Genetic Diversity, Antibiotic Resistance, and Pathogenicity of Aeromonas Species from Food Products in Shanghai, China.

Objective: Aeromonas has recently been recognized as an emerging human pathogen. Aeromonas-associated diarrhea is a phenomenon occurring worldwide. This study was designed to determine the prevalence, genetic diversity, antibiotic resistance, and pathogenicity of Aeromonas strains isolated from food products in Shanghai. Methods: Aeromonas isolates ( n = 79) collected from food samples were analyzed using concatenated gyrB- cpn60 sequencing. The antibiotic resistance of these isolates was determined using antimicrobial susceptibility testing. Pathogenicity was assessed using ß-hemolytic, extracellular protease, virulence gene detection, C. elegans liquid toxicity (LT), and cytotoxicity assays. Results: Eight different species were identified among the 79 isolates. The most prevalent Aeromonas species were A. veronii [62 (78.5%)], A. caviae [6 (7.6%)], A. dhakensis [3 (3.8%)], and A. salmonicida [3 (3.8%)]. The Aeromonas isolates were divided into 73 sequence types (STs), of which 65 were novel. The isolates were hemolytic (45.6%) and protease-positive (81.0%). The most prevalent virulence genes were act (73.4%), fla (69.6%), aexT (36.7%), and ascV (30.4%). The results of C. elegans LT and cytotoxicity assays revealed that A. dhakensis and A. hydrophila were more virulent than A. veronii, A. caviae, and A. bivalvium. Antibiotic resistance genes [ tetE, blaTEM, tetA, qnrS, aac(6)-Ib, mcr -1, and mcr-3] were detected in the isolates. The multidrug-resistance rate of the Aeromonas isolates was 11.4%, and 93.7% of the Aeromonas isolates were resistant to cefazolin. Conclusion: The taxonomy, antibiotic resistance, and pathogenicity of different Aeromonas species varied. The Aeromonas isolates A. dhakensis and A. hydrophila were highly pathogenic, indicating that food-derived Aeromonas isolates are potential risks for public health and food safety. The monitoring of food quality and safety will result in better prevention and treatment strategies to control diarrhea illnesses in China.

Comparative Study of the Genetic Diversity, Antimicrobial Resistance, and Pathogenicity of Aeromonas Isolates from Clinical Patients and Healthy Individuals.

OBJECTIVE: This study was performed to compare the genetic diversity, virulence, and antimicrobial resistance of Aeromonas strains isolated from patients and healthy individuals. METHODS: A total of 38 clinical strains and 19 strains from healthy individuals were isolated from the samples collected in Ma'anshan City, Anhui Province. Their taxonomy was investigated using concatenated gyrB- cpn60 sequences, and their resistance to 12 antibiotics was evaluated. The pathogenicity of these strains was examined through beta-hemolysis, protease activity, and virulence gene assays. RESULTS: The 57 Aeromonas strains were divided into 55 sequence types. Of these types, 21 were novel, suggesting that their genetic diversity was high. These Aeromonas isolates could be divided into 7 species, and the positive rates of beta-hemolysis and protease activity were 49.1% and 73.7%, respectively. The detection rate of clinical patients in terms of beta-hemolysis and protease activity was higher than that of healthy individuals. Among the four most common Aeromonas strains, A. dhakensis had the highest detection rate of virulence genes. The multidrug resistance rate of the clinical isolates was much higher than that of the strains isolated from healthy individuals. CONCLUSIONS: The taxonomy, virulence properties, and antibiotic resistance of Aeromonas isolates from patients differ from those of the isolates from healthy individuals.

Emergence of an NDM-5-Producing Escherichia coli Sequence Type 410 Clone in Infants in a Children's Hospital in China.

