Displaying publications 1 - 20 of 114 in total

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  1. Yap CH, Ramle AQ, Lim SK, Rames A, Tay ST, Chin SP, et al.
    Bioorg Med Chem, 2023 Nov 15;95:117485.
    PMID: 37812886 DOI: 10.1016/j.bmc.2023.117485
    Staphylococcus aureus is a highly adaptable opportunistic pathogen that can form biofilms and generate persister cells, leading to life-threatening infections that are difficult to treat with antibiotics alone. Therefore, there is a need for an effective S. aureus biofilm inhibitor to combat this public health threat. In this study, a small library of indolenine-substituted pyrazoles and pyrimido[1,2-b]indazole derivatives were synthesised, of which the hit compound exhibited promising antibiofilm activities against methicillin-susceptible S. aureus (MSSA ATCC 29213) and methicillin-resistant S. aureus (MRSA ATCC 33591) at concentrations significantly lower than the planktonic growth inhibition. The hit compound could prevent biofilm formation and eradicate mature biofilms of MSSA and MRSA, with a minimum biofilm inhibitory concentration (MBIC50) value as low as 1.56 µg/mL and a minimum biofilm eradication concentration (MBEC50) value as low as 6.25 µg/mL. The minimum inhibitory concentration (MIC) values of the hit compound against MSSA and MRSA were 50 µg/mL and 25 µg/mL, respectively, while the minimum bactericidal concentration (MBC) values against MSSA and MRSA were > 100 µg/mL. Preliminary structure-activity relationship analysis reveals that the fused benzene ring and COOH group of the hit compound are crucial for the antibiofilm activity. Additionally, the compound was not cytotoxic to human alveolar A549 cells, thus highlighting its potential as a suitable candidate for further development as a S. aureus biofilm inhibitor.
  2. Tay ST, Cheong YM
    Malays J Pathol, 1995 Jun;17(1):35-7.
    PMID: 8907003
    The results of a Mycoplasma pneumoniae serology test performed routinely at the Bacteriology Division, Institute for Medical Research were reviewed. A total of 1402 patients were screened over a period of 4 years (January, 1990-December, 1993), of which 327 (23.3%) were seropositive. The seropositivity rates among Malays, Chinese and Indians were 25.2, 25.4 and 17.8% respectively. The male to female ratio was 1:1. The age specific rate was highest amongst patients of the 6-12 years (35.1%) followed by the 13-20 years age groups (35.0%). In general, infection with M. pneumoniae appears to be relatively common in this country.
  3. Tay ST, Na SL, Chong J
    J Med Microbiol, 2009 Feb;58(Pt 2):185-191.
    PMID: 19141735 DOI: 10.1099/jmm.0.004242-0
    The genetic heterogeneity and antifungal susceptibility patterns of Candida parapsilosis isolated from blood cultures of patients were investigated in this study. Randomly amplified polymorphic DNA (RAPD) analysis generated 5 unique profiles from 42 isolates. Based on the major DNA fragments of the RAPD profiles, the isolates were identified as RAPD type P1 (29 isolates), P2 (6 isolates), P3 (4 isolates), P4 (2 isolates) and P5 (1 isolate). Sequence analysis of the internal transcribed spacer (ITS) gene of the isolates identified RAPD type P1 as C. parapsilosis, P2 and P3 as Candida orthopsilosis, P4 as Candida metapsilosis, and P5 as Lodderomyces elongisporus. Nucleotide variations in ITS gene sequences of C. orthopsilosis and C. metapsilosis were detected. Antifungal susceptibility testing using Etests showed that all isolates tested in this study were susceptible to amphotericin B, fluconazole, ketoconazole, itraconazole and voriconazole. C. parapsilosis isolates exhibited higher MIC(50) values than those of C. orthopsilosis for all of the drugs tested in this study; however, no significant difference in the MICs for these two Candida species was observed. The fact that C. orthopsilosis and C. metapsilosis were responsible for 23.8 and 4.8 % of the cases attributed to C. parapsilosis bloodstream infections, respectively, indicates the clinical relevance of these newly described yeasts. Further investigations of the ecological niche, mode of transmission and virulence of these species are thus essential.
