RESUMO
@#Abstract： Objective To analyze the species distribution of microorganisms in culture tubes reported positive byBACTEC™ MGIT960 (hereafter referred to as "MGIT960") after species identification using matrix-assisted laser desorption/ionization time of flight massspectrometry (MALDI-TOF MS) technique. Methods From 2021 to 2022, a total of 2 662 positive tubes reported by the MGIT 960 instrument at Tuberculosis Reference Laboratory of Tianjin Center for Tuberculosis Control were collected. Liquid cultures were independently inoculated to blood plate and neutral L-J medium, and the resulting isolate strains were identified using the MALDI-TOF MS method. According to the MALDI-TOF MS results, the non-repetitive results of the same patient on the same culture medium were analyzed for the composition ratio of strain distribution. For the strains not identified by MALDI-TOF MS, 38 strains were selected for 16S rRNA gene sequencing. Results A total of 605 isolates were obtained from blood plates, and 501 of those were analyzed. Among them, Mycobacterium accounted for 17.76% (89/501), predominant by Mycobacterium abscess 10.18% (51/501) and Mycobacterium fortuitum 3.19% (16/501). Bacteria other than Mycobacterium accounted for 68.06% (341/501), with the main ones being Nocardia farcinica 15.57% (78/501), Gordonia sputa 9.38% (47/501) and Gordonia bronchialis 7.58% (38/501). There were 71 unidentifiable strains, making up 14.17% (71/501). A total of 2 378 strains were isolated from neutral L-J mediums, 1 748 of which were used in the incoming analysis. Among these, 78.72% (1 376/1 748) were Mycobacterium, 60.53% (1 058/1 748) were Mycobacterium tuberculosis (MTB), 4.69% (82/1 748) were Mycobacterium chimaer intracellulare group and 3.55% (62/1 748) were Mycobacterium Lentiflavum. Bacteria other than Mycobacterium accounted for 17.11% (299/1 748) in neutral L-J medium isolates, with Nocardia farcinica 4.35% (76/1 748), Gordonia sputa 2.69% (47/1 748) and Gordonia bronchialis 2.12% (37/1 748) as the main species. There were 73 strains that couldn't be identified, comprising 4.18% (73/1 748). The 38 strains that not identified by MALDI-TOF MS were all found to be Actinobacteria and Firmicutes by sequencing. Conclusions A variety of nontuberculous Mycobacterium and bacteria other than Mycobacterium were found in the positive culture tubes reported by the MGIT960 instrument, most of which could be quickly identified by mass spectrometry. Bacteria other than Mycobacterium are mainly Nocardia and Gordonia, which should be paid attention to in differential diagnosis.