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Evaluation of basic science knowledge retention in clinical teaching

Vadivelu J

Med Educ, 2008 May;42(5):520-1.
PMID: 18412895 DOI: 10.1111/j.1365-2923.2008.03047.x
Molecular analysis of vibrio cholerae strains isolated in Malaysia: public health implications

Iyer L, Vadivelu J

Asia Pac J Public Health, 2006;18(3):33-41.
PMID: 17153080

The genetic diversity or clonality among Vibrio cholerae O1, O139 and non-O1/ non-O139 of clinical and environmental origin using ribotyping and PFGE was performed in order to ascertain the public health implications of the different genotypes circulating within the Malaysian environment. Using an in-house typing scheme, of the 214 strains included, 202 strains were isolated locally between 1992 and 1998, seven were obtained from Bangladesh and five were reference strains. Amongst the 176 El Tor O1 strains, 152 clinical strains demonstrated five ribotypes--E1a, E1b, E2a, E3 and E1c. E1b was the most predominant ribotype demonstrated by 84% of the El Tor O1 strains and was present in all years demonstrating that this strain was intrinsic to Malaysia. PFGE analysis of these strains demonstrated minimal variation amongst the 15 PFGE profiles obtained. Ribotpye E2a amongst five clinical and two environmental O1 strains, were from one location and had previously been reported in Indonesia and the Philippines, thus demonstrating strong evidence that these strains may have been imported into Malaysia. Among Vibrio cholerae O139 strains, 91.7% were of ribotype A1a similar to the original O139, while two others were of ribotype A1b and one of A1e, corresponding to ribotypes 1, 2 and 3 of Dalsgaard and colleagues' scheme for O139 strains. PFGE analysis demonstrated that 89% of ribotype A1a could be differentiated into three PFGE genotypes which were very closely related. The eight non-O1/non-O139 serogroup strains were heterogeneous in both ribotype and PFGE patterns.
Diagnostic and prognostic value of an immunofluorescent assay for melioidosis

Vadivelu J, Puthucheary SD

Am J Trop Med Hyg, 2000 Feb;62(2):297-300.
PMID: 10813488

Melioidosis caused by Burkholderia pseudomallei is endemic in southeast Asia. The clinical manifestations range from wound infections to acute septicemia. In some cases, recurrence can also occur following complete recovery. Case fatality rates are high and a major factor is the delay in the culture and identification of the bacterium. An immunofluorescent assay (IFAT) using whole-cell antigen for the detection of total antibodies to B. pseudomallei was tested with 650 sera. Using a cut-off value of 1:80, 66 sera from culture-confirmed cases were positive with titers > or = 320. In another 523 sera from patients in which no other etiology could be found, 149 (23.4%) were positive. To monitor disease activity, persistence of antibody levels was investigated on 61 serial sera samples collected from 14 other confirmed cases on follow-up visits while on oral maintenance therapy. The IFAT demonstrated a reduction in titers in cases of localized infections, suggesting that either the infection was being resolved or arrested while septicemic patients maintained high IFAT titers on follow-up, suggesting the possibility of continuous sequestration of antigen from an intracellular source.
Fulltext Characteristics of childhood diarrhea associated with enterotoxigenic Escherichia coli in Malaysia

Samuel S, Vadivelu J, Parasakthi N

Southeast Asian J. Trop. Med. Public Health, 1997 Mar;28(1):114-9.
PMID: 9322293

Amongst 107 diarrheal cases studied a bacterial agent was isolated from 71 (66%) cases of which 60 (85%) were due to a single agent and the remaining 11 (15%) were of mixed infections. Enterotoxigenic Escherichia coli (ETEC) was isolated from 65 cases. Other pathogens isolated included Salmonella spp, Shigella spp and rotavirus. There was a higher isolation rate of ETEC from females and rotavirus from males. The infection rate was found to higher for the 0-2 year age group as compared to the 3-5 year age group. Amongst the ETEC isolated the STa 2 toxotype was the predominant type.
Fulltext Colonisation factors amongst clinical isolates of enterotoxigenic Escherichia coli

