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Fulltext Diagnosis of scrub typhus in Malaysian aborigines using nested polymerase chain reaction

Tay ST, Nazma S, Rohani MY

Southeast Asian J. Trop. Med. Public Health, 1996 Sep;27(3):580-3.
PMID: 9185274

A rapid diagnostic system for scrub typhus using nested polymerase chain reaction (PCR) was applied to clinical samples from Malaysian Aborigines. Whole blood from twenty-four patients suspected of scrub typhus infection were tested using nested polymerase chain reaction and sera were evaluated by the indirect immunoperoxidase test. Antibody responses towards Rickettsia tsutsugamushi were observed in seventeen patients with the majority having high titers of IgG antibodies. Seven patients were seronegative. The nested PCR amplified R. tsutsugamushi DNA from six patients, of which two were negative serologically and four had high titers of IgG antibodies. Second samples collected seven days after treatment were negative by PCR testing. Nested PCR is highly sensitive and specific and may be used to provide rapid confirmation of scrub typhus cases in endemic region.
Fulltext Use of hemolymph test for detection of rickettsiae in Malaysian ticks

Tay ST, Ho TM, Rohani MY

Southeast Asian J. Trop. Med. Public Health, 1996 Sep;27(3):642-4.
PMID: 9185285
Emergence of Klebsiella pneumoniae producing dual carbapenemases (NDM-1 and OXA-232) and 16S rRNA methylase (armA) isolated from a Malaysian patient returning from India

Al-Marzooq F, Ngeow YF, Tay ST

Int J Antimicrob Agents, 2015 Apr;45(4):445-6.
PMID: 25631676 DOI: 10.1016/j.ijantimicag.2014.12.013
Analysis of integrons and associated gene cassettes of metallo-β-lactamase-positive Pseudomonas aeruginosa in Malaysia

Khosravi Y, Tay ST, Vadivelu J

J Med Microbiol, 2011 Jul;60(Pt 7):988-994.
PMID: 21436370 DOI: 10.1099/jmm.0.029868-0

In this study, 90 non-replicate imipenem-resistant Pseudomonas aeruginosa (IRPA) Malaysian isolates collected between October 2005 and March 2008 were subjected to a screening test for detection of the integron and the gene cassette. Class 1 integrons were detected in 54 IRPA clinical isolates, whilst three isolates contained class 2 integrons. Analysis of the gene cassettes associated with the class 1 integrons showed the detection of accC1 in isolates carrying bla(IMP-7) and aacA7 in isolates carrying bla(VIM-2). aadA6 was detected in two isolates carrying bla(IMP-4). Using random amplification of polymorphic DNA analysis, 14 PCR fingerprint patterns were generated from the 32 isolates carrying metallo-β-lactamase (MBL) genes (35.5 %), whilst 20 patterns were generated from the 58 non-MBL gene isolates (64.4 %). Based on the differences in the fingerprinting patterns, two clusters (A and B) were identified among the MBL-producing isolates. Cluster A comprised 18 isolates (56 %) carrying the bla(VIM) gene, whereas cluster B comprised 14 (44 %) isolates carrying the bla(IMP) gene. The non-MBL isolates were divided into clusters C and D. Cluster C comprised 22 non-MBL isolates harbouring class 1 integrons, whilst cluster D consisted of three isolates carrying class 2 integrons. These findings suggest that the class 1 integron is widespread among P. aeruginosa isolated in Malaysia and that characterization of cassette arrays of integrons will be a useful epidemiological tool to study the evolution of multidrug resistance and the dissemination of antibiotic resistance genes.
Molecular differentiation and antifungal susceptibilities of Candida parapsilosis isolated from patients with bloodstream infections

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.
Fulltext Molecular detection of Anaplasma platys and Babesia gibsoni in dogs in Malaysia

Mokhtar AS, Lim SF, Tay ST

Trop Biomed, 2013 Jun;30(2):345-8.
PMID: 23959500 MyJurnal

This study reports for the first time molecular detection of Anaplasma platys infection in 4 (13.3%) of 30 Malaysian dogs investigated. A low occurrence (3.3%) of Babesia gibsoni was also noted, being detected in one of the 30 dogs. Rickettsia, Bartonella, Orientia tsutsugamushi, and Ehrlichia DNA were not detected in the dog blood samples. The role of A. platys as an agent of canine anaplasmosis and its transmission through Rhipicephalus sanguineus ticks merits further investigation.
Fulltext Colonial morphotypes and biofilm forming ability of Burkholderia pseudomallei

