Bacteremia caused by Nocardia farcinica: a case report and literature review.

BACKGROUND: Nocardia farcinica is one of the most common Nocardia species causing human infections. It is an opportunistic pathogen that often infects people with compromised immune systems. It could invade human body through respiratory tract or skin wounds, cause local infection, and affect other organs via hematogenous dissemination. However, N. farcinica-caused bacteremia is uncommon. In this study, we report a case of bacteremia caused by N. farcinica in China. CASE PRESENTATION: An 80-year-old woman was admitted to Peking Union Medical College Hospital with recurrent fever, right abdominal pain for one and a half month, and right adrenal gland occupation. N. farcinica was identified as the causative pathogen using blood culture and plasma metagenomics next-generation sequencing (mNGS). The clinical considerations included bacteremia and adrenal gland abscess caused by Nocardia infection. As the patient was allergic to sulfanilamide, imipenem/cilastatin and linezolid were empirically administered. Unfortunately, the patient eventually died less than a month after the initiation of anti-infection treatment. CONCLUSION: N. farcinica bacteremia is rare and its clinical manifestations are not specific. Its diagnosis depends on etiological examination, which can be confirmed using techniques such as Sanger sequencing and mNGS. In this report, we have reviewed cases of Nocardia bloodstream infection reported in the past decade, hoping to improve clinicians' understanding of Nocardia bloodstream infection and help in its early diagnosis and timely treatment.

Whole Genome Sequencing Highlights the Pathogenic Profile in Nocardia Keratitis.

Purpose: Nocardia keratitis is a serious and sight-threatening condition. This study aims to reveal the virulence and antimicrobial resistance gene profile of Nocardia strains using whole genome sequencing. Methods: Whole-genome sequencing was performed on 23 cornea-derived Nocardia strains. Together with genomic data from the respiratory tract and the environment, 141 genomes were then utilized for phylogenetic and pan-genome analyses, followed by virulence and antibiotic resistance analysis. The correlations between virulence genes and pathogenicity were experimentally validated, including the characteristics of Nocardia colonies and clinical and histopathological evaluations of Nocardia keratitis mice models. Results: Whole-genome sequencing of 141 Nocardia strains revealed a mean of 220 virulence genes contributed to bacterial pathogenesis. The mce gene family analysis led to the categorization of strains from the cornea into groups A, B, and C. The colonies of group C had the largest diameter, height, and fastest growth rate. The size of corneal ulcers and the clinical scores showed a significant increase in mouse models induced by group C. The relative expression levels of pro-inflammatory cytokines (CD4, IFN-γ, IL-6Rα, and TNF-α) in the lesion area exhibited an increasing trend from group A to group C. Antibiotic resistance genes (ARGs) spanned nine distinct drug classes, four resistance mechanisms, and seven primary antimicrobial resistance gene families. Conclusions: Whole genome sequencing highlights the pathogenic role of mce gene family in Nocardia keratitis. Its distribution pattern may contribute to the distinct characteristics of the growth of Nocardia colonies and the clinical severity of the mice models.

Clinical characteristics and drug resistance of Nocardia in Henan, China, 2017-2023.