Iyer L, Vadivelu J, Parasakthi N

Singapore Med J, 1995 Oct;36(5):495-7.
PMID: 8882532

The production of heat-labile (LT) and heat-stable (ST) enterotoxins, colonisation factor antigens (CFAs) and haemagglutinins was investigated amongst 310 Escherichia coli (E. coli) isolates obtained from 62 children under the age of five, with diarrhoea. Twenty-one isolates were found to produce enterotoxins, of which fifteen (71%) isolates produced ST only, 2 (10%) produced LT only and 4 (19%) produced both LT and ST. However, none of the isolates demonstrated any of the common CFAs identified to date, but 8 out of the 21 isolates demonstrated haemagglutination with rabbit, sheep or human group A erythrocytes, suggesting the presence of putative CFAs, yet unidentified.
Detection of virulence associated genes, haemolysin and protease amongst Vibrio cholerae isolated in Malaysia

Iyer L, Vadivelu J, Puthucheary SD

Epidemiol Infect, 2000 Aug;125(1):27-34.
PMID: 11057956

Eighty-four strains of Vibrio cholerae O1, O139 and non-O1/non-O139 from clinical and environmental sources were investigated for the presence of the toxin co-regulated pilus gene, tcpA, the virulence cassette genes ctxA, zot, ace and cep and also for their ability to elaborate haemolysin and protease. The ctxA and zot genes were detected using DNA-DNA hybridization while the ace, cep and tcpA genes were detected using PCR. Production of haemolysin and protease was detected using mammalian erythrocytes and an agar diffusion assay respectively. Analysis of their virulence profiles showed six different groups designated Type I to Type VI and the major distinguishing factor among these profiles was in the in vitro production of haemolysin and/or protease. Clinical O1, O139 and environmental O1 strains were similar with regard to presence of the virulence cassette genes. All environmental O1 strains with the exception of one were found to possess ctxA, zot and ace giving rise to the probability that these strains may actually be of clinical origin. One strain which had only cep but none of the toxin genes may be a true environmental isolate. The virulence cassette and colonization factor genes were absent in all non-O1/non-O139 environmental strains but production of both the haemolysin and protease was present, indicating that these may be putative virulence factors. These findings suggest that with regard to its pathogenic potential, only strains of the O1 and O139 serogroup that possess the tcpA gene which encodes the phage receptor, have the potential to acquire the CTX genetic element and become choleragenic.
Detection of immunoglobulins M and G using culture filtrate antigen of Burkholderia pseudomallei

Chenthamarakshan V, Vadivelu J, Puthucheary SD

Diagn Microbiol Infect Dis, 2001 Jan;39(1):1-7.
PMID: 11173184

IgM and IgG based ELISA systems were developed using the culture filtrate antigen (CFA) of Burkholderia pseudomallei. The assays were evaluated using 95 sera from 66 septicemic cases and 47 sera from 20 cases with localized melioidosis. In addition 65 sera from culture negative cases that were also serologically negative for other endemic infections clinically suspected of melioidosis were included. These were compared with sera from 260 non-melioidosis cases, 169 sera from individuals with high risk of acquiring the infection and 48 sera from healthy controls. The IgG-ELISA was 96% sensitive and 94% specific. All sera from cases with septicemic and localized infections and 61 of 63 sera from clinically suspected melioidosis cases were positive for IgG antibody. The geometric mean titre index (GMTI) values of IgG antibody in melioidosis cases were significantly higher (p < 0.0005) compared to that of healthy subjects, high risk group and subjects with non-melioidosis infections. The sensitivity and specificity of IgM ELISA was 74 and 99% respectively. The GMTI value of IgM antibody in the sera of melioidosis cases was significantly higher as compared to that of non-melioidosis disease controls (p < or = 0.001). These results demonstrate that the detection of IgG is a better indicator of the disease in the diagnosis of melioidosis.
Exotoxin profiles of clinical isolates of Aeromonas hydrophila

