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T Ramamurthy

Publications and source records attributed to T Ramamurthy.

At least 73 records · Page 4Linked to original sources
PubMed1995

Studies on the genesis of Vibrio cholerae O139: identification of probable progenitor strains.

Four lines of evidence suggest that the recent outbreak strains of Vibrio cholerae O139 could have emerged from serogroup O1 strains typified by isolates M01 and M0477 described in this paper, which are neither truly classical nor truly E1 Tor in their biotype attributes. Firstly, like all O139 isolates, these O1 strains, isolated in Madras during and before the O139 outbreak, were resistant not only to polymyxin B but also to all biotype-specific choleraphages, i.e. classical phage phi 149 and E1 Tor phages e4 and e5. Secondly, the restriction fragment pattern (RFP) polymorphism displayed by these strains for the cholera toxin (ctx) gene, were identical with those produced by O139 isolates but were different from those of O1 type strains, namely V. cholerae 569B (classical) and V. cholerae MAK757 (E1 Tor). Thirdly, all the O139 isolates and the two O1 isolates carried an identical large number of copies of cholera toxin gene in their chromosomes. Finally, the outer-membrane protein profiles of strains M01 and M0477 were identical to those of O139 isolates but were different from those displayed by strains 569B and MAK757.

Bacterial Outer Membrane Proteins↗
PubMed1995

Geographical heterogeneity between Far East and Europe in prevalence of ypm gene encoding the novel superantigen among Yersinia pseudotuberculosis strains.

Yersinia pseudotuberculosis is known to produce a novel superantigen designated Y. pseudotuberculosis-derived mitogen. In the present study, we demonstrated that there was a distinct geographical heterogeneity between the Far East (higher prevalence) and Europe (lower prevalence) in the prevalence of the ypm gene encoding the superantigen among Y. pseudotuberculosis strains.

Antigens, Bacterial↗
PubMed1995

Evaluation of DNA probes for specific detection of Vibrio cholerae O139 Bengal.

Two DNA probes, 2R1 and 2R3, prepared from a region in the chromosome specific for the lipopolysaccharide O side chains of Vibrio cholerae O139 (M.K. Waldor and J.J. Mekalanos, Lancet 343:1366, 1994) were examined for their specificity and sensitivity. Both probes did not hybridize with any strain of V. cholerae belonging to serogroups other than O139 and to any of the other species examined belonging to the family Vibrionaceae. Among the 126 strains of V. cholerae O139 examined, probe 2R1 hybridized with 125 strains while probe 2R3 hybridized with all 126 strains. Both probes were found to be highly specific and sensitive and can be used for the specific identification of V. cholerae O139.

Bacteriological Techniques↗
PubMed1995

Monoclonal antibodies against Ogawa specific & Ogawa-Inaba common antigenic determinants of Vibrio cholerae O1 & their diagnostic utility.

Monoclonal antibodies to Ogawa-Inaba common antigenic determinant and Ogawa specific antigenic determinant of V. cholerae belonging to the serogroup O1 were generated from BALB/c mice immunized with V. cholerae O1 Eltor Ogawa strain. Reactivity and specificities of the monoclonal antibodies were examined by slide agglutination method. The monoclonal antibodies agglutinated all the V. cholerae O1 strains tested but did not agglutinate with any of the other currently recognized 140 serogroups of V. cholerae non-O1 as well as with a variety of other enteric pathogens. Diagnostic utility of the MAbs produced in this study as compared to polyclonal O1 and monospecific antisera showed that the MAbs were as good as the latter for serological diagnosis of the two serotypes of V. cholerae O1.

Antibodies, Monoclonal↗
PubMed1994

Spread of Vibrio cholerae O139 Bengal in India.

Vibrio cholerae serogroup O139 Bengal, a novel strain with epidemic potential, completely displaced V. cholerae serogroup 01 in Calcutta in January 1993, which was followed by an epidemic caused by V. cholerae O139 in March-May 1993. From November 1992 to July 1993, 95.6% of 916 V. cholerae isolates submitted to the National Institute of Cholera and Enteric Diseases from 28 locations in India were confirmed as serogroup O139. As of July 1993, V. cholerae O139 had been isolated from 13 Indian states and a union territory, and large outbreaks of cholera caused by the O139 serogroup had occurred in several cities. The extent of spread of V. cholerae O139 Bengal in India and its ability to swiftly disseminate leaves little doubt that this is the beginning of the eighth pandemic of cholera.