BACKGROUND: The aim of this study was to investigate the clinical features of Nocardia infections, antibiotic resistance profile, choice of antibiotics and treatment outcome, among others. In addition, the study compared the clinical and microbiological characteristics of nocardiosis in bronchiectasis patients and non-bronchiectasis patients. METHODS: Detailed clinical data were collected from the medical records of 71 non-duplicate nocardiosis patients from 2017 to 2023 at a tertiary hospital in Zhengzhou, China. Nocardia isolates were identified to the species level using MALDI-TOF MS and 16S rRNA PCR sequencing. Clinical data were collected from medical records, and drug susceptibility was determined using the broth microdilution method. RESULTS: Of the 71 cases of nocardiosis, 70 (98.6%) were diagnosed as pulmonary infections with common underlying diseases including bronchiectasis, tuberculosis, diabetes mellitus and chronic obstructive pulmonary disease (COPD). Thirteen different strains were found in 71 isolates, the most common of which were N. farcinica (26.8%) and N. cyriacigeorgica (18.3%). All Nocardia strains were 100% susceptible to both TMP-SMX and linezolid, and different Nocardia species showed different patterns of drug susceptibility in vitro. Pulmonary nocardiosis is prone to comorbidities such as bronchiectasis, diabetes mellitus, COPD, etc., and Nocardia is also frequently accompanied by co-infection of the body with pathogens such as Mycobacterium and Aspergillus spp. Sixty-one patients underwent a detailed treatment regimen, of whom 32 (52.5%) received single or multi-drug therapy based on TMP-SMX. Bronchiectasis was associated with a higher frequency of Nocardia infections, and there were significant differences between the bronchiectasis and non-bronchiectasis groups in terms of age distribution, clinical characteristics, identification of Nocardia species, and antibiotic susceptibility (P < 0.05). CONCLUSIONS: Our study contributes to the understanding of the species diversity of Nocardia isolates in Henan, China, and the clinical characteristics of patients with pulmonary nocardiosis infections. Clinical and microbiologic differences between patients with and without bronchiectasis. These findings will contribute to the early diagnosis and treatment of patients.

Genomic insights and anti-phytopathogenic potential of siderophore metabolome of endolithic Nocardia mangyaensis NH1.

Actinobacteria are one of the predominant groups that successfully colonize and survive in various aquatic, terrestrial and rhizhospheric ecosystems. Among actinobacteria, Nocardia is one of the most important agricultural and industrial bacteria. Screening and isolation of Nocardia related bacteria from extreme habitats such as endolithic environments are beneficial for practical applications in agricultural and environmental biotechnology. In this work, bioinformatics analysis revealed that a novel strain Nocardia mangyaensis NH1 has the capacity to produce structurally varied bioactive compounds, which encoded by non-ribosomal peptide synthases (NRPS), polyketide synthase (PKS), and post-translationally modified peptides (RiPPs). Among NRPS, five gene clusters have a sequence homology with clusters encoding for siderophore synthesis. We also show that N. mangyaensis NH1 accumulates both catechol- and hydroxamate-type siderophores simultaneously under iron-deficient conditions. Untargeted LC-MS/MS analysis revealed a variety of metabolites, including siderophores, lipopeptides, cyclic peptides, and indole-3-acetic acid (IAA) in the culture medium of N. mangyaensis NH1 grown under iron deficiency. We demonstrate that four CAS (chrome azurol S)-positive fractions display variable affinity to metals, with a high Fe3+ chelating capability. Additionally, three of these fractions exhibit antioxidant activity. A combination of iron scavenging metabolites produced by N. mangyaensis NH1 showed antifungal activity against several plant pathogenic fungi. We have shown that the pure culture of N. mangyaensis NH1 and its metabolites have no adverse impact on Arabidopsis seedlings. The ability of N. mangyaensis NH1 to produce siderophores with antifungal, metal-chelating, and antioxidant properties, when supplemented with phytohormones, has the potential to improve the release of macro- and micronutrients, increase soil fertility, promote plant growth and development, and enable the production of biofertilizers across diverse soil systems.

WarA, a remote homolog of NpmA and KamB from Nocardia wallacei, confers broad spectrum aminoglycoside resistance in Nocardia and Mycobacteria.

OBJECTIVES: Aminoglycoside resistance in bacteria is typically conferred by specific drug-modifying enzymes. Infrequently, such resistance is achieved through 16S ribosomal RNA methyltransferases, such as NpmA and KamB encoded by Escherichia coli and Streptoalloteichus tenebrarius, respectively. These enzymes are not widespread and have not been described in Nocardia species to date. METHODS: We report the genomic mining of 18 Nocardia wallacei isolates that were found to be specifically and substantially resistant to amikacin. RESULTS: We identified a gene coding for a protein with very distant homology to NpmA and KamB. However, 3-D modeling revealed that the tertiary structure of these three proteins was highly similar. Cloning and expressing this gene in two susceptible bacteria Nocardia asteroides, and Mycobacterium smegmatis (another Actinobacterium) led to high-level, pan-aminoglycoside resistance in both cases. We named this gene warA (Wallacei Amikacin Resistance A). CONCLUSIONS: This is the first description and experimental characterization of a gene of this family in Nocardia, and the first demonstration that such activity could lead to pan-aminoglycoside resistance in Mycobacteria as well. The discovery of this novel gene has important biotechnology and clinical implications.