Koh SF, Tay ST, Puthucheary SD

Trop Biomed, 2013 Sep;30(3):428-33.
PMID: 24189672 MyJurnal

Burkholderia pseudomallei the causative agent of melioidosis, is being increasingly recognized as an important cause of morbidity and mortality in South East Asia. Biofilm formation of B. pseudomallei may be responsible for dormancy, latency and relapse of melioidosis. Based on the colonial morphology of the bacteria on B. pseudomallei selective agar medium, seven distinct morphotypes were identified. This study was conducted to assess the in vitro biofilm produced by B. pseudomallei and to investigate possible correlation between B. pseudomallei morphotypes with biofilm forming abilities of the isolates. Using a standard biofilm crystal violet staining assay, comparison was made between the biofilm forming ability of 76 isolates of B. pseudomallei and Burkholderia thailandensis ATCC 700388. Amongst the blood isolates, 30.2% were considered as high biofilm producers and 27.9% were low producers, 33.3% of the pus isolates were considered as high and 16% low biofilm producers. Most of the isolates were identified as morphotype group 1 which displayed a rough centre with irregular circumference on the agar medium. However, we did not find any correlation of B. pseudomallei morphotypes with biofilm forming abilities (p > 0.05). Additional studies are needed to identify internal and external factors which contribute to the high and low biofilm formation of B. pseudomallei.
Fulltext Reduced susceptibility of Malaysian clinical isolates of Burkholderia pseudomallei to ciprofloxacin

Liew FY, Tay ST, Puthucheary SD

Trop Biomed, 2011 Dec;28(3):646-50.
PMID: 22433895 MyJurnal

Ciprofloxacin, a quinolone with good intracellular penetration may possibly be used for treatment of melioidosis caused by Burkholderia pseudomallei, but problems with resistance may be encountered. Amino acid substitutions in gyrA/gyrB have given rise to fluoroquinolone resistance in various microorganisms. Using published primers for gyrA and gyrB, PCR was performed on 11 isolates of B. pseudomallei with varying degrees of sensitivity to ciprofloxacin, followed by DNA sequencing to detect possible mutations. Results showed an absence of any point mutation in either gene. Local isolates have yet to develop full resistance to ciprofloxacin and probably other mechanisms of resistance may have been involved in the decreased sensitivity to ciprofloxacin.
Diversity of Rickettsiae in Feeding and Questing Ticks Collected From a Malaysian Forest Reserve Area

Kho KL, Tan PE, Tay ST

J Med Entomol, 2019 02 25;56(2):547-552.
PMID: 30304529 DOI: 10.1093/jme/tjy168

High seropositivity to Rickettsia conorii and Rickettsia felis has been reported in Malaysian indigenous community living in settlements adjacent to forest areas. The current study was conducted to determine the type and distribution of rickettsiae in feeding and questing ticks that were collected from a forest reserve area at Kuala Lompat in Pahang, Malaysia. Using PCR assays targeting citrate synthase (gltA), outer membrane protein A (ompA) and B (ompB) genes, rickettsiae were detected from approximately one-third of 98 ticks (mainly Dermacentor and Haemaphysalis spp.) collected from the forest reserve. BLAST analysis reveals the predominance of Rickettsia sp. RF2125 in both feeding and questing ticks and Rickettsia sp. TCM1 in the questing ticks. Sequences exhibiting close genetic relationship with Rickettsia raoultii, Rickettsia tamurae, Rickettsia heilongjiangensis, and Rickettsia asiatica were also detected from the ticks. This study highlights the diversity of rickettsial species and potential tick vectors which may contribute to the high seropositivity observed among the local communities.
A study on Candida biofilm growth characteristics and its susceptibility to aureobasidin A

Munusamy K, Vadivelu J, Tay ST

Rev Iberoam Micol, 2018 03 12;35(2):68-72.
PMID: 29544734 DOI: 10.1016/j.riam.2017.07.001

BACKGROUND: Biofilm is known to contribute to the antifungal resistance of Candida yeasts. Aureobasidin A (AbA), a cyclic depsipeptide targeting fungal sphingolipid biosynthesis, has been shown to be effective against several Candida species.
AIMS: The aim of this study was to investigate Candida biofilm growth morphology, its biomass, metabolic activity, and to determine the effects of AbA on the biofilm growth.
METHODS: The biofilm forming ability of several clinical isolates of different Candida species from our culture collection was determined using established methods (crystal violet and XTT assays). The determination of AbA planktonic and biofilm MICs was performed based on a micro-broth dilution method. The anti-biofilm effect of AbA on Candida albicans was examined using field emission scanning electron microscope (FESEM) analysis.
RESULTS: A total of 35 (29.7%) of 118 Candida isolates were regarded as biofilm producers in this study. Candida parapsilosis was the largest producer, followed by Candida tropicalis and C. albicans. Two morphological variants of biofilms were identified in our isolates, with 48.6% of the isolates showing mainly yeast and pseudohyphae-like structures, while the remaining ones were predominantly filamentous forms. The biofilm producers were divided into two populations (low and high), based on the ability in producing biomass and their metabolic activity. Candida isolates with filamentous growth, higher biomass and metabolic activity showed lower AbA MIC50 (at least fourfold), compared to those exhibiting yeast morphology, and lower biomass and metabolic activity. The observation of filament detachment and the almost complete removal of biofilm from AbA-treated C. albicans biofilm in FESEM analysis suggests an anti-biofilm effect of AbA.
CONCLUSIONS: The variability in the growth characteristics of Candida biofilm cultures affects susceptibility to AbA, with higher susceptibility noted in biofilm cultures exhibiting filamentous form and high biomass/metabolic activity.
Fulltext Characterisation of Campylobacters from Malaysia