Adolescent↗
PubMed1994

Vibrio mimicus with multiple toxin types isolated from human and environmental sources.

A collection of 13 strains of Vibrio mimicus, including both clinical and environmental isolates from different geographic regions, was examined for various toxins. One strain of environmental origin produced cholera-like toxin (CT) which was completely absorbed with anti-CT immunoglobulin G, five strains produced a haemolysin that cross-reacted with the thermostable direct haemolysin of V. parahaemolyticus and DNA from two strains hybridised with a DNA probe specific for the heat-stable enterotoxin of V. cholerae non-O1. Culture supernates of all strains produced a factor that was cytotoxic to Vero and Chinese hamster ovary cells. In this study, we were able to identify strains of V. mimicus that produced, or had the genetic potential to produce, several toxin types simultaneously. The role of these strains as genetic reservoirs is discussed.

Animals↗
PubMed1994

Production and cross-reactivity patterns of a panel of high affinity monoclonal antibodies to Vibrio cholerae O139 Bengal.

A series of monoclonal antibodies of different isotypes specific for Vibrio cholerae O139, the new pandemic strain of cholera, was produced. These mAbs reacted only with the reference strain (MO45) representing serovar O139 but did not react with any of the other reference strains representing serovars O1 to O140. Significantly, the mAbs did not agglutinate the R-cultures of V. cholerae (CA385, 20-93) which demonstrated the exceptional specificity of these mAbs and indicated that the mAbs recognized antigenic determinants unique for the O139 serovar. There was heterogeneity in the intensity of reactivity of the mAbs with strains of V. cholerae O139 isolated from diverse sources. Apart from 4H6, the other mAbs agglutinated all the O139 strains examined. 2D12 and 2F8 were the best mAbs based on the intensity of agglutination with all the O139 strains. Evaluation of 3A10 in comparison with a polyclonal anti-O139 antibody raised in rabbit using the slide agglutination format revealed that 3A10 fared as well as the polyclonal antibody for the laboratory identification of the O139 serovar. The acquisition of these mAbs provide reagents which would be very useful in the development of simple immunodiagnostic assays for the diagnosis of V. cholerae O139 infections.

Agglutination Tests↗
PubMed1993

Evidence for the presence of a receptor for the cytolethal distending toxin (CLDT) of Campylobacter jejuni on CHO and HeLa cell membranes and development of a receptor-based enzyme-linked immunosorbent assay for detection of CLDT.

Using ligand blotting, it was found that partially purified cytolethal distending toxin prepared from an enterotoxigenic strain of Campylobacter jejuni, bound to two peptides of molecular masses of approximately 59 kDa and 45 kDa and to a single peptide of 59 kDa in protein blots prepared from HeLa and CHO cell membranes, respectively. In contrast, labile toxin of Escherichia coli and cholera toxin bound to a single peptide of the same molecular mass (15 kDa) on protein blots prepared from both CHO and HeLa cell crude membranes resolved by gel electrophoresis. This banding pattern was identical using SDS-solubilized membrane, with or without heat treatment, but no band was obtained when reduced (treatment with 2-mercaptoethanol) samples were used for the gel electrophoresis. The differences between receptors of cytolethal distending toxin and cholera toxin/labile toxin were exploited to develop a receptor-based enzyme-linked immunosorbent assay for detection of cytolethal distending toxin which involved the consecutive addition of either solubilized CHO or HeLa membranes, antigen and antibody. This enzyme-linked immunosorbent assay consistently detected crude cytolethal distending toxin diluted up to 16-fold. The receptor-based enzyme-linked immunosorbent assay for detection of cytolethal distending toxin developed in this study is a suitable alternative assay which can be performed easily in laboratories with minimal facilities and, more importantly, the results are available within a few hours as compared to times of up to 5 days in the conventional tissue culture detection of cytolethal distending toxin.

Animals↗
PubMed1993

Distribution of the zot (zonula occludens toxin) gene among strains of Vibrio cholerae 01 and non-01.

