Displaying publications 1 - 20 of 40 in total

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  1. Fulltext Genetic fine structure of a Salmonella enterica serovar Typhi strain associated with the 2005 outbreak of typhoid fever in Kelantan, Malaysia
    Baddam R, Kumar N, Thong KL, Ngoi ST, Teh CS, Yap KP, et al.
    J Bacteriol, 2012 Jul;194(13):3565-6.
    PMID: 22689247 DOI: 10.1128/JB.00581-12
    Among enteric pathogens, Salmonella enterica serovar Typhi is responsible for the largest number of food-borne outbreaks and fatalities. The ability of the pathogen to cause systemic infection for extended durations leads to a high cost of disease control. Chronic carriers play important roles in the evolution of Salmonella Typhi; therefore, identification and in-depth characterization of isolates from clinical cases and carriers, especially those from zones of endemicity where the pathogen has not been extensively studied, are necessary. Here, we describe the genome sequence of the highly virulent Salmonella Typhi strain BL196/05 isolated during the outbreak of typhoid in Kelantan, Malaysia, in 2005. The whole-genome sequence and comparative genomics of this strain should enable us to understand the virulence mechanisms and evolutionary dynamics of this pathogen in Malaysia and elsewhere.
    Matched MeSH terms: Salmonella typhi/genetics
  2. Analysis and construction of pathogenicity island regulatory pathways in Salmonella enterica serovar Typhi
    Ong SY, Ng FL, Badai SS, Yuryev A, Alam M
    J Integr Bioinform, 2010;7(1).
    PMID: 20861532 DOI: 10.2390/biecoll-jib-2010-145
    Signal transduction through protein-protein interactions and protein modifications are the main mechanisms controlling many biological processes. Here we described the implementation of MedScan information extraction technology and Pathway Studio software (Ariadne Genomics Inc.) to create a Salmonella specific molecular interaction database. Using the database, we have constructed several signal transduction pathways in Salmonella enterica serovar Typhi which causes Typhoid Fever, a major health threat especially in developing countries. S. Typhi has several pathogenicity islands that control rapid switching between different phenotypes including adhesion and colonization, invasion, intracellular survival, proliferation, and biofilm formation in response to environmental changes. Understanding of the detailed mechanism for S. Typhi survival in host cells is necessary for development of efficient detection and treatment of this pathogen. The constructed pathways were validated using publically available gene expression microarray data for Salmonella.
    Matched MeSH terms: Salmonella typhi/genetics*
  3. Fulltext Complete genome sequence of Salmonella enterica subsp. enterica serovar Typhi P-stx-12
    Ong SY, Pratap CB, Wan X, Hou S, Abdul Rahman AY, Saito JA, et al.
    J Bacteriol, 2012 Apr;194(8):2115-6.
    PMID: 22461552 DOI: 10.1128/JB.00121-12
    We report here the complete genome sequence of Salmonella enterica subsp. enterica serovar Typhi P-stx-12, a clinical isolate obtained from a typhoid carrier in India.
    Matched MeSH terms: Salmonella typhi/genetics*
  4. Ribotyping of Salmonella enterica serovar Typhi isolates from Papua New Guinea over the period 1977 to 1996
    Combs BG, Passey M, Michael A, Pang T, Lightfoot D, Alpers MP
    P N G Med J, 2005 Sep-Dec;48(3-4):158-67.
    PMID: 17212062
    The prevalence of typhoid in the Papua New Guinea (PNG) highlands region increased rapidly in the mid-1980s, and now remains endemic. In this study ribotyping has been used to examine the number and types of Salmonella enterica serovar Typhi strains present during the 1977-1996 period. The ribotyping banding pattern results were based on Cla I and Eco RV digests. The 57 PNG isolates were divided into 11 different ribotypes. Comparison of ribotypes using coefficient of similarity values revealed a diverse group of ribotypes. Several strains appear to be endemic in PNG For instance, ribotypes 1, 2 and 3 were most commonly found among PNG isolates and isolates with these ribotypes have been cultured over a period of at least 11 years (1985-1996). Ribotype 3 was also observed in isolates from Malaysia and Thailand. Also found in PNG were ribotypes 4, 5, 6, 7, 8, 9, 16 and 17. The ribotyping suggests that serovar Typhi strains present in PNG include unique strains of serovar Typhi and also strains that are common to other countries.