  4. Choo S, Chin VK, Wong EH, Madhavan P, Tay ST, Yong PVC, et al.
    Folia Microbiol (Praha), 2020 Jun;65(3):451-465.
    PMID: 32207097 DOI: 10.1007/s12223-020-00786-5
    Garlic (Allium sativum L.) is a well-known spice widely utilised for its medicinal properties. There is an extensive record of the many beneficial health effects of garlic which can be traced back to as early as the ancient Egyptian era. One of the most studied properties of garlic is its ability to cure certain ailments caused by infections. In the 1940s, the antimicrobial activities exhibited by garlic were first reported to be due to allicin, a volatile compound extracted from raw garlic. Since then, allicin has been widely investigated for its putative inhibitory activities against a wide range of microorganisms. Allicin has demonstrated a preference for targeting the thiol-containing proteins and/or enzymes in microorganisms. It has also demonstrated the ability to regulate several genes essential for the virulence of microorganisms. Recently, it was reported that allicin may function better in combination with other antimicrobials compared to when used alone. When used in combination with antibiotics or antifungals, allicin enhanced the antimicrobial activities of these substances and improved the antimicrobial efficacy. Hence, it is likely that combination therapy of allicin with additional antimicrobial drug(s) could serve as a viable alternative for combating rising antimicrobial resistance. This review focuses on the antimicrobial activities exhibited by allicin alone as well as in combination with other substances. The mechanisms of action of allicin elucidated by some of the studies are also highlighted in the present review in order to provide a comprehensive overview of this versatile bioactive compound and the mechanistic evidence supporting its potential use in antimicrobial therapy.
  5. Tay ST, Kho KL, Wee WY, Choo SW
    Acta Trop, 2016 Mar;155:25-33.
    PMID: 26658020 DOI: 10.1016/j.actatropica.2015.11.019
    Bartonella elizabethae has been known to cause endocarditis and neuroretinitis in humans. The genomic features and virulence profiles of a B. elizabethae strain (designated as BeUM) isolated from the spleen of a wild rat in Kuala Lumpur, Malaysia are described in this study. The BeUM strain has a genome size of 1,932,479bp and GC content of 38.3%. There is a high degree of conservation between the genomes of strain BeUM with B. elizabethae type strains (ATCC 49927 and F9251) and a rat-borne strain, Re6043vi. Of 2137 gene clusters identified from B. elizabethae strains, 2064 (96.6%) are indicated as the core gene clusters. Comparative genome analysis of B. elizabethae strains reveals virulence genes which are known in other pathogenic Bartonella species, including VirB2-11, vbhB2-B11, VirD4, trw, vapA2-5, hbpA-E, bepA-F, bepH, badA/vomp/brp, ialB, omp43/89 and korA-B. A putative intact prophage has been identified in the strain BeUM, in addition to a 8kb pathogenicity island. The whole genome analysis supports the zoonotic potential of the rodent-borne B. elizabethae, and provides basis for future functional and pathogenicity studies of B. elizabethae.
  6. Tay ST, Rohani MY, Ho TM, Devi S
    PMID: 12757225
    Isolation of rickettsiae from patients' blood samples and organ samples of wild rodents from areas with high seroprevalence of rickettsial infections was attempted using cell culture assay and animal passages. L929 mouse fibroblast cells grown in 24 well tissue culture plate were inoculated with buffy coat of febrile patients and examined for the growth of rickettsiae by Giemsa, Gimenez staining and direct immunofluorescence assay. No rickettsiae were isolated from 48 patients' blood samples. No symptomatic infections were noted in mice or guinea pigs infected with 50 organ samples of wild rodents. There was no rickettsial DNA amplified from these samples using various PCR detection systems for Orientia tsutsugamushi, typhus and spotted fever group rickettsiae.