Vadivelu J, Puthucheary SD, Navaratnam P

J Med Microbiol, 1991 Jun;34(6):363-7.
PMID: 2056519

Eighty-six clinical isolates of Aeromonas hydrophila were studied for their ability to produce four exotoxins: a haemolysin active against rabbit erythrocytes, cytotoxin and enterotoxin detectable with Vero cell cultures, and the cholera toxin-like factor detected by an enzyme-linked immunosorbent assay. At least one exotoxin was produced by 80% of enteric and 96% of non-enteric isolates. The exotoxin profiles of non-enteric isolates were more restricted than those of enteric isolates, with haemolysin and cytotoxin producers preponderant. Although haemolysin and cytotoxin were produced by isolates from all sources, the enterotoxin and cholera toxin-like factor were more common amongst enteric isolates. The production of haemolysin and cytotoxin were closely related but the association between the enterotoxin and the cholera toxin-like factor was not significant.
Fulltext Comparison of two assays for the detection of haemolysins of Aeromonas species

Vadivelu J, Puthucheary SD, Navaratnam P

Singapore Med J, 1992 Aug;33(4):375-7.
PMID: 1411668

The haemolysins produced by Aeromonas species were detected and compared by two assay methods--a modified blood agar plate assay and the rabbit erythrocyte haemolysin method. Both assays showed a high level of agreement (86%). The titres of the rabbit erythrocyte haemolysin assay correlated with the haemolytic zone diameter of the ox blood agar assay. In addition the agar haemolysin assay had simple media requirements, was easy to perform and results were well defined.
First characterization of bla(VIM-11) cassette-containing integron in metallo-beta-lactamase producing Pseudomonas aeruginosa in Malaysia

Khosravi Y, Tay ST, Vadivelu J

Eur Rev Med Pharmacol Sci, 2010 Nov;14(11):999-1000.
PMID: 21284350
Metallo-beta-lactamase-producing imipenem-resistant Pseudomonas aeruginosa clinical isolates in a university teaching hospital in Malaysia: detection of IMP-7 and first identification of IMP-4, VIM-2, and VIM-11

Khosravi Y, Tee Tay S, Vadivelu J

Diagn Microbiol Infect Dis, 2010 Jul;67(3):294-6.
PMID: 20462725 DOI: 10.1016/j.diagmicrobio.2010.02.010

Ninety (n = 90) imipenem-resistant Pseudomonas aeruginosa (IRPA) clinical isolates collected randomly during 2005 to 2008 from University Malaya Medical Center were assessed for the presence of different variants of metallo-beta-lactamase (MBL) genes. Polymerase chain reaction (PCR) assay detected 32 (n = 32) MBL gene PCR-positive isolates with the presence of bla(IMP) gene in 14 (n = 14) and bla(VIM) in 18 (n = 18) isolates. Four allelic variants, bla(IMP-7) (12 isolates), bla(IMP-4) (2 isolates), bla(VIM-2) (17 isolates), and bla(VIM-11) (1 isolate), of MBL genes were identified. This study is the first report of detection of bla(IMP-4), bla(VIM-2), and bla(VIM-11) MBL genes from IRPA clinical isolates in Malaysia.

Study site: University Malaya Medical Center (UMMC)
Antibacterial and antifungal properties of human cerumen

Lum CL, Jeyanthi S, Prepageran N, Vadivelu J, Raman R

J Laryngol Otol, 2009 Apr;123(4):375-8.
PMID: 18694532 DOI: 10.1017/S0022215108003307

To assess the antibacterial and antifungal properties of human cerumen by studying its effect on the growth of Staphylococcus aureus, Esherichia coli, Pseudomonas aeruginosa and Candida albicans.
Distribution of CBP genes in Streptococcus pneumoniae isolates in relation to vaccine types, penicillin susceptibility and clinical site

Desa MN, Sekaran SD, Vadivelu J, Parasakthi N

Epidemiol Infect, 2008 Jul;136(7):940-2.
PMID: 17678563

Choline-binding proteins (CBP) have been associated with the pathogenesis of Streptococcus pneumoniae. We screened, using PCR, for the presence of genes (cbpA, D, E, G) encoding these proteins in 34 isolates of pneumococci of known serotypes and penicillin susceptibility from invasive and non-invasive disease. All isolates harboured cbpD and cbpE whereas cbpA and cbpG were found in 47% and 59% respectively; the latter were more frequent in vaccine-associated types and together accounted for 77% of these isolates. No association was observed with penicillin susceptibility but 85% of non-invasive isolates were positive for these genes.
Epidemiology and molecular characterization of nosocomially transmitted multidrug-resistant Klebsiella pneumoniae