PURPOSE: Outbreaks of infection due to carbapenem-resistant Enterobacterales (CRE), including New Delhi metallo-ß-lactamase (NDM)-producing Escherichia coli, have been increasingly reported worldwide, primarily in adults and rarely in children. The goal of this study was to characterize an outbreak of infection caused by NDM-5-producing E. coli in a children's hospital in China. METHODS: A total of 86 CRE isolates were collected from 85 hospitalized children between June 2017 and May 2018. These isolates were subjected to multiple phenotypic and molecular tests, including in vitro antimicrobial susceptibility testing, PCR, pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and whole-genome sequencing (WGS). RESULTS: Among the 86 CRE isolates, we identified 9 NDM-5-producing E. coli isolates, with 5 of them sharing the same PFGE pattern, same MLST type (ST410), same plasmid replicon type (IncFII), and nearly the same set of additional resistance genes. All 9 isolates were resistant to most antimicrobial agents, including carbapenems, cephalosporins, and levofloxacin, while being sensitive to trimethoprim/sulfamethoxazole, amikacin, tigecycline, and colistin. According to the clinical background, all 9 isolates were collected in a period of < 3 months from infants among whom there was overlap in the time of hospitalization. None of them had a travel history. CONCLUSION: Our analysis suggests an outbreak of clonal dissemination, presumably due to nosocomial transmission. This study represents the first documented outbreak of NDM-5-producing E. coli mediated by IncFII in infants. Close monitoring is urgently needed to prevent and control the spread of this difficult-to-treat superbug.

Genotypic differences in CC224, CC363, CC449 and CC446 of Moraxella catarrhalis isolates based on whole genome SNP, MLST and PFGE typing.

Understanding the evolutionary path of M. catarrhalis from macrolide-susceptible to macrolide-resistant organism, is important for hindering macrolide resistance from propagation. Multilocus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE) and whole genome SNP typing (WGST), as useful and practical typing tools, have both advantages and disadvantages. We studied the utility of these 3 typing methods, including the level of agreement, consistency and drawbacks, in characterizing M. catarrhalis clones and clonal complexes. We focused on four clonal complexes [CC224, CC363, CC449 (CCN10) and CC446 (CCN08)] and found that PFGE and WGST had a high level of agreement and a proper consistency of the same clone or very closely related clones, while MLST is less discriminatory for different clones. Furthermore, we also established an evolutionary distance cut-off value for "The same clone". Moreover, we detected macrolide-resistant M. catarrhalis in CC224, which had previously been considered as a macrolide-susceptible clonal complex. A higher number of isolates belonged to ST215 compared to ST446, implying that ST215 is more likely to be the primary founder. Our study also demonstrated that all the four clonal complexes belong to the M. catarrhalis lineage 1, which is considered to be related to increased virulence potential and serum resistance. We also observed that copB II was highly related to CC449 and LOS type B was mainly confined in CC224. In conclusion, these findings provide further insight into the evolutionary characteristics of M. catarrhalis.

An Investigation on the Molecular Characteristics and Intracellular Growth Ability among Environmental and Clinical Isolates of Legionella pneumophila in Sichuan Province, China.

OBJECTIVE: To investigate the molecular characteristics and intracellular growth ability of Legionella pneumophila (L. pneumophila) strains from 1989 to 2016 in Sichuan Province, China. METHODS: Seventy-nine isolates of L. pneumophila were collected from environmental and clinical sources, including cooling towers, hot springs, bath water, fountains, and patients, and identified with 16S rRNA gene analysis and serum agglutination assay. The isolates were then typed by Sequence-Based Typing (SBT), and Genotyping of forty-two LP1 strains were analyzed by means of multiple-locus VNTR analysis with 8 loci (MLVA-8). All strains were further analyzed for two virulence genes: Legionella vir homologue (lvh) and repeats in structural toxin (rtxA). The intracellular growth ability of 33 selected isolates was determined by examining their interaction with J774 cells. RESULTS: All isolates were identified to L. pneumophila including 11 serogroups, among which the main serogroup were LP1, accounting for 54.43%. Thirty-three different sequence types (STs) from five main clonal groups and five singletons were identified, along with 8 different MLVA patterns. Both the lvh and rtxA loci were found in all 79 strains. Thirty isolates showed high intracellular growth ability in J774 cells. CONCLUSION: L. pneumophila is a potential threat to public health, and effective control and prevention strategies are urgently needed.

Simultaneous Detection of 13 Key Bacterial Respiratory Pathogens by Combination of Multiplex PCR and Capillary Electrophoresis.

