MLSA phylogeny and antimicrobial susceptibility of clinical Nocardia isolates: a multicenter retrospective study in China

Functional activity of endophytic bacteria G9H01 with high salt tolerance and anti-Magnaporthe oryzae that isolated from saline-alkali-tolerant rice

It holds significant practical importance to screen and investigate endophytic bacteria with salt-tolerant activity in rice for the development of relevant microbial agents. A total of 179 strains of endophytic bacteria were isolated from 24 samples of salt-tolerant rice seeds, with almost 95 % of these bacteria exhibiting tolerance to a salt content of 2 % (0.34 mol/L). Following the screening process, a bacterium named G9H01 was identified, which demonstrated a salt tolerance of up to 15 % (2.57 mol/L) and resistance to Magnaporthe oryzae, the causal agent of rice blast disease. Phylogenetic analysis confirmed G9H01 as a strain of Bacillus paralicheniformis. The complete genome of G9H01 was sequenced and assembled, revealing a considerable number of genes encoding proteins associated with salt tolerance. Further analysis indicated that G9H01 may alleviate salt stress in a high-salt environment through various mechanisms. These mechanisms include the utilization of proteins such as K+ transporters, antiporters, and Na+/H+ antiporters, which are involved in K+ absorption and Na+ excretion. G9H01 also demonstrated the ability to uptake and accumulate betaine, as well as secrete extracellular polysaccharides. Collectively, these findings suggest that Bacillus paralicheniformis G9H01 has potential as a biocontrol agent, capable of promoting rice growth under saline-alkali-tolerant conditions.

A Rare Case Report of Disseminated Nocardia Farcinica Granulomatous Hepatitis and Clinical Management Experience

Background

Nocardiosis is primarily an opportunistic infection affecting immunocompromised individuals, with a predilection for the lungs, brain, or skin in those with compromised immune function. Granulomatous hepatitis caused by Nocardia is a rare clinical manifestation. This study aims to provide a systematic overview of the clinical features of Nocardiosis caused by Nocardia farcinica, enhancing our understanding of this disease.

Methods

We report a case of a 75-year-old male with no underlying diseases presenting with a history of "recurrent fever for more than 4 months", along with fatigue, poor appetite, and pleural and abdominal effusion. Despite treatment at multiple hospitals, the patient showed little improvement. Chest CT revealed chronic inflammation, small nodules, bilateral pleural effusion, and pleural thickening. Abdominal CT indicated multiple low-density lesions in the liver, multiple small calcifications, and abdominal effusion.

Results

Liver biopsy suggested inflammatory changes, with focal granuloma formation. Metagenomic next-generation sequencing (mNGS) of liver tissue indicated Nocardia farcinica, leading to the final diagnosis of disseminated Nocardia farcinica granulomatous hepatitis.

Conclusion

Nocardia infection is a rare disease primarily observed in immunocompromised patients but can also occur in those with normal immune function. The clinical and radiological features lack specificity; however, the utilization of mNGS technology enables rapid identification of the pathogenic microorganism. Nocardia farcinica is generally susceptible to sulfonamide drugs and amikacin, offering viable treatment options.

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.

The species distribution and antimicrobial resistance profiles of Nocardia species in China: A systematic review and meta-analysis

BACKGROUND

Nocardia species can cause local or disseminated infection. Prompt diagnosis and appropriate treatment of nocardiosis are required, because it can cause significant morbidity and mortality. Knowledge of local species distribution and susceptibility patterns is important to appropriate empiric therapy. However, knowledge on the epidemiology and antimicrobial susceptibility profiles of clinical Nocardia species remains limited in China.

METHODS

The data of isolation of Nocardia species were collected from databases such as Pubmed, Web of Science, Embase as well as Chinese databases (CNKI, Wanfang and VIP). Meta-analysis was performed using RevMan 5.3 software. Random effect models were used and tested with Cochran's Q and I2 statistics taking into account the possibility of heterogeneity between studies.

