June M. Brown

Clinical and Laboratory Features of the Nocardia spp. Based on Current Molecular Taxonomy

SUMMARY The recent explosion of newly described species of Nocardia results from the impact in the last decade of newer molecular technology, including PCR restriction enzyme analysis and 16S rRNA sequencing. These molecular techniques have revolutionized the identification of the nocardiae by providing rapid and accurate identification of recognized nocardiae and, at the same time, revealing new species and a number of yet-to-be-described species. There are currently more than 30 species of nocardiae of human clinical significance, with the majority of isolates being N. nova complex, N. abscessus, N. transvalensis complex, N. farcinica, N. asteroides type VI (N. cyriacigeorgica), and N. brasiliensis. These species cause a wide variety of diseases and have variable drug susceptibilities. Accurate identification often requires referral to a reference laboratory with molecular capabilities, as many newer species are genetically distinct from established species yet have few or no distinguishing phenotypic characteristics. Correct identification is important in deciding the clinical relevance of a species and in the clinical management and treatment of patients with nocardial disease. This review characterizes the currently known pathogenic species of Nocardia, including clinical disease, drug susceptibility, and methods of identification.

The medically important aerobic actinomycetes: epidemiology and microbiology.

The aerobic actinomycetes are soil-inhabiting microorganisms that occur worldwide. In 1888, Nocard first recognized the pathogenic potential of this group of microorganisms. Since then, several aerobic actinomycetes have been a major source of interest for the commercial drug industry and have proved to be extremely useful microorganisms for producing novel antimicrobial agents. They have also been well known as potential veterinary pathogens affecting many different animal species. The medically important aerobic actinomycetes may cause significant morbidity and mortality, in particular in highly susceptible severely immunocompromised patients, including transplant recipients and patients infected with human immunodeficiency virus. However, the diagnosis of these infections may be difficult, and effective antimicrobial therapy may be complicated by antimicrobial resistance. The taxonomy of these microorganisms has been problematic. In recent revisions of their classification, new pathogenic species have been recognized. The development of additional and more reliable diagnostic tests and of a standardized method for antimicrobial susceptibility testing and the application of molecular techniques for the diagnosis and subtyping of these microorganisms are needed to better diagnose and treat infected patients and to identify effective control measures for these unusual pathogens. We review the epidemiology and microbiology of the major medically important aerobic actinomycetes. Images

Antimicrobial-resistant nocardia isolates, United States, 1995-2004.

We conducted a 10-year retrospective evaluation of the epidemiology and identification of Nocardia isolates submitted to the Centers for Disease Control and Prevention for antimicrobial susceptibility testing. The species most commonly identified were N. nova (28%), N. brasiliensis (14%), and N. farcinica (14%). Of 765 isolates submitted, 61% were resistant to sulfamethoxazole and 42% were resistant to trimethoprim-sulfamethoxazole.

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.

Rothia, gen. nov. an aerobic genus of the family Actinomycetaceae

SUMMARY Rothia gen. nov. (Actinomycetaceae) is proposed as the name of a monotypic genus with the species Rothia dentocariosus comb. nov. (basionym Actinomyces dentocariosus Onisi 1949), synonyms Nocardia dentocariosus (Onisi) Roth 1957; Nocardia salivae Davis and Freer 1960, No strain of Onisis original isolates is extant. ATCC 17931 is described and proposed as the neotype strain of Rothia dentocariosus (Onisi) Georg and Brown 1967.

Clinical and Laboratory Features of Mycobacterium porcinum

ABSTRACT Recent molecular studies have shown Mycobacterium porcinum, recovered from cases of lymphadenitis in swine, to have complete 16S rDNA sequence identity and >70% DNA-DNA homology with human isolates within the M. fortuitum third biovariant complex. We identified 67 clinical and two environmental isolates of the M. fortuitum third biovariant sorbitol-negative group, of which 48 (70%) had the same PCR restriction enzyme analysis (PRA) profile as the hsp65 gene of M. porcinum (ATCC 33776T) and were studied in more detail. Most U.S. patient isolates were from Texas (44%), Florida (19%), or other southern coastal states (15%). Clinical infections included wound infections (62%), central catheter infections and/or bacteremia (16%), and possible pneumonitis (18%). Sequencing of the 16S rRNA gene (1,463 bp) showed 100% identity with M. porcinum ATCC 33776T. Sequencing of 441 bp of the hsp65 gene showed four sequevars that differed by 2 to 3 bp from the porcine strains. Clinical isolates were positive for arylsulfatase activity at 3 days, nitrate, iron uptake, d-mannitol, i-myo-inositol, and catalase at 68°C. They were negative for l-rhamnose and d-glucitol (sorbitol). Clinical isolates were susceptible to ciprofloxacin, sulfamethoxazole, and linezolid and susceptible or intermediate to cefoxitin, clarithromycin, imipenem, and amikacin. M. porcinum ATCC 33776T gave similar results except for being nitrate negative. These studies showed almost complete phenotypic and molecular identity between clinical isolates of the M. fortuitum third biovariant d-sorbitol-negative group and porcine strains of M. porcinum and confirmed that they belong to the same species. Identification of M. porcinum presently requires hsp65 gene PRA or 16S rRNA or hsp65 gene sequencing.

