Margaret M. Floyd

Comparison of Methods for Identification of Mycobacterium abscessus and M. chelonae Isolates

ABSTRACT Mycobacterium abscessus and Mycobacterium chelonae are two closely related species that are often not distinguished by clinical laboratories despite the fact they cause diseases requiring different treatment regimens. Multilocus enzyme electrophoresis, PCR-restriction fragment length polymorphism analysis of the 65-kDa heat shock protein gene, biochemical tests, and high-performance liquid chromatography of mycolic acids were used to identify 75 isolates as either M. abscessus or M. chelonae that were originally submitted for drug susceptibility testing. Only 36 of these isolates were submitted with an identification at the species level. Using the above methods, 46 of the isolates were found to be M. abscessus and 29 were identified as M. chelonae. Eight isolates originally submitted as M. chelonae were identified as M. abscessus, and one isolate submitted as M. abscessuswas found to be M. chelonae. The four identification methods were in agreement in identifying 74 of the 75 isolates. In drug susceptibility testing, all isolates of M. abscessusexhibited resistance to tobramycin (MIC of 8 to ≥16 μg/ml), while all isolates of M. chelonae were susceptible to this drug (MIC of ≤4 μg/ml). The results suggest that once an identification method is selected, clinical laboratories should be able to easily identify isolates of M. abscessus and M. chelonae.

Mycobacterium septicum sp. nov., a new rapidly growing species associated with catheter-related bacteraemia.

Rapidly growing mycobacteria are capable of causing several clinical diseases in both immunosuppressed and immunocompetent individuals. A previously unidentified, rapidly growing mycobacterium was determined to be the causative agent of central line sepsis in a child with underlying metastatic hepatoblastoma. Four isolates of this mycobacterium, three from blood and one from the central venous catheter tip, were studied. Phenotypic characterization, HPLC and genetic analysis revealed that while this organism most closely resembled members of the Mycobacterium fortuitum complex and Mycobacterium senegalense, it differed from all previously described species. Phenotypic tests useful in differentiating this species from similar rapidly growing mycobacteria included: growth at 42 degrees C, hydrolysis of acetamide, utilization of citrate, production of arylsulfatase (3-d), acidification of D-mannitol and i-myo-inositol, and susceptibility to erythromycin, vancomycin and tobramycin. The name Mycobacterium septicum is proposed for this new species. The type strain has been deposited in Deutsche Sammlung von Mikroorganismen und Zellkulturen as DSM 44393T and in the American Type Culture Collection as strain ATCC 700731T.

Characterization of a novel rapidly growing Mycobacterium species associated with sepsis.

ABSTRACT A rapidly growing mycobacterium was isolated five times from blood cultures from a 6-year-old female patient with relapsed pre-B-cell acute lymphocytic leukemia. All five isolates had identical nucleotide sequences for the first 500 bp of the 16S rRNA gene, indicative of a single species. High-performance liquid chromatography analysis of mycolic acids indicated that the species was similar to Mycobacterium smegmatis. Sequence analysis of the 16S rRNA gene (1,455 bp) for one isolate demonstrated that the species was closely related to Mycobacterium diernhoferi. Based on the phenotypic features and phylogenetic analysis, it was concluded that the isolates represented a novel rapidly growing Mycobacterium species. The name “Mycobacterium hackensackense” is proposed for this unique strain, 147-0552T, which was deposited in the American Type Culture Collection as ATCC BAA-823T.

The Use of DNA Probes for Rapidly Identifying Cultures of Mycobacterium

There has been an explosion of new technology for the rapid, specific identification of many microorganisms pathogenic for humans. These new methods have been especially welcomed in the mycobacteriology laboratory, plagued by long bacterial generation times that translated into specific identification periods measured in months. The race to develop these methods and to make them easy to perform and the secrecy surrounding new patent applications for some of the unique procedures employed have spawned such terms as “dipstick- or black box-technology” to describe these welcome additions to diagnostic microbiology.