Nocardia veterana as a pathogen in North American patients

First Report of Clivus Osteomyelitis Caused by Nocardia veterana in a Lung Transplant Recipient

Nocardia species have been implicated as a cause of pulmonary, cutaneous, ocular, and disseminated central nervous system disease. Dissemination to the bones, commonly the spine, has also been described in the literature. However, isolated osteomyelitis of the skull base is rare. Additionally, advances in the use of molecular techniques have identified many new Nocardia species, including Nocardia veterana that was thought to be clinically insignificant when it was first identified. Here, we report the clinical features and treatment approach for a lung transplant patient who developed N. veterana clivus osteomyelitis secondary to sphenoid sinusitis. It is the first case of skull base osteomyelitis caused by this rare species of Nocardia.

Nocardia Infection in Nephrotic Syndrome Patients: Three Case Studies and A Systematic Literature Review

Objective

The multicenter literature review and case studies of 3 patients were undertaken to provide an updated understanding of nocardiosis, an opportunistic bacterial infection affecting immunosuppressed nephrotic syndrome (NS) patients receiving long-term glucocorticoid and immunosuppressant treatment. The results provided clinical and microbiological data to assist physicians in managing nocardiosis patients.

Methods

Three cases between 2017 and 2018 from a single center were reported. Additionally, a systematic review of multicenter cases described in the NCBI PubMed, Web of Science, and Embase in English between January 1, 2001 and May 10, 2021 was conducted.

Results

This study described three cases of Nocardia infection in NS patients. The systematic literature review identified 24 cases with sufficient individual patient data. A total of 27 cases extracted from the literature review showed that most patients were > 50 years of age and 70.4% were male. Furthermore, the glucocorticoid or corticosteroid mean dose was 30.9 ± 13.7 mg per day. The average time between hormone therapy and Nocardia infection was 8.5 ± 9.7 months. Pulmonary (85.2%) and skin (44.4%) infections were the most common manifestations in NS patients, with disseminated infections in 77.8% of patients. Nodule/masses and consolidations were the major radiological manifestations. Most patients showed elevated inflammatory biomarkers levels, including white blood cell counts, neutrophils percentage, and C-reactive protein. Twenty-five patients received trimethoprim-sulfamethoxazole monotherapy (18.5%) or trimethoprim-sulfamethoxazole-based multidrug therapy (74.1%), and the remaining two patients (7.4%) received biapenem monotherapy. All patients, except the two who were lost to follow-up, survived without relapse after antibiotic therapy.

Conclusions

Nephrotic syndrome patients are at high risk of Nocardia infection even if receiving low-dose glucocorticoid during the maintenance therapy. The most common manifestations of nocardiosis in NS patients include abnormal lungs revealing nodules and consolidations, skin and subcutaneous abscesses. The NS patients have a high rate of disseminated and cutaneous infections but a low mortality rate. Accurate and prompt microbiological diagnosis is critical for early treatment, besides the combination of appropriate antibiotic therapy and surgical drainage when needed for an improved prognosis.

Nocardia veterana infections: case report and systematic review

Members of the genus Nocardia are filamentous, Gram-positive, aerobic bacteria and exist ubiquitously in most environments. In 2001, the species Nocardia veterana was first isolated, and it predominantly causes pulmonary infections in immunocompromised hosts. We present the first report of a soft-tissue abscess caused by N. veterana in a 59-year-old woman being treated for chronic cutaneous graft-versus-host disease. After failing to improve with empirical treatment, two incision and drainage procedures were required. She subsequently completed a 1-year course of oral antibiotic therapy consisting of trimethoprim-sulfamethoxazole then azithromycin. No relapse occurred over the next 5 years of follow up. To better characterize N. veterana infections, we performed a systematic literature review and summarized all previously reported cases. Overall, the rising prevalence of immunocompromising conditions warrants increased vigilance for infections caused by atypical or opportunistic pathogens.

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Systematic review of Nocardia veterana infections.

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First report of N. veterana soft tissue abscess.

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N. veterana typically causes pulmonary infections in immunocompromised hosts.

Lung Infections

A review of pulmonary infections of all types with diagnostic and morphological features.