  7. Tay ST, Rohani MY, Ho TM, Devi S
    PMID: 12693592
    The pathogenicity of Malaysian isolates of Orientia tsutsugamushi was investigated by a mouse virulence assay. The isolates could be differentiated as low (4 isolates), moderately (3 isolates) and highly virulent (2 isolates) based on the different responses in infected mice. No direct correlation between severity of human scrub typhus infections and virulence of the O. tsutsugamushi in mice was observed. Mice infected with virulent strains of O. tsutsugamushi showed splenomegaly, ascitis accumulation and enlargement of kidneys and livers whereas avirulent O. tsutsugamushi strains were asymptomatic and exhibited ruffled fur for a short period after infection. There was low antibody response in mice infected with isolates of low pathogenicity as compared with those of highly virulent isolates. Upon dissection of the infected mice, enlargement of mouse organs such as spleen, kidney and liver was noted. Presence of rickettsemia in mice was confirmed by the growth of O. tsutsugamushi in the L929 cells when inoculated with blood from infected mice. O. tsutsugamushi was also cultured from the peritoneal exudates of the infected mice. However, DNA of O. tsutsugamushi was only detected in the peritoneal exudates (by PCR) and blood (by cell culture) and not from other tissue samples.
  8. Tay ST, Rohani MY, Ho TM, Devi S
    PMID: 12693591
    The seroprevalence of various Orientia tsutsugamushi (OT) strains among Malaysian patients with suspected scrub typhus infections was determined using an indirect immunoperoxidase (IIP) assay. IgG against a single OT strain were detected in six sera (3 Karp, 1 Gilliam and 2 TC586), whereas IgM antibodies against a single OT strain (Gilliam) were noted in 3 sera (Gilliam). IgG reactive to all OT strains were present in 33 (47.1%) of the 70 sera and IgM reactive to all OT strains were present in 22 (78.6%) of the 28 sera. The fact that most sera were reactive to multiple OT strains suggests that group-specific antigens are involved in scrub typhus infections, whereas very few were due to strain-specific epitopes present on these strains. Peak IgG and IgM titers were noted more frequently against Gilliam, Karp, and TA763 strains: this suggests that these strains may be the commonest infecting strains among Malaysian patients. Two predominant OT polypeptides consistently reacted with patients' sera were the 70 kDa and 56 kDa proteins.
  9. Tay ST, Rohani MY, Ho TM, Devi S
    Diagn Microbiol Infect Dis, 2002 Oct;44(2):137-42.
    PMID: 12458119
    In this study, recombinant proteins that encompassed the AD I-AD III regions of 56 kDa immunodominant gene of 2 Orientia tsutsugamushi (OT) serotypes; Gilliam and TA763 were expressed in Escherichia coli. Both recombinant proteins exhibited serologic cross-reactivity with the rabbit antisera against various OT serotypes, as evaluated by enzyme-linked immunosorbent assay (ELISA), but not against other rickettsial species, including Rickettsia typhi, R. prowazekii and TT118 SFG rickettsiae. The feasibility of using the recombinant proteins as a diagnostic reagent was further evaluated by ELISA using sera from blood donors and scrub typhus patients. The results suggested a higher affinity of the antihuman IgM than IgG with both recombinant proteins. The IgM ELISA findings were agreeable with the results of indirect immunoperoxidase (IIP) assay especially with sera of high antibody (1:1600). However, more than one antigen are probably needed for development of an effective assay for serodiagnosis of scrub typhus in endemic areas.
  10. Tay ST, Ho TM, Rohani MY, Devi S
    Trans R Soc Trop Med Hyg, 2000 9 7;94(3):280-4.
