1.Diversity and killer activity of yeasts in Malaysian fermented food samples
Tropical Biomedicine 2011;28(2):438-443
The biodiversity and the killer activity of yeasts isolated from various types of
fermented food in Malaysia were investigated in this study. Of 252 yeasts isolated from 48
fermented food samples in this study, 19 yeast species were identified based on sequence
analysis of the ITS1-5.8S-ITS2 partial fragments of the yeasts. A total of 29 (11.5%) of the
yeast isolates demonstrated killer activity to at least one Candida species tested in this
study; including 22 isolates of Trichosporon asahii, 4 isolates of Pichia anomala, and one
isolate each of Pichia norvegensis, Pichia fermentans and Issatchenkia orientalis,
respectively. The presence of killer yeasts reflects antagonism that occurs during microbial
interaction in the fermented food, whereby certain yeasts produce killer toxins and possibly
other toxic substances in competition for limited nutrients and space. The anti-Candida
activity demonstrated by killer yeasts in this study should be further explored for development
of alternative therapy against candidiasis.
2.Investigation on the conA binding properties of Klebsiella pneumoniae
Tropical Biomedicine 2014;31(4):802-812
Klebsiella pneumoniae is a healthcare-associated bacterial pathogen which causes
severe diseases in immunocompromised individuals. Concanavalin A (conA), a lectin which
recognizes proteins with mannose or glucose residues, has been reported to agglutinate K.
pneumoniae and hence, is postulated to have therapeutical potential for K. pneumoniaeinduced
liver infection. This study investigated the conA binding properties of a large collection
of clinical isolates of K. pneumoniae. ConA agglutination reaction was demonstrated by 94
(51.4%) of 183 K. pneumoniae isolates using a microtiter plate assay. The conA agglutination
reactions were inhibited in the presence of 2.5 mg/ml D-mannose and 2.5 mg/ml glucose, and
following pretreatment of the bacterial suspension with protease and heating at 80ºC. Majority
of the positive isolates originated from respiratory specimens. Isolation of conA-binding
proteins from K. pneumoniae ATCC 700603 strain was performed using conA affinity column
and the conA binding property of the eluted proteins was confirmed by western blotting
analysis using conA-HRP conjugates. Proteins with molecular weights ranging from 35 to 60
kDa were eluted from the conA affinity column, of which four were identified as outer
membrane protein precursor A (37 kDa), outer membrane protein precursor C (40 kDa),
enolase (45 kDa) and chaperonin (60 kDa) using mass spectrometry analysis. Several conA
binding proteins (including 45 and 60 kDa) were found to be immunogenic when reacted with
rabbit anti-Klebsiella antibody. The function and interplay of the conA binding proteins in
bacterium-host cell relationship merits further investigation.
3.Burkholderia pseudomallei lectins: occurrence and expression
Koh, S.F. ; Tay, S.T. ; Puthucheary, S.D
Tropical Biomedicine 2016;33(4):853-861
Lectins, also known as sugar binding proteins, play an essential role in the initiation
of bacterial infections and biofilm production. To date, several lectins of Gram-negative
bacteria such as Pseudomonas aeruginosa, Burkholderia cenocepacia, Ralstonia
solanacearum and Chromobacterium violaceum have been identified. There are no published
reports on the presence of lectins in Burkholderia pseudomallei, the causative agent of
melioidosis. The aim of this study was to identify possible lectin genes of B. pseudomallei and
generate recombinant proteins for assessment of hemagglutinating activity. Seven hypothetical
lectins of B. pseudomallei were retrieved from the UniProt database. Four lectin domains,
i.e., ricin B, C-type, H-type and Bulb-type lectins were identified. In silico analysis using a
ligand binding site prediction server (3DLigandSite) predicted the presence of Nacetylglucosamine
and calcium binding sites in two C-type lectins. Four recombinant proteins
with the molecular weights of 11.7, 30.2, 36.2 and 46.4 kDa were expressed from the cloned
genes; however none of them expressed any hemagglutinating activity. Further
characterization of B. pseudomallei lectins may be able to provide insights into bacterial-host
interaction that are required to initiate infections.
4.Reduced susceptibility of Malaysian clinical isolates of Burkholderia pseudomallei to ciprofloxacin
Liew, F.Y. ; Tay, S.T. ; Puthucheary, S.D.*
Tropical Biomedicine 2011;28(3):646-650
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.
