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Biomedical subjects

G Sridharan

Publications and source records attributed to G Sridharan.

At least 55 records · Page 3Linked to original sources
PubMed1998

Diagnosis of typhoid fever by the detection of anti-LPS & anti-flagellin antibodies by ELISA.

In a developing country like ours where typhoid fever is endemic and there are very few microbiology laboratories to provide diagnosis by culture, a search for non culture techniques for rapid and reliable diagnosis continues. The Widal test has a low sensitivity. We have attempted to adapt the well established enzyme linked immunosorbent assay (ELISA) technique to provide a serological test of better sensitivity and specificity. The ELISA described here to detect anti-LPS antibodies was found to have a sensitivity of 89.4 per cent and a specificity of 94.9 per cent. The sensitivity for the antiflagellin ELISA was 68.1 per cent and specificity was 97.4 per cent. The likelihood ratio was 17.5 for anti-LPS ELISA and 26.2 for the anti-flagellin ELISA. Considering the positivity of either one ELISA as diagnostic, the sensitivity was 93.6 per cent and specificity was 94.9 per cent.

Antibodies, Bacterial↗
PubMed1998

Importance of RT-PCR for detection of hepatitis C virus among different patient groups.

A pilot study was undertaken to evaluate a sensitive single step reverse transcription polymerase chain reaction (RT-PCR) to detect hepatitis C virus (HCV) RNA in plasma samples as an adjunct to antibody detection. In this study, digoxiginin labelling of the amplicon was carried out during the PCR and the product was detected by an ELISA format (DIG-ELISA) as well as ethidium bromide stained gel detection. DIG-ELISA detection of PCR product compared favourably with gel detection. We tested 42 individuals with either parenteral risk factors or chronic liver disease and found the RT-PCR enhanced the detection rate by 19 per cent. Considering either plasma RNA or antibody positivity, HCV infection was detected in 64.3 per cent of patients.

Chronic Disease↗
PubMed1997

Chemokine-independent in vitro resistance to human immunodeficiency virus (HIV-1) correlating with low viremia in long-term and recently infected HIV-1-positive persons.

Chemokines have been implicated as protective factors against human immunodeficiency virus (HIV) infection, competing for binding to receptors that also function as coreceptors for HIV. In this study of HIV-positive donors, peripheral blood mononuclear cell (PBMC) culture resistance to endogenous and exogenous HIV correlated with low plasma viremia and high in vitro RANTES production. However, resistant cells were not rendered susceptible by neutralization of C-C chemokines, and addition of C-C chemokines did not consistently suppress endogenous virus or exogenous HIV-1MN. In contrast, CD8 T cell depletion markedly decreased the frequency of resistant cultures without reducing C-C chemokine production. Among newly infected persons, half exhibited phenotype switching from preinfection susceptibility to postinfection resistance, suggesting that genetically predetermined constitutive cytokine production or allelic receptor expression are not generally responsible for in vitro resistance and nonprogression.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Monovalent latex agglutination reagents for the diagnosis of nonmeningitic pneumococcal infection.

The pneumococcus is a leading cause of serious bacterial infection worldwide. Given the difficulties with available assays for the diagnosis of invasive nonmeningitic pneumococcal infection, we evaluated monovalent slide latex agglutination reagents among patients with blood culture-confirmed pneumococcal infection and control patients in Baltimore, Maryland, USA; São Paulo, Brazil; and Cairo, Egypt. Among 50 patients with invasive nonmeningitic pneumococcal infection, 23 had a positive urine test for a sensitivity of 46% (95% confidence intervals of 32% and 61%). Among 39 healthy children, 36 had a negative assay, for a specificity of 92% (95% confidence intervals of 78% and 98%). Among 80 children with pneumonia without a positive blood culture for Streptococcus pneumoniae, the specificity was 88% (95% confidence intervals of 78% and 94%). Although the assay was fairly specific, the positive predictive value using optimistic assumptions was only 73%-83%. This study suggests that this assay has a sensitivity and positive predictive value that may limit its value in some settings.

Child, Preschool↗
PubMed1996

Serotyping of Streptococcus pneumoniae by agglutination assays: a cost-effective technique for developing countries.

There is a need for additional data on the distribution of pneumococcal serotypes in developing countries. We report the use of a coagglutination (COA) and a latex agglutination (LA) test for serotyping Streptococcus pneumoniae which were evaluated using 114 clinical isolates in Vellore, India. In tests to serotype 30 fresh isolates of pneumococci from meningitis (8 isolates), bacteraemia/septicaemia (21 isolates) and peritonitis (1 isolate) cases, there was complete concordance among the three methods. An additional 20 isolates (11 from cerebrospinal fluid and 9 from blood cultures) were serotyped using both LA and COA, with full agreement between the results. With a further 30 isolates, there was 93% concordance for the COA types with serotypes assigned by a WHO reference laboratory. The COA and LA serotyping results were equivalent in accuracy to those obtained using quellung serotyping. Both these agglutination tests are rapid, valid, and relatively cheap, and with appropriate validation by reference laboratories they could be more widely used in developing countries to obtain local and regional data on pneumococcal serotype distribution.