The distribution of the zot gene that encodes the zonula occludens toxin, a newly described toxin of Vibrio cholerae, among clinical, environmental and food isolates of V. cholerae 01 and non-01 was investigated. Both the zot gene and the ctx gene that encode cholera toxin were found in 247 of 257 clinical strains and 62 of 415 environmental or food isolates of V. cholerae 01. The zot gene, but not the ctx gene was found in 37 strains (one clinical strain and 36 environmental or food isolates). In addition, two of 31 clinical strains and six of 98 environmental or food isolates of V. cholerae' non-01 possessed both the zot gene and the ctx gene. These results demonstrated the predominantly concurrent occurrence of the zot gene and ctx genes among strains of V. cholerae 01 which suggests a possible synergistic role of ZOT in the causation of acute dehydrating diarrhea produced by V. cholerae 01.

Cholera Toxin↗
PubMed1993

Clinical profile of acute diarrhoea cases infected with the new epidemic strain of Vibrio cholerae O139: designation of the disease as cholera.

A total of 113 patients suffering from acute watery diarrhoea caused by the novel epidemic strain of Vibrio cholerae non-O1, currently assigned to a new serogroup O139, were investigated in order to determine the clinical presentation of the new epidemic strain causing outbreaks of cholera-like infection in the Indian subcontinent. Estimations of electrolyte concentration in serum and stool were also performed in a representative number of the above cases. The clinical features and blood and stool biochemical parameters of V. cholerae serogroup O139 diarrhoeal patients were indistinguishable from those in typical cholera, except for 44.3% cases infected by O139 had abdominal cramps. In view of the above, we propose to designate the disease caused by V. cholerae O139 as cholera.

Acute Disease↗
PubMed1993

Virulence patterns of Vibrio cholerae non-O1 strains isolated from hospitalised patients with acute diarrhoea in Calcutta, India.

A collection of 28 strains of Vibrio cholerae non-O1 isolated during a 3-year period (1989-1991) from hospitalised patients with acute diarrhoea in Calcutta, India, were examined with regard to virulence-associated factors. Of the 28 isolates (each representing a case), 18 were isolated as the sole infecting agent; the remaining 10 were recovered as co-cultures from cases infected with V. cholerae O1. Of the strains isolated in this study, 82% could be serotyped, with serovars O5 (32.1%), O11 and O34 (14.3% each) predominant. Serovars O7, O14, O34, O39 and O97 were associated exclusively with sole infections. Two strains of V. cholerae non-O1 produced anti-cholera toxin IgG-absorbable cholera toxin (CT). Both CT-producing V. cholerae non-O1 strains hybridised with the DNA probe specific for the zonula occludens toxin (ZOT) but none of the remaining 26 strains hybridised with the ZOT probe. The majority of the strains were cytotoxic for CHO, HeLa and Vero cells, with end-point titres of 4-512. Fewer strains produced a cytotonic effect, with end-point titres of 2-16. Of the 28 strains of V. cholerae non-O1 examined, 75%, 75%, 25% and 14.3% produced haemolysin that was active against erythrocytes of rabbit, sheep (Eltor haemolysin), chicken and man, respectively. Strains that produced a haemolysin active against both rabbit and sheep erythrocytes were dominant (35.7%). Ten (35.7%) of the 28 strains examined showed cell-associated haemagglutinating activity on human blood. Of the 10 strains, nine were isolated as sole pathogen and only one strain was associated with mixed infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Detection of cholera toxin gene in stool specimens by polymerase chain reaction: comparison with bead enzyme-linked immunosorbent assay and culture method for laboratory diagnosis of cholera.

Stool specimens obtained from 123 hospitalized patients with acute secretory diarrhea admitted to the Infectious Diseases Hospital, Calcutta, India, were examined for isolation of Vibrio cholerae O1 by direct or enrichment plating on selective media for cholera toxin (CT) by bead enzyme-linked immunosorbent assay (bead-ELISA) and for the CT gene by polymerase chain reaction (PCR). V. cholerae O1 was isolated either by direct culture or by enrichment culture from 70 stool specimens, all of which gave positive results by PCR. Eleven specimens which were culture negative and bead-ELISA positive also gave positive results by PCR. In addition, 13 more specimens which were negative by both the culture method and bead-ELISA, were positive by PCR. With the combined results of both the culture method and the CT bead-ELISA, a confirmed laboratory diagnosis of cholera could be made from 81 stool specimens, while the combined results of the three methods, including PCR, yielded a positive result for 94 specimens examined. From these data, we conclude that PCR provides a more sensitive and specific assay for rapid diagnosis of cholera than currently available methods.

