Characterization of quinolone resistance in Salmonella enterica serovar Typhimurium and its monophasic variants from food and patients in China.

OBJECTIVES: The study aimed to characterize the quinolone resistance of Salmonella enterica serovar Typhimurium and its monophasic variant (Salmonella enterica serovar 1,4,[5],12:i:-) isolated from food and patients in China. METHODS: All of the isolates were assessed for quinolone susceptibility via the broth microdilution method. Then, the isolates were checked for mutations within quinolone resistance-determining regions of gyrA, gyrB, parC, and parE and were examined for plasmid-mediated quinolone resistance genes. RESULTS: High rates of resistance to nalidixic acid in the S. Typhimurium (70.7%) and S. 1,4,[5],12:i:- (41.9%) isolates were observed, and a considerable proportion of isolates with reduced susceptibility to ciprofloxacin and levofloxacin were also detected. The high frequency of mutations in GyrA (60.8%) and a variety of genes (aac[6']-Ib-cr [23.2%], oqxAB [19.2%], qnrS [13.6%], and qnrA [3.2%]) conferring quinolone resistance in these Salmonella isolates were noteworthy. Lastly, the isolates carrying qnrS for transferability and transmission of the quinolone resistance were analysed by conjugation. Multiple locus variable-number tandem repeat analysis profiles indicated that some qnrS-positive isolates were clonally related, whilst the other isolates were genetically divergent. This suggested that both clonal spread of resistant strains and horizontal transmission of the plasmid-mediated resistance genes contributed to the dissemination of qnrS-positive Salmonella isolates. CONCLUSION: This study highlights the prevalence of quinolone-resistant S. Typhimurium and S. 1,4,[5],12:i:- in China, posing a threat to public health.

Nitrogen-metabolising microorganism analysis in rapid sand filters from drinking water treatment plant.

Sand filters (SFs) are common treatment processes for nitrogen pollutant removal in drinking water treatment plants (DWTPs). However, the mechanisms on the nitrogen-cycling role of SFs are still unclear. In this study, 16S rRNA gene amplicon sequencing was used to characterise the diversity and composition of the bacterial community in SFs from DWTPs. Additionally, metagenomics approach was used to determine the functional microorganisms involved in nitrogen cycle in SFs. Our results showed that Pseudomonadota, Acidobacteria, Nitrospirae and Chloroflexi dominated in SFs. Subsequently, 85 high-quality metagenome-assembled genomes (MAGs) were retrieved from metagenome datasets of selected SFs involving nitrification, assimilatory nitrogen reduction, denitrification and anaerobic ammonia oxidation (anammox) processes. Read mapping to reference genomes of Nitrospira and the phylogenetic tree of the ammonia monooxygenase subunit A gene, amoA, suggested that Nitrospira is abundantly found in SFs. Furthermore, according to their genetic content, a nitrogen metabolic model in SFs was proposed using representative MAGs and pure culture isolate. Quantitative real-time polymerase chain reaction (qPCR) showed that ammonia-oxidising bacteria (AOB) and archaea (AOA), and complete ammonia oxidisers (comammox) were ubiquitous in the SFs, with the abundance of comammox being higher than that of AOA and AOB. Moreover, we identified a bacterial strain with a high NO3-N removal rate as Pseudomonas sp. DW-5, which could be applied in the bioremediation of micro-polluted drinking water sources. Our study provides insights into functional nitrogen-metabolising microbes in SFs of DWTPs.

Highly efficient removal of Sb(V) from water by franklinite-containing nano-FeZn composites.