Successful Treatment of Disseminated Nocardiosis Caused by Nocardia veterana in a Dog

A 5‐year‐old male castrated Lhasa Apso cross was evaluated for a 1‐month history of inappetence, lethargy, gagging, and progressive right thoracic limb lameness. Synovial fluid analysis revealed nonseptic suppurative inflammation, and a diagnosis of immune‐mediated polyarthritis (IMPA) was made. After 3 months of treatment with prednisone and later cyclosporine, the dog developed multiple firm cutaneous and subcutaneous masses and a focal mass within the jejunum. Cultures of blood, urine, skin lesions, and the jejunal mass identified Nocardia veterana by matrix‐absorption laser desorption ionization‐time‐of‐flight mass spectrometry (MALDI‐TOF MS) and allowed for earlier identification of the organism compared to more traditional secA1 gene sequencing. Immunosuppressive drug treatment was discontinued, and the dog was treated for 3 months by administration of trimethoprim‐sulfamethoxazole (TMS). No recurrence of clinical signs was reported 1 year later. This case report highlights the clinical utility of MALDI‐TOF MS, particularly for the rapid identification of slow‐growing, fastidious organisms.

Clinical significance, antimicrobial susceptibility and molecular identification of Nocardia species isolated from children with cystic fibrosis

Nocardia is an opportunistic pathogen that causes respiratory infections in immunocompromised patients. The aim of this study was to analyze the epidemiology, clinical significance and antimicrobial susceptibility of Nocardia species isolated from eight children with cystic fibrosis. The isolated species were identified as Nocardia farcinica, Nocardia transvalensis, Nocardia pneumoniae, Nocardia veterana and Nocardia wallacei. N. farcinica was isolated in three patients and all of them presented lung affectation with a chronic colonization and pneumonia. N. farcinica showed resistance against gentamicin, tobramycin, cefotaxime, but was susceptible to trimethoprim-sulfamethoxazole and amikacin. N. transvalensis, which was isolated from two patients, showed an association with chronic colonization. N. transvalensis was resistant to tobramycin and amikacin, but susceptible to ciprofloxacin, trimethoprim-sulfamethoxazole and cefotaxime. N. veterana, N. pneumoniae and N. wallacei were isolated from three different patients and appeared in transitory lung colonization. N. veterana and N. pneumoniae were susceptible to imipenem, trimethoprim-sulfamethoxazole, amikacin, tobramycin, and cefotaxime. N. wallacei was resistant to amikacin, tobramycin, imipenem, and trimethoprim-sulfamethoxazole and susceptible to ciprofloxacin and cefotaxime. All the isolates were identified up to species level by 16S rRNA gene sequencing. The presence of Nocardia in the sputum of patients with cystic fibrosis is not always an indication of an active infection; therefore, the need for a treatment should be evaluated on an individual basis. The detection of multidrug-resistant species needs molecular identification and susceptibility testing, and should be performed for all Nocardia infections.

Human Nocardia Infections: A Review of Pulmonary Nocardiosis

Human nocardiosis may present as an acute or a chronic infection. Although a saprophyte Nocardia spp are responsible for superficial skin infections, pulmonary infections, and disseminated nocardiosis usually involving patients who are immunosuppressed and debilitated. Infections in immunocompetent individuals are usually chronic and present non-specific symptoms. Invasive and disseminated nocardiosis is common among patients with weakened cellular immune systems. Clinical diagnosis of pulmonary nocardiosis is difficult owing to the similarity of its presentation with other respiratory pathogens that include Actinomycetes members and Mycobacteriumtuberculosis. Laboratory diagnosis of human nocardiosis is plagued by the fact that a culture of Nocardia spp requires prolonged incubation periods for isolation which most laboratories fail to follow. The lack of clinical, laboratory, and epidemiological data on the incidence of nocardiosis in humans undermines its significance as a potential pathogen. This review attempts to reexamine the pathogenic potential of Nocardia in human infections

