Study on clinical separation characteristics of L-form of mycobacterium tuberculosis

Abstract

Objective To explore the laboratory culture and identification of Mycobacterium tuberculosis L forms (MTB-L), isolation rate and drug resistance in smear-positive tuberculosis patients, and to improve clinical attention to MTB-L. Methods 222 smear-positive pulmonary tuberculosis patients treated in our hospital from September 2017 to December 2017 were randomly selected for MGIT 960 and 92-3TB-L liquid culture. After MGIT 960 was reported positive, acid-fast staining was performed on the precipitated smears of 92-3TB-L liquid medium for preliminary screening. The suspected L-positive strain culture was transformed into improved TSA-L solid medium to observe the colony characteristics and microscopic characteristics. The properties of the strain were confirmed by acid-fast staining and tuberculosis DNA amplification. Drug susceptibility and mutation sites of drug resistance genes were analyzed in MTB-L. Results Identification of MTB-L: after the positive strain has been cultured, the colonies have the characteristics of fried egg sample , particle-like and filament-like . MTB confirmed by tubercle DNA amplification experiments. Isolation rate: after cultured by MGIT 960 and Modified 92-3TB-L medium, the positive rate of single bacterial type was 50.90%, (113/222) the positive rate of both bacterial type and L type was 15.32% (34/222), and the positive rate of MTB-L type was 2.25% (5/222). Drug resistance: MTB-L was resistant to Streptomycin, Isoniazid, Rifampin, and Ethanol butylamine. No mutation was found in the drug resistance gene loci. Conclusions Clinical laboratory should routinely develop the culture of L-form of Mycobacterium tuberculosis bacteria, and increase the clinical attention to MTB-L. Key words: Mycobacterium tuberculosis; Drug resistance, bacterial; Bacteriological techniques