Exploring Nocardia's ecological spectrum and novel therapeutic frontiers through whole-genome sequencing: unraveling drug resistance and virulence factors.

Nocardia farcinica is the leading pathogen responsible for nocardiosis, a life-threatening infection primarily affecting immunocompromised patients. In this study, the genomic sequence of a clinically isolated N. farcinica sample was sequenced. Subsequently, the assembled genome was annotated to identify antimicrobial resistance and virulence genes, as well as plasmid and prophages. The analysis of the entire genome size was 6,021,225 bp, with a GC content of 70.78% and consists of 103 contigs and N50 values of 292,531 bp. The genome analysis revealed the presence of several antimicrobial resistance genes, including RbpA, mtrA, FAR-1, blaFAR-1, blaFAR-1_1, and rox. In addition, virulence genes such as relA, icl, and mbtH were also detected. The present study signifies that N. farcinica genome is pivotal for the understanding of antimicrobial resistance and virulence genes is crucial for comprehending resistance mechanism, and developing effective strategies to combat bacterial infections effectively, especially adhesins and toxins. This study aids in identifying crucial drug targets for combating multidrug-resistant N. farcinica in the future.

Biochemical and structural characterization of a class A ß-lactamase from Nocardia cyriacigeorgica.

Nocardia are Gram-positive bacteria from the Actinobacteria phylum. Some Nocardia species can infect humans and are usually considered to be opportunist pathogens, as they often infect immunocompromised patients. Although their clinical incidence is low, many Nocardia species are now considered to be emerging pathogens. Primary sites of infection by Nocardia are the skin or the lungs, but dissemination to other body parts is very frequent. These disseminated infections are very difficult to treat and thus are tackled with multiple classes of antibiotics, in addition to the traditional treatment targeting the folate pathway. ß-Lactams are often included in the regimen, but many Nocardia species present moderate or strong resistance to some members of this drug class. Genomic, microbiological and biochemical studies have reported the presence of class A ß-lactamases (ABLs) in a handful of Nocardia species, but no structural investigation of Nocardia ß-lactamases has yet been performed. In this study, the expression, purification and preliminary biochemical characterization of an ABL from an N. cyriacigeorgica (NCY-1) clinical strain are reported. The crystallization and the very high resolution crystal structure of NCY-1 are also described. The sequence and structural analysis of the protein demonstrate that NCY-1 belongs to the class A1 ß-lactamases and show its very high conservation with ABLs from other human-pathogenic Nocardia. In addition, the presence of one molecule of citrate tightly bound in the catalytic site of the enzyme is described. This structure may provide a solid basis for future drug development to specifically target Nocardia spp. ß-lactamases.

Disruption of a kasB homolog gene (kasB) causes attenuation of cell invasion and virulence of Nocardia seriolae.

Nocardia seriolae is the primary aetiological agent of nocardiosis in fish, which causes mass mortality in freshwater and marine fish. ß-ketoacyl-ACP synthase (KAS) is one of the essential enzymes in the synthesis of mycolic acids (MASs) in Mycobacterium spp. and has been chosen as the target for therapeutic intervention in mycobacterial diseases. In the present study, a kasB homologue gene (kasB) was identified in the genome of N. seriolae, and the gene-deficient mutant (ΔkasB) was generated based on a clinical isolate, XSYC-Ns. Compared to the wild-type (WT) strain, the ΔkasB showed a measurably growth defect in vitro but retained the acid-fastness in acid-fast staining. Observation of the cell ultrastructure showed some alterations in the cell wall of the ΔkasB strain. Compared to its original strain, the cell wall lipid layer seemed sparser, and a wider electron-transparent zone was observed in the cell wall of ΔkasB strain. Moreover, the ΔkasB strain showed impaired ability of cell invasion as well as intracellular survival in the cell line originating from the head-kidney of the large yellow croaker (LYC-hK), compared to its original strain. In addition, the deficiency of ΔkasB significantly attenuated the virulence of N. seriolae in largemouth bass. The present study suggested that the ΔkasB gene might be involved in the synthesis of extracellular cell-wall lipids in N. seriolae and play a crucial role in its pathogenicity.