The existence of toxic and carcinogenic pentavalent antimony in water is a great safety problem. In order to remove antimony(V) from water, the purpose of this study was to prepare a novel graphene nano iron zinc (rGO/NZV-FeZn) photocatalyst via hydrothermal method followed by ultrasonication. Herein, weakly magnetic nano-Fe-Zn materials (NZV-FeZn, GACSP/NZV-FeZn, and rGO/NZV-FeZn) capable of rapid and efficient Sb(V) adsorption from water were prepared and characterised. In particular, rGO/NZV-FeZn was shown to comprise franklinite, Fe0, and graphite. Adsorption data were fitted by a quasi-second-order kinetic equation and Langmuir model, revealing that among these materials, NZV-FeZn exhibited the best Sb removal performance (543.9 mgSb gNZV-FeZn-1, R2 = 0.951). In a practical decontamination test, Sb removal efficiency of 99.38% was obtained for a reaction column filled with 3.5 g of rGO/NZV-FeZn. Column regenerability was tested at an initial concentration of 0.8111 mgSb L-1, and the treated water obtained after five consecutive runs complied with the GB5749-2006 requirement for Sb. rGO/NZV-FeZn was suggested to remove Sb(V) through adsorption-photocatalytic reduction and flocculation sedimentation mechanisms and, in view of its high cost performance, stability, and upscalable synthesis, was concluded to hold great promise for source water and wastewater treatment.

Genomic Analysis and Stability Evaluation of the Phenol-Degrading Bacterium Acinetobacter sp. DW-1 During Water Treatment.

Phenol is a toxic organic molecule that is widely detected in the natural environment, even in drinking water sources. Biological methods were considered to be a good tool for phenol removal, especially microbial immobilized technology. However, research on the "seed" bacteria along with microbial community analysis in oligotrophic environment such as drinking water system has not been addressed. In this study, Acinetobacter sp. DW-1 with high phenol degradation ability had been isolated from a drinking water biofilter was used as seeded bacteria to treat phenol micro-polluted drinking water source. Meanwhile, the whole genome of strain DW-1 was sequenced using nanopore technology. The genomic analysis suggests that Acinetobacter sp. DW-1 could utilize phenol via the ß-ketoadipate pathway, including the catechol and protocatechuate branches. Subsequently, a bio-enhanced polyhedral hollow polypropylene sphere (BEPHPS) filter was constructed to investigate the stability of the seeded bacteria during the water treatment process. The denatured gradient gel electrophoresis (DGGE) profile and the quantification of phenol hydroxylase gene results indicate that when the BEPHPS filter was operated for 56 days, Acinetobacter sp. was still a persistent and competitive bacterium in the treatment group. In addition, 16S rRNA gene amplicon sequencing results indicate that Acinetobacter sp., as well as Pseudomonas sp., Nitrospira sp., Rubrivivax sp. were the predominant bacteria in the treatment group, which were different from that in the CK group. This study provides a better understanding of the mechanisms of phenol degradation by Acinetobacter sp. DW-1 at the gene level, and provides new insights into the stability of seeded bacteria and its effects on microbial ecology during drinking water treatment.

Prevalence, Virulence, Antimicrobial Resistance, and Molecular Characterization of Pseudomonas aeruginosa Isolates From Drinking Water in China.

Pseudomonas aeruginosa is an important opportunistic pathogen and remains a major threat to the microbial safety of drinking water. There is a lack of comprehensive data on P. aeruginosa contamination in drinking water in China. Therefore, this study aimed to determine the prevalence, genetic diversity, virulence genes, and antimicrobial resistance of P. aeruginosa isolated from mineral water and spring water in China. From January 2013 to January 2014, 314 drinking water samples were collected from 23 cities in China. Of the collected samples, 77 (24.5%) were contaminated with P. aeruginosa, and these comprised 34 raw water (30.4%), 39 activated carbon-filtered water (30.6%), and four final water product (3.9%). A total of 132 P. aeruginosa isolates were obtained, and all of them showed the presence of virulence genes, with the detection rates of ExoU, ExoS, phzM, toxA, and lasB genes being 7.6, 86.3, 95.5, 89.4, and 100%, respectively. All isolates were sensitive to the 14 antibiotics (ciprofloxacin, levofloxacin, ofloxacin, norfloxacin, gentamicin, tobramycin, amikacin, polymyxin B, imipenem, meropenem, aztreonam, ceftazidime, cefepime, and piperacillin/tazobactam) tested. The 132 isolates were categorized into 42 sequence types according to multilocus sequence typing, and ST235 accounted for 8.3% (11) of the total isolates. Thus, this study provides comprehensive data on the prevalence and characteristics of P. aeruginosa in drinking water in China and can aid in developing preventive measures against contamination during the drinking water treatment process.

