[Etiological characterization of invasive non-typhoid Salmonella strains in Guangdong Province from 2018 to 2022]

Objective: To understand the serotype distribution, drug resistance and molecular characterization of invasive non-typhoid Salmonella (iNTS) in Guangdong Province from 2018 to 2022 and provide scientific evidence for the prevention and treatment of blood flow infection caused by Salmonella. Methods: Serological identification, antimicrobial susceptibility testing, multilocus sequence typing (MLST), and whole genome sequencing were performed on Salmonella isolated from blood and stool samples in Guangdong from 2018 to 2022. Simultaneously, annotated the sequencing results for drug resistance genes and virulence factors by a microbial gene annotation system. Results: The 136 iNTS strains were divided into 25 serotypes, and Salmonella enteritidis accounted for 38.24% (52/136). The OR of other iNTS serotypes were calculated with Salmonella typhimurium as the control. The OR values of Oreninburg, Rysson, and Pomona serotypes were the highest, which were 423.50, 352.92, and 211.75, respectively. The drug resistance rate of iNTS was 0.74%-66.91%, which was lower than that of non-iNTS (3.90%-77.21%). The main iNTS of drug resistance were ampicillin and tetracycline, with resistance rates of 66.91% (91/136) and 50.00% (68/136), respectively, while the resistance rates to ciprofloxacin (5.88%,8/136), ceftazidime (5.88%,8/136), gentamicin (5.13%,7/136) and cefoxitin (0.74%, 1/136) were relatively low. iNTS carried a variety of drug-resistance genes and virulence factors, but no standard virulence factor distribution has been found. MLST cluster analysis showed that iNTS was divided into 26 sequence types, and ST11 accounted for 38.24% (52/136). Conclusions: The iNTS strains in Guangdong were dominated by Salmonella enteritidis, of which three serotypes, Oreninburg, Rison, and Pomona, may be associated with a higher risk of invasive infection during 2018 to 2022. iNTS was sensitive to clinical first-line therapeutic drugs (cephalosporins and fluoroquinolones), with highly diverse sequences and clear phylogenetic branches. ST11 was the local dominant clone group.

Global clonal spread of mcr-3-carrying MDR ST34 Salmonella enterica serotype Typhimurium and monophasic 1,4,[5],12:i:- variants from clinical isolates

OBJECTIVES

To investigate the prevalence and transmission of mcr-3 among Salmonella enterica serotype Typhimurium and 1,4,[5],12:i:-.

METHODS

A total of 4724 clinical Salmonella isolates were screened for the presence of mcr-3 in China during 2014-19. The clonal relationship of the mcr-3-positive isolates and their plasmid contents and complete sequence were also characterized based on WGS data from the Illumina and MinION platforms.

RESULTS

We identified 10 mcr-3-positive isolates, and all were MDR, mostly resistant to colistin, cefotaxime, ciprofloxacin, doxycycline and florfenicol. mcr-3 was co-present with blaCTX-M-55-qnrS1 on hybrid ST3-IncC-FII conjugatable plasmids (n = 6) and an ST3-IncC non-conjugatable plasmid (n = 1) and embedded into a pCHL5009T-like IncFII plasmid on the Salmonella chromosome (n = 3). Four distinctive genetic contexts surrounded mcr-3 and all but one were closely related to each other and to the corresponding region of IncFII plasmid pCHL5009T. IS15DI was most likely the vehicle for integration of mcr-3-carrying IncFII plasmids into ST3-IncC plasmids and the chromosome and for shaping the MDR regions. In addition, a phylogenetic tree based on the core genome revealed a unique Salmonella lineage (≤665 SNPs) that contained these 10 mcr-3-positive isolates and another 38 (33 from patients) mcr-3-positive Salmonella from five countries. In particular, most of the 51 mcr-3-positive isolates belonged to ST34 and harboured diverse antibiotic resistance genes (ARGs), including mcr-3-blaCTX-M-55-qnrS1, and possessed similar ARG profiles.

CONCLUSIONS

Our findings revealed global clonal spread of MDR ST34 Salmonella from clinical isolates co-harbouring mcr-3 with blaCTX-M-55 and qnrS1 and a flexibility of mcr-3 co-transmittance with other ARGs mediated by mobile genetic elements.