MOLECULAR IDENTIFICATION AND ANTIMICROBIAL RESISTANCE PATTERN OF SEVEN CLINICAL ISOLATES OF Nocardia spp. IN BRAZIL

Nocardia is a ubiquitous microorganism related to pyogranulomatous infection, which is difficult to treat in humans and animals. The occurrence of the disease is on the rise in many countries due to an increase in immunosuppressive diseases and treatments. This report of cases from Brazil presents the genotypic characterization and the antimicrobial susceptibility pattern using the disk-diffusion method and inhibitory minimal concentration with E-test® strips. In summary, this report focuses on infections in young adult men, of which three cases were cutaneous, two pulmonary, one neurological and one systemic. The pulmonary, neurological and systemic cases were attributed to immunosuppressive diseases or treatments. Sequencing analysis of the 16S rRNA segments (1491 bp) identified four isolates of Nocardia farcinica, two isolates of Nocardia nova and one isolate of Nocardia asiatica. N. farcinica was involved in two cutaneous, one systemic and other pulmonary cases; N. nova was involved in one neurological and one pulmonary case; and Nocardia asiatica in one cutaneous case. The disk-diffusion antimicrobial susceptibility test showed that the most effective antimicrobials were amikacin (100%), amoxicillin/clavulanate (100%), cephalexin (100%) and ceftiofur (100%), while isolates had presented most resistance to gentamicin (43%), sulfamethoxazole/trimethoprim (43%) and ampicillin (29%). However, on the inhibitory minimal concentration test (MIC test), only one of the four isolates of Nocardia farcinica was resistant to sulfamethoxazole/trimethoprim.

First case report of Nocardia veterana causing nodular lymphangitis in an immunocompromised host

We report a unique case of ascending cutaneous lymphangitis in a 72-year-old immunocompromised man from which a newly described Nocardia species was isolated by 16S ribosomal gene sequencing. Treatment with trimethoprim-sulfamethoxazole resulted in successful resolution of symptoms. To the best of our knowledge, this is the first case report of N. veterana implicated in causing ascending cutaneous lymphangitis.

Nocardia veterana endogenous endophthalmitis in a cardiac transplant patient

Background

Endogenous endophthalmitis secondary to Nocardia species is extremely rare but often portends a poor visual prognosis often owing to the advanced nature of disease at presentation and delay in diagnosis. Patients who are systemically immunosuppressed are at greatest risk and early suspicion of the role of this organism in patients with acute panuveitis is paramount.

Findings

A 66-year-old cardiac transplant patient on oral prednisone, Myfortic, and tacrolimus developed unilateral panuveitis with a focal white subretinal and retinal lesion. His past medical history was notable for Aspergillus pneumonia and cytomegalovirus retinitis in the contralateral eye 12 months prior. Aqueous humor sampling for eubacterial, eufungal, and viral PCR testing, as well as vitreous cultures for bacteria and fungi were unsuccessful in the identification of a causative organism. Progressive enlargement of the lesion was noted despite intravitreal foscarnet, vancomycin, ceftazidime, and voriconazole. A pars plana vitrectomy and retinal and subretinal biopsy led to the identification of Nocardia veterana, a recently identified Nocardia species. A combination of linezolid, meropenem, azithromycin, ceftriaxone, and intravitreal amikacin resulted in eradication of the infection.

Conclusion

This is the first reported case of N. veterana endogenous endophthalmitis in an immunosuppressed patient. Pars plana vitrectomy with a subretinal biopsy was required to establish a diagnosis, as other testing including aqueous PCR and vitreous cultures were negative. The poor visual outcome in our patient highlights the importance of early consideration of Nocardia in the differential diagnosis of panuveitis with subretinal disease in the context of immunosuppression.

Molecular identification and susceptibility pattern of clinical Nocardia species: Emergence of Nocardia crassostreae as an agent of invasive nocardiosis

BACKGROUND

Nocardia species are rare, opportunistic organisms that cause disease in both immunocompetent and immunocompromised individuals.

OBJECTIVE

To investigate the clinical presentations of various Nocardia infections based on the 16S ribosomal RNA gene of the isolate, as well as related risk factors and susceptibility patterns to antimicrobial agents.

METHODS

Thirteen patients with a diagnosis of nocardiosis were included in the present study. Seven Nocardia species were identified by 16S ribosomal RNA. Susceptibility testing was performed using six antimicrobial agents.