Adult↗
PubMed1992

Virulence traits of Aeromonas strains in relation to species and source of isolation.

The virulence traits of 39 well-defined clinical (29 strains) and environmental (10 strains) isolates of Aeromonas (16 A. hydrophila, 12 A. sobria and 11 A. caviae) were examined by a variety of assays to delineate differences, if any, in the enteropathogenic potential in relation to species and the source of isolation. The distribution of enterotoxin (ent), cytotoxin (cyt) and haemolysin (hae) producing strains of Aeromonas did not correlate to species and source of isolation. The extracellular virulence phenotype Ent+ Cyt+ Hae+ was the most common one among all the three species although unique phenotypes associated prominently with either A. hydrophila or A. sobria were also discernible. None of the cytotoxin or haemolysin producing strains hybridized with the vt1/vt2 or the tdh/trh gene probes, respectively, indicating that these two factors of Aeromonas were distinct. Haemagglutination of human O group erythrocytes was not related to the source of isolation or production of enterotoxin, cytotoxin or haemolysin but appeared to be related to species. The strains which did not exhibit cell-associated haemagglutination belonged to either A. hydrophila or A. caviae. Haemagglutination unaffected by fucose, mannose and galactose was the dominant inhibition pattern exhibited mainly by the clinical haemagglutinating strains of the three species. Only one clinical strain of A. caviae showed a diffuse pattern of adherence to HeLa cells. Expression of the 5 bacterial enzymes by strains of Aeromonas did not fall into a readily discernible pattern in relation to species or source of isolation. From this study, it is clear that the mechanism of the pathogenesis of Aeromonas is a multifactorial one.

Aeromonas↗
PubMed1992

Reassessment of the prevalence of heat-stable enterotoxin (NAG-ST) among environmental Vibrio cholerae non-O1 strains isolated from Calcutta, India, by using a NAG-ST DNA probe.

A collection of 521 environmental isolates of Vibrio cholerae which were previously examined by the suckling mouse assay and found to be negative for the heat-stable enterotoxin NAG-ST were reassessed by a recently developed DNA probe for NAG-ST. A total of 12 (2.3%) of the isolates hybridized with the NAG-ST probe. By using a cholera toxin (CT) DNA probe, the CT gene was detected in six of the strains in the collection, although none of the isolates of V. cholerae non-O1 hybridized with both of the toxin probes. All of the NAG-ST and CT probe-positive strains were hemolysin positive. Thirty-fold-concentrated supernatants of the three representative NAG-ST DNA probe-positive V. cholerae non-O1 strains gave positive fluid accumulation ratios in the suckling mouse assay even after heating (100 degrees C for 5 min) and also inhibited the binding of a NAG-ST monoclonal antibody to the bound NAG-ST in a competitive enzyme-linked immunosorbent assay (ELISA). Likewise, all six CT probe-positive V. cholerae non-O1 strains produced in vitro CT when examined by the CT bead ELISA. HindIII digest patterns of chromosomal DNA from the representative NAG-ST gene-positive strains were visually indistinguishable. Between the groups of NAG-ST probe-positive strains examined, there was a variation in the hybridizable fragments, with one group of strains exhibiting a hybridizable fragment similar to that of the NRT 36 reference strain; a smaller HindIII fragment hybridized with the NAG-ST probe in the other group of strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Taxonomical implications of the emergence of high frequency of occurrence of 2,4-diamino-6,7-diisopropylpteridine-resistant strains of Vibrio cholerae from clinical cases of cholera in Calcutta, India.

Of the 110 consecutive isolates of Vibrio cholerae recovered from cholera patients admitted to the Infectious Diseases Hospital, Calcutta, India, between July 1989 and October 1990, 90 and 82.7% were resistant to 10 and 150 micrograms of 2,4-diamino-6,7-diisopropylpteridine (O/129), respectively. Additionally, all O/129-resistant strains of V. cholerae were multiply resistant to antimicrobial agents. Except in the cases of four strains, resistance to O/129 was invariably linked with resistance to co-trimoxazole. Although O/129 susceptibility is still a useful test for Vibrio identification, resistance of V. cholerae to this compound in local areas might occasionally pose a problem.

Cholera↗