Occurrence and Characterization of Fungi and Mycotoxins in Contaminated Medicinal Herbs.

Traditional medicinal herbs are widely used and may be contaminated with mycotoxigenic fungi during cultivation, harvesting, and storage, causing spoilage and mycotoxin production. We evaluated the predominant mycoflora and extent of mycotoxin contaminations in 48 contaminated samples of 13 different medicinal herbs. In total, 70.8% of herbs were slightly contaminated with aflatoxins (<5 µg kg-1). Codonopsis radix samples contained ochratoxin A (OTA) (360-515 µg kg-1), and Scutellariae radix samples contained OTA (49-231 µg kg-1) and citrinin (15-53 µg kg-1). Forty samples (83.3%) contained fungal contamination. Sixty-nine strains were characterized via morphological and molecular identification. The predominant mycoflora comprised four genera, Aspergillus spp. (26.1%), Penicillium spp. (24.6%), Rhizopus spp. (14.5%), and Trichoderma spp. (11.6%). Aflatoxins, OTA, and citrinin were detected in 37 cultures by high-performance liquid chromatography-tandem mass spectrometry. Approximately 21.6% of Aspergillus and Penicillium isolates produced mycotoxins. One Penicillium polonicum strain isolated from Scutellariae radix synthesized citrinin. Multiplex PCR analysis showed that three Aspergillus flavus strains harbored aflatoxin biosynthesis genes. One Aspergillus flavus strain isolated from Amomi fructus produced AFB1 and AFB2. To the best of our knowledge, the citrinin production by Aspergillus chevalieri and Penicillium sacculum was first reported in this study, which poses a potential risk of mycotoxin contamination in medicinal herbs.

Composition and Dynamics of Bacterial Communities in a Full-Scale Mineral Water Treatment Plant.

The aim of this study was to gain insight into the bacterial composition and dynamics in a mineral water treatment system (MWTS). The bacterial community of a full-scale mineral water treatment plant in the Maofeng Mountain, South China, was studied using high-throughput sequencing combined with cultivation-based techniques in both the dry and wet season. Overall, adenosine tri-phosphate (ATP) concentration (6.47 × 10-11 - 3.32 × 10-8 M) and heterotrophic plate counts (HPC) (3 - 1.29 × 103 CFU/mL) of water samples in the wet season were lower than those (ATP concentration 5.10 × 10-11 - 6.96 × 10-8 M, HPC 2 - 1.97 × 103 CFU/mL) in the dry season throughout the whole MWTS. The microbial activity and biomass of water samples obviously changed along with treatment process. All 300 isolates obtained using cultivation-based techniques were distributed in 5 phyla, 7 classes, and 19 genera. Proteobacteria accounted for 55.7% (167) of the total isolates, among which predominant genus was Pseudomonas (19.3%). Illumina sequencing analysis of 16s rRNA genes revealed 15 bacterial phyla (relative abundance >0.1%) as being identified in all water samples. Among these, Proteobacteria constituted the dominant bacteria microbiota in all water samples. A large shift in the proportion of Bacteroidetes, Actinobacteria, and Firmicutes was obtained during the treatment process, with the proportion of Bacteroidetes, Actinobacteria decreasing sharply, whereas that of Firmicutes increased and predominated in the final water product. The core microbiome, which was still present in whole MWTS comprised several genera including Pseudomonas, Acinetobacter, Clostridium, and Mycobacterium, that contain species that are opportunistic pathogens, suggesting a potential threat for mineral water microbiology safety. This study is the first to investigate the bacterial community of a full-scale mineral water treatment plant in China. The results provided data regarding the bacteria composition and dynamics in an MWTS, which will contribute to the beneficial manipulation of the mineral water microbiome.

Chromium ion removal from raw water by magnetic iron composites and Shewanella oneidensis MR-1.