RESULTS

Five patients were immunocompromised, and eight were immunocompetent with predisposing factors including cystic fibrosis, tuberculosis and ophthalmic infections. Nocardia caused pulmonary infections in eight patients (61.5%), invasive systemic infections in three patients (23%) and local (ophthalmic) infections in two patients (15.4%). In the patients with pulmonary disease, nocardiosis was caused by six species (Nocardia cyriacigeorgica, Nocardia otitidiscaviarum, Nocardia farcinica, Nocardia carnea, Nocardia testacea and Nocardia asiatica). The seventh species identified in the present study was Nocardia crassostreae.

DISCUSSION

N crassostreae is a multidrug-resistant organism that was reported to be an emerging human pathogen causing invasive nocardiosis in a patient with non-Hodgkin's lymphoma. N farcinica was isolated from blood in a patient with breast cancer. None of the Nocardia isolates were resistant to linezolid. One N otitidiscaviarum isolate was a multidrug-resistant organism. All patients in the present study were treated with the appropriate antibiotics and their condition resolved without further sequelae.

CONCLUSIONS

The present study is the first report on N crassostreae as a human pathogen. The detection of multidrug-resistant species necessitate molecular identification and susceptibility testing, and should be performed for all Nocardia infections. Nocardiosis manifests various clinical features depending on the Nocardia species and underlying conditions.

Multisite reproducibility of the broth microdilution method for susceptibility testing of Nocardia species

Antimicrobial susceptibility testing (AST) of clinical isolates of Nocardia is recommended to detect resistance to commonly used antimicrobial agents; such testing is complicated by difficulties in inoculum preparation and test interpretation. In this study, six laboratories performed repetitive broth microdilution testing on single strains of Nocardia brasiliensis, Nocardia cyriacigeorgica, Nocardia farcinica, Nocardia nova, and Nocardia wallacei. For each isolate, a total of 30 microdilution panels from three different lots were tested at most sites. The goal of the study was to determine the inter- and intralaboratory reproducibility of susceptibility testing of this group of isolates. Acceptable agreement (>90% agreement at ±1 dilution of the MIC mode) was found for amikacin, ciprofloxacin, clarithromycin, and moxifloxacin. After eliminating MIC values from single laboratories whose results showed the greatest deviation from those of the remaining laboratories, acceptable agreement was also found for amoxicillin-clavulanic acid, linezolid, minocycline, and tobramycin. Results showed unsatisfactory reproducibility of broth microdilution testing of ceftriaxone with N. cyriacigeorgica and N. wallacei, tigecycline with N. brasiliensis and N. cyriacigeorgica, and sulfonamides with N. farcinica and N. wallacei. N. nova ATCC BAA-2227 is proposed as a quality control organism for AST of Nocardia sp., and the use of a disk diffusion test for sulfisoxazole is proposed as a check of the adequacy of the inoculum and to confirm sulfonamide MIC results.

Central venous catheter-associated Nocardia bacteremia in cancer patients

TOC Summary: Heavy biofilm growth can be reduced through use of antimicrobial lock solutions.

Central venous catheters, often needed by cancer patients, can be the source of Nocardia bacteremia. We evaluated the clinical characteristics and outcomes of 17 cancer patients with Nocardia bacteremia. For 10 patients, the bacteremia was associated with the catheter; for the other 7, it was a disseminated infection. N. nova complex was the leading cause of bacteremia. Nocardia promoted heavy biofilm formation on the surface of central venous catheter segments tested in an in vitro biofilm model. Trimethoprim- and minocycline-based lock solutions had potent in vitro activity against biofilm growth. Patients with Nocardia central venous catheter–associated bloodstream infections responded well to catheter removal and antimicrobial drug therapy, whereas those with disseminated bacteremia had poor prognoses.

First report of a brain abscess caused by Nocardia veterana

Among Nocardia species causing infections, Nocardia veterana is rarely isolated and is mostly described as causing pulmonary infections. This is the first presentation of a case of brain abscess attributable to an N. veterana infection in a patient with type 2 diabetes. Prolonged antibiotic therapy with trimethoprim-sulfamethoxazole led to successful clinical recovery.

