culture medium without and with rifampin (L-J R100). A R-resistant Mtb is defined as culture-positive bacterium which grew better in L-J R100 than that in L-J (R-dependent), and an absolute R-dependent Mtb is defined as positive culture only in L-J R100 but negative culture in L-J. A total of 5362 specimens were examined during the period of March 7, 2011 to February, 15, 2012 in Chongqing Public Health Medical Center, and results were analyzed with LIS software system (Ruimei, Shanghai, China). Results Of 5362 cases, the total positive rate of the combined three methods of BD960, L-J and L-J R100 was 43.92% (2355/5362), the positive rates of BD960 and L-J culture were 39.56% (2121/5362) and 25.57% (1371/5362) respectively. 234 specimens were L-J positive and BD960 negative. Of 2355 culture-positive specimens, 703 (29.85%,703/2355) were L-J R100 positive, in which 258 isolates from 221 cases were R-dependent and 14 isolates were absolute R-dependent. The R-dependent phenomenon was also observed repeatedly twice in 33 isolates, 3 times in 1 isolate and 4 times in 3 isolates.  Conclusion The synchronously screening the rifampin-dependent Mtb strains during routine Mycobacterium culture is a simple method for early diagnosing the TB patients infected by the rifampin-dependent or rifampin-resistant strains of M. tuberculosis. It also improves the positive rate of Mycobacterium culture.

Key words: Mycobacterium tuberculosis, Rifampin, Bacteriological techniques, Culture media