In this study, nanoiron active carbon composites (NZVI/GAC) were used to remove chromium ions from raw water. The composites were synthesized from a novel formula of biological activated carbon and characterized by various techniques. The adsorption test data were fit by a pseudo-second-order kinetic model and Langmuir model. The qe and R2 values were 187 mg Cr/g and 0.9960, respectively, with 0.2 g/L NZVI/GAC at an initial concentration of 118 mg/L Cr according to the Langmuir isotherm model. Moreover, a Cr6+ detoxification reactor was constructed with the magnetic iron composite. The results indicated that the synthesized magnetic iron composite was a significant adsorbent for Cr6+ removal from aqueous solutions. The detoxification reactor was able to remove Cr6+ from raw water at an initial concentration of 26.5 mg/L within a short time period (3-5 min), with a removal efficiency of up to 99.90% and a treatment capacity of 45.0 mg Cr6+/g of adsorbent; the Cr6+ concentrations in the outflow met the GB5749-2006 requirements for drinking water. A synergistic effect between NZVI/GAC and a suspension of the bacterium Shewanella oneidensis MR-1 was found, showing that this bacterium can be used as a regeneration agent for iron-depleted activated carbon materials.

Isolation and Transcriptome Analysis of Phenol-Degrading Bacterium From Carbon-Sand Filters in a Full-Scale Drinking Water Treatment Plant.

Phenol is a typical organic contaminant in the environment. To date, the biodegradation of phenol by microorganisms remains the preferred method for its removal and remediation, but data on phenol removal by drinking water biofilters are lacking. In this study, we used high-throughput sequencing to investigate the microbial community structure in a carbon-sand biofilter. The results indicated that the predominant bacterial group was Bacilli, followed by Gammaproteobacteria, Clostridia, and Alphaproteobacteria. In addition, a strain was capable of degrading phenol at low concentrations of 500 µg/L within 100 min was isolated and identified as Rhodococcus sp. CS-1. Transcriptome analysis results showed that Rhodococcus sp. CS-1 was able to degrade phenol via both the catechol and protocatechuate branch of the ß-ketoadipate pathway. Furthermore, some novel candidate biomarkers (copper oxidase, copper chaperone, and MarR/DeoR/TetR family transcriptional regulators) were successfully identified to be potentially involved in phenol biodegradation. This study indicates that carbon-sand filters have the potential for remediation of phenol. The application of native microorganisms to drinking water treatment system is an adaptive strategy in oligotrophic water environments.

Prevalence and Molecular and Antimicrobial Characteristics of Cronobacter spp. Isolated From Raw Vegetables in China.

Cronobacter spp. is a foodborne pathogen that causes life-threatening and invasive diseases, such as necrotizing enterocolitis, meningitis, and sepsis. In this study, we aimed to investigate the prevalence, molecular characteristics and antimicrobial resistance of Cronobacter spp. in raw vegetables marketed in China. Based on dietary habits in China, 403 raw vegetables that could be eaten without additional cooking were collected. Of the 403 samples tested, 122 (30.27%) were positive for Cronobacter spp., and the contamination levels exceeded 110 most probable number (MPN)/g for 16.39% (20/122) of the samples. Coriander samples had the highest contamination rate of 52.81%, and the MPN values of 19.15% of positive coriander samples exceeded 100 MPN/g. Eleven serotypes were identified among 171 isolates, with Cronobacter sakazakii serogroup O1 (41 isolates) being the dominant serotype. Molecular characterization indicated that there was quite high genetic diversity in Cronobacter spp., and multilocus sequence typing analyses yielded 106 sequence types (STs), 55 of which were newly identified. Notably, the most prevalent ST (eight isolates) was C. malonaticus ST60, which appeared in a recent clinical infectious disease study in China. Five C. sakazakii ST4, seven C. malonaticus ST7, and three C. sakazakii ST8 confirmed as pathogenic STs in other countries were also detected in this study. Furthermore, all isolates were susceptible to amikacin, amoxicillin-clavulanic, cefepime, ciprofloxacin, and imipenem, but some isolates exhibited a high ratio of resistance to cephalothin (59.65%). In this study, the high contamination rate and the detection of pathogenic and new STs in raw vegetables indicated potential hazards to customers. To the best of our knowledge, this is the first report to provide valuable information on the contamination status of Cronobacter spp. in vegetables that can be eaten raw in China.

Prevalence and Genetic Diversity of Enterococcus faecalis Isolates from Mineral Water and Spring Water in China.