Evaluation of the integrated database network system (IDNS) SmartGene software for analysis of 16S rRNA gene sequences for identification of Nocardia species

16S rRNA gene sequences of 102 Nocardia isolates were analyzed using the Integrated Database Network System (IDNS) SmartGene centroid database. A total of 76% of the isolates were correctly identified. Discordant identifications were due to inadequate centroid length (3 species), inaccurate or insufficient entries in the public databases (5 species), and heterogeneous sequences among members of a species (1 species).

"Mycobacterium tilburgii," a newly described, uncultivated opportunistic pathogen

Molecular methods are increasingly used to identify pathogens that are difficult to cultivate. We report a case of disseminated infection with "Mycobacterium tilburgii," a proposed species that has never been cultivated. The case illustrates the diagnostic utility of sequence analysis of the 16S rRNA gene directly from clinical specimens.

Nocardia wallacei sp. nov. and Nocardia blacklockiae sp. nov., human pathogens and members of the "Nocardia transvalensis Complex"

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).

Organisms designated as Nocardia asteroides drug pattern type VI are members of the species Nocardia cyriacigeorgica

Nocardia cyriacigeorgica has recently been described as an "emerging" pathogen. However, DNA-DNA hybridization results confirm that Nocardia asteroides drug pattern type VI, which has long been recognized as a common and significant pathogen in the United States, belongs to the species N. cyriacigeorgica.

Clinical and microbiological features of nocardiosis 1997–2003

Nocardiosis has been believed to be caused by the members of the Nocardia asteroides complex and the Nocardia brasiliensis species. However, recent advances in genotypic identification have shown that the genus exhibits considerable taxonomic complexity and the phenotypic markers used in the past for its identification can be ambiguous. The aim of this study was to assess the species distribution of Nocardia isolates and to determine whether there are differences in pathogenicity or antimicrobial susceptibility between the different species identified. Nocardia isolates obtained over a 7 year period were retrospectively reviewed. The isolates were identified genotypically, their antibiotic susceptibility was tested and the clinical data of the 27 patients were retrieved. Eight different Nocardia species were identified: Nocardia farcinica (n=9), Nocardia abscessus (n=6), Nocardia cyriacigeorgica (n=6), Nocardia otitidiscaviarum (n=2), Nocardia nova (n=1), N. nova complex (n=1), Nocardia carnea (n=1) and Nocardia transvalensis complex (n=1). All species were susceptible to co-trimoxazole but different patterns of susceptibility to other agents were observed. All patients had active comorbidities at the time of infection. A total of 19 patients were immunosuppressed, due to human immunodeficiency virus infection, chronic corticosteroid therapy, immunosupressive therapy or haematological malignancies. Six patients displayed a Charlson comorbidity index score above 4. Global mortality was 50 % while attributable mortality was 34.6 %. Patients infected with N. farcinica – the most resistant species – had the highest Charlson index score and the highest mortality rate. Accurate identification of the species and susceptibility testing of Nocardia isolates may play an important role in diagnosis and treatment.

Analysis of multiple differing copies of the 16S rRNA gene in five clinical isolates and three type strains of Nocardia species and implications for species assignment

Five clinical isolates of Nocardia that showed ambiguous bases within the variable region of the 16S rRNA gene sequence were evaluated for the presence of multiple copies of this gene. The type strains of three Nocardia species, Nocardia concava, Nocardia ignorata, and Nocardia yamanashiensis, which also showed ambiguous bases in the variable region, were also examined. Cloning experiments using an amplified region of the 16S rRNA that contains the variable region showed that each isolate possessed 16S rRNA genes with at least two different sequences. In addition, hybridization studies using a 16S rRNA gene-specific probe and extracted genomic DNA of the patient isolates and of the type strain of N. ignorata showed that each isolate possessed at least three copies of the gene. These multiple differing copies of the 16S rRNA gene and the results of DNA-DNA hybridization studies indicate problems of species definition and identification for such isolates. A broader species concept than that currently in vogue may be required to accommodate such organisms.