The immunodominant and neutralization linear epitopes for SARS-CoV-2

Although vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are under development, the antigen epitopes on the virus and their immunogenicity are poorly understood. Here, we simulate the 3D structures and predict the B cell epitopes on the spike (S), envelope (E), membrane (M), and nucleocapsid (N) proteins of SARS-CoV-2 using structure-based approaches and validate epitope immunogenicity by immunizing mice. Almost all 33 predicted epitopes effectively induce antibody production, six of these are immunodominant epitopes in individuals, and 23 are conserved within SARS-CoV-2, SARS-CoV, and bat coronavirus RaTG13. We find that the immunodominant epitopes of individuals with domestic (China) SARS-CoV-2 are different from those of individuals with imported (Europe) SARS-CoV-2, which may be caused by mutations on the S (G614D) and N proteins. Importantly, we find several epitopes on the S protein that elicit neutralizing antibodies against D614 and G614 SARS-CoV-2, which can contribute to vaccine design against coronaviruses.

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B cell epitopes of SARS-CoV-2 are obtained using structure-based approaches

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The predicted epitopes effectively induce robust antibody responses

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D614 and G614 SARS-CoV-2 display different immunodominant epitopes

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Epitopes on S protein elicit D614 and/or G614 SARS-CoV-2-neutralizing antibodies

First co-infection case of melioidosis and Japanese encephalitis in China

BACKGROUND

Melioidosis is endemic in Southeast Asia and northern Australia. Infection usually follows percutaneous inoculation or inhalation or ingestion of the causative bacterium, Burkholderia pseudomallei, which is present in soil and surface water in endemic regions. Japanese encephalitis (JE) is a vector-borne viral zoonosis caused by Japanese encephalitis virus (JEV), leading to epidemic encephalitis in Southeast Asia. Both B. pseudomallei and JEV have spread dominantly in the Hainan and Guangdong provinces in China. Here we reported the first case of co-infection of B. pseudomallei and JEV, which was discovered in Huizhou in the Guangdong province in June 2016.

CASE PRESENTATION

A 52-year-old man was admitted to the hospital with acute febrile illness and headache, diagnosed as respiratory infection, central nervous system (CNS) infection, septicemia, and hepatic dysfunction. Based on B. pseudomallei-positive blood and cerebrospinal fluid (CSF) cultures, the patient was diagnosed with melioidosis and treated aggressively with antibiotics. However, the patient failed to make a full recovery. Further laboratory tests focused on CNS infection were conducted. The co-infection of B. pseudomallei and JEV was confirmed after the positive IgM antibodies of JEV were detected in both CSF and blood. After diagnosis of co-infection with B. pseudomallei and JEV, the patient was provided supportive care in hospital and recovered after approximately 3 weeks.

CONCLUSION

Given the possibility of co-infection of B. pseudomallei and JEV, as well as variable case presentations, it is critical to enhance the awareness, detection, and treatment of co-infection in regard to melioidosis.

[Circulation and etiological characterization of Salmonella enterica serotype in human in Guangdong province, 2007-2016]

Objective: To understand the circulation, drug resistance and molecular characteristics of Salmonella1, 4, [5], 12: i:- in human in Guangdong province. Methods:Salmonella1, 4, [5], 12: i:- isolated from diarrhea patients in Guangdong during 2007-2016 were detected for drug resistance, genes and PFGE characteristics. Results: A total of 2 960 strains Salmonella1, 4, [5], 12: i: - were isolated from human diarrhea cases during this period. The positive rates of the isolation increased year by year. The male to female ratio of the infection cases was 1.58∶1, and the infection mainly occurred in infants and young children. Except imipenem, Salmonella1, 4, [5], 12: i: - was resistant to other 17 antibiotics to some extent. The drug resistant rates to ceftazidime, cefotaxime and ciprofloxacin increased from 2011 to 2016. Multi-drug resistance was serious, for example, the multi-drug resistant strains with ASSuT accounted for 70.62% (435/616) and the multi-drug resistant strains with ACSuGSTTm accounted for 27.11% (167/616). The lack of fljA, fljB and hin genes, as well as the retaining of iroB, STM2740, STM2757 genes, resulted in the unable expression of FljBenx gene with 8 different defection profiles. There were 934 different PFGE patterns observed in 2 347 strains, which displayed a relatively large fingerprint polymorphism. The major PFGE pattern was JPXX01. GD0226, which was found in 97 strains, accounting for 4.13% (97/2 347). The PFGE patterns in 168 Salmonella1, 4, [5], 12: i: - strains were consistent with that of Salmonella typhimurium. Conclusions:Salmonella1,4,[5], 12: i: - strains has become the major serotype of Salmonella that cause diarrhea in human in Guangdong. The multi-drug resistance of Salmonella1,4, [5], 12: i: - was serious, and since the defection of fljA, fljB and hin genes, the expression of FljBenx protein failed. The PFGE results were diverse, which displayed polymorphism in inheritance.