OBJECTIVE: Lower respiratory tract infections continue to pose a significant threat to human health. It is important to accurately and rapidly detect respiratory bacteria. To compensate for the limits of current respiratory bacteria detection methods, we developed a combination of multiplex polymerase chain reaction (PCR) and capillary electrophoresis (MPCE) assay to detect thirteen bacterial pathogens responsible for lower respiratory tract infections, including Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Staphylococcus aureus, Mycoplasma pneumoniae, Legionella spp., Bordetella pertussis, Mycobacterium tuberculosis complex, Corynebacterium diphtheriae, and Streptococcus pyogenes. METHODS: Three multiplex PCR reactions were built, and the products were analyzed by capillary electrophoresis using the high-throughput DNA analyzer. The specificity of the MPCE assay was examined and the detection limit was evaluated using DNA samples from each bacterial strain and the simulative samples of each strain. This assay was further evaluated using 152 clinical specimens and compared with real-time PCR reactions. For this assay, three nested-multiplex-PCRs were used to detect these clinical specimens. RESULTS: The detection limits of the MPCE assay for the 13 pathogens were very low and ranged from 10-7 to 10-2 ng/µL. Furthermore, analysis of the 152 clinical specimens yielded a specificity ranging from 96.5%-100.0%, and a sensitivity of 100.0% for the 13 pathogens. CONCLUSION: This study revealed that the MPCE assay is a rapid, reliable, and high-throughput method with high specificity and sensitivity. This assay has great potential in the molecular epidemiological survey of respiratory pathogens.

Legionella dumoffii Tex-KL Mutated in an Operon Homologous to traC-traD is Defective in Epithelial Cell Invasion.

OBJECTIVE: To understand the mechanism of invasion by Legionella dumoffii. METHODS: The L. dumoffii strain Tex-KL was mutated using the Tn903 derivative, Tn903dIIlacZ. After screening 799 transposon insertion mutants, we isolated one defective mutant. We then constructed the gene-disrupted mutant, KL16, and studied its invasion of and intracellular growth in HeLa and A549 cells, and in A/J mice survival experiments. The structure of traC-traD operon was analyzed by RT-PCR. RESULTS: The transposon insertion was in a gene homologous to Salmonella typhi traC, which is required for the assembly of F pilin into the mature F pilus structure and for conjugal DNA transmission. Results from RT-PCR suggested that the traC-traD region formed an operon. We found that when the traC gene was disrupted, invasion and intracellular growth of L. dumoffii Tex-KL were impaired in human epithelial cells. When mice were infected by intranasal inoculation with a traC deficient mutant, their survival significantly increased when compared to mice infected with the wild-type strain.. CONCLUSION: Our results indicated that the traC-traD operon is required for the invasion and intracellular growth abilities of L. dumoffii Tex-KL in epithelial cells.

Multilocus sequence typing analysis of Cronobacter spp. isolated from China.

Multilocus sequence typing (MLST) has proven to be an effective approach for the subtyping isolates of the Cronobacter genus and to exhibit a high level of discrimination between isolates. In this study, 151 Cronobacter strains were isolated from different sources and provinces across China from 2010 to 2012 and analyzed by MLST. Their sequence type profiles were compared with strains from other countries which were widely geographically and temporally distributed. Out of 151 strains in this study, the majority of strains were Cronobacter sakazakii (70.9 %), C. malonaticus (15.9 %), C. dublinensis (10.6 %), C. turicensis (2.0 %), and C. muytjensii (0.7 %). The strains were divided into 85 sequence types (STs), among which only 17 had previously been reported in other countries. The 85 identified STs for the Cronobacter genus were grouped into 14 clonal complexes and 47 singletons according to eBURST algorithm. The Cronobacter isolated from China showed a high diversity when they were subtyped using the MLST method. When compared to the Cronobacter PubMLST database, some sequence types of strains cultured from food and/or water in this study were also the same with strains isolated from patients in other countries as reported previously. This result showed the potential hazard of strains contaminating water and weaning food from China.

Multilocus microsatellite markers for molecular typing of Candida tropicalis isolates.