Agglutination Tests↗
PubMed1996

Prevalence of pneumococcal serotypes in invasive diseases in southern India.

Forty two pneumococcal strains obtained in Vellore, Tamil Nadu, from 42 patients with invasive diseases, namely pneumonia, meningitis, or peritonitis were typed. Over one-third of pneumococci in children and nearly half in adults were serotype followed by serogroups/types 5, 6 and 7 which were most common in children and adults taken together. These 4 serogroups/types accounted for 11 (79%) of 14 strains in children and 20 (71%) of 28 strains in adults. The remaining 11 strains belonged to 8 serogroups/types, namely 3, 4, 10, 11, 12, 13, 19 and 20.

Adolescent↗
PubMed1995

C substance--specific latex agglutination for early & rapid detection of Streptococcus pneumoniae in blood cultures.

A slide agglutination test was developed using latex particles coated with antiserum against the C substance, a common antigen for all serotypes of Streptococcus pneumoniae. This test was used for the rapid identification of pneumococci in blood culture broths which contained Gram positive cocci (GPC) in pairs or short chains on smear examination. Of 238 consecutive blood cultures with GPC tested, 72 were positive for Strep. pneumoniae by the latex test and conventional methods. The remaining 166 cultures were negative for both these, indicating a 100 per cent specificity and sensitivity for the test.

Antigens, Bacterial↗
PubMed1994

Serotypes of Streptococcus pneumoniae causing meningitis in southern India. Use of new direct latex agglutination antigen detection tests in cerebrospinal fluid.

The utility of a new latex agglutination (LA) test to directly determine serotypes of Streptococcus pneumoniae in cerebrospinal fluid (CSF) was assessed in prospective evaluation at a referral hospital in southern India. Samples from 18 ill patients with Gram-positive organisms in CSF were tested. The presence of C polysaccharide or specific serotype antigen (types 1, 3, 4, 5, 6, 12, 14, 18, 19, and 23) of S. pneumoniae was detected by slide LA test. Pneumococcal antigen was detected in 17 (94%) of 18 CSF specimens; in 14 (78%) the serotype was determined directly. Serotypes 1, 5, 6, 19, 23, 7, 10, 34, and 38 were found in these patients. A quellung test of the cultured isolates confirmed the serotypes. Information regarding the serotype distribution of pneumococci in varied geographic locations is important for the design and evaluation of pneumococcal vaccines. The slide LA tests seemed useful in detecting S. pneumoniae antigens and in determining the serotype, and have promise in simplifying the gathering of serotype data.

Adult↗
PubMed1994

Vi-specific latex agglutination for early and rapid detection of Salmonella serotype typhi in blood cultures.

Latex particles coated with rabbit antisera against Salmonella serotype typhi (S. typhi) Vi and O (STO) antigens were used in slide agglutination tests for the rapid identification of S. typhi in blood culture broths as soon as Gram-negative bacilli (GNB) were detected in them. Among 231 consecutive blood cultures showing GNB tested for Vi, and a subset of 163 tested for STO, by latex agglutination (LA), 125 and 32, respectively, were positive. The GNB in 127 blood cultures were confirmed by conventional methods as S. typhi, 125 (98.4%) of which had been identified by the Vi LA test. In the subset of 163, 81 grew S. typhi, of which only 32 (39.5%) had been identified by the STO LA tests. Thus, the sensitivity of the Vi and STO LA tests was 98.4% and 39.5%, respectively, whereas the specificity was 100% for both tests. Of the S. typhi isolates, 38 (30.4%) were detected by the Vi LA test on day 2 and 73 (58.4%) on day 3, day 1 being the date of inoculation of the blood culture broths. Thus, the Vi LA test is suitable for the early and rapid confirmation of S. typhi in blood culture.

Agglutination Tests↗
PubMed1994

Prevalence of genital mycoplasma & ureaplasma infections in pregnancy & their effect on pregnancy outcome.