RESULTS

In total, 791 Nocardia isolates were identified to 19 species levels among all the recruited studies. The most common species were N. farcinica (29.1%, 230/791), followed by N. cyriacigeorgica (25.3%, 200/791), N. brasiliensis (11.8%, 93/791) and N. otitidiscaviarum (7.8%, 62/791). N. farcinica and N. cyriacigeorgica are widely distributed, N. brasiliensis mainly prevalent in the Southern, N. otitidiscaviarum mainly distributed in the east coastal provinces of China. Totally, 70.4% (223/317) Nocardia were cultured from respiratory tract specimens, 16.4% (52/317) from extra-pulmonary specimens, and 13.3% (42/317) from disseminated infection. The proportion of susceptible isolates as follows: linezolid 99.5% (197/198), amikacin 96.0% (190/198), trimethoprim-sulfamethoxazole 92.9% (184/198), imipenem 64.7% (128/198). Susceptibility varied by species of Nocardia.

CONCLUSIONS

N. farcinica and N. cyriacigeorgica are the most frequently isolated species, which are widely distributed in China. Pulmonary nocardiosis is the most common type of infection. Trimethoprim-sulfamethoxazole can still be the preferred agent for initial Nocardia infection therapy due to the low resistance rate, linezolid and amikacin could be an alternative to treat nocardiosis or a choice in a combination regimen.

Molecular detection of Nocardia: development and application of a real-time PCR assay in sputum and bronchoalveolar lavage fluid samples

The diagnosis of pulmonary nocardiosis remains challenging. Rapid detection of Nocardia is of primary importance for early diagnosis and precise treatment of nocardiosis. In this study, our objective was to develop and validate a new TaqMan real-time PCR (qPCR) assay for rapidly detecting Nocardia spp. in respiratory samples. Based on published sequence data, primers in a conserved region of the 16S rRNA gene and a probe within that region that was specific for Nocardia were designed. The distinction effect of the qPCR assay was assessed between Nocardia and other respiratory-associated bacteria. Furthermore, the specificity and sensitivity of the assay were evaluated in respiratory clinical samples (n = 205), compared to the results of 16S rRNA gene amplicon sequencing and clinical diagnosis. The qPCR assay exhibited high specificity, sensitivity, repeatability, and reproducibility. The limit of detection of standard plasmid DNA was 3 × 10² copies/mL. Additionally, the qPCR assay was applied to the direct detection of 205 clinical respiratory samples. The specificity and sensitivity of the qPCR were all 100% compared to 16S rRNA gene amplicon sequencing, as well as 98.4% and 100% compared to clinical diagnosis respectively. The qPCR yielded results within 3 h of sample processing, compared to several days for culture, significantly reducing turnaround time. The results suggest that the new qPCR assay developed in this study provides reliable and rapid detection of Nocardia spp. in the respiratory tracts and is expected to reduce the time required for diagnosing and treating nocardiosis.

Epidemiology of Nocardia Species at a Tertiary Hospital in Southern Taiwan, 2012 to 2020: MLSA Phylogeny and Antimicrobial Susceptibility

The identification and antimicrobial susceptibility of Nocardia spp. are essential for guiding antibiotic treatment. We investigated the species distribution and evaluated the antimicrobial susceptibility of Nocardia species collected in southern Taiwan from 2012 to 2020. A total of 77 Nocardia isolates were collected and identified to the species level using multi-locus sequence analysis (MLSA). The susceptibilities to 15 antibiotics for Nocardia isolates were determined by the broth microdilution method, and the MIC₅₀ and MIC₉₀ for each antibiotic against different species were analyzed. N. cyriacigeorgica was the leading isolate, accounting for 32.5% of all Nocardia isolates, and the prevalence of Nocardia isolates decreased in summer. All of the isolates were susceptible to trimethoprim/sulfamethoxazole, amikacin, and linezolid, whereas 90.9% were non-susceptible to cefepime and imipenem. The phylogenic tree by MLSA showed that the similarity between N. beijingensis and N. asiatica was as high as 99%, 73% between N. niigatensis and N. crassostreae, and 86% between N. cerradoensis and N. cyriacigeorgica. While trimethoprim/sulfamethoxazole, amikacin, and linezolid remained fully active against all of the Nocardia isolates tested, 90.9% of the isolates were non-susceptible to cefepime and imipenem.