Nocardia farcinica abortion in a goat.

A female goat fetus was received by the Colorado State University-Veterinary Diagnostic Laboratory following an isolated abortion of twins by a reportedly healthy doe. Postmortem examination did not reveal any gross abnormalities. Histologic evaluation revealed pyogranulomatous and necrotizing bronchopneumonia with intracellular and extracellular gram-positive and non-acid-fast filamentous bacilli. Aerobic culture of the stomach contents and pooled lung and liver tissue yielded light growth of Nocardia sp., which was identified by MALDI-TOF MS and 16s rDNA sequencing as Nocardia farcinica.

Diagnosis of cutaneous primary nocardiosis in patients with normal immune function by metagenomic next-generation sequencing.

Nocardia primarily affects immunocompromised individuals, and Infection with Nocardia is uncommon and primary cutaneous nocardiosis caused by percutaneous inoculation is even rarer. Primary cutaneous nocardiosis remains a diagnostic challenge and should be considered in the differential diagnosis for any superficial cutaneous infection that arises in patients with normal immune function. We report a case that was diagnosed with primary cutaneous Nocardia by metagenomic next-generation sequencing technology.

[A case of disseminated nocardiosis in a non-immunosuppressed host].

Nocardia is an opportunistic pathogen that most commonly affects immunosuppressed hosts, while disseminated infections in healthy hosts are rare. In this paper, we described a case of disseminated Nocardia infection in a non-immunosuppressed host whose initial imaging was strikingly similar to systemic metastasis from a tumor. Since no tumor cells were found in any of the numerous biopsies taken, we considered infection by specific pathogens before metagenomic next-generation sequencing of a lumbar spine tissue biopsy finally confirmed the diagnosis of Nocardia infection. To help doctors better understand this condition and avoid misdiagnosis a, this article provided a summary of the clinical characteristics, diagnostic techniques, and therapeutic options for disseminated nocardiosis.

Clinical screening of Nocardia in sputum smears based on neural networks.

Objective: Nocardia is clinically rare but highly pathogenic in clinical practice. Due to the lack of Nocardia screening methods, Nocardia is often missed in diagnosis, leading to worsening the condition. Therefore, this paper proposes a Nocardia screening method based on neural networks, aiming at quick Nocardia detection in sputum specimens with low costs and thereby reducing the missed diagnosis rate. Methods: Firstly, sputum specimens were collected from patients who were infected with Nocardia, and a part of the specimens were mixed with new sputum specimens from patients without Nocardia infection to enhance the data diversity. Secondly, the specimens were converted into smears with Gram staining. Images were captured under a microscope and subsequently annotated by experts, creating two datasets. Thirdly, each dataset was divided into three subsets: the training set, the validation set and the test set. The training and validation sets were used for training networks, while the test set was used for evaluating the effeteness of the trained networks. Finally, a neural network model was trained on this dataset, with an image of Gram-stained sputum smear as input, this model determines the presence and locations of Nocardia instances within the image. Results: After training, the detection network was evaluated on two datasets, resulting in classification accuracies of 97.3% and 98.3%, respectively. This network can identify Nocardia instances in about 24 milliseconds per image on a personal computer. The detection metrics of mAP50 on both datasets were 0.780 and 0.841, respectively. Conclusion: The Nocardia screening method can accurately and efficiently determine whether Nocardia exists in the images of Gram-stained sputum smears. Additionally, it can precisely locate the Nocardia instances, assisting doctors in confirming the presence of Nocardia.

Central nervous system nocardiosis diagnosed by metagenomic next-generation sequencing: A case series and literature review.