Parasakthi N, Vadivelu J, Ariffin H, Iyer L, Palasubramaniam S, Arasu A

Int J Infect Dis, 2000;4(3):123-8.
PMID: 11179914

OBJECTIVES: To describe the epidemiology, antimicrobial susceptibility, genomic profiles, and control of a nosocomial outbreak of multidrug-resistant Klebsiella pneumoniae (MRKP) that occurred in the pediatric oncology unit of the University of Malaya Medical Centre in Kuala Lumpur.
MATERIALS AND METHODS: A prospective epidemiologic and microbiologic study was conducted of MRKP isolated from the blood and wound of a boy with necrotizing fasciitis after a 7-day course of ceftazidime and amikacin. In the following 2 weeks, phenotypically similar MRKP were isolated from the blood cultures of four other patients and rectal swabs of another three patients and two liquid soap samples located in the same ward.
RESULTS: Antimicrobial profiles demonstrated that all the isolates were resistant to ceftazidime, sensitive to imipenem and ciprofloxacin, and confirmed to be extended-spectrum beta-lactamase producers. Plasmids of varying molecular weights were present in all isolates. In eight of these isolates, which included four from blood, there were common large molecular weight plasmids ranging from 80 kb to 100 kb. Pulsed-field gel electrophoresis analysis using XbaI demonstrated six different DNA profiles, A to F. Profile A was shared by two blood culture isolates and were related by 91%. Profile B was found in one rectal swab isolate and one isolate from liquid soap and were related by 94%. Profile C was shared by one blood isolate and one liquid soap isolate and showed 100% relatedness. Profiles D, E, and F each were demonstrated by one blood isolate and two rectal swab isolates, respectively. These showed only 65% relatedness.
CONCLUSIONS: The MRKP strains in this outbreak were not clonal in origin. The decline of the outbreak after 4 weeks was attributed to the reemphasis of standard infection control procedures and the implementation of a program that addressed sites of environmental contamination.
Molecular evidence of clonality amongst Vibrio cholerae O1 biotype El Tor during an outbreak in Malaysia

Vadivelu J, Iyer L, Kshatriya BM, Puthucheary SD

Epidemiol Infect, 2000 Feb;124(1):25-30.
PMID: 10722126

Forty-three clinical strains of V. cholerae O1 biotype E1 Tor were isolated between 3 May and 10 June 1998 during an outbreak in the metropolitan area of Kuala Lumpur and its suburbs. With the exception of three Inaba strains that were restricted to three members of a family, all the others belonged to the Ogawa serotype. The strains were analysed for clonality using ribotyping and pulsed-field gel electrophoresis (PFGE). Two ribotypes, V/B21a and B27, were identified among 40 Ogawa isolates using BglI restriction endonuclease. Ribotype V/B21a has been described previously from Taiwan and Colombia and several Asian countries while B27 has been reported among isolates from Senegal. The three Inaba strains belonged to one ribotype, designated type A, not previously reported. PFGE analysis using NotI revealed that all isolates within a ribotype had identical profiles demonstrating clonality amongst the strains. Dice coefficient analysis of the two Ogawa genotypes revealed 89% similarity on ribotype patterns and 91.3% on PFGE profiles. Ribotype V/B21a isolates were associated with cases from dispersed areas of Kuala Lumpur and its suburbs while ribotype B27 was restricted to cases from one particular area suggesting a common-source outbreak.
The histopathology of human melioidosis

Wong KT, Puthucheary SD, Vadivelu J

Histopathology, 1995 Jan;26(1):51-5.
PMID: 7713483

We examined human tissues infected by Burkholderia (Pseudomonas) pseudomallei which is endemic in Malaysia to study the types of inflammation invoked, and to look for histopathological clues to its diagnosis. The lesions which varied from acute to chronic granulomatous inflammation were not tissue-specific. In five autopsy cases, the inflammation was usually a focal or diffuse, acute necrotising inflammation with varying numbers of neutrophils, macrophages, lymphocytes and 'giant cells'. The 'giant cells' probably represent giant macrophages with phagocytosed leukocytes. There were numerous gram-negative, non-acid-fast, intra- and extracellular bacilli, occurring either singly or in chains. Intracellular bacteria within macrophages and 'giant cells' were so numerous as to resemble globi. This feature has not been previously reported and may be a useful diagnostic clue in melioidosis. In 14 surgical cases biopsies showed acute inflammatory lesions that appeared no different from acute inflammation due to other causes. In many biopsies, however, the inflammation was either an acute-on-chronic inflammation with a focal granulomatous component, or was purely granulomatous in character. Bacilli were difficult to demonstrate in surgical biopsies even with the gram strain.
Possible virulence factors involved in bacteraemia caused by Aeromonas hydrophila