BACKGROUND: Candida tropicalis is considered to be the leading pathogen causing nosocomial fungemia and hepatosplenic fungal infections in patients with cancer, particularly those with leukemia. Microsatellite-based typing methods using sets of genetic markers have been developed and reported for population structure analysis of C. albicans, C. glabrata, and C. parapsilosis, but no studies have been published for genetic analysis of C. tropicalis. The objective of this study was to develop new microsatellite loci that have the ability to distinguish among C. tropicalis isolates. RESULTS: DNA sequences containing over 10 bi- or tri-nucleotide repeats were selected from the C. tropicalis genome database. Thirty PCR primers sets specific for the microsatellite loci were designed and tested using eight clinically independent isolates. According to the amplification efficiency, specificity, and observed polymorphisms, eight markers were selected for further population structure analysis and molecular typing. Sixty-five independent C. tropicalis isolates were genotyped using these 8 markers. Based on these analyses, six microsatellite loci were confirmed, although two loci were found to be with unstable flanking areas. The six polymorphic loci displayed 4-22 alleles and 7-27 genotypes. The discriminatory power of the six loci ranged from 0.70 to 0.95. Genotyping results obtained by microsatellite analysis were compared to PCR-fingerprinting and multi-locus sequence typing (MLST). The comparisons showed that microsatellite analysis and MLST had the similar discriminatory power for C. tropicalis, which were more powerful than PCR-fingerprinting. CONCLUSIONS: This is the first attempt to develop new microsatellite loci for C. tropicalis. These newly developed markers will be a valuable resource for the differentiation of C. tropicalis isolates. More C. tropicalis isolates will need to be sequenced and analyzed in order to fully show the potential of these newly developed microsatellite markers.

[Three quantitative methods to continuously monitor Legionella in spring water].

OBJECTIVE: To compare the detection effect of Legionella pollution in spring water by three methods, namely traditional plating method, fluorescent quantitation PCR method and ethidium monoazide (EMA) fluorescent quantitation PCR method. METHODS: Every month (except May), we collected 11 water samples from the 5 selected hot spring pools in one hot spring resort in Beijing in 2011. A total of 121 water samples were collected, and then were detected by the above three methods qualitatively and quantitatively. RESULTS: In our study, the Legionella pollution rate was separately 74.4% (90/121), 100.0% (121/121) and 100.0% (121/121) by the above three methods. The quantitative value of Legionella in the 121 water samples detected by the three methods were around 0.10-216.00 colony-forming units (CFU)/ml, 1.47-1557.75 gene units (GU)/ml and 0.20-301.69 GU/ml, respectively. The median (25th and 75th percentiles) was 75.30 (32.51-192.10) GU/ml, 36.46 (16.08-91.21) GU/ml and 5.30 (0.00-33.70) CFU/ml, respectively. The difference in the quantitative value of Legionella detected by the three methods showed statistical significance (χ(2) = 187.900, P < 0.01). The quantitative value of Legionella detected by fluorescent quantitation PCR method was the highest, followed by the value Legionella detected by EMA-fluorescent quantitation PCR method and traditional plating method. CONCLUSION: The sensitivity of the PCR methods was higher than traditional plating method, in detecting Legionella pollution in spring water, especially the EMA- fluorescent quantitation PCR method, which was more suitable for detecting Legionella in water.

[Analysis of molecular subtypes and microflora structure of Neisseria meningitidis strains isolated in Jiangxi province].