    Matched MeSH terms: Salmonella typhi/genetics*
  5. Genotypic characterization of Salmonella typhi by amplified fragment length polymorphism fingerprinting provides increased discrimination as compared to pulsed-field gel electrophoresis and ribotyping
    Nair S, Schreiber E, Thong KL, Pang T, Altwegg M
    J Microbiol Methods, 2000 Jun;41(1):35-43.
    PMID: 10856775
    Amplified fragment length polymorphism (AFLP) is a recently developed, PCR-based high resolution fingerprinting method that is able to generate complex banding patterns which can be used to delineate intraspecific genetic relationships among bacteria. In the present study, AFLP was evaluated for its usefulness in the molecular typing of Salmonella typhi in comparison to ribotyping and pulsed-field gel electrophoresis (PFGE). Six S. typhi isolates from diverse geographic areas (Malaysia, Indonesia, India, Chile, Papua New Guinea and Switzerland) gave unique, heterogeneous profiles when typed by AFLP, a result which was consistent with ribotyping and PFGE analysis. In a further study of selected S. typhi isolates from Papua New Guinea which caused fatal and non-fatal disease previously shown to be clonally related by PFGE, AFLP discriminated between these isolates but did not indicate a linkage between genotype with virulence. We conclude that AFLP (discriminatory index=0.88) has a higher discriminatory power for strain differentiation among S. typhi than ribotyping (DI=0.63) and PFGE (DI=0.74).
    Matched MeSH terms: Salmonella typhi/genetics
  6. Fulltext Crystal structure of an antigenic outer-membrane protein from Salmonella Typhi suggests a potential antigenic loop and an efflux mechanism
    Guan HH, Yoshimura M, Chuankhayan P, Lin CC, Chen NC, Yang MC, et al.
    Sci Rep, 2015 Nov 13;5:16441.
    PMID: 26563565 DOI: 10.1038/srep16441
    ST50, an outer-membrane component of the multi-drug efflux system from Salmonella enterica serovar Typhi, is an obligatory diagnostic antigen for typhoid fever. ST50 is an excellent and unique diagnostic antigen with 95% specificity and 90% sensitivity and is used in the commercial diagnosis test kit (TYPHIDOT(TM)). The crystal structure of ST50 at a resolution of 2.98 Å reveals a trimer that forms an α-helical tunnel and a β-barrel transmembrane channel traversing the periplasmic space and outer membrane. Structural investigations suggest significant conformational variations in the extracellular loop regions, especially extracellular loop 2. This is the location of the most plausible antibody-binding domain that could be used to target the design of new antigenic epitopes for the development of better diagnostics or drugs for the treatment of typhoid fever. A molecule of the detergent n-octyl-β-D-glucoside is observed in the D-cage, which comprises three sets of Asp361 and Asp371 residues at the periplasmic entrance. These structural insights suggest a possible substrate transport mechanism in which the substrate first binds at the periplasmic entrance of ST50 and subsequently, via iris-like structural movements to open the periplasmic end, penetrates the periplasmic domain for efflux pumping of molecules, including poisonous metabolites or xenobiotics, for excretion outside the pathogen.
    Matched MeSH terms: Salmonella typhi/genetics
  7. In silico 'fishing' using known small regulatory RNA (sRNA) candidates as the decoy from Escherichia coli, Salmonella typhi and Salmonella typhimurium manifested 14 novel sRNA candidates in the orthologous region of Proteus mirabilis
    KishanRaj S, Sumitha S, Siventhiran B, Thiviyaa O, Sathasivam KV, Xavier R, et al.
    Mol Biol Rep, 2018 Dec;45(6):2333-2343.
    PMID: 30284142 DOI: 10.1007/s11033-018-4397-z
    Proteus mirabilis, a gram-negative bacterium of the family Enterobacteriaceae, is a leading cause of urinary tract infection (UTI) with rapid development of multi-drug resistance. Identification of small regulatory RNAs (sRNAs), which belongs to a class of RNAs that do not translate into a protein, could permit the comprehension of the regulatory roles this molecules play in mediating pathogenesis and multi-drug resistance of the organism. In this study, comparative sRNA analysis across three different members of Enterobacteriaceae (Escherichia coli, Salmonella typhi and Salmonella typhimurium) was carried out to identify the sRNA homologs in P. mirabilis. A total of 232 sRNA genes that were reported in E. coli, S. typhi and S. typhimurium were subjected to comparative analysis against P. mirabilis HI4320 genome. We report the detection of 14 sRNA candidates, conserved in the orthologous regions of P. mirabilis, that are not included in Rfam database. Northern-blot analysis was carried out for selected three sRNA candidates from the current investigation and three known sRNA from Rfam of P. mirabilis. The expression pattern of the six sRNA candidates shows that they are growth stage-dependant. To the best of our knowledge, this is the first report on the identification of sRNA candidates in P. mirabilis.