BACKGROUND: Central nervous system (CNS) nocardiosis is a rare suppurative disease caused by the genus Nocardia. It is found most frequently in immunocompromised individuals. OBJECTIVES: In this study, we retrospectively reviewed the clinical presentations, laboratory examination, therapy and outcomes of 9 patients with CNS nocardiosis diagnosed using metagenomic next-generation sequencing (mNGS) in our hospital. MATERIAL AND METHODS: We reviewed 9 patients with confirmed diagnosis of CNS Nocardia infection from January 2017 to December 2021 in the Department of Neurology at The Third Affiliated Hospital, Sun Yat-sen University (Guangzhou, China). In addition, we searched literature related to CNS Nocardia infection on PubMed and included all case reports with proven CNS nocardiosis since 2016. RESULTS: The metagenomic next-generation sequencing (mNGS) of CSF can be used for the rapid diagnosis of nocardiosis in CNS and N. farcinica are the most commonly isolated species. Underlying autoimmune diseases, immunosuppressive agents including corticosteroids and organ transplantation are predisposing factors of developing CNS nocardiosis. Single or multiple hyper-enhanced ring lesions indicative of cerebral abscesses are commonly presented in brain imaging. Trimethoprim-sulfamethoxazole (TMP-SMX) is used as the primary agent for the antibacterial therapy and in combination with other antibacterial agents. CONCLUSION: Our study demonstrated that mNGS of CSF can be conducted for definitive and rapid diagnosis for CNS nocardiosis.

Clinical characteristics of hospitalized patients with Nocardia genus detection by metagenomic next generation sequencing in a tertiary hospital from southern China.

OBJECTIVE: As an opportunistic pathogen, Nocardia often occurring in the immunocompromised hosts. As the unspecifc clinical presentation and low identification rate of the culture dependent methods, Nocardia infection may be under-diagnosis. Recent study have reported physicians could benefit from metagenomic next-generation sequencing (mNGS) in Nocardia diagnosis. Herein, we present patients with a positive detection of nocardiosis in mNGS, aiming to provide useful information for an differential diagnosis and patients management. METHODS: A total of 3756 samples detected for mNGS from March 2019 to April 2022 at the Fifth Affifiliated Hospital of Sun Yat-sen University, were screened. Clinical records, laboratory finding, CT images and mNGS results were reviewed for 19 patients who were positive for Nocardia genus. RESULTS: Samples from low respiratory tract obtained by bronchoscope took the major part of the positive (15/19). 12 of 19 cases were diagnosis as Nocardiosis Disease (ND) and over half of the ND individuals (7/12) were geriatric. Nearly all of them (10/12) were immunocompetent and 2 patients in ND group were impressively asymptomatic. Cough was the most common symptom. Nocardia cyriacigeorgica (4/12) was more frequently occurring in ND, followed by Nocardia abscessus (3/12). There are 3 individuals detected more than one kind of Nocardia species (Supplementary table 1). Except one with renal failure and one allergic to sulfamethoxazole, all of them received co-sulfonamide treatment and relieved eventually. CONCLUSION: Our study deciphered the clinical features of patients with positive nocardiosis detected by mNGS. Greater attention should be paid to the ND that occurred in the immunocompetent host and the geriatric. Due to the difficulties in establishing diagnosis of Nocardiosis disease, mNGS should play a much more essential role for a better assessment in those intractable cases. Co-sulfonamide treatment should still be the first choice of Nocardiosis disease.

A complicated infection by cutaneous Nocardia wallacei and pulmonary Mycobacterium abscessus in a Chinese immunocompetent patient: a case report.

Nocardiosis is an infectious disease caused by Nocardia that primarily affects immunocompromised hosts. Mycobacterium abscessus is a common opportunistic pathogen that causes disease in humans, including pulmonary and extrapulmonary infection. Nocardia spp. infection is uncommon, and infection with Nocardia wallacei and Mycobacterium abscessus is even rarer. A 59-year-old immunocompetent woman with risk factors for environmental exposure developed nocardiosis and presented to the hospital with a cough, shortness of breath, hemoptysis, and a back abscess. An enhanced computed tomography (CT) of the chest revealed partial destruction of the right lung, as well as consolidation of the right upper lobe. Rare pathogens N. wallacei and Mycobacterium abscessus were detected by metagenomic next-generation sequencing (mNGS) from abscess on the back and lung puncture tissue, respectively. She was treated with a combination of antibiotics and was finally discharged with a good prognosis. In this case, we present a patient who was successfully diagnosed with N. wallacei and Mycobacterium abscessus infection using mNGS. This importance of using mNGS in pathogen detection and the effective use of antibiotics in treating patients with long-term rare infections is highlighted in this report.

