Nocardia mexicana sp. nov., a New Pathogen Isolated from Human Mycetomas

Abstract

Three isolates collected from human mycetomas and showing an unusual brownish purple pigmentation on Bennett agar plates were analyzed by a polyphasic taxonomic approach, including morphological, biochemical, physiological, and chemotaxonomic properties coupled with genomic and phylogenetic analysis. It clearly appeared that these microorganisms were distinct from their closest phenotypic and genetic match, the most related species according to 16S rRNA gene sequence analysis being Nocardia pseudobrasiliensis. The data obtained indicated that the three clinical strains should be recognized as a new species for which the name Nocardia mexicana sp. nov. is proposed.The Nocardia genus consists of gram-positive, variably acid fast, strictly aerobic bacteria that form filamentous, branched cells that fragment into pleomorphic, rod-shaped, or coccoid elements (1). It is widely distributed in the environment and causes a variety of suppurative and granulomatous infections of humans and animals, including cutaneous, subcutaneous, lymphocutaneous, pulmonary, cerebral, or disseminated nocardiosis. These bacteria are increasingly recognized as a cause of opportunistic infections (28).The identification of new species was based for a long time on investigation of epidemiology, clinical disease spectrum, and/or drug susceptibility combined to culture features and biochemical or chemotaxonomic characteristics. Such a phenotypic approach was probably responsible for the low number (n ϭ 12) of species described between the first description of the genus by Nocard in 1888 (32) and 1995. In the last decade, the introduction of genomic methods based on the analysis of sequences and polymorphism of the 16S rRNA gene or of the hsp65 gene has been of value for the description of many species. Thus, 17 new species had been validated from 1995 to 2003, leading to a major taxonomic revolution for this genus. It seems that it was just the beginning of the story and that the Nocardia genus will undergo the same dramatic taxonomic changes as Mycobacterium genus, for which almost a hundred species have now been described. This promoted a radical reappraisal of nocardial systematics.According to this new taxonomic background, we decided to reevaluate the taxonomic status of the strains deposited in the culture collection of the French Observatory for Nocardiosis (OFN; Lyon, France). We observed that three of them revealed atypical characteristics. These strains originated from mycetoma samples collected from Mexican patients. The strains were initially identified as Nocardia brasiliensis but showed morphological differences compared to this species. The nocardial systematic position of these three strains was investigated extensively according to an integrated use of phenotypic, chemotaxonomic, and molecular methods. The data obtained indicated that these strains should be recognized as a new species, for which the name Nocardia mexicana sp. nov. is proposed. MATERIALS AND METHODSStrains and culture conditions. The analysis of a large number...

Distribution of Nocardia Species in Clinical Samples and Their Routine Rapid Identification in the Laboratory

“…Since that time, several of the new species are represented by only one strain or a few strains, so their occurrence in humans still has to be assessed (6,8,11,12,17,28).…”

“…Not all of them have been found in humans, and Nocardia asteroides, previously most frequently isolated from clinical specimens, has proved to be heterogeneous and has been divided into several species (18). More recently, additional species of human origin have been described (6,8,9,11,12,17,28).…”

Hoyosella altamirensis gen. nov., sp. nov., a new member of the order Actinomycetales isolated from a cave biofilm

“…Growth in the presence of NaCl at: 5 % (w/v) (Brosius et al, 1978)] of the 16S rRNA gene of strain OFN S31 T was amplified by using primers SQ1 and SQ6 as described previously by Rodríguez-Nava et al (2004). The PCR products were purified by using a Microspin gel extraction kit (Omega; Bio-tek) and sequenced by using a Taq DyeDeoxy terminator cycle sequencing kit (Applied Biosystems) in an Applied Biosystems model 373A DNA sequencer.…”

Mycetoma Caused by Nocardia yamanashiensis, Papua New Guinea

“…This has also been reported for mycetomas caused by other Nocardia species, such Nocardia farcinica, N. otitidiscaviarum, Nocardia nova, N. pseudobrasiliensis, and, Nocardia mexicana. [8][9][10][11][12] Therapeutic efficacy in individual patients may depend on species identity and on in vitro susceptibility studies. Therefore, for the majority of Nocardia species, that have not been studied for antimicrobial susceptibility, such as the newly described N. yamanashiensis, obtaining susceptibility testing would be prudent, especially when using an agent known to have variable activity against the genus.…”