Enterococcus faecalis is an important opportunistic pathogen which is frequently detected in mineral water and spring water for human consumption and causes human urinary tract infections, endocarditis and neonatal sepsis. The aim of this study was to determine the prevalence, virulence genes, antimicrobial resistance and genetic diversity of E. faecalis from mineral water and spring water in China. Of 314 water samples collected from January 2013 to January 2014, 48 samples (15.3%) were contaminated E. faecalis. The highest contamination rate occurred in activated carbon filtered water of spring water (34.5%), followed by source water of spring water (32.3%) and source water of mineral water (6.4%). The virulence gene test of 58 E. faecalis isolates showed that the detection rates of asa1, ace, cylA, gelE and hyl were 79.3, 39.7, 0, 100, 0%, respectively. All 58 E. faecalis isolates were not resistant to 12 kinds of antibiotics (penicillin, ampicillin, linezolid, quinupristin/dalfopristin, vancomycin, gentamicin, streptomycin, ciprofloxacin, levofloxacin, norfloxacin, nitrofurantoin, and tetracycline). Enterobacterial repetitive intergenic consensus-PCR classified 58 isolates and three reference strains into nine clusters with a similarity of 75%. This study is the first to investigate the prevalence of E. faecalis in mineral water and spring water in China. The results of this study suggested that spring water could be potential vehicles for transmission of E. faecalis.

Acinetobacter sp. DW-1 immobilized on polyhedron hollow polypropylene balls and analysis of transcriptome and proteome of the bacterium during phenol biodegradation process.

Phenol is a hazardous chemical known to be widely distributed in aquatic environments. Biodegradation is an attractive option for removal of phenol from water sources. Acinetobacter sp. DW-1 isolated from drinking water biofilters can use phenol as a sole carbon and energy source. In this study, we found that Immobilized Acinetobacter sp. DW-1cells were effective in biodegradation of phenol. In addition, we performed proteome and transcriptome analysis of Acinetobacter sp. DW-1 during phenol biodegradation. The results showed that Acinetobacter sp. DW-1 degrades phenol mainly by the ortho pathway because of the induction of phenol hydroxylase, catechol-1,2-dioxygenase. Furthermore, some novel candidate proteins (OsmC-like family protein, MetA-pathway of phenol degradation family protein, fimbrial protein and coenzyme F390 synthetase) and transcriptional regulators (GntR/LuxR/CRP/FNR/TetR/Fis family transcriptional regulator) were successfully identified to be potentially involved in phenol biodegradation. In particular, MetA-pathway of phenol degradation family protein and fimbrial protein showed a strong positive correlation with phenol biodegradation, and Fis family transcriptional regulator is likely to exert its effect as activators of gene expression. This study provides valuable clues for identifying global proteins and genes involved in phenol biodegradation and provides a fundamental platform for further studies to reveal the phenol degradation mechanism of Acinetobacter sp.

Synthesis of precipitating chromogenic/fluorogenic ß-glucosidase/ß-galactosidase substrates by a new method and their application in the visual detection of foodborne pathogenic bacteria.

We developed a new efficient method for the synthesis of important indoxyl glycoside substrates for ß-glucosidase and ß-galactosidase by using 1-acetylindol-3-ones as intermediates. This method was used to synthesise novel precipitating fluorogenic substrates for ß-glucosidase based on 2-(benzothiazol-2'-yl)-phenols. We also assessed the application of these substrates in the detection of foodborne pathogenic bacteria.

[Application of Multiplex PCR for the Screening Di(b-),Co(a-) Rare Blood Group in Chinese Xinjiang Minorities].

OBJECTIVE: To investigate the distribution of Colton and Diego rare blood group antigens of blood donors in Chinese Xinjiang minorities. METHODS: A multiplex PCR was applied to screen for alleles antigens Dia and Cob in 1020 randomly selected healthy donors of Chinese Xinjiang minorities by using each 5 samples mixed detection method. The samples in the positive pools were further tested individually. Furthermore, the positive samples, including Di(a+b-)/Di(a+b+) and Co(a-b+)/ Co(a+b+) genotypes were tested via 2 PCR-SSP assays for high frequency allele Dib and Coa to get the rare genotypes Di(b-), Co(a-). RESULTS: Among 1020 samples 12 cases with Cob+ allele, 45 cases with Di(a+b+) and 1 case with Di(a+b-) were identified. CONCLUSION: The frequencies of Dia and Cob alleles are 2.30% and 0.59%, respectively. The information of rare blood donors obtained from the screening can provide a reference for matched blood transfusion, and further enrich the National Rare Blood Bank of China.