5.The integron prevalence of extended-spectrum beta-lactamase Malaysian teaching hospital
Ibrahim, N. ; Wajidi, M.F. ; Yusof, M.Y. ; Tay, S.T.*
Tropical Biomedicine 2011;28(3):668-671
The increased frequency of antibiotic resistance is known to be associated with
the dissemination of integrons in the Enterobacteriaceae. This study determined the prevalence
and type of integrons amongst 160 extended-spectrum beta-lactamase producing
enterobacterial isolates kept in our culture collection. Integrons were detected in 98(61.3%)
isolates, including 28(62.2%) Escherichia coli, 34(64.2%) Klebsiella spp., 27(61.4%), Enterobacter
spp. and 9(50.0%) Citrobacter spp. investigated in this study. Restriction analysis of the
integron gene fragments revealed that class I integron was the principal integron detected in
92(57.5%) of our isolates. Class II integron was detected in 6(3.8%) of our isolates, while no
class III integron was detected in this study. The high rates of integron prevalence particularly
of the class I integron in the E. coli and Klebsiella spp. concur with previous studies in other
geographical regions. The higher (>50%) integron prevalence of Citrobacter and Enterobacter
isolates comparing to previous studies suggests the potential of these isolates as sources for
dissemination of resistance determinants. The finding in this study serves as a basis for
further study on the antibiotic resistance mechanisms of enterobacterial species in this
teaching hospital.
6.Enzymatic profiling of clinical and environmental isolates of Burkholderia pseudomallei
Liew, S.M. ; Tay, S.T. ; Wongratanacheewin, S. ; Puthucheary, S.D.
Tropical Biomedicine 2012;29(1):160-168
Abstract. Melioidosis has been recognized as an important cause of sepsis in the tropics. The disease caused by an environmental saprophyte Burkholderia pseudomallei, affects mostly adults with underlying immunocompromised conditions. In this study, the enzymatic profiles
of 91 clinical and 9 environmental isolates of B. pseudomallei were evaluated using the APIZYM system, in addition to assessment of protease, phospholipase C and sialidase activities using agar plate methods and other assays. The activity of 10 enzymes - alkaline phosphatase,
esterase, esterase lipase, lipase, leucine arylamidase, valine arylamidase, cystine arylamidase, acid phosphatase, naphthol-AS-BI-phosphohydrolase and N-acetyl-β-glucosaminidase were detected in >75% of the clinical isolates. The majority of B. pseudomallei isolates in this study exhibited protease and phospholipase activities. No sialidase activity was detected. Five Burkholderia thailandensis isolates had similar APIZYM profiles as B. pseudomallei clinical isolates except for the lower detection rate for N-acetyl-β-glucosaminidase. The subtle
differences in the number of enzymes secreted and the levels of enzymatic activities of phenotypically identical clinical and environmental strains of B. pseudomallei give weight to the fact that the causative agent of melioidodis originates from the environment.
7.Molecular survey and sequence analysis of Anaplasma spp. in cattle and ticks in a Malaysian farm
Tay, S.T. ; Koh, F.X. ; Kho, K.L. ; Ong, B.L.
Tropical Biomedicine 2014;31(4):769-776
This study was conducted to determine the occurrence of Anaplasma spp. in the
blood samples of cattle, goats, deer and ticks in a Malaysian farm. Using polymerase chain
reaction (PCR) and sequencing approach, Anaplasma spp. was detected from 81(84.4%) of
96 cattle blood samples. All blood samples from 23 goats and 22 deer tested were negative.
Based on the analysis of the Anaplasma partial 16S ribosomal RNA gene, four sequence types
(genotypes 1 to 4) were identified in this study. Genotypes 1-3 showed high sequence similarity
to those of Anaplasma platys/ Anaplasma phagocytophilum, whilst genotype 4 was identical
to those of Anaplasma marginale/ Anaplasma centrale/ Anaplasma ovis. Anaplasma DNA
was detected from six (5.5%) of 109 ticks which were identified as Rhipicephalus (formely
known as Boophilus) microplus ticks collected from the cattle. This study reported for the
first time the detection of four Anaplasma sequence types circulating in the cattle population
in a farm in Malaysia. The detection of Anaplasma DNA in R. microplus ticks in this study
provides evidence that the ticks are one of the potential vectors for transmission of
anaplasmosis in the cattle.
8.Serological review of Bartonella henselae and Bartonella quintana infection among Malaysian patients with unknown causes of febrile illnesses
Hou, S.L. ; Idris, N. ; Tay, S.T.