Analysis of secA1 gene sequences for identification of Nocardia species

Molecular methodologies, especially 16S rRNA gene sequence analysis, have allowed the recognition of many new species of Nocardia and to date have been the most precise methods for identifying isolates reliably to the species level. We describe here a novel method for identifying Nocardia isolates by using sequence analysis of a portion of the secA1 gene. A region of the secA1 gene of 30 type or reference strains of Nocardia species was amplified using secA1-specific primers. Sequence analysis of 468 bp allowed clear differentiation of all species, with a range of interspecies similarity of 85.0% to 98.7%. Corresponding 16S rRNA gene sequences of a 1,285-bp region for the same isolates showed a range of interspecies similarity of 94.4 to 99.8%. In addition to the type and reference strains, a 468-bp fragment of the secA1 gene was sequenced from 40 clinical isolates of 12 Nocardia species previously identified by 16S rRNA gene sequence analysis. The secA1 gene sequences of most isolates showed >99.0% similarity to the secA1 sequences of the type or reference strain to which their identification corresponded, with a range of 95.3 to 100%. Comparison of the deduced 156 amino acid sequences of the SecA1 proteins of the clinical isolates showed between zero and two amino acid residue differences compared to that of the corresponding type or reference strain. Sequencing of the secA1 gene, and using deduced amino acid sequences of the SecA1 protein, may provide a more discriminative and precise method for the identification of Nocardia isolates than 16S rRNA gene sequencing.

Native valve endocarditis due to Gordonia polyisoprenivorans: case report and review of literature of bloodstream infections caused by Gordonia species

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

Clinical and laboratory features of the Nocardia spp. based on current molecular taxonomy

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.

Multiple copies of the 16S rRNA gene in Nocardia nova isolates and implications for sequence-based identification procedures

Molecular investigation of two Nocardia patient isolates showed unusual restriction fragment length polymorphism patterns with restriction endonuclease assays (REA) using an amplified portion of the 16S rRNA gene. Patterns typical of Nocardia nova were obtained with REA of an amplified portion of the 65-kDa heat shock protein gene. Subsequent sequence analysis of the 16S rRNA gene regions of these isolates showed the presence of ambiguous bases within an expected restriction endonuclease recognition site which were not able to be resolved on repeat testing. Cloning of amplified regions of the 16S rRNA genes and subsequent sequencing of the resulting clones from the two patient isolates showed three different 16S rRNA gene sequences which corresponded to sequences found in N. nova, a molecular variant of N. nova, and a previously undescribed sequence. Hybridization studies using a DNA probe corresponding to an 89-bp conserved region of the 16S rRNA gene confirmed the presence of at least two copies of the 16S rRNA gene in the N. nova type strain, in a patient isolate identical to the molecular variant of N. nova, and in the two other patient isolates. All isolates were found to belong to the species N. nova as determined by DNA-DNA hybridization. Because minimal variation has been found in the 16S rRNA gene sequences of different species of Nocardia, those laboratories employing molecular methods for identification of these species must be aware of the potential identification complications that may be caused by the presence of differing 16S rRNA genes in the same isolate.

Nocardia kruczakiae sp. nov., a pathogen in immunocompromised patients and a member of the "N. nova complex"

Molecular methodologies have become useful techniques for the identification of pathogenic Nocardia species and for the recognition of novel species that are capable of causing human disease. Two isolates recovered from immunocompromised patients were characterized as Nocardia nova by biochemical and susceptibility testing results. The restriction fragment length polymorphism (RFLP) patterns obtained by restriction endonuclease analysis (REA) of an amplified portion of the heat shock protein gene were identical to those obtained with the type strain of N. nova. REA of an amplified portion of the 16S rRNA gene showed RFLP patterns that were unlike those obtained for the type strain of N. nova but that were similar to those obtained for the type strains of N. africana and N. veterana. Subsequent sequencing of a portion of the 16S rRNA gene produced identical results for the two patient isolates. Sequence analysis of 1,352-bp portions of the 16S rRNA gene indicated that these isolates were 99.8% similar to the recently described species N. veterana but were only 99.3, 98.1, and 98.1% similar to the type strains of N. africana, N. nova, and N. vaccinii, respectively. DNA-DNA hybridization studies confirmed that the two patient isolates belonged to the same species but were not closely related to N. africana, N. nova, N. vaccinii, or N. veterana. The patient isolates have been designated N. kruczakiae sp. nov. Because N. africana, N. veterana, and the new species are not readily differentiated from N. nova by phenotypic methods alone, the designation "N. nova complex" can be used to designate isolates such as these that phenotypically resemble N. nova but that have not been definitively characterized by 16S rRNA gene sequencing or DNA-DNA hybridization.