Comprehensive Analysis of the Nocardia cyriacigeorgica Complex Reveals Five Species-Level Clades with Different Evolutionary and Pathogenicity Characteristics

Nocardia cyriacigeorgica is a common etiological agent of nocardiosis that has increasingly been implicated in serious pulmonary infections, especially in immunocompromised individuals. However, the evolution, diversity, and pathogenesis of N. cyriacigeorgica have remained unclear. Here, we performed a comparative genomic analysis using 91 N. cyriacigeorgica strains, 45 of which were newly sequenced in this study. Phylogenetic and average nucleotide identity (ANI) analyses revealed that N. cyriacigeorgica contained five species-level clades (8.6 to 14.6% interclade genetic divergence), namely, the N. cyriacigeorgica complex (NCC). Further pan-genome analysis revealed extensive differences among the five clades in nine functional categories, such as energy production, lipid metabolism, secondary metabolites, and signal transduction mechanisms. All 2,935 single-copy core genes undergoing purifying selection were highly conserved across NCC. However, clades D and E exhibited reduced selective constraints, compared to clades A to C. Horizontal gene transfer (HGT) and mobile genetic elements contributed to genomic plasticity, and clades A and B had experienced a higher level of HGT events than other clades. A total of 129 virulence factors were ubiquitous across NCC, such as the mce operon, hemolysin, and type VII secretion system (T7SS). However, different distributions of three toxin-coding genes and two new types of mce operons were detected, which might contribute to pathogenicity differences among the members of the NCC. Overall, our study provides comprehensive insights into the evolution, genetic diversity, and pathogenicity of NCC, facilitating the prevention of infections.

IMPORTANCENocardia species are opportunistic bacterial pathogens that can affect all organ systems, primarily the skin, lungs, and brain. N. cyriacigeorgica is the most prevalent species within the genus, exhibits clinical significance, and can cause severe infections when disseminated throughout the body. However, the evolution, diversity, and pathogenicity of N. cyriacigeorgica remain unclear. Here, we have conducted a comparative genomic analysis of 91 N. cyriacigeorgica strains and revealed that N. cyriacigeorgica is not a single species but is composed of five closely related species. In addition, we discovered that these five species differ in many ways, involving selection pressure, horizontal gene transfer, functional capacity, pathogenicity, and antibiotic resistance. Overall, our work provides important clues in dissecting the evolution, genetic diversity, and pathogenicity of NCC, thereby advancing prevention measures against these infections.

Identification and molecular epidemiology of routinely determined Streptococcus pneumoniae with negative Quellung reaction results

Background

Some streptococci strains identified as Streptococcus pneumoniae (S. pneumoniae) by routine clinical methods exhibiting negative Quellung reaction results may belong to other species of viridans group streptococci or non‐typeable S. pneumoniae. The purpose of this study was to investigate the identification and molecular characteristics of S. pneumoniae with negative Quellung reaction results.

Methods

One hundred and five isolates identified as S. pneumoniae using routine microbiological methods with negative Quellung reaction results were included. Multilocus sequence analysis (MLSA) was used as a gold standard in species identification, and the capacity of matrix‐assisted laser desorption ionization‐time of flight mass spectrometry (MALDI‐TOF MS) in identification was evaluated. Capsular genes and sequence types of S. pneumoniae isolates were determined by sequential multiplex PCR and multilocus sequence typing. Antimicrobial susceptibility patterns were determined via broth microdilution with a commercialized 96‐well plate.

Results

Among the isolates, 81 were identified as S. pneumoniae and 24 were S. pseudopneumoniae by MLSA. MALDI‐TOF MS misidentified six S. pneumoniae isolates as S. pseudopneumoniae and nine S. pseudopneumoniae isolates as S. pneumoniae or S. mitis/S. oralis. Thirty‐one sequence types (STs) were detected for these 81 S. pneumoniae isolates, and the dominant ST was ST‐bj12 (16, 19.8%). The non‐susceptibility rates of S. pseudopneumoniae were comparable to those of NESp strains.

Conclusions

Some S. pneumoniae isolates identified by routine methods were S. pseudopneumoniae. Most NESp strains have a different genetic background compared with capsulated S. pneumoniae strains. The resistance patterns of S. pseudopneumoniae against common antibiotics were comparable to those of NESp.