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.
Natural occurrence and growth reaction on canavanine-glycine-bromothymol blue agar of non-neoformans Cryptococcus spp. in Malaysia

Tay ST, Na SL, Tajuddin TH

Mycoses, 2008 Nov;51(6):515-9.
PMID: 18498307 DOI: 10.1111/j.1439-0507.2008.01516.x

Cryptococcus albidus and C. laurentii were the predominant non-neoformans cryptococci isolated during an environmental sampling study for C. gattii at Klang Valley, Malaysia. Cryptococcus gattii was not isolated from any of the environmental samples. Cryptococcus albidus and C. laurentii were isolated mainly from vegetative samples of Eucalyptus trees and bird droppings. Upon testing on canavanine-glycine-bromothymol blue (CGB) agar, all the C. albidus isolates remained unchanged. Interestingly, a total of 29 (76.3%) C. laurentii isolates formed blue colours on the CGB agar. Sequence analysis of ITS1-5.8rDNA-ITS2 gene sequences (468 bp) of four CGB-blue C. laurentii isolates demonstrated the closest match (99%) with that of C. laurentii CBS 7140. This study demonstrated the diverse environmental niche of C. albidus and C. laurentii in Malaysia.
Fulltext Sequence polymorphism and PCR-restriction fragment length polymorphism analysis of the flagellin gene of Burkholderia pseudomallei

Tay ST, Cheah PC, Puthucheary SD

J Clin Microbiol, 2010 Apr;48(4):1465-7.
PMID: 20089759 DOI: 10.1128/JCM.01131-09

Four flagellin allelic types (I to IV) of Burkholderia pseudomallei were identified based on their sequence variation and restriction fragment length polymorphism (RFLP) analysis of the amplified flagellin gene. Flagellin allelic type I was the most predominantly (75.0%) found among the 100 clinical isolates of B. pseudomallei investigated in this study.
Whole-genome sequence analysis and exploration of the zoonotic potential of a rat-borne Bartonella elizabethae

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.
Fulltext Molecular analysis of ciprofloxacin resistance mechanisms in Malaysian ESBL-producing Klebsiella pneumoniae isolates and development of mismatch amplification mutation assays (MAMA) for rapid detection of gyrA and parC mutations

Al-Marzooq F, Mohd Yusof MY, Tay ST

Biomed Res Int, 2014;2014:601630.
PMID: 24860827 DOI: 10.1155/2014/601630

Ninety-three Malaysian extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae isolates were investigated for ciprofloxacin resistance. Two mismatch amplification mutation (MAMA) assays were developed and used to facilitate rapid detection of gyrA and parC mutations. The isolates were also screened for plasmid-mediated quinolone resistance (PMQR) genes including aac(6')-Ib-cr, qepA, and qnr. Ciprofloxacin resistance (MICs 4- ≥ 32 μ g/mL) was noted in 34 (37%) isolates, of which 33 isolates had multiple mutations either in gyrA alone (n = 1) or in both gyrA and parC regions (n = 32). aac(6')-Ib-cr was the most common PMQR gene detected in this study (n = 61), followed by qnrB and qnrS (n = 55 and 1, resp.). Low-level ciprofloxacin resistance (MICs 1-2 μ g/mL) was noted in 40 (43%) isolates carrying qnrB accompanied by either aac(6')-Ib-cr (n = 34) or a single gyrA 83 mutation (n = 6). Ciprofloxacin resistance was significantly associated with the presence of multiple mutations in gyrA and parC regions. While the isolates harbouring gyrA and/or parC alteration were distributed into 11 PFGE clusters, no specific clusters were associated with isolates carrying PMQR genes. The high prevalence of ciprofloxacin resistance amongst the Malaysian ESBL-producing K. pneumoniae isolates suggests the need for more effective infection control measures to limit the spread of these resistant organisms in the hospital.
Fulltext Isolation and molecular identification of Bartonellae from wild rats (Rattus species) in Malaysia

