Abstract
Traditionally Nocardia asteroids was considered the predominant species of causing no-cardiosis. The improved identification of isolates using molecular techniques have shown that the genus exhibits considerable taxonomic complexity and phenotypic base identification can be ambiguous. The aim of this study was to assess the species distribution of Nocardia strains mostly recovered from patients suspected of having tuberculosis, during three years period (2009-2012). The clinical isolates were identified to species level using conventional tests and genotypic methods using single and multi locus sequence analysis (MLSA) of 16S rRNA, gyrB and secA1 genes. Nocardiosis was diagnosed in 46 patients. The most frequent underlying condition were organ transplantation (6 patients; 13%), cancer (6 patients; 13%), human immunodeficiency virus (HIV) (6 patients; 13%), non-infectious chronic lung disease (5 patients; 10.8%) and tuberculosis (4 patients; 8.7%). Nocardia species was recovered from 46 different clinical specimens, the most common of which was bronchoalveolar lavage (BAL) (43.5%). Eleven different Nocardia species were identified: N. asteroides (n = 12), N. cyriacigeorgica (n = 9), N. farcinica (n = 7), N. wallacei (n = 6), N. carnea (n = 3), N. otitidiscaviarum (n = 3), N. abscessus (n = 1), N. arthritidis (n = 1), N. kruczakiae (n = 1), N. nova (n = 2) and N. veterana (n = 1). In conclusion, infection caused by Nocardia species appears to be more common than generally appreciated. The current study provides further evidence that Nocardia species are capable of causing a wide range of human diseases in healthy and immunocompromised patients. MLSA is a reliable method for accurate species identification of Nocardia isolates and would be more feasible for routine use in clinical laboratories.
Highlights
Members of the genus Nocardia are aerobic, filamentous branching bacilli, gram positive and Partial acid-fast, which include more than 90 different species
Analysis of 16S rRNA The determined nucleotide sequences were compared pairwise for similarity; the results showed that the 46 Nocardia strains were closely related to each other and were distinct from other genera
16S rRNA gene sequencing, remains first choice for bacterial identification and different molecular targets represent promising alternatives [1] [11], the reliability of species delineation on the basis of the sequence of a single gene suffers from different factors such as stochastic genetic variation, horizontal gene transfer and recombination [12]
Summary
Members of the genus Nocardia are aerobic, filamentous branching bacilli, gram positive and Partial acid-fast, which include more than 90 different species (http://www.bacterio.cict.fr/n/nocardia.html). Nocardia have increasingly been isolated as infectious agents in immune-suppressed patients and sometimes in healthy individuals and causing localized or disseminated infections, ranging from pulmonary and wound infections to brain abscesses, and bacteremia [1]. In Iran, where tuberculosis is prevalent and considers as one of the most challenges of public health, the role of Nocardia as causative agent of pulmonary and other form of infections has been neglected. Due to little information available from Iran, the aim of the present study was to clarify the species spectrum of the isolates presumptively assigned to the genus Nocardia, recovered from different clinical samples of patients by morphological tests. For definite and reliable identification, the clinical isolates were subjected to sequence base identification by using MLSA of 16S rRNA [5], subunit A of the SecA preprotein translocase (secA1) and the subunit of a type II DNA topoisomerase (gyrB) [6]
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