A cohort of 200 women with singleton pregnancies attending the antenatal clinic, were studied to determine the prevalence of genital mycoplasma and ureaplasma infections in pregnant women and the effect of infection on pregnancy outcome. Vaginal and endocervical swabs were taken at 26-30 wk and again at 36-38 wk of pregnancy and cultured for mycoplasma and ureaplasma. Forty (20%, 95% CI 14.5-25.6%) women were found to be infected with arginine metabolising mycoplasmas and 79 (39.5%, 95% CI 32.7-46.3%) with ureaplasma at either site or either time. The mean +/- SD birth weight of infants born to women infected with mycoplasma alone was 2879 +/- 471 g while that of infants born to women infected with ureaplasma alone was 2964 +/- 412 g. Mean +/- SD birthweight of infants born to women infected with both organisms was 2969 +/- 389 g while that of infants born to uninfected women was 2919 +/- 432 g. These differences were not statistically significant. The median gestation at delivery was 39 wk in the cohort; the differences among the groups were minor and statistically not significant. Thus, although genital mycoplasma/ureaplasma infections were frequent, no association was observed between infection and pregnancy outcome.

Female↗
PubMed1993

A simple method to prepare Salmonella (A-E) polyvalent antiserum.

The preparation of Salmonella O serogroup (A-I) polyvalent antiserum is laborious. In an alternate method, rabbit antiserum raised to cell surface proteins of Salmonella serotype typhi was compared with a commercial Salmonella polyvalent (A-I) antiserum; 51 Salmonella (A-E) and 16 strains of related organisms tested gave comparable agglutination with both sera.

Bacteriological Techniques↗
PubMed1992

Evaluation of modified passive haemagglutination assay for Vi antibody estimation in Salmonella typhi infections.

A simple passive haemmagglutination assay (PHA) was developed to detect Vi antibodies, to improve the diagnosis of typhoid fever by small laboratories. The Vi capsular antigen of Salmonella typhi was extracted by alternate alcohol and acetone precipitation. Formalin fixed, sheep red blood cells treated with chromium chloride were sensitised with this Vi antigen and antibodies detected and measured by PHA. The test had a sensitivity of 83.3% among 30 cases of typhoid fever confirmed by culture. The specificity of the test was 94%, making it suitable for use in laboratories without facilities for IFAT or ELISA.

Antibodies, Bacterial↗
PubMed1992

Salmonella typhi cell wall protein showing antigenic similarity to transferrin.

Antiserum to cell wall proteins of S. typhi showed immunoprecipitin lines of identity with homologous antigen, normal human serum and human transferrin. Also, anti-transferrin antibody showed immunoprecipitin band with S. typhi cell wall proteins and agglutinated S. typhi whole cells, but not Eschericia coli. It is speculated that transferrin or a transferrin-like protein present in the cell wall may play a role in iron-uptake by S. typhi.

Agglutination Tests↗
PubMed1991

Immune response to intradermally injected inactivated poliovirus vaccine.

Immune response to intradermal inoculation of a fractional dose of inactivated poliovirus vaccine (IPV) was measured in 8 adults and 10 children who were previously immune. A striking 4-fold to 1024-fold antibody booster response to all 3 poliovirus serotypes was found in 15 subjects and a similar response to 2 poliovirus serotypes occurred in the other 3 children. Induration and erythema of 3 mm diameter or above, indicative of a cell-mediated immune response, was seen in 12 subjects. Intradermal inoculation of IPV may be a useful technique for secondary immunisation programmes against polio and its use for primary immunisation merits investigation.

Adult↗
PubMed1991

Antigen sharing of Salmonella typhi non-flagellar proteins with other salmonellae and some shigellae and Escherichia coli.

Cathodal moving protein components were identified in agarose gel electrophoresis of the Veronal buffer extract of a non-motile strain of S. typhi (8393, Colindale). Rabbit antiserum was raised against these cationic proteins; it had both agglutinating and precipitating activity. A total of 80 salmonella strains belonging to serogroups A, B, C1, C2, D, E1 and E2 including 26 S. typhi and 10 S. paratyphi A were tested against this antiserum in a slide agglutination test; all strains were agglutinated. Among 94 other bacterial strains tested, the antiserum agglutinated all 16 strains of Shigella flexneri, 2 of 5 Shigella sonnei, 5 of 34 E. coli and 1 of 8 Citrobacter species. These results show that there is antigenic sharing of the non-flagellar proteins of S. typhi with many other salmonellae as well as with some shigellae and E. coli.

Agglutination Tests↗
PubMed1990

Isolation and typing of herpes simplex viruses in the infections of mouth, respiratory and genital tracts.

A total of 60 herpes simplex virus (HSV) isolates obtained from individuals with genital herpes lesions in the mouth or respiratory illness were typed in this study. The HSV isolation rate in genital herpes was 31%. The typing was done by a direct fluorescent monoclonal antibody technique using commercial reagents. All the 60 Vero cell grown isolates were successfully typed without any indeterminate results. Nine isolates were typed as HSV 1 and 51 as HSV 2. The technique was easy to perform and read. HSV 2 was found to predominate in genital infections and HSV 1 in respiratory infections.

Fluorescent Antibody Technique↗