    PMID: 10974999
    A serosurvey was conducted in 1995-97 among 1596 febrile patients from 8 health centres in Malaysia for antibodies against Orientia tsutsugamushi (OT), Rickettsia typhi (RT) and TT118 spotted fever group rickettsiae (SFGR) by using an indirect immunoperoxidase assay. A total of 51.4% patients had antibody against at least 1 of those rickettsiae. Antibody to SFGR was most prevalent (42.5%), followed by RT (28.1%) and OT (24.9%). The seroprevalences of antibodies to SFGR, RT or OT alone were 12.4, 3.6 and 4.3%, respectively. Antibodies against more than 1 species of rickettsiae were presence in 31.1% of the patients, suggesting the possibility of co-infection, previous exposures or serological cross-reactivities. Seroprevalence of the various rickettsiae varied according to locality, with SFGR antibodies being the most prevalent in most areas. There was no significant association of prevalence of rickettsial antibody with gender. The seroprevalence of OT, SFGR and RT increased with patient age but an increase of antibody titre with age was not significant. Those working in the agricultural sectors had significantly higher seroprevalence of OT, SFGR and RT than those not related with agricultural activities. Scrub typhus remains a public health problem with an estimated annual attack rate of 18.5%. Tick typhus and murine typhus as shown in this serosurvey appear much more widespread than scrub typhus in this country.
  11. Tay ST, Rohani MY, Ho TM, Devi S
    PMID: 12971561
    Using cultured mouse fibroblast L929 cells, this study demonstrated the hemolytic and cytotoxic activities and induction of apoptosis in cells infected with Orientia tsutsugamushi. Low levels of hemolytic activity were detected using heavily infected cells. No hemolysin or cytotoxin were detected in the infected culture fluid regardless of the pathogenicity of the O. tsutsugamushi strains in mice. Using propidium iodide uptake assay, acridine orange/ethidium bromide staining and terminal deoxynucleotide transferase-mediated dUTP-digoxigenin nick-end labeling assay, apoptosis was observed in L929 cells infected with Karp and Gilliam strains.
  12. Tay ST, Tanty Haryanty T, Ng KP, Rohani MY, Hamimah H
    Mycoses, 2006 Jul;49(4):324-30.
    PMID: 16784448
    The in vitro susceptibilities of Malaysian clinical isolates of Cryptococcus neoformans var. grubii and C . gattii to five antifungal drugs (amphotericin B, flucytosine, fluconazole, itraconazole and ketoconazole) were determined using the Etest method. None of the Malaysian isolates was resistant to amphotericin B and ketoconazole. Isolates resistant to flucytosine, fluconazole and itraconazole were observed in this study. Minimum inhibition concentrations (MICs) of > or = 32 microg ml(-1) against flucytosine, > or = 64 microg ml(-1) against fluconazole and > or = 1 microg ml(-1) against itraconazole were noted in four (8.3%), two (4.2%) and one (2.1%) isolates respectively. There was no significant difference in the MICs for both Cryptococcus species (P > 0.05), indicating that C. gattii was as susceptible as var. grubii to all the antifungal drugs tested. No significant difference in the MICs for both Cryptococcus species collected from 1980 to 1990 and 2002 to 2004 were observed (P > 0.05).
  13. Tay ST, Rohani MY, Hoo TS, Hamimah H
    Mycoses, 2010 Nov;53(6):509-14.
    PMID: 19627508 DOI: 10.1111/j.1439-0507.2009.01750.x
    This study describes the isolation of Cryptococcus neoformans and Cryptococcus gattii from patients with chronic meningitis who were admitted to 16 Malaysian hospitals, from 2003 to 2004. Of the 96 cryptococcal cases reported over the 2-year period, 74 (77.1%) patients were male and 45 (46.9%) patients were between 30 and 39 years old. Cryptococcosis was uncommon in children. A total of 57 (59.4%) and 23 (24.0%) patients were Malay and Chinese respectively. Human immunodeficiency virus infection was the major underlying disease reported in 36 (37.5%) patients. C. neoformans var. grubii (serotype A and molecular type VNI) was the predominant Cryptococcus species isolated from 88.5% of cryptococcal cases in this country. Cryptococcal cases due to C. neoformans var. grubii were reported from all the five regions in Malaysia, with the most number of cases reported from the central and northern regions. Cryptococcus gattii (all were serotype B and molecular types VGI/II) was isolated from all regions except the southern region. Compared with a study conducted prior to the AIDS era, our findings show substantial changes in the demographical characteristics of patients.