[Etiologic characteristics of Shigella sonnei strains isolated from some areas of Guangdong province and Guangxi Zhuang Autonomous Region of China, 2014-2016]

Objective: To investigated the etiologic characteristics of Shigella (S.) sonnei strains causing outbreaks and sporadic cases in some areas of Guangdong province and Guangxi Zhuang Autonomous Region during 2014-2016. Methods: Fourteen S. sonnei strains isolated from outbreaks and 6 S. sonnei strains from sporadic cases from Guangdong and Liuzhou of Guangxi Zhuang Autonomous Region were tested for antimicrobial resistance and analyzed by pulsed-field gel electrophoresis (PFGE). Six typical strains were selected for whole genome sequencing typing and compared with 51 strains isolated both at home and abroad from NCBI genome database. Results: The antibiotic resistance test indicated the isolates had high resistance rate to ampicillin, tetracycline, gentamicin, trimethoprim/sulfamethoxazole and nalidixic acid, while sensitive to azithromycin, chloromycetin and imipenem. PFGE showed high similarity (93.2%) among the strains isolated from different areas. The whole genome sequencing analysis also revealed that all the typical strains were clustered into a same evolution branch, close to some strains from Korea. Conclusions: The S. sonnei strains isolated from some areas of Guangdong and Guangxi Zhuang Autonomous Region showed high resistance to commonly used antibiotics, but they were sensitive to azithromycin, chloramphenicol and imipenem. The isolates in this study also showed similar PFGE patterns and close phylogenic evolution.

No evidence of a role for mitochondrial complex I in Helicobacter pylori pathogenesis

BACKGROUND

Complex I is the first enzyme complex in the mitochondrial respiratory chain, responsible for generating a large fraction of energy during oxidative phosphorylation. Recently, it has been identified that complex I deficiency can result in increased inflammation due to the generation of reactive oxygen species by innate immune cells. As a reduction in complex I activity has been demonstrated in human stomachs with atrophic gastritis, we investigated whether complex I deficiency could influence Helicobacter pylori pathogenesis.

MATERIALS AND METHODS

Ndufs6^gt/gt mice have a partial complex I deficiency. Complex I activity was quantified in the stomachs and immune cells of Ndufs6^gt/gt mice by spectrophotometric assays. Ndufs6^gt/gt mice were infected with H. pylori and bacterial colonization assessed by colony-forming assay, gastritis assessed histologically, and H. pylori -specific humoral response quantified by ELISA.

RESULTS

The immune cells and stomachs of Ndufs6^gt/gt mice were found to have significantly decreased complex I activity, validating the model for assessing the effects of complex I deficiency in H. pylori infection. However, there was no observable effect of complex I deficiency on either H. pylori colonization, the resulting gastritis, or the humoral response.

CONCLUSIONS

Although complex I activity is described to suppress innate immune responses and is decreased during atrophic gastritis in humans, our data suggest it does not affect H. pylori pathogenesis.

[Study on Salmonella serotyping by use of Microsphere-based Liquid Array method]

OBJECTIVE

To understand the effect of serotyping on Salmonella isolates, by use of Microsphere-based Liquid Array method, among diarrhea patients, in Guangdong.

METHODS

Salmonella isolated from humans in Guangdong province were serotyped on the Microsphere-based Liquid Array platform with SSA kit.

RESULTS

A total of 4 942 Salmonella strains with 189 serotypes, were identified in Guangdong province in 2010-2014. The top 100 serotypes accounted for 98.08% (4 847/4 942) of all the strains. 98% of the top 100 species serotypes could completely be serotyped with SSA kit. In order to detect O antigen among 198 isolates with SSA kit, 181 strains were carrying the O antigen, with the coincidence rate as 100%. However, under the SSA, 98.32% (528/537) of the H antigen could be detected and were consistent with the traditional serum agglutination test. The coincidence rate of fljB gene was 93.09% (175/188), with false negative rate and false positive rate of fljB gene as 7.35% (9/134) and 7.41% (4/54) respectively. The coincidence rate of sdf gene and Vi gene were 100%. 11 out of the 12 Salmonella strains could not be serotyped under the traditional methods but were successfully serotyped by the molecular serotyping method.