Vadivelu J, Puthucheary SD, Phipps M, Chee YW

J Med Microbiol, 1995 Mar;42(3):171-4.
PMID: 7884797

Eighteen strains of Aeromonas hydrophila from patients with bacteraemia were investigated for possible virulence factors. Cytotoxin and haemolysin were produced by all strains, whereas cholera toxin-like factor was produced by 33% of strains only. Enterotoxin production was not detected. Haemagglutination of guinea-pig, fowl and rabbit erythrocytes was demonstrated by 83%, 67% and 61% of strains, respectively. Fucose- and mannose-sensitive haemagglutinins were predominant. None of the strains agglutinated sheep erythrocytes. Extrachromosomal DNA was detected in 17 strains, 16 of which had a plasmid (3.6-5.1 MDa), the majority being between 4.6 and 5.1 MDa.
Distribution of immunoglobulin classes and IgG subclasses against a culture filtrate antigen of Burkholderia pseudomallei in melioidosis patients

Chenthamarakshan V, Kumutha MV, Vadivelu J, Puthucheary SD

J Med Microbiol, 2001 Jan;50(1):55-61.
PMID: 11192506 DOI: 10.1099/0022-1317-50-1-55

The class and subclass distribution of antibody response to the culture filtrate antigen (CFA) of Burkholderia pseudomallei was examined in the sera of 45 septicaemic and 17 localised melioidosis cases and 40 cases clinically suspected of melioidosis and the results were compared with those from high-risk and healthy control groups. The geometric mean titre index (GMTI) values for all classes and subclasses of immunoglobulins examined were higher for sera from the proven and clinically suspected melioidosis cases than for the control groups. However, the highest response in the three patient groups was that of IgG with GMTIs ranging from 219.4 to 291.6 and the lowest was for IgM with GMTIs of 22.5, 24.3 and 28.7. The IgA response was intermediate with GMTIs ranging from 119.2 to 170. The GMTIs were highest for IgG in septicaemic and localised infections and for IgA and IgM in localised infections. As regards IgG subclass distribution, IgG1 and IgG2 were the predominant subclasses produced against the CFA in contrast to IgG3 and IgG4, which were produced in low amounts. None of the sera from the control groups had any significant titres of antibodies.
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.
Fulltext Eukaryotic pathways targeted by the type III secretion system effector protein, BipC, involved in the intracellular lifecycle of Burkholderia pseudomallei

Kang WT, Vellasamy KM, Vadivelu J

Sci Rep, 2016 09 16;6:33528.
PMID: 27634329 DOI: 10.1038/srep33528

Burkholderia pseudomallei, the etiological agent for melioidosis, is known to secrete a type III secretion system (TTSS) protein into the host's internal milieu. One of the TTSS effector protein, BipC, has been shown to play an important role in the B. pseudomallei pathogenesis. To identify the host response profile that was directly or indirectly regulated by this protein, genome-wide transcriptome approach was used to examine the gene expression profiles of infected mice. The transcriptome analysis of the liver and spleen revealed that a total of approximately 1,000 genes were transcriptionally affected by BipC. Genes involved in bacterial invasion, regulation of actin cytoskeleton, and MAPK signalling pathway were over-expressed and may be specifically regulated by BipC in vivo. These results suggest that BipC mainly targets pathways related to the cellular processes which could modulate the cellular trafficking processes. The host transcriptional response exhibited remarkable differences with and without the presence of the BipC protein. Overall, the detailed picture of this study provides new insights that BipC may have evolved to efficiently manipulate host-cell pathways which is crucial in the intracellular lifecycle of B. pseudomallei.

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