    Matched MeSH terms: Salmonella typhi/genetics
  8. Typhoid fever--important issues still remain
    Pang T, Levine MM, Ivanoff B, Wain J, Finlay BB
    Trends Microbiol., 1998 Apr;6(4):131-3.
    PMID: 9587187
    Matched MeSH terms: Salmonella typhi/genetics
  9. Analysis of plasmid and chromosomal DNA of multidrug-resistant Salmonella enterica serovar typhi from Asia
    Mirza S, Kariuki S, Mamun KZ, Beeching NJ, Hart CA
    J Clin Microbiol, 2000 Apr;38(4):1449-52.
    PMID: 10747124
    Molecular analysis of chromosomal DNA from 193 multidrug-resistant (MDR) Salmonella enterica serovar Typhi isolates from 1990 to 1995 from Pakistan, Kuwait, Malaysia, Bangladesh, and India produced a total of five major different pulsed-field gel electrophoresis (PFGE) patterns. Even within a particular country MDR S. enterica serovar Typhi DNA was found to be in different PFGE groups. Similar self-transferable 98-MDa plasmids belonging to either incompatibility group incHI1 or incHI1/FIIA were implicated in the MDR phenotype in S. enterica serovar Typhi isolates from all the locations except Quetta, Pakistan, where the majority were of incFIA. A total of five different PFGE genotypes with six different plasmids, based on incompatibility and restriction endonuclease analysis groups, were found among these MDR S. enterica serovar Typhi isolates.
    Matched MeSH terms: Salmonella typhi/genetics
  10. Amplification of ST50 gene using dry-reagent-based polymerase chain reaction for the detection of Salmonella typhi
    Aziah I, Ravichandran M, Ismail A
    Diagn Microbiol Infect Dis, 2007 Dec;59(4):373-7.
    PMID: 17964105
    Conventional polymerase chain reaction (PCR) testing requires many pipetting steps and has to be transported and stored in cold chain. To overcome these limitations, we designed a ready-to-use PCR test for Salmonella typhi using PCR reagents, primers against the ST50 gene of S. typhi, a built-in internal amplification control (IAC), and gel loading dye mixed and freeze-dried in a single tube. The 2-step dry-reagent-based assay was used to amplify a 1238-bp target gene and an 810-bp IAC gene from 73 BACTEC blood culture broths (33 true positives for S. typhi and 40 true negatives for non-S. typhi). The sensitivity, specificity, positive predictive value, and negative predictive value of the PCR assay were 87.9%, 100%, 100%, and 90.9%, respectively. We suggest that this rapid 2-step PCR test could be used for the rapid diagnosis of typhoid fever.
    Matched MeSH terms: Salmonella typhi/genetics
  11. Development of two salmonella-based oral vaccines against human respiratory syncytial virus
    Azizi Jalilian F, Yusoff K, Suhaimi S, Amini R, Sekawi Z, Jahanshiri F
    J Biol Regul Homeost Agents, 2015 Jan-Mar;29(1):7-18.
    PMID: 25864737
    Human respiratory syncytial virus is the most common cause of bronchiolitis and other respiratory infections in infants and the elderly worldwide. We have developed two new oral vaccines using Salmonella typhi TY21a to carry and express the immunogenic epitopes of RSV fusion (F) and attachment (G) glycoproteins on its surface, separately. To evaluate the efficacy of the designed vaccines, BALB/c mice were orally immunized and then infected with RSV. Immune response analyses showed that cellmediated, mucosal and humoral immunity in the vaccinated mice were significantly enhanced compared to the control group. Both vaccines generated a balanced Th1/Th2 immune response which is crucial for efficiency of vaccines against RSV. Furthermore, histopathological examination proved that these vaccines were safe as they did not cause any Th2-associated adverse effects in the lungs of RSV-infected mice. The findings of this research suggest that Salmonella-F and Salmonella-G vaccine candidates may have strong potential to prevent RSV infection.
    Matched MeSH terms: Salmonella typhi/genetics
  12. Fulltext Multi-isotype antibody responses against the multimeric Salmonella Typhi recombinant hemolysin E antigen
    Ong EB, Ignatius J, Anthony AA, Aziah I, Ismail A, Lim TS
    Microbiol. Immunol., 2015 Jan;59(1):43-7.