OBJECTIVE: To study the molecular subtypes and microflora structure of Neisseria meningitidis (Nm) strains isolated in Jiangxi province. METHODS: A total of 123 Nm strains separately isolated from patients, close contacts and health people in 1976-1987 and 2005-2008 were investigated by multilocus sequence typing (MLST) and PorA subtyping, to test the characteristics of gene Nm and sequence porA. Minimum spanning tree was constructed by using BioNumerics software based on data of MLST; and the microflora structure was then analyzed. RESULTS: The serogroups of 67 Nm strains isolated in 1976-1987 included group A (43 strains), group B (18 strains), group C (1 strains) and group W135 (5 strains); while the serogroups of 56 Nm strains isolated in 2005-2008 included group A (3 strains), group B (7 strains), group C (45 strains) and 1 ungrouped strain. The total 123 Nm strains could be divided into 40 MLST types; while the 46 strains in group A could be divided into 14 MLST types, 29 out of which belonged to ST-3 type, accounting for 63.0% (29/46) as the dominant type. All of the 29 strains were isolated between 1976 and 1987, while 14 strains were isolated from patients, 9 were from close contacts and 6 were from health people. The 46 strains in group C could be divided into 5 MLST types, 41 out of which belonged to ST-4821 type, accounting for 89.1% (41/46). All of the strains were isolated between 2005 and 2008, 6 strains were isolated from patients, 6 were from close contacts and 29 were from health people. The porA gene of the total 123 Nm strains were classified to 32 different types, including 24 different VR1 types and 22 different VR2 types. The dominant PorA type of the prevalent strain (ST-3 type, group A) between 1976 and 1987 was P1.7-1, 10, accounting for 39.1% (18/46) of the strains in group A; while the 18 strains were isolated from 11 patients, 4 close contacts and 3 health people. The dominant PorA type of the prevalent strain (ST-4821 type, group C) between 2005 and 2008 was P1.20, 9, accounting for 46.3% (19/41) of the ST-4821 strains in group C; while the 19 strains were isolated from 1 close contacts and 18 health people. P1.7-2, 14 dominated since 2006, including 22 strains, accounting for 53.7% (22/41) of the ST-4821 strains in group C, isolated from 6 patients, 5 close contacts and 11 health people. There were no dominant PorA type found in group B and all the 5 strains in group W135 belonged to ST-174 and the PorA type was P1.21, 16, isolating from 3 close contacts and 2 health people between 1979 and 1980. CONCLUSION: Nm isolated in Jiangxi province showed significant gene polymorphism, as well as predominant lineages existing. In different periods, the prevalent lineages varied a lot, as translating from serogroup A: ST-3:P1.7-1, 10 to serogroup C: ST-4821:P1.7-2, 14 nowadays.

Optimization of pulse-field gel electrophoresis for Borrelia burgdorferi subtyping.

OBJECTIVE: To optimize the performance of Pulsed-Field Gel Electrophoresis (PFGE) for the comparison of inter-laboratory results and information exchange of Borrelia burgdorferi subtyping. METHODS: A panel of 34 strains of B. burgdorferi were used to optimize PFGE for subtyping. In order to optimize the electrophoretic parameters (EPs), all 34 strains of B. burgdorferi were analyzed using four EPs, yielding different Simpson diversity index (D) values and the epidemiological concordance was also evaluated. RESULTS: The EP of a switch time of 1 s to 25 s for 13 h and 1 s to 10 s for 6 h produced the highest D value and was declared to be optimal for MluI and SmaI PFGE of B. burgdorferi. MluI and SmaI were selected as the first and second restriction enzymes for PFGE subtyping of B. burgdorferi according to discrimination and consistency with epidemiological data. CONCLUSION: PFGE can be used as a valuable test for routine genospecies identification of B. burgdorferi.

Molecular characteristics of Neisseria meningitidis isolated during an outbreak in a jail: association with the spread and distribution of ST-4821 complex serogroup C clone in China.

OBJECTIVE: To characterize the meningococcal strains isolated from cases and close contacts with meningococcal disease associated with an outbreak in a jail in May 2010 by investigating the national distribution of hyperinvasive ST-4821 serogroup C clone associated with this outbreak. METHODS: The cases were described based on the clinical symptoms and laboratory results. Pharyngeal swabs were cultured for N. meningitidis from men in the jail. Meningococcal isolates were identified by serogrouping, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST), respectively. Four hundred and sixteen serogroup C N. meningitidis strains were collected from 27 provinces between 2003 and 2010 for a nationwide survey and analyzed by PFGE and MLST. RESULTS: Three persons in a jail system were infected with invasive N. meningitidis serogroup C. All isolates tested had matching PFGE patterns and belonged to the multilocus sequence type (ST) 4821 clonal complex. All 47 N. meningitidis strains were identified from the pharyngeal swabs of 166 peoples in the jail, and 26 of them belonged to ST-4821 serogroup C clone, and 90.14% (375/416) serogroup C strains identified in the nationwide survey belonged to the ST-4821 complex. The ST-4821 serogroup C clone was spread nationwide, distributed in 24 provinces, especially in eastern provinces between 2003 and 2010. CONCLUSION: Endemic transmission and carriage rate of ST-4821 serogroup C clone are high in this jail system. The ST-4821 serogroup C clone is spreading in China and nationwide distributed despite the existence of some effective vaccines.