Tropical Biomedicine 2022;39(No.3):328-331
Limited information is available on human exposure to Bartonella infection, i.e., Bartonella henselae
(causative agent of cat scratch disease) and Bartonella quintana (causative agent of trench fever) in
West Malaysia. This study reports a review of serological findings obtained from patients attending
to a teaching hospital in Klang Valley, Malaysia. An indirect immunofluorescence assay (IFA) was
used to determine IgG and IgM antibody titers against B. henselae and B. quintana. In a pilot study
conducted between 2013-2015, IgG antibodies against Bartonella spp. (either B. quintana and B.
henselae) were detected in 14 (36.8%) of 38 patients who were clinically suspected of rickettsial
infections, while IgM antibody was detected in 4 (10.5%) patients. This has prompted us to
investigate the serologic responses of patients who were clinically suspected of other febrile causes
besides rickettsial infection. Of the 59 serum samples analysed in a follow-up investigation,
Bartonella IgG antibodies were detected from 7 (11.9%) patients, of which 5 (27.8%) and 2 (18.2%)
patients were clinically suspected of rickettsial infection (n=18) and dengue (n=11), respectively.
None of the sera obtained from the leptospirosis (n=10), legionellosis (n=10) and mycoplasma
infection (n=10) groups were seropositive to Bartonella spp. The review of Bartonella serological
findings in this study highlights that Bartonella infection is not uncommon and should be considered
as one of the causes for febrile illness in Malaysia.
9.Investigation of possible rickettsial infection in patients with malaria
Tay, S.T. ; Kho, K.L. ; Vythilingam, I. ; Ooi, C.H. ; Lau, Y.L.
Tropical Biomedicine 2019;36(1):257-262
Rickettsioses are a common health problem in many geographical areas, including
rural areas in Southeast Asia. Co-infection of rickettsioses and malaria has been reported in
Africa, where common reservoir and vectors are available. In this study, blood samples of
Malaysian patients microscopically positive (n=148) and negative (n=88) for malaria parasites
(Plasmodium knowlesi, Plasmodium malariae, Plasmodium falciparum, and Plasmodium
vivax) were screened for the presence of rickettsial DNA, using PCR assays targeting specific
genes. A partial fragment of rickettsial ompB gene was successfully amplified and sequenced
from a patient microscopically positive for Plasmodium spp. and PCR-positive for P. vivax.
BLAST analysis of the ompB sequence demonstrated the highest sequence similarity (99.7%
similarity, 408/409nt) with Rickettsia sp. RF2125 (Genbank accession no. JX183538) and
91.4% (374/409 nt) similarity with Rickettsia felis URRWXCal2 (Genbank accession no.
CP000053). This study reports rickettsial infection in a malaria patient for the first time in the
Southeast Asia region.
10.Genetic diversity, antifungal susceptibility and enzymatic characterisation of Malaysian clinical isolates of Candida glabrata
Lotfalikhani, A. ; Khosravi, Y. ; Sabet, N.S. ; Na, S.L. ; Ng, K.P ; Tay, S.T.
Tropical Biomedicine 2018;35(4):1123-1130
Candida glabrata has been reported as the second or third most common yeast
species isolated from patients with vaginitis and invasive candidiasis. This study was aimed
to determine the genetic diversity, antifungal susceptibility and enzymatic profiles of C.
glabrata isolated from vaginal and blood samples in the Medical Microbiology Diagnostic
Laboratory, University Malaya Medical Centre. A random amplified polymorphic DNA (RAPD)
analysis method, using M13 and (GTG)5 primers, was used for strain differentiation of C.
glabrata isolates. Antifungal susceptibility testing of C. glabrata isolates was determined
using E-test against amphotericin B, caspofungin, fluconazole and voriconazole and microbroth
dilution method against clotrimazole. The enzymic profiles of C. glabrata were determined
using APIZYM semi-quantitation kit and egg-yolk agar method. A total of 14 RAPD patterns
were identified amongst C. glabrata isolates investigated this study. Susceptibility to
amphotericin B, caspofungin, fluconazole and voriconazole was noted. Approximately one
third of the isolates demonstrated resistance to clotrimazole (MIC>1 μg/ml). A single isolate
of C. glabrata was resistant to caspofungin (MIC:1.5 μg/ml). Enzymatic activities of acid and
alkaline phosphatase, aminopeptidases, esterase and lipase and phospholipase were detected
in the C. glabrata isolates. The genetic diversity and antifungal susceptibility profiles of C.
glabrata isolates were presented in this study. Continued surveillance and monitoring of the
incidence and antifungal resistance in C. glabrata isolates is necessary.