Nocardiosis from 1888 to 2017
Introduction
The study and identification of the Actinomycetes family has been on for more than one hundred years and they are depend on prokaryotes (bacteria) and eukaryotes (fungi). In terms of structure and chemical compositions such as cell wall envelope and peptidoglycan, investigations have shown that they are bacteria and to date, they are in the Actinomycetales order and were raised under fungal family [1], [2], [3]. For accurate identification in this order, a combination of biochemical and molecular methods is necessary. In this order of bacteria, we have genera that are pathogenic to humans [3] and contains mycolic acids in their cell walls (such as Dietzia, Nocardia, Gordonia, Rhodococcus, Tsukamurella, Williamsia, and Segniliparus) [4], [5], [6]. The genus Nocardia is one of the pathogenic bacteria that is Gram-positive, partially acid-fast, aerobic, catalase-positive, and non-motile. This bacterium is the cause of nocardiosis in human and animals [3], [7], [8], [9]. This genus of bacteria belongs to the class: Actinobacteria, order: Actinomycetales, suborder: Corynebacteriaceae, Family: Nocardiaceae [2], [10]. Other genera such as Gordonia, Millisia, Mycobacterium, Rhodococcus, Skermania, Williamsia, and Smaragdicoccus are in this suborder [2], [11], [12].
Section snippets
History of Nocardia
The history and taxonomic classification of the genus Nocardia is complicated and controversial. The first description of Nocardia was reported in Guadeloupe (islands in French) by Edmond Nocard for bovine farcy disease in 1888 that caused granulomatous, abscess and pulmonary contention [3], [13]. Trevisan (1889) proposed the genus Nocardia [2] and introduced Nocardia farcinica [9]. Significant progress was made in Nocardia classification by Gordon and Mihm [14], [15], [16], [17], and Gordon
Cell wall structure of the genus Nocardia
The cell wall in the Actinomycetes family is of type IV and their peptidoglycan is including meso-diaminopimelic acid, arabinose, and galactose. The mycolic acid is classified into two categories [30], [31]. The most important combination of the cell wall in the genus Nocardia is a long fatty acid chain called mycolic acid (alpha-alkyl, beta-hydroxy fatty acids), which is connected to the arabinose arabinogalactan cell wall as a covalent. Nocardia species are a Gram-positive aerobic bacteria,
Isolation methods
The gold standard for nocardial infections (nocardiosis) identification is the isolation and culture of Nocardia. This is the main step for identification the genus, species and antibacterial susceptibility testing [37]. The genus Nocardia is a slow growing bacteria and the isolation of various clinical samples, especially samples with normal microflora such as lung samples (sputum and bronchoalveolar lavage) is laborious [38]. Nocardia spp. are susceptible to decontamination methods (sodium
Phenotypic identification
- I.
Nocardia identification at the genus level
The genus Nocardia has phenotypic characterizations similar to other genera such as Gordonia, Mycobacterium, and Rhodococcus, etc., in the Actinomycetes family. To differentiate the genus Nocardia from others, the following are used: colonial morphology properties and pigmentation [2], [54], [55], conventional staining methods such as Gram stain (crystal violet, Lugol's iodine solution, alcohol/acetone and carbol fuchsin solution); acid-fast stain such
Molecular typing in Nocardia spp.
For epidemiological investigations, various DNA fingerprint methods were used in the genus Nocardia. Louie et al., in 1997, used of pulsed-field gel electrophoresis (PFGE) and random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) techniques for N. asteroides [120]. In another study, was reported with amplified fragment length polymorphisms (AFLP), PFGE and RAPD-PCR for N. farcinica [121].
Pathogenesis of the Nocardia spp.
Nocardia spp. are an optional intracellular organism that grows within the macrophage and host tissues, and iron plays an important role in their growth. A major pathogenic agent for the genus Nocardia is resistance for phagocytosis and it has been shown that the bacterium in the filamentary stage is 1000 times more toxic for mice macrophages. Nocardia spp. reduce the integration of phagosomes and lysosomes by cord factor and lysosomal enzyme activity in macrophages is reduced. Also, phagosomal
Antibiogram and Nocardia treatment
Given the fact that the antibiotic profile varies in Nocardia spp., accurate identification of the species is necessary for proper and efficient treatment [129]. The reasons for performing antibiogram for Nocardia include [1]: fatal nocardiosis in the absence of treatment [2]; defective treatment with sulfonamides (antibiotic resistant to sulfonamides) [3]; antibiotic sensitivity in N. asteroides varies, especially antibiotics outside the sulfonamide family; and [4] to date, new antibiotics
Clinical disease with Nocardia
The genus Nocardia is causing various infections in humans. One of the most common infections is pulmonary nocardiosis and N. asteroides complex is most common species in pulmonary infection (pulmonary nocardiosis) [167]. Pulmonary nocardiosis is often caused by the inhalation and entry of Nocardia carrier aerosols to the host's respiratory tract. These bacteria are the main cause of infection in the respiratory tract, which usually causes systemic disease by creating metastatic abscesses [168]
Epidemiology with Nocardia
The weakness of the immune system, especially the cellular immune disorder, provides the context for invasive opportunistic microorganisms. In literature, several studies have been reported from different countries about nocardiosis such as Africa [257], Australia [258] Brazil [259], Canada [260], China [261], Cuba [262], France [263], Greece [264], Iran [22], India [265], Japan [266], Kuwait [107], Pakistan [129], Saudi Arabia [267], Spain [268], Taiwan [77], Tanzania [269], Thailand [141],
Conclusion
To date, Nocardia novel species are increasing and the use of molecular methods is important for accurate identification in the genus and species levels. The rate of nocardiosis is increasing in different parts of the world and Nocardia isolation, identification, and antibacterial susceptibility testing are necessary for nocardial infections treatment. We proposed that clinical laboratories send isolates suspected to Nocardia to reference laboratories for accurate identification and antibiogram.
Acknowledgment
There is no conflict of interest.
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