[Application of PulseNet China Database in tracking and warning 4 cholerae outbreaks in Anhui province, in 2012].

OBJECTIVE: To track the source of infection regarding 4 Cholerae outbreaks in Anhui province in 2012 through the application of PulseNet China Database (PNCD). METHODS: Cholerae virulence genes were amplified by PCR and typed by pulse field gel electrophoresis(PFGE). Results from electrophoresis were cluster-analyzed by BioNumericsV4.0 software and compared with PNCD. RESULTS: Virulence gene CT and TCP of the tested vibrio cholera showed both positive. Homology of the strains from four cholera outbreaks was more than 98%, based on the homologous and cluster analysis through enzyme digested PFGE electrophoresis. Those strains were highly homologous with the cholera epidemic strains identified in Hunan, Sichuan,Zhejiang, Shanghai and Hubei by PNCD, with the homology as 100% . CONCLUSION: Four cholera outbreaks in Anhui province, 2012 were highly correlated with the outbreaks occurring in Hunan and Sichuan during the same time period, indicating that PNCD could effectively and quickly tracking down the source of infection on the cholera outbreaks and providing early warning of the situation.

[Comparison on the levels of human serum antibody against Neisseria meningitidis serogroup C measured using serum bactericidal assay and ELISA].

OBJECTIVE: To analyze the levels of human serum antibody against Neisseria meningitidis serogroup C measured by serum bactericidal assay (SBA) and ELISA. METHODS: SBA and a modified ELISA were applied to measure the serum bactericidal titer and the specific concentration of immunoglobulin G (IgG) against meningococcal serogroup C in sera samples. Seventy-five sera were from healthy adults without undertaking vaccination while another 429 and 388 pre- and post-vaccinated sera were from 143 infants and 194 young children immunized with conjugate vaccine or polysaccharide vaccine, respectively. Correlation between serum bactericidal titer and the concentration of specific IgG against meningococcal serogroup C was analyzed. RESULTS: The concentration of meningococcal serogroup C specific IgG in healthy adults showed a strong correlation (r=0.814 33, P<0.001) with serum bactericidal titer through linear regression analysis. Weak correlation was observed between SBA titers and IgG concentration in pre vaccinated sera of infants and children (conjugate/polysaccharide vaccine) (infants: r=0.140 64, P>0.100/r=0.2899, P<0.05; children: r=0.540 40, P<0.05/r=0.194 36, P<0.05). After immunization with 2-dose conjugate vaccine in infants and 1-dose in children, a strong correlation between the two panels of results was observed (r=0.809 38, P<0.001 and r=0.837 23, P<0.001 respectively). However after immunization with polysaccharide vaccine, the correlation between serum bactericidal titer and concentration of specific IgG was weak (r<0.50000). CONCLUSION: Among healthy adults and post vaccinated infants or young children immunized with conjugate vaccine, the concentration of specific IgG was comparable to the serum bactericidal titer against meningococcal serogroup C. However, it was not unfavorable to use ELISA as the principal means of measuring serum antibody responses to polysaccharide vaccine for infants under 1 year old.

[Molecular analysis on non-O1 and non-O139 Vibrio cholerae isolates].

OBJECTIVE: According to results from the two-month consecutive surveillance program in Maanshan, six suspected cases of non-O1 non-O139 Vibrio (V.) cholerae infection, were found that called for identification of pathogens as well as molecular-epidemiological analysis to determine the aggregation of the epidemic situation. METHODS: Biochemical and serotype identification, hemolysis test, and drug sensitive test were used to detect the drug resistance spectrum. Real-time PCR and conventional PCR were used to detect the presence of V. cholerae specific genes, virulent genes and its related genes, including ompW, ctx, tcpA, toxR, hlyA, zot, ace, rstR and gIII(CTX). Pulsed-field gel electrophoresis (PFGE) was used to analyze the molecular type of strains. RESULTS: All the six isolates of non-O1 non-O139 V. cholerae were identified by biochemical and serologic tests, and appeared to be ß hemolytic. Twelve out of the 14 kinds of drugs showed 100% sensitive. All isolates were positive of ompW gene by real-time PCR, but negative for ctx, tcpA, zot, ace, rstR and gIII(CTX). Five of the six isolates were positive for toxR and hlyA, except for strain 1001434446. All strains had different PFGE types, but two strains had similar types. All strains had a low similarity compared to the toxigenic V. cholerae. CONCLUSION: Six cases of non-O1 and non-O139 nontoxigenic V. cholerae infection appeared in the same period. Along with epidemiological information, we noticed that these cases had a sporadic nature, but frequently appeared in the same area. We got the impression that public health measurements should be strengthened, with special attention paid to those diarrhea outbreaks caused by non-O1/non-O139 strains since V. cholerae had appeared in low incidence.

