Abstract:

Objective To explore the potential use of fluorescent probe CDG-3 (a BlaC-specific green fluorescent probe) in the diagnosis of tuberculosis (TB).Methods To clarify the specificity of CDG-3, it was tested with Mycobacterium tuberculosis (MTB) H37Rv, Mycobacterium bovis, Mycobacterium africanum, standard strains of 35 clinically relatively different nontuberculous mycobacteria (NTM) and six different standard strains of respiratory tract pathogens by microscopic examination. To understand the clinical value of CDG-3, a total of 200 morning sputum specimens of outpatients with suspected pulmonary tuberculosis were collected between January and September 2016 in Beijing Chest Hospital. The specimens were evaluated by smear-microscopy, solid Roche culture, MGIT 960 liquid culture and the CDG-3 probe. Culture results were considered positive as long as either the solid Roche culture or MGIT 960 liquid culture results were positive.Results were analyzed statistically with SPSS 19.0 software.Results Using H37Rv as a standard, results obtained with the CDG-3 fluorescence probe for the detection of standard strains of Mycobacterium bovis and Mycobacterium africanum were all positive. Three of the 35 kinds of NTM standard strains (M.kansassi, M.malmoense and M.phlei) also tested positive, while the other 32 strains gave negative results. CDG-3 gave a positive fluorescence signal with Nocardia, but not with the other five respiratory tract pathogens. Testing sputum specimens using CDG-3 gave a positive rate for MTB of 53.0% (106/200), significantly higher than that for smear-microscopy (29.5%, 59/200) and mycobacterium culture (35.0%, 70/200) (χ ²=33.587,P=0.000;χ ²=21.121,P=0.000). Using culture results as the standard, the sensitivity of the CDG-3 probe (84.3%, 59/70) was higher than that of smear-microscopy (70.0%, 49/70); while its specificity was lower (63.8%, 83/130, compared to 92.3%, 120/130). Relative to clinical diagnosis (149 confirmed TB patients), the sensitivity of the CDG-3 probe (64.4%, 96/149) was higher than that of smear-microscopy (39.6%,59/149) and culture (44.3%,66/149), while the specificity of the CDG-3 probe (95%, 19/20) was lower than that of smear-microscopy (100%, 20/20) but higher than that of culture (90%, 18/20). Conclusion The CDG-3 fluorescent probe offers excellent specificity for MTB over many NTMs. The interaction between CDG-3 and respiratory tract pathogens needs further study. The CDG-3 probe has the advantages of being rapid, simple and giving a high detection efficiency, but its specificity is not so ideal.

Key words: Mycobacterium tuberculosis, Mycobacteria,atypical, Laboratory techniques and procedures, Controlled clinical trial, CDG-3 fluorescent probe