  14. Ghane Kisomi M, Wong LP, Tay ST, Bulgiba A, Zandi K, Kho KL, et al.
    PLoS One, 2016;11(6):e0157987.
    PMID: 27341678 DOI: 10.1371/journal.pone.0157987
    BACKGROUND: Farmworkers are at high-risk for tick bites, which potentially transmit various tick-borne diseases. Previous studies show that personal prevention against tick bites is key, and certain factors namely, knowledge, experience of tick bites, and health beliefs influence compliance with tick bites preventive behaviour. This study aimed to assess these factors and their associations with tick bite preventive practices among Malaysian farmworkers.

    METHODS: A total of eight cattle, goat and sheep farms in six states in Peninsular Malaysia participated in a cross-sectional survey between August and October 2013.

    RESULTS: A total of 151 (72.2%) out of 209 farmworkers answered the questionnaire. More than half of the farmworkers (n = 91) reported an experience of tick bites. Farms with monthly acaricide treatment had significantly (P<0.05) a low report of tick bites. Tick bite exposure rates did not differ significantly among field workers and administrative workers. The mean total knowledge score of ticks for the overall farmworkers was 13.6 (SD±3.2) from 20. The mean total tick bite preventive practices score for all farmworkers was 8.3 (SD±3.1) from 15. Fixed effect model showed the effects of four factors on tick bite prevention: (1) farms, (2) job categories (administrative workers vs. field workers), (3) perceived severity of tick bites, and (4) perceived barriers to tick bite prevention.

    CONCLUSIONS: A high proportion of farmworkers, including administrative workers, reported an experience of tick bites. The effectiveness of monthly acaricide treatment was declared by low reports of tick bites on these farms. Tick bite preventive practices were insufficient, particularly in certain farms and for administrative workers. Our findings emphasise the need to have education programmes for all farmworkers and targeting farms with low prevention practices. Education and health programmes should increase the perception of the risk of tick bites and remove perceived barriers of tick bite prevention.

  15. Tay ST, Wong PL, Chiu CK, Tang SN, Lee JL, Hamdan NW, et al.
    Eur Rev Med Pharmacol Sci, 2021 01;25(2):605-608.
    PMID: 33577013 DOI: 10.26355/eurrev_202101_24618
    OBJECTIVE: Nocardia kroppenstedtii was isolated from the spinal vertebral abscess of a 78-year-old patient presenting with mid-thoracic pain and bilateral lower limb weakness and numbness. The patient was on long-term immunosuppressive therapy with steroids for underlying autoimmune hemolytic anemia. Investigations showed a T5 pathological fracture and vertebra plana with the erosion of the superior and inferior endplates. There was evidence of paraspinal collection from the T4-T6 vertebrae with an extension into the spinal canal. Analysis of Nocardia 16S rRNA (99.9%, 1395/1396 nt) and secA1 gene (99.5%, 429/431 nt) fragments showed the highest sequence similarity with Nocardia kroppenstedtii type strain (DQ157924), and next with Nocardia farcinica (Z36936). The patient was treated with intravenous carbapenem and oral trimethoprim-sulfamethoxazole for four weeks, followed by another six months of oral trimethoprim-sulfamethoxazole. Despite the improvement of neurological deficits, the patient required assistive devices to ambulate at discharge. This study reports the first isolation of N. kroppenstedtii from the spinal vertebral abscess of a patient from Asia. Infections caused by N. kroppenstedtii may be underdiagnosed as the bacterium can be misidentified as N. farcinica in the absence of molecular tests in the clinical laboratory.