Multilocus sequence analysis (MLSA) of a Nocardia cyriacigeorgica strain causing severe bovine mastitis in Bosnia and Herzegovina.

Nocardia cyriacigeorgica is a well-known agent of human nocardiosis and is considered an emerging pathogen, however, its identification to the species level is complex for many clinical laboratories. Available data on the clinical significance of N. cyriacigeorgica in veterinary medicine are sparse and mainly concern isolated reports of pyogranulomatous lesions in domestic animals. We report a case of severe bovine mastitis caused by N. cyriacigeorgica that did not respond to conventional antimicrobial therapy in a small holding in Bosnia and Herzegovina. After isolation of the pathogen, further identification by routine microbiological methods was not possible. Susceptibility to antimicrobials was tested using the disc diffusion method according to published recommendations. The sample was also tested by MALDI-ToF MS with inconclusive results. In addition, 16S rRNA sequence analysis, verified by multilocus sequence analysis (MLSA) using the gyrB, 16S rRNA, secA1, and hsp65 sequences, confirmed the species N. cyriacigeorgica. To our knowledge, this is the first report of isolation of N. cyriacigeorgica from a clinical case of bovine mastitis in a European dairy farm and the first MLSA method approach to distinguish a Nocardia spp. strain isolated from animals.

Pairing comparative genomics with tandem mass-based molecular networking allows to highly efficient discovery of nonribosomal peptides from Nocardia spp.

Microbial natural products, particularly nonribosomal peptides (NRPs), have attracted significant attention due to their structural diversity and therapeutic potential. Nocardia, a genus of Actinomyces, is an important reservoir for natural products, especially NRPs. However, rediscovery is a significant challenge for mining new specialized metabolites from Nocardia, as well as from other sources. To overcome this challenge, we developed a strategy that combines comparative genomics with tandem mass-based molecular networking, which allows to efficiently discover new NRPs from Nocardia spp.. As a proof of concept, all genomes of Norcardia in NCBI database, including three strains from our lab, were compared with each other to prioritize unique biosynthetic gene clusters (BGCs) in the three in-house Nocardia strains, particularly those containing nonribosomal peptide synthases (NRPSs). Subsequently, the metabolomics data of those three in-house strains were analyzed employing tandem mass-based molecular networking. This led to the identification of a known lipopeptide, nocarjamide (1), and five new congeners (2-6) of nocarjamide, as well as a new decalipopeptide, nocarlipoamide (7), along with nocardimicin, a known compound found in Nocardia. The structure of the new decalipopeptide 7 was further extensively characterized using NMR, MS/MS, Marfey's analysis, and X-ray. In addition, the biosynthesis pathways for 1-7 were proposed through bioinformatics analysis, and thus the gene clusters responsible for biosynthesizing them were confirmed. Our results indicate that this strategy enables prompt dereplication of known compounds, rapid linkage of identified compounds with their biosynthesis gene cluster, and efficient discovery of new compounds.

Phenotypic and genotypic analysis of antimicrobial resistance in Nocardia species.