Tay ST, Mokhtar AS, Zain SN, Low KC

Am J Trop Med Hyg, 2014 Jun;90(6):1039-42.
PMID: 24732465 DOI: 10.4269/ajtmh.13-0273

This study describes our investigation on the prevalence and molecular identification of bartonellae from Rattus diardii and R. norvegicus in the urban areas of Malaysia. Of 95 rats investigated, Bartonella tribocorum, B. rattimassiliensis, B. coopersplainsensis, B. elizabethae, and B. queenslandensis were isolated from kidney and spleen homogenates of four rats. Bartonellae DNA was amplified from the rat organ tissues by using primers specific for the bartonellae RNA polymerase beta subunit (rpoB) gene in nine other rats. Sequence analysis of the rpoB gene fragments shows the identification of B. queenslandensis in five rats, B. elizabethae in three rats, and B. tribocorum in one rat. Combining the results of isolation and molecular detection of bartonellae, we found that the prevalence of Bartonella infection in the Rattus spp. investigated in this study was 13.7%. Implementation of effective rat control program in the urban areas is necessary to prevent the spillover of bartonellosis from rats to humans.
Prevalence of plasmid-mediated qnr determinants and gyrase alteration in Klebsiella pneumoniae isolated from a university teaching hospital in Malaysia

Saiful Anuar AS, Mohd Yusof MY, Tay ST

Eur Rev Med Pharmacol Sci, 2013 Jul;17(13):1744-7.
PMID: 23852897

The ciprofloxacin resistance of Klebsiella (K.) pneumoniae is mediated primarily through alterations in type II topoisomerase (gyrA) gene and plasmid-mediated quinolone resistance-conferring genes (qnr). This study aimed to define the prevalence of plasmid-mediated quinolone resistance-conferring genes (qnr) and type II topoisomerase (gyrA) alterations of a population of ciprofloxacin-resistant (n = 21), intermediate (n = 8), and sensitive (n = 18) K. pneumoniae isolates obtained from a teaching hospital at Kuala Lumpur, Malaysia.
Fulltext Antibody prevalence and factors associated with exposure to Orientia tsutsugamushi in different aboriginal subgroups in West Malaysia

Tay ST, Mohamed Zan HA, Lim YA, Ngui R

PLoS Negl Trop Dis, 2013;7(8):e2341.
PMID: 23936576 DOI: 10.1371/journal.pntd.0002341

Limited data is available on the current status of scrub typhus infection in the aboriginal population in Malaysia. This study was aimed to provide recent data on the degree of exposure of 280 individuals from seven aboriginal subgroups to Orientia tsutsugamushi (causative agent of scrub typhus) in West Malaysia. The environment, socioeconomic and behavioural risk factors associated with the disease were also investigated.
Diagnostic use of Burkholderia pseudomallei selective media in a low prevalence setting

Roesnita B, Tay ST, Puthucheary SD, Sam IC

Trans R Soc Trop Med Hyg, 2012 Feb;106(2):131-3.
PMID: 22112687 DOI: 10.1016/j.trstmh.2011.10.007

Routine use of selective media improves diagnosis of Burkholderia pseudomallei, but resources may be limited in endemic developing countries. To maximise yield in the relatively low-prevalence setting of Kuala Lumpur, Malaysia, B. pseudomallei selective agar and broth were compared with routine media for 154 respiratory specimens from patients with community-acquired disease. Selective media detected three additional culture-positive specimens and one additional melioidosis patient, at a consumables cost of US$75. Burkholderia pseudomallei was not isolated from 74 diabetic foot ulcer samples. Following careful local evaluation, focused use of selective media may be cost-effective.
Sequence analysis of the hypervariable regions of the 56 kDa immunodominant protein genes of Orientia tsutsugamushi strains in Malaysia

Tay ST, Rohani YM, Ho TM, Shamala D

Microbiol. Immunol., 2005;49(1):67-71.
PMID: 15665455

The DNA sequences encompassing two hypervariable regions, VD II and III of the 56 kDa immunodominant protein gene of 21 Malaysian strains of Orientia tsutsugamushi were determined. Two strains demonstrated a 100% DNA homology with the Gilliam prototype strain, and one with TH1817 strain and TA678 strain respectively. High percentages of DNA similarity (95-99%) were observed with Karp (4 strains), Gilliam (2 strains), TH1817 (4 strains), TC586 (3 strains) and TA763 (1 strain). The remaining strains demonstrated the highest DNA similarity with TA763 (1 strain, 89%), TA678 (1 strain, 86%) and TA686 (1 strain, 87%). Our study provides additional evidence on the existence and the genetic heterogeneity of TA strains of the Southeast Asia and their closely related strains in Malaysia.

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