CONCLUSIONS

Using the SSA kit, more than 96% of the anthropogenic Salmonella strains could be serotyped in Guangdong province. Comparing with the traditional methods, the coincidence rate of serotyping appeared over 98% . Under the Microsphere-based Liquid Array techniques, the molecular serotyping method appeared faster and more accurate on Salmonella serotyping than those traditional methods.

Deficiency in mitochondrial complex I activity due to Ndufs6 gene trap insertion induces renal disease

AIMS

Defects in the activity of enzyme complexes of the mitochondrial respiratory chain are thought to be responsible for several disorders, including renal impairment. Gene mutations that result in complex I deficiency are the most common oxidative phosphorylation disorders in humans. To determine whether an abnormality in mitochondrial complex I per se is associated with development of renal disease, mice with a knockdown of the complex I gene, Ndufs6 were studied.

RESULTS

Ndufs6 mice had a partial renal cortical complex I deficiency; Ndufs6gt/gt, 32% activity and Ndufs6gt/+, 83% activity compared with wild-type mice. Both Ndufs6gt/+ and Ndufs6gt/gt mice exhibited hallmarks of renal disease, including albuminuria, urinary excretion of kidney injury molecule-1 (Kim-1), renal fibrosis, and changes in glomerular volume, with decreased capacity to generate mitochondrial ATP and superoxide from substrates oxidized via complex I. However, more advanced renal defects in Ndufs6gt/gt mice were observed in the context of a disruption in the inner mitochondrial electrochemical potential, 3-nitrotyrosine-modified mitochondrial proteins, increased urinary excretion of 15-isoprostane F2t, and up-regulation of antioxidant defence. Juvenile Ndufs6gt/gt mice also exhibited signs of early renal impairment with increased urinary Kim-1 excretion and elevated circulating cystatin C.

INNOVATION

We have identified renal impairment in a mouse model of partial complex I deficiency, suggesting that even modest deficits in mitochondrial respiratory chain function may act as risk factors for chronic kidney disease.

CONCLUSION

These studies identify for the first time that complex I deficiency as the result of interruption of Ndufs6 is an independent cause of renal impairment.

Respiratory chain complex I deficiency caused by mitochondrial DNA mutations

Defects of the mitochondrial respiratory chain are associated with a diverse spectrum of clinical phenotypes, and may be caused by mutations in either the nuclear or the mitochondrial genome (mitochondrial DNA (mtDNA)). Isolated complex I deficiency is the most common enzyme defect in mitochondrial disorders, particularly in children in whom family history is often consistent with sporadic or autosomal recessive inheritance, implicating a nuclear genetic cause. In contrast, although a number of recurrent, pathogenic mtDNA mutations have been described, historically, these have been perceived as rare causes of paediatric complex I deficiency. We reviewed the clinical and genetic findings in a large cohort of 109 paediatric patients with isolated complex I deficiency from 101 families. Pathogenic mtDNA mutations were found in 29 of 101 probands (29%), 21 in MTND subunit genes and 8 in mtDNA tRNA genes. Nuclear gene defects were inferred in 38 of 101 (38%) probands based on cell hybrid studies, mtDNA sequencing or mutation analysis (nuclear gene mutations were identified in 22 probands). Leigh or Leigh-like disease was the most common clinical presentation in both mtDNA and nuclear genetic defects. The median age at onset was higher in mtDNA patients (12 months) than in patients with a nuclear gene defect (3 months). However, considerable overlap existed, with onset varying from 0 to >60 months in both groups. Our findings confirm that pathogenic mtDNA mutations are a significant cause of complex I deficiency in children. In the absence of parental consanguinity, we recommend whole mitochondrial genome sequencing as a key approach to elucidate the underlying molecular genetic abnormality.

Role of glutaredoxin1 and glutathione in regulating the activity of the copper-transporting P-type ATPases, ATP7A and ATP7B

The copper-transporting P-type ATPases (Cu-ATPases), ATP7A and ATP7B, are essential for the regulation of intracellular copper homeostasis. In this report we describe new roles for glutathione (GSH) and glutaredoxin1 (GRX1) in Cu homeostasis through their regulation of Cu-ATPase activity. GRX1 is a thiol oxidoreductase that catalyzes the reversible reduction of GSH-mixed disulfides to their respective sulfhydryls (deglutathionylation). Here, we demonstrated that glutathionylation of the Cu-ATPases and their interaction with GRX1 were affected by alterations in Cu levels. The data support our hypothesis that the Cu-ATPases serve as substrates for Cu-dependent GRX1-mediated deglutathionylation. This in turn liberates the Cu-ATPase cysteinyl thiol groups for Cu binding and transport. GSH depletion experiments led to reversible inhibition of the Cu-ATPases that correlated with effects on intracellular Cu levels and GRX1 activity. Finally, knockdown of GRX1 expression resulted in an increase in intracellular Cu accumulation. Together, these data directly implicate GSH and GRX1 with important new roles in redox regulation of the Cu-ATPases, through modulation of Cu binding by the Cu-ATPase cysteine motifs.