[Assessment of the application of variable-number tandem repeat loci of Salmonella Enteritidis in subtyping multiple-locus variable-number tandem repeat analysis].

OBJECTIVE: To evaluate the feasibility of the application of variable-number tandem repeat (VNTR) loci of Salmonella Enteritidis (S. enteritidis) in subtyping mutiple-locus variable-number tandem repeat analysis (MLVA). METHODS: A total of 16 isolates of S.enteritidis from different place and time in China were preliminarily assessed by choosing 11 reported VNTR loci, the loci with single amplified bands were picked to subtype all 104 S. enteritidis isolates. The isolates were also analyzed by pulse field gel electrophoresis (PFGE) to compare the superiority or inferiority of MLVA method and PFGE method. RESULTS: Seven VNTR loci were selected from the preliminary screening to expand the analysis, and the 7 VNTR loci had grouped 104 of S.enteritidis isolates into either 16 MLVA subtypes or 22 PFGE subtypes, with the D value at 0.7222 and 0.7974, respectively. Comparing with the isolates in MLVA subtypes, the isolates in PFGE showed a stronger resolving power. Meanwhile the results in PFGE showed a more disperse frequency distribution than those in MLVA. CONCLUSION: These results indicate that some VNTR locus which have shown a good polymorphism internationally, may fail to show polymorphism in China, thereby, more VNTR loci should be included in MLVA and the wide screening may benefit the unity of global laboratorial methods.

[Molecular typing of Legionella pneumophila isolates from China with pulsed field gel electrophoresis].

OBJECTIVE: To analyze the molecular types of Legionella (L.) pneumophila strains isolated in China, and to develop the PulseNet-China Database of L. pneumophila. METHODS: Pulsed field gel electrophoresis (PFGE) was used to analyze 262 L. pneumophila strains collected from 11 provinces between 2004 and 2009 in China. Different kinds of genomic DNA in different L. pneumophila strains were isolated and separated after digesting with Asc I. BioNumerics software was used to analysis the PFGE fingerprints. RESULTS: L. pneumophila strains isolated in China were quite different regarding their PFGE patterns. There were 108 PFGE types among the 262 strains tested in this study. The similarity value of these strains was in the range of 16% - 100% and the same types were discovered in different provinces and years. CONCLUSION: L. pneumophila strains isolated in China were with high genetic variations. There might be different clones existed in China. The development of PulseNet China Database was thus of great significance in monitoring the L. pneumophila strains in the future.

Structural variation of the superintegron in the toxigenic Vibrio cholerae O1 El Tor.

OBJECTIVE: To understand the genetic structures and variations of the superintegron (SI) in Vibrio cholerae isolated in the seventh cholera pandemic. METHODS: Polymerase chain reaction scanning and fragment sequencing were used. Sixty toxigenic V. cholerae O1 El Tor strains isolated between 1961 and 2008 were analyzed. RESULTS: Some variations were found, including insertions, replacements, and deletions. Most of the deletions were probably the result of recombination between V. cholerae repeat sequences. The majority of the variations clustered together. The SIs of the strains isolated in the 1960s and 1970s showed more diversity, whereas SI cassette variations in strains isolated in the 1990s and after were lower, with ∼24 kb signature sequence deletion. This indicates the predominant SI in the host during the epidemic in the 1990s and after. The insertion cassettes suggested the mobilization from the SIs of other V. cholerae serogroups and Vibrio mimicus. CONCLUSION: The study revealed that structural variations of SIs were obvious in the strains isolated in epidemics in different decades, whereas the divergence was based on syntenic structure of SIs in these El Tor strains. Also, the continuing cassette flows in the SIs of the host strains during the seventh cholera pandemics were displayed.