Characterization of a Novel Group of Mycobacteria and Proposal of Mycobacterium sherrisii sp. nov

Abstract

We describe here the characterization of five isolates of Mycobacterium simiae-like organisms representing a novel group based on whole-cell fatty acid analysis and genotypic evaluation. Two of the five isolates in this study, W55 and W58, were previously considered to belong to M. simiae serotype 2. Analysis of cellular fatty acids by gas-liquid chromatography indicated a close clustering of this group, which was well differentiated from the other M. simiae-like species. Molecular characterization was performed by nucleic acid sequencing of the small subunit rRNA gene and the gene encoding the 65-kDa heat shock protein and genomic DNA hybridization. Sequence analysis of the entire 16S rRNA gene showed a unique sequence most closely related to those of M. triplex and M. simiae. The hsp65 partial gene sequence was identical for the five isolates, with 97% identity to the M. simiae type strain. However, qualitative whole genomic DNA hybridization analysis confirmed that this group is genetically distinct from M. simiae and M. triplex. Antimicrobial susceptibilities for this group resemble those of M. simiae and M. lentiflavum. We conclude that this group represents a unique Mycobacterium species for which we propose the name Mycobacterium sherrisii sp. nov.The genus Mycobacterium consists of a diverse group of acidfast bacilli that exist in the environment and cause infections in humans and animals (22). Conventional methods for identification of these organisms are well established and inexpensive, but these methods are also time-consuming and labor-intensive and can provide inconsistent results, leading to species identifications based on a "best-fit" method. The introduction of several molecular tools and improved techniques in the last two decades has not only revolutionized the identification process by reducing the time to identification but also has provided clues to the presence of novel strains. Mycolate analysis has proven to be a powerful phenotypic method for determining the presence of new species based on novel patterns (9, 25). Fatty acid analysis techniques such as high-performance liquid chromatography (HPLC) and gas-liquid chromatography (GLC) were developed to analyze the mycolic acid and whole-cell fatty acid profiles, respectively, to identify characteristic patterns of established mycobacterial species (7,10,12,30).The advent of nucleotide probes designed to hybridize to specific rRNA gene sequences allowed rapid identification of the most common mycobacterial species (16). Lately, genotypic analyses aimed at identifying nucleotide sequences of several chromosomal genes in the Mycobacterium genus coding for 16S rRNA, internal transcribed spacer 1, and 65-kDa heat shock protein (hsp65) have proven to be useful in the molecular characterization of well-established species and in identifying new ones, including previously misidentified groups (8,15,17,26). Analysis of the hypervariable region in the 16S rRNA gene sequence has a high species specificity and also has been useful to assign new spec...

Mycobacterium sherrisii sp. nov., a slow-growing non-chromogenic species

“…Recently described strains were linked to an African source, as they were isolated from patients who were currently (Crump et al, 2009) (Gämperli et al, 2005;Loulergue et al, 2007;Tortoli et al, 2007a). For two strains isolated in Italy and one in Thailand, no evident link with Africa was detected (Tortoli et al, 2007b;Ballard et al, 2007), while for the five strains of the first report (Selvarangan et al, 2004) one was isolated in Germany and the others in three different states of the USA. From the available literature, 'M.…”

“…Colonies were smooth and generally non-chromogenic, with photochromogenicity noted in strains W55 and 283416 and scotochromogenicity in the three strains from Italy (FI-94099, FI-05200 and FI-95229). In the description by Selvarangan et al (2004), photochromogenicity was noted only in strain VA2, which was non-chromogenic in the current analysis. Ziehl-Neelsen staining of bacterial smears revealed acid-alcohol-fast rods, with occasional coccid forms.…”

“…sherrisii' (Selvarangan et al, 2004), the rules of the Bacteriological Code were not fully met. To clarify 'M.…”

“…In 2004, a group of five Mycobacterium isolates related to, but different from, Mycobacterium simiae was first described and provisionally named as representing 'Mycobacterium sherrisii' (Selvarangan et al, 2004). Additional clinical isolates of 'M.…”

“…We included the five strains (4733, VA2, 283416, W55 and W58) reported in the primary publication (Selvarangan et al, 2004), three strains (FI-94099, FI-95229 and FI-05200) reported in Italy (Tortoli et al, 2007a, b), the two strains reported from Tanzania (Crump et al, 2009) and a novel isolate from Tanzania. For all 11 isolates, the full 16S rRNA gene, the 16S-23S internal transcribed spacer (ITS) region and partial hsp65 and rpoB genes were sequenced by using previously published approaches (Springer et al, 1996;Roth et al, 1998;Telenti et al, 1993;Adékambi et al, 2003).…”