BACKGROUND: Antimicrobial resistance is common in Nocardia species but data regarding the molecular mechanisms beyond their resistance traits are limited. Our study aimed to determine the species distribution, the antimicrobial susceptibility profiles, and investigate the associations between the resistance traits and their genotypic determinants. METHODS: The study included 138 clinical strains of Nocardia from nine Israeli microbiology laboratories. MIC values of 12 antimicrobial agents were determined using broth microdilution. WGS was performed on 129 isolates of the eight predominant species. Bioinformatic analysis included phylogeny and determination of antimicrobial resistance genes and mutations. RESULTS: Among the isolates, Nocardia cyriacigeorgica was the most common species (36%), followed by Nocardia farcinica (16%), Nocardia wallacei (13%), Nocardia abscessus (9%) and Nocardia brasiliensis (8%). Linezolid was active against all isolates, followed by trimethoprim/sulfamethoxazole (93%) and amikacin (91%). Resistance to other antibiotics was species-specific, often associated with the presence of resistance genes or mutations: (1) aph(2″) in N. farcinica and N. wallacei (resistance to tobramycin); (ii) blaAST-1 in N. cyriacigeorgica and Nocardia neocaledoniensis (resistance to amoxicillin/clavulanate); (iii) blaFAR-1 in N. farcinica (resistance to ceftriaxone); (iv) Ser83Ala substitution in the gyrA gene in four species (resistance to ciprofloxacin); and (v) the 16S rRNA m1A1408 methyltransferase in N. wallacei isolates (correlating with amikacin resistance). CONCLUSIONS: Our study provides a comprehensive understanding of Nocardia species diversity, antibiotic resistance patterns, and the molecular basis of antimicrobial resistance. Resistance appears to follow species-related patterns, suggesting a lesser role for de novo evolution or transmission of antimicrobial resistance.

Clinical and microbiological characteristics of nocardiosis: A 5-year single-center study in Crete, Greece.

Nocardiosis is a rare disease affecting both immunocompromised and immunocompetent hosts, presented in various clinical forms ranging from localized to disseminated infection. Aim of the present study was to investigate the clinical and microbiological characteristics of nocardiosis, antimicrobial resistance profiles, treatment, and outcomes of Nocardia infection over the last 5 years at our institution. The medical records and microbiological data of patients affected by nocardiosis and treated at the university hospital of Heraklion, Crete, Greece, between 2018 and 2022, were retrospectively analyzed. The isolates were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and through sequencing of 16S rRNA. Antimicrobial susceptibility for 17 agents was determined by E-test and results were interpreted according to CLSI guidelines. Among the 28 Nocardia isolates, eight species were identified, with Nocardia brasiliensis being the most prevalent (32.1%), followed by Nocardia otitidiscaviarum (25%), and Nocardia farcinica (14.3%). Skin and soft tissue infections were the most common presentations, noted in 13 (50%) patients, followed by pulmonary infection presented in 10 (38.5%) patients. Fifteen patients (57.7%) had at least one underlying disease, and 11 (42.3%) were on immunosuppressive or long-term corticosteroid treatment. Susceptibility rates of linezolid, tigecycline, amikacin, trimethoprim-sulfamethoxazole, moxifloxacin, and imipenem were 100, 100, 96.4, 92.9, 82.1, and 42.9%, respectively. The 26 patients in this study were treated with various antibiotics. Mortality rate was 3.8%, and the patient who died had disseminated infection. Since epidemiology and antimicrobial susceptibility are evolving, continuous surveillance is mandatory in order to initiate appropriate treatment in a timely manner.

Discovery and Biosynthesis of the Cytotoxic Polyene Terpenomycin in Human Pathogenic Nocardia.

Nocardia are opportunistic human pathogens that can cause a range of debilitating and difficult to treat infections of the lungs, brain, skin, and soft tissues. Despite their close relationship to the well-known secondary metabolite-producing genus, Streptomyces, comparatively few natural products are known from the Nocardia, and even less is known about their involvement in the pathogenesis. Here, we combine chemistry, genomics, and molecular microbiology to reveal the production of terpenomycin, a new cytotoxic and antifungal polyene from a human pathogenic Nocardia terpenica isolate. We unveil the polyketide synthase (PKS) responsible for terpenomycin biosynthesis and show that it combines several unusual features, including "split", skipped, and iteratively used modules, and the use of the unusual extender unit methoxymalonate as a starter unit. To link genes to molecules, we constructed a transposon mutant library in N. terpenica, identifying a terpenomycin-null mutant with an inactivated terpenomycin PKS. Our findings show that the neglected actinomycetes have an unappreciated capacity for the production of bioactive molecules with unique biosynthetic pathways waiting to be uncovered and highlights these organisms as producers of diverse natural products.