  16. Tay ST, Merican AM, Abdul Jabar K, Velayuthan RD, Ayob KA, Lee JL, et al.
    Int J Infect Dis, 2023 Nov;136:77-80.
    PMID: 37660726 DOI: 10.1016/j.ijid.2023.08.025
    We report the isolation of a rare Gram-positive coccobacillary bacterium from synovial fluids of a patient with periprosthetic joint infection on three occasions over an 8-month period. As routine microbiological methods were not able to identify the isolate definitely, sequence analyses of the bacterial 16S ribosomal RNA gene and whole genome were performed. Analysis of the bacterial 16S ribosomal RNA gene showed the highest similarity (98.1%) with that of Falsarthrobacter (previously known as Arthrobacter) nasiphocae, which was first isolated from the nasal cavities of common seals (Phoca vitulina). The genome size of the strain (designated as UM1) is 2.4 Mb. With a high G+C content (70.4 mol%), strain UM1 is phylogenetically most closely related to F. nasiphocae based on whole genome analysis. Strain UM1 was susceptible to vancomycin, linezolid, trimethoprim-sulfamethoxazole, doxycycline, and intermediate to penicillin and ciprofloxacin. Ceftriaxone resistance was noted. The patient who was also on hemodialysis for his end stage kidney disease died approximately 3 weeks following implant removal and fusion with an external fixator. This study describes the first isolation of F. nasiphocae from human clinical samples. The use of emerging technologies has supported more definitive etiological diagnosis associated with rarely encountered organisms in periprosthetic joint infection.
  17. Tay ST, Devi S, Puthucheary S, Kautner I
    Zentralbl. Bakteriol., 1996 Mar;283(3):306-13.
    PMID: 8861868
    By means of the gentamicin HEp-2 cell invasion assay, it was demonstrated that 82% of the Campylobacters tested were cell-invasive, including 83% of isolates from bloody diarrhoea and 80% of isolates from watery diarrhoea. The large number of invasive strains from watery diarrhoea suggests the possible role of invasiveness in the production of watery diarrhoea. Whether this stage can progress further to more severe symptoms such as bloody diarrhoea remains to be elucidated. Whether this progression to bloody diarrhoea occurs as a result of toxin production is still debatable. In Vero cells, invasion was less efficient and intracellular multiplication was not observed.
  18. Tay ST, Puthucheary SD, Devi S, Kautner I
    Singapore Med J, 1995 Jun;36(3):282-4.
    PMID: 8553093
    Eight-five clinical and 15 poultry isolates of Campylobacter species were characterised by biotyping, serotyping and by using a radiolabelled DNA probe. A total of 80% of the isolates from both sources were identified as C. jejuni. Also amongst the clinical strains were 5 c. jejuni subsp. doylei, 7 C. coli, 3 C. lari and 8 were untypable. The similarity in the distribution of C. jejuni in the clinical and poultry isolates adds credibility to published reports of chickens being the most common source of Campylobacter infections. Although the gold standard for identification of C. jejuni is the DNA probe, serotyping is more discriminating while biotyping is the most feasible method in most laboratories.
  19. Tay ST, Devi S, Puthucheary SD, Kautner IM
    J Med Microbiol, 1995 Mar;42(3):175-80.
    PMID: 7884798
    There are several methods for the detection of haemolytic activity in campylobacters. However, we found the haemolytic effect of campylobacters on conventional blood agar plates to be variable, inconsistent and difficult to interpret. Blood agarose plates showed campylobacter haemolytic activity more clearly. The incubation conditions (temperature and gaseous) appear to be important for the expression of this activity. Ninety four percent of the Campylobacter isolates examined were found to be haemolytic by the microplate assay with minimal haemolytic units that ranged from 1 to 64. Haemolytic activity was detected only from live bacterial cultures and not from any of the 50 bacterial culture supernates, which suggests that campylobacters may possess a cell-associated haemolysin. The identification of such haemolytic activity in a large number of campylobacters (94%) suggests its potential role as a virulence factor in campylobacter gastroenteritis.
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