    PMID: 25399538 DOI: 10.1111/1348-0421.12211
    The detection and measurement of different antibody isotypes in the serum provide valuable indicators of the different stages of typhoid infection. Here, the ability of S. Typhi recombinant hemolysin E (HlyE) to detect multi-isotype antibody responses in sera of patients with typhoid and paratyphoid A was investigated using an indirect antibody immunoassay. Nanogram amounts of HlyE were found to be sufficient for detection of IgG and IgA isotypes and, in a study of individuals' sera (n = 100), the immunoassay was able to distinguish between typhoid and non-typhoid sera. The overall sensitivity, specificity and efficiency of the ELISA were 70% (39/56), 100% (44/44) and 83% respectively.
    Matched MeSH terms: Salmonella typhi/genetics
  13. Cloning, expression, and purification of the hemolysin/cytolysin (HlyE antigen) from Salmonella enterica serovar Typhi: potential application for immunoassay development
    Ong EB, Anthony AA, Ismail A, Ismail A, Lim TS
    Diagn Microbiol Infect Dis, 2013 Sep;77(1):87-9.
    PMID: 23790417 DOI: 10.1016/j.diagmicrobio.2013.05.010
    The hemolysin (HlyE) protein of Salmonella enterica serovar Typhi was reported to be antigenic. This work describes the cloning, expression, and purification of a hexahistidine-tagged HlyE protein under native conditions. Immunoblot analysis and a competitive enzyme-linked immunosorbent assay using sera from typhoid patients showed the presence of HlyE-specific antibodies in circulation.
    Matched MeSH terms: Salmonella typhi/genetics
  14. Generation of a naïve human single chain variable fragment (scFv) library for the identification of monoclonal scFv against Salmonella Typhi Hemolysin E antigen
    Lim BN, Chin CF, Choong YS, Ismail A, Lim TS
    Toxicon, 2016 Jul;117:94-101.
    PMID: 27090555 DOI: 10.1016/j.toxicon.2016.04.032
    Antibody phage display is a useful tool for the isolation and identification of monoclonal antibodies. Naive antibody libraries are able to overcome the limitations associated with the traditional hybridoma method for monoclonal antibody generation. Antibody phage display is also a preferred method for antibody generation against toxins as it does not suffer from toxicity mediated complications. Here, we describe a naïve multi ethnic scFv antibody library generated via two-step cloning with an estimated diversity of 2 × 10(9). The antibody library was used to screen for monoclonal antibodies against Hemolysin E antigen, a pore forming toxin produced by Salmonella enterica serovar Typhi. A soluble monoclonal scFv antibody against the HlyE toxin (IgM scFv D7 anti-hlyE) was isolated from the library. This shows the value of the naïve library to generate antibodies against toxin targets in addition to the potential use of the library to isolate antibodies against other immunogenic targets.
    Matched MeSH terms: Salmonella typhi/genetics
  15. Fulltext Delineation of B-cell Epitopes of Salmonella enterica serovar Typhi Hemolysin E: Potential antibody therapeutic target
    Chin CF, Lai JY, Choong YS, Anthony AA, Ismail A, Lim TS
    Sci Rep, 2017 05 19;7(1):2176.
    PMID: 28526816 DOI: 10.1038/s41598-017-01987-8
    Hemolysin E (HlyE) is an immunogenic novel pore-forming toxin involved in the pathogenesis of typhoid fever. Thus, mapping of B-cell epitopes of Salmonella enterica serovar Typhi (S. Typhi) is critical to identify key immunogenic regions of HlyE. A random 20-mer peptide library was used for biopanning with enriched anti-HlyE polyclonal antibodies from typhoid patient sera. Bioinformatic tools were used to refine, analyze and map the enriched peptide sequences against the protein to identify the epitopes. The analysis identified both linear and conformational epitopes on the HlyE protein. The predicted linear GAAAGIVAG and conformational epitope PYSQESVLSADSQNQK were further validated against the pooled sera. The identified epitopes were then used to isolate epitope specific monoclonal antibodies by antibody phage display. Monoclonal scFv antibodies were enriched for both linear and conformational epitopes. Molecular docking was performed to elucidate the antigen-antibody interaction of the monoclonal antibodies against the epitopes on the HlyE monomer and oligomer structure. An in-depth view of the mechanistic and positional characteristics of the antibodies and epitope for HlyE was successfully accomplished by a combination of phage display and bioinformatic analysis. The predicted function and structure of the antibodies highlights the possibility of utilizing the antibodies as neutralizing agents for typhoid fever.