Rapid identification of Nocardia farcinica clinical isolates by a PCR assay targeting a 314-base-pair species-specific DNA fragment

Nocardia farcinica is the most clinically significant species within the Nocardia asteroides complex. Differentiation of N. farcinica from other members of N. asteroides complex is important because this species characteristically demonstrates resistance to several extended-spectrum antimicrobial agents. Traditional phenotypic characterization of this species is time- and labor-intensive and often leads to misidentification in the clinical microbiology laboratory. We previously observed a 409-bp product for all strains of N. farcinica by using randomly amplified polymorphic DNA analysis with the primer DKU49. In this investigation, the 409-bp fragment was sequenced and then used to design a specific primer pair, Nf1 (16-mer) and Nf2 (16-mer), complementary to the 409-bp fragment. PCR amplification of genomic DNA from 28 N. farcinica isolates with Nf1 and Nf2 generated a single intense 314-bp fragment. The specificity of the assay with these primers was verified, since there were no PCR amplification products observed from heterologous nocardial species (n = 59) or other related bacterial genera (n = 41). Restriction enzyme digestion using CfoI and direct sequencing of the 314-bp fragment further confirmed the specificity of the assay for N. farcinica. This highly sensitive and specific PCR assay provides a rapid (within 1 day of obtaining DNA) method for identification of this medically important emerging pathogen. Rapid diagnosis of N. farcinica infection may allow for earlier initiation of effective therapy, thus improving patient outcome.

Evaluation of partial 16S ribosomal DNA sequencing for identification of nocardia species by using the MicroSeq 500 system with an expanded database

Identification of clinically significant nocardiae to the species level is important in patient diagnosis and treatment. A study was performed to evaluate Nocardia species identification obtained by partial 16S ribosomal DNA (rDNA) sequencing by the MicroSeq 500 system with an expanded database. The expanded portion of the database was developed from partial 5' 16S rDNA sequences derived from 28 reference strains (from the American Type Culture Collection and the Japanese Collection of Microorganisms). The expanded MicroSeq 500 system was compared to (i). conventional identification obtained from a combination of growth characteristics with biochemical and drug susceptibility tests; (ii). molecular techniques involving restriction enzyme analysis (REA) of portions of the 16S rRNA and 65-kDa heat shock protein genes; and (iii). when necessary, sequencing of a 999-bp fragment of the 16S rRNA gene. An unknown isolate was identified as a particular species if the sequence obtained by partial 16S rDNA sequencing by the expanded MicroSeq 500 system was 99.0% similar to that of the reference strain. Ninety-four nocardiae representing 10 separate species were isolated from patient specimens and examined by using the three different methods. Sequencing of partial 16S rDNA by the expanded MicroSeq 500 system resulted in only 72% agreement with conventional methods for species identification and 90% agreement with the alternative molecular methods. Molecular methods for identification of Nocardia species provide more accurate and rapid results than the conventional methods using biochemical and susceptibility testing. With an expanded database, the MicroSeq 500 system for partial 16S rDNA was able to correctly identify the human pathogens N. brasiliensis, N. cyriacigeorgica, N. farcinica, N. nova, N. otitidiscaviarum, and N. veterana.

Implantable defibrillator pocket infection and bacteremia caused by Nocardia nova complex isolate

Nocardia spp. are common environmental organisms that, to our knowledge, have never been implicated as causing an implantable defibrillator or pacemaker infection. We describe a 70-year-old male with a recent implantable cardiac defibrillator revision and subsequent device infection and bacteremia caused by a Nocardia nova complex isolate.