Prevalence of Staphylococcus aureus and Methicillin-Resistant Staphylococcus aureus in Retail Ready-to-Eat Foods in China.

Staphylococcus aureus, particularly methicillin-resistant S.aureus (MRSA), is a life-threatening pathogen in humans, and its presence in food is a public health concern. MRSA has been identified in foods in China, but little information is available regarding MRSA in ready-to-eat (RTE) foods. We aimed to investigate the prevalence of S. aureus and MRSA in Chinese retail RTE foods. All isolated S. aureus were tested for antimicrobial susceptibility, and MRSA isolates were further characterized by multilocus sequence typing (MLST) and staphylococcal cassette chromosome mec (SCCmec) typing. Of the 550 RTE foods collected from 2011 to 2014, 69 (12.5%) were positive for S. aureus. Contamination levels were mostly in the range of 0.3-10 most probable number (MPN)/g, with five samples exceeding 10 MPN/g. Of the 69 S. aureus isolates, seven were identified as MRSA by cefoxitin disc diffusion test. Six isolates were mecA-positive, while no mecC-positive isolates were identified. In total, 75.8% (47/62) of the methicillin-susceptible S. aureus isolates and all of the MRSA isolates were resistant to three or more antibiotics. Amongst the MRSA isolates, four were identified as community-acquired strains (ST59-MRSA-IVa (n = 2), ST338-MRSA-V, ST1-MRSA-V), while one was a livestock-associated strain (ST9, harboring an unreported SCCmec type 2C2). One novel sequence type was identified (ST3239), the SCCmec gene of which could not be typed. Overall, our findings showed that Chinese retail RTE foods are likely vehicles for transmission of multidrug-resistant S. aureus and MRSA lineages. This is a serious public health risk and highlights the need to implement good hygiene practices.

Community Analysis and Recovery of Phenol-degrading Bacteria from Drinking Water Biofilters.

Phenol is a ubiquitous organic contaminant in drinking water. Biodegradation plays an important role in the elimination of phenol pollution in the environment, but the information about phenol removal by drinking water biofilters is still lacking. Herein, we study an acclimated bacterial community that can degrade over 80% of 300 mg/L phenol within 3 days. PCR detection of genotypes involved in bacterial phenol degradation revealed that the degradation pathways contained the initial oxidative attack by phenol hydroxylase, and subsequent ring fission by catechol 1,2-dioxygenase. Based on the PCR denatured gradient gel electrophoresis (PCR-DGGE) profiles of bacteria from biological activated carbon (BAC), the predominant bacteria in drinking water biofilters including Delftia sp., Achromobacter sp., and Agrobacterium sp., which together comprised up to 50% of the total microorganisms. In addition, a shift in bacterial community structure was observed during phenol biodegradation. Furthermore, the most effective phenol-degrading strain DW-1 that correspond to the main band in denaturing gradient gel electrophoresis (DGGE) profile was isolated and identified as Acinetobacter sp., according to phylogenetic analyses of the 16S ribosomal ribonucleic acid (rRNA) gene sequences. The strain DW-1 also produced the most important enzyme, phenol hydroxylase, and it also exhibited a good ability to degrade phenol when immobilized on granular active carbon (GAC). This study indicates that the enrichment culture has great potential application for treatment of phenol-polluted drinking water sources, and the indigenous phenol-degrading microorganism could recover from drinking water biofilters as an efficient resource for phenol removal. Therefore, the aim of this study is to draw attention to recover native phenol-degrading bacteria from drinking water biofilters, and use these native microorganisms as phenolic water remediation in drinking water sources.

Molecular characterization of new emerging GII.17 norovirus strains from South China.