ATP7A transgenic and nontransgenic mice are resistant to high copper exposure

The protein affected in Menkes disease, ATP7A, is a copper (Cu)-transporting P-type ATPase that plays an important role in Cu homeostasis, but the full extent of this role has not been defined at a systemic level. Transgenic mice that overexpress the human ATP7A from the chicken beta-actin composite promoter (CAG) were used to further investigate the physiological function of ATP7A. Overexpression of ATP7A in the mice caused disturbances in Cu homeostasis, with depletion of Cu in some tissues, especially the heart. To investigate the effect of overexpression of ATP7A when dietary Cu intake was markedly increased, normal and transgenic mice were exposed to drinking water containing 300 mg/L of Cu as Cu acetate for 3 mo. Cu exposure resulted in partial restoration of heart Cu concentrations in male transgenic mice. Despite the extended period of Cu exposure, Cu concentrations in the liver remained relatively unaffected, with a significant increase in male nontransgenic mice. Liver pathology was unremarkable except for small areas of fibrosis that were detected only in livers of the Cu-exposed transgenic mice. Intracellular localization of ATP7A in various tissues was not affected by Cu exposure. Plasma Cu concentration and ceruloplasmin oxidase activity were reduced in both Cu-exposed transgenic and nontransgenic mice. The expression levels of other candidate Cu homeostatic proteins, endogenous Atp7b, ceruloplasmin, Ctr1, and transgenic ATP7A were not altered significantly by Cu exposure. Overall, mice are remarkably resistant to high Cu loads and the overexpression of ATP7A has only moderate effects on the response to Cu exposure.

Correction of a mouse model of Menkes disease by the human Menkes gene

The brindled mouse is an accurate model of the fatal human X-linked copper deficiency disorder, Menkes disease. Males carrying the mutant allele of the Menkes gene orthologue Atp7a die in the second week of life. To determine whether the genetic defect in the brindled mice could be corrected by expression of the human Menkes gene, male transgenic mice expressing ATP7A from the chicken beta-actin composite promoter (CAG) were mated with female carriers of the brindled mutation (Atp7a(Mo-br)). Mutant males carrying the transgene survived and were fertile but the copper defect was not completely corrected. Unexpectedly males corrected with one transgenic line (T25#5) were mottled and resembled carrier females, this effect appeared to be caused by mosaic expression of the transgene. In contrast, males corrected with another line (T22#2) had agouti coats. Copper concentrations in tissues of the rescued mutants also resembled those of the heterozygous females, with high levels in kidney (84.6+/-4.9 microg/g in corrected males vs. 137.0+/-44.3 microg/g in heterozygotes) and small intestine (15.6+/-2.5 microg/g in corrected males vs. 15.7+/-2.8 microg/g in heterozygotes). The results show that the Menkes defect in mice is corrected by the human Menkes gene and that adequate correction is obtained even when the transgene expression does not match that of the endogenous gene.

Alteration of copper physiology in mice overexpressing the human Menkes protein ATP7A

The Menkes protein (ATP7A) is defective in the Cu deficiency disorder Menkes disease and is an important contributor to the maintenance of physiological Cu homeostasis. To investigate more fully the role of ATP7A, transgenic mice expressing the human Menkes gene ATP7A from chicken beta-actin composite promoter (CAG) were produced. The transgenic mice expressed ATP7A in lung, heart, liver, kidney, small intestine, and brain but displayed no overt phenotype resulting from expression of the human protein. Immunohistochemical analysis revealed that ATP7A was found primarily in the cardiac muscle, smooth muscle of the lung, distal tubules of the kidney, intestinal enterocytes, and patches of hepatocytes, as well as in the hippocampus, cerebellum, and choroid plexus of the brain. In 60-day- and 300-day-old mice, Cu concentrations were reduced in most tissues, consistent with ATP7A playing a role in Cu efflux. The reduction in Cu was most pronounced in the hearts of older T22#2 females (24%), T22#2 males (18%), and T25#5 females (23%), as well as in the brains of 60-day-old T22#2 females and males (23% and 30%, respectively).