    Matched MeSH terms: Salmonella typhi/genetics
  16. Rapid detection of Salmonella Typhi by loop-mediated isothermal amplification (LAMP) method
    Abdullah J, Saffie N, Sjasri FA, Husin A, Abdul-Rahman Z, Ismail A, et al.
    Braz J Microbiol, 2014;45(4):1385-91.
    PMID: 25763045
    An in-house loop-mediated isothermal amplification (LAMP) reaction was established and evaluated for sensitivity and specificity in detecting the presence of Salmonella Typhi (S. Typhi) isolates from Kelantan, Malaysia. Three sets of primers consisting of two outer and 4 inner were designed based on locus STBHUCCB_38510 of chaperone PapD of S. Typhi genes. The reaction was optimised using genomic DNA of S. Typhi ATCC7251 as the template. The products were visualised directly by colour changes of the reaction. Positive results were indicated by green fluorescence and negative by orange colour. The test was further evaluated for specificity, sensitivity and application on field samples. The results were compared with those obtained by gold standard culture method and Polymerase Chain Reaction (PCR). This method was highly specific and -10 times more sensitive in detecting S. Typhi compared to the optimised conventional polymerase chain reaction (PCR) method.
    Matched MeSH terms: Salmonella typhi/genetics
  17. Salmonella enterica serovar Typhi cutF is upregulated during environmental stress
    Lau KL, Ong EB, Zainudin ZF, Samian MR, Ismail A, Najimudin N
    J Gen Appl Microbiol, 2013;59(3):239-44.
    PMID: 23863294
    Matched MeSH terms: Salmonella typhi/genetics
  18. Multidrug-resistant strains of Salmonella enterica serotype typhi are genetically homogenous and coexist with antibiotic-sensitive strains as distinct, independent clones
    Thong KL, Bhutta ZA, Pang T
    Int J Infect Dis, 2000;4(4):194-7.
    PMID: 11231181
    OBJECTIVE: The goal of this study was to report the molecular analysis of antibiotic-sensitive and multidrug-resistant (MDR) strains of Salmonella typhi, using pulsed-field gel electrophoresis (PFGE), with a particular emphasis on the coexistence of these strains in a typhoid-endemic region of Karachi, Pakistan.

    METHODS: One hundred isolates of S. typhi in humans (50 MDR and 50 antibiotic-sensitive isolates) from sporadic cases of typhoid fever were analyzed by Vi-phage typing, antibiograms and PFGE.

    RESULTS: The MDR S. typhi strains were resistant to ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole. Analysis by PFGE showed that 50 MDR isolates of S. typhi had a single, homogenous PFGE profile, which was distinctly different from that of 50 antibiotic-sensitive isolates obtained in the same time frame from the same area. This latter group of isolates showed much greater diversity of PFGE profiles, as has been observed in other endemic regions.

    CONCLUSIONS: Multidrug-resistant and antibiotic-susceptible strains of S. typhi can coexist in endemic areas as epidemiologically independent pathogens and are not in competition for continued persistence and transmission.

    Matched MeSH terms: Salmonella typhi/genetics
  19. Genetic dynamics of Salmonella typhi--diversity in clonality
    Pang T
    Trends Microbiol., 1998 Sep;6(9):339-42.
    PMID: 9778724
    Matched MeSH terms: Salmonella typhi/genetics*
  20. Genome size variation among recent human isolates of Salmonella typhi
    Thong KL, Puthucheary SD, Pang T
    Res. Microbiol., 1997 Mar-Apr;148(3):229-35.
    PMID: 9765803
    We performed genome size estimation of 17 recent human isolates of Salmonella typhi from geographically diverse regions using pulsed-field gel electrophoresis (PFGE) after digestion of chromosomal DNA with restriction endonucleases XbaI (5'-TCTAGA-3'), AvrII (5'-CCTAGG-3') and SpeI (5'-ACTAGT-3'), and summation of the sizes of restriction fragments obtained. All 17 isolates had circular chromosomes, and genome sizes differed by as much as 959 kb, ranging from 3,964 to 4,923 kb (mean genome size = 4,528 kb). The data obtained confirm the usefulness of PFGE in studies of bacterial genome size and are in agreement with recent results indicating considerable genetic diversity and genomic plasticity of S. typhi. The variation in genome sizes noted may be relevant to the observed biological properties of this important human pathogen, including its virulence.
    Matched MeSH terms: Salmonella typhi/genetics*
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