Noroviruses are still the primary cause of non-bacterial acute gastroenteritis worldwide. Recently, a novel GII.17 norovirus variant emerged and caused an infection peak in the cold season of 2014/2015 in some Asian countries, including China. In this study, in order to understand the evolutionary advantage of the novel variant, complete genomic sequences of GII.17 NoV strains from South China were comprehensively analyzed. Pairwise alignments of new GII.17 genomes with representative sequences of each GII genotype were performed. Inconsistent homology was observed between different protein-encoding regions, of which VPg (NS5) and P2 were found to be the most conserved and variable ones, respectively. The differences between new sequences and other reported GII.17 genomes were also compared, and 84 mismatched nucleotides were found, resulting in 15 amino acid changes. Then, all capsid sequences of different GII.17 NoV variants were collected for multiple alignments, and a total of 87 spots were identified during their evolution process. Homology modeling of capsid proteins of four GII.17 variants was carried out based on comparison with GII.4 VA387 strain, and structural differences were mainly embodied in five extended loops. Furthermore, positions of potential conformational epitope regions of new GII.17 variants were found more similar or adjacent to those of GII.4 rather than those of the former GII.17 variants. In summary, nine GII.17 strains from South China were extensively characterized based on their complete genomes, and a different distribution pattern of epitope residues was predicted on the new GII.17 variant capsid from that of the former ones.

Analysis of Multilocus Sequence Typing and Virulence Characterization of Listeria monocytogenes Isolates from Chinese Retail Ready-to-Eat Food.

Eighty Listeria monocytogenes isolates were obtained from Chinese retail ready-to-eat (RTE) food and were previously characterized with serotyping and antibiotic susceptibility tests. The aim of this study was to characterize the subtype and virulence potential of these L. monocytogenes isolates by multilocus sequence typing (MLST), virulence-associate genes, epidemic clones (ECs), and sequence analysis of the important virulence factor: internalin A (inlA). The result of MLST revealed that these L. monocytogenes isolates belonged to 14 different sequence types (STs). With the exception of four new STs (ST804, ST805, ST806, and ST807), all other STs observed in this study have been associated with human listeriosis and outbreaks to varying extents. Six virulence-associate genes (inlA, inlB, inlC, inlJ, hly, and llsX) were selected and their presence was investigated using PCR. All strains carried inlA, inlB, inlC, inlJ, and hly, whereas 38.8% (31/80) of strains harbored the listeriolysin S genes (llsX). A multiplex PCR assay was used to evaluate the presence of markers specific to epidemic clones of L. monocytogenes and identified 26.3% (21/80) of ECI in the 4b-4d-4e strains. Further study of inlA sequencing revealed that most strains contained the full-length InlA required for host cell invasion, whereas three mutations lead to premature stop codons (PMSC) within a novel PMSCs at position 326 (GAA → TAA). MLST and inlA sequence analysis results were concordant, and different virulence potentials within isolates were observed. These findings suggest that L. monocytogenes isolates from RTE food in China could be virulent and be capable of causing human illness. Furthermore, the STs and virulence profiles of L. monocytogenes isolates have significant implications for epidemiological and public health studies of this pathogen.

Molecular epidemiology of noroviruses associated with sporadic gastroenteritis in Guangzhou, China, 2013-2015.

Norovirus diarrhea is a great threat to public health worldwide. To characterize the prevalence of circulating noroviruses associated with sporadic gastroenteritis cases in Guangzhou, 215 stool specimens were collected during two consecutive cold seasons in 2013-2015. Noroviruses were detected in 25 (11.63 %) samples, and GII.4 (6/9) and GII.17 (10/16) were identified as the most predominant variants of each of those seasons. The remaining strains belonged to the genotypes GII.P12/GII.3, GII.2, and GI.Pb/GI.6. The phylogenetic relationships of the GII.17 strains were analyzed based on their capsid protein sequences. This study suggests a significant shift of predominant variants associated with sporadic gastroenteritis in Guangzhou.

Development of a sensitive method for directly sequencing GII.4 norovirus genome.

A new strategy was proposed for amplifying and sequencing GII.4 norovirus genomes directly. A set of primer pairs was rationally designed, which amplified 6 overlapping fragments encompassing the whole genome. The sensitivity of new primers was comparable to that of detection primers, and 10 viral genome sequences were successfully obtained.