Native Valve Endocarditis Due to Gordonia polyisoprenivorans: Case Report and Review of Literature of Bloodstream Infections Caused by Gordonia Species

ABSTRACT We report the first case of endocarditis caused by Gordonia polyisoprenivorans and concisely review the English literature regarding bloodstream infections caused by Gordonia species.

Nocardia veterana as a Pathogen in North American Patients

ABSTRACT The molecular methodologies used in our laboratories have allowed us to define a group of Nocardia isolates from clinical samples which resemble the type strain of Nocardia veterana. Three patient isolates and the type strain of N. veterana gave identical and distinctive restriction fragment length polymorphisms (RFLPs) for an amplified portion of the 16S rRNA gene. These three isolates and the N. veterana type strain also gave identical RFLPs for an amplified portion of the 65-kDa heat shock protein gene, but this pattern was identical to that obtained for the Nocardia nova type strain. Sequence analysis of both a 1,359-bp region of the 16S rRNA gene and a 441-bp region of the heat shock protein gene of the patient isolates showed 100% identities with the same regions of the N. veterana type strain. DNA-DNA hybridization of the DNA of one of the patient isolates with the DNA of the N. veterana type strain showed a relative binding ratio of 82%, with 0% divergence, confirming that the isolate was N. veterana. Biochemical and susceptibility testing showed no significant differences among the patient isolates and the N. veterana type strain. Significantly, the results of antimicrobial susceptibility testing obtained for our isolates were similar to those obtained for N. nova, indicating that susceptibility testing alone cannot discriminate between these species. We present two case studies which show that N. veterana is a causative agent of pulmonary disease in immunocompromised patients residing in North America. We also describe difficulties encountered in using 16S rRNA gene sequences alone for discrimination of N. veterana from the related species Nocardia africana and N. nova because of the very high degree of 16S rRNA gene similarity among them.

Nocardia wallacei sp. nov. and Nocardia blacklockiae sp. nov., Human Pathogens and Members of the “Nocardia transvalensis Complex”

ABSTRACT Nocardia isolates that share the property of in vitro amikacin resistance are grouped together by some authors in the Nocardia transvalensis complex. Our examination of 13 isolates that are amikacin resistant has revealed the existence of three distinct species. Sequence analysis of the 16S rRNA, 65-kDa heat shock protein, and secA1 genes, coupled with DNA-DNA hybridization, indicated that “N. asteroides drug pattern IV,” “N. transvalensis new taxon 1,” and N. transvalensis sensu stricto should each be considered a distinct species. The phenotypic and molecular characteristics of the proposed new species Nocardia wallacei (N. asteroides drug pattern IV) and N. blacklockiae (N. transvalensis new taxon 1) are presented and compared with those of N. transvalensis sensu stricto. The relative genetic diversity of isolates best placed with the species N. blacklockiae is also discussed. Case studies demonstrating the pathogenicity of N. wallacei and N. blacklockiae are presented. The type strain of N. wallacei is ATCC 49873 (DSM 45136), and that of N. blacklockiae is ATCC 700035 (DSM 45135).

Recognition of Oerskovia Species in the Clinical Laboratory: Characterization of 35 Isolates

Fifty-seven clinical isolates of previously unidentified gram-positive, fermentative, nonsporeforming rods were studied and compared to the type strains of Oerskovia turbata and O. xanthineolytica. Thirty-five of the isolates were identified as Oerskovia species: 9 were identified as O. turbata, and 26 were identified as O. xanthineolytica. The Oerskovia cultures could be differentiated from the other isolates on the basis of the development of filamentous colonies.