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Biomedical subjects

R K Ghosh

Publications and source records attributed to R K Ghosh.

At least 19 recordsLinked to original sources
PubMed2005

Nuclear spin gyroscope based on an atomic comagnetometer.

We describe a nuclear spin gyroscope based on an alkali-metal-noble-gas comagnetometer. Optically pumped alkali-metal vapor is used to polarize the noble-gas atoms and detect their gyroscopic precession. Spin precession due to magnetic fields as well as their gradients and transients can be cancelled in this arrangement. The sensitivity is enhanced by using a high-density alkali-metal vapor in a spin-exchange relaxation free regime. With a K-3He comagnetometer we demonstrate rotation sensitivity of 5 x 10(-7) rad s(-1) Hz(-1/2), equivalent to a magnetic field sensitivity of 2.5 fT/Hz(1/2). The rotation signal can be increased by a factor of 10 using 21Ne with a smaller magnetic moment. The comagnetometer is also a promising tool in searches for anomalous spin couplings beyond the standard model.

Journal Article↗
PubMed2000

Conversion of Vibrio eltor MAK757 to classical biotype: role of phage PS166.

Temperate phage PS166 infection of Vibrio eltor MAK757 resulted in complete changes in all biotype-specific determinants. About 10% of the PS166 lysogens of MAK757 lost their eltor-specific determinants, namely, the ability to produce soluble hemolysin, cell-associated hemagglutinin for chicken erythrocytes, and resistance to polymyxin B, as well as resistance to Mukherjee's group IV phage and sensitivity to eltor phage e4. These lysogens were found to have acquired the properties of classical strains, most significantly becoming sensitive to group IV phage but resistant to eltor-specific e4. The remainder of these lysogens, however, retained their parental biotype and serotype but acquired auxotrophy for glycine and histidine. The differential behavior of the two types of lysogen was due to the integration of the phage PS166 genome at different locations in the host chromosome. A 800-bp BglII fragment was found to contain the attP site. Phage PS166 has a polyhedral head (95 nm in diameter) and a contractile tail (98 nm in length). The phage chromosome is a linear double-stranded DNA of 110 kb and a G + C content of 58.7%.

Absorption↗
PubMed2000

Mechanism of phage PS166-mediated biotype conversion in Vibrio cholerae: role of the hlyA locus.

Temperate phage PS166 lysogens of Vibrio eltor MAK757 biotype eltor belong to two major categories. Seventy percent of the lysogens acquire auxotrophy for glycine and histidine and maintain their parental biotype. About 10% of the lysogens become Cys(-) or Cys(-) Met(-) and are converted to the classical biotype with complete changes in all biotype-specific determinants. PCR and RFLP analysis revealed that in the latter lysogens, the phage genome integrated at the hlyA locus, whereas the same locus remained unaffected in lysogens that retained their parental biotype. These results suggest that the two types of lysogens arose due to integration of the phage genome at two different locations on the chromosome. A restriction map of the phage genome was constructed using AvaII and BglII. An 800-bp BglII fragment carrying the attP site, located at one of the termini of the phage genome, was used to distinguish the two classes of lysogen.

Bacterial Proteins↗
PubMed1999

Construction of a recombinant live oral vaccine from a non-toxigenic strain of Vibrio cholerae O1 serotype inaba biotype E1 Tor and assessment of its reactogenicity and immunogenicity in the rabbit model.

The disease cholera is an important cause of mortality in many developing countries. Though it can be controlled through improved sanitation, this goal is not easily attainable in many countries. Development of an efficacious vaccine offers the best immediate solution. A new oral candidate vaccine has been constructed from a non-toxigenic strain of Vibrio cholerae E1 Tor, Inaba, which is not only devoid of the cholera toxin (CT) virulence cassette but also is completely non-reactogenic in rabbit ileal loop assay. The strain, however, had toxR and tcpA genes. Through a series of manipulations, the ctxB gene of V. cholerae, responsible for the production of the 'B' subunit of the cholera toxin (CTB) was introduced into the cryptic hemolysin locus of the strain. The resulting strain, named vaccine attempt 1.3 (VA1.3), was found to be able to produce copious amounts of CTB. In the RITARD model this strain was found to be non-reactogenic and provided full protection against the challenge doses of both V. cholerae O1, classical and E1 Tor. In the immunized rabbit it invoked significant levels of anti-bacterial and anti-toxin immunity.

Administration, Oral↗
PubMed1998

Molecular evidence that a distinct Vibrio cholerae O1 biotype El Tor strain in Calcutta may have spread to the African continent.

We present molecular evidence that a distinct genotype of Vibrio cholerae O1 which appeared in Calcutta, India, in September 1993 and which is characterized by a unique ribotype that is not found in the standardized ribotyping scheme of V. cholerae and that shows a specific pulsed-field gel electrophoresis profile may have spread to the west African country of Guinea-Bissau where it was responsible for an epidemic of cholera which began in October 1994 and continued into 1996.

Bacterial Typing Techniques↗
PubMed1998

Molecular analysis of the cholera toxin gene & antibiotic sensitivity profile of Vibrio cholerae O1 & O139 associated with mixed infection.

In the context of the reemergence of V. cholerae O1 in India and the recent evidence that O139 strains could have evolved from O1 E1 Tor strains, restriction fragment length polymorphism (RFLP) of the rRNA and the ctx genes and the antibiotic sensitivity profile of the two strains of V. cholerae, one an O1 and the other an O139, associated with mixed infection, were examined to determine their relatedness. Our results demonstrate that although the strains belonged to different clones of V. cholerae, they showed similar antibiotic sensitivity, profile indicating some exchange of genetic elements.

Cholera↗
PubMed1997

Molecular characterization of Vibrio cholerae O1 biotype El Tor strains isolated between 1992 and 1995 in Calcutta, India: evidence for the emergence of a new clone of the El Tor biotype.

Sixty-one clinical strains of Vibrio cholerae O1 El Tor isolated in Calcutta before, during, and after the V. cholerae O139 Bengal outbreak were examined to see if the O1 strains of the post-O139 period were different from those in existence before. Comparison of the restriction fragment length polymorphism of the rRNA genes (ribotyping) and the CTX genetic element revealed that all "before" strains except 1 belonged to a single known ribotype, whereas all "after" strains except 2 belonged to a hitherto undescribed ribotype. Also, 23 of 25 "before" strains harbored two or more copies of CTX in tandem and also a "free" RS1 element away from CTX, whereas 19 of 21 "after" strains had a single copy of CTX and no free RS1 element. CTX occupied different chromosomal locations in "before" and "after" strains. These studies clearly showed that El Tor O1 strains, which displaced V. cholerae O139 in Calcutta, belonged to a new clone and suggested that there is a continuous genetic reassortment among El Tor strains of V. cholerae O1.

Blotting, Southern↗
PubMed1997

Unique organization of the CTX genetic element in Vibrio cholerae O139 strains which reemerged in Calcutta, India, in September 1996.

We studied the restriction fragment length polymorphism of the rRNA gene and CTX genetic element in Vibrio cholerae O139 Bengal, which resurged in Calcutta in September 1996 after a gap of 32 months. While the strains from this resurgence were indistinguishable from the earlier strains by ribotyping, the structure of the CTX genetic element present in the current O139 strains was found to be unconventional.

Cholera↗
PubMed1996

Integration of the DNA of a novel filamentous bacteriophage VSK from Vibrio cholerae 0139 into the host chromosomal DNA.

An unusual filamentous bacteriophage, VSK, containing single-stranded, circular DNA as its genome was isolated from Vibrio cholerae 0139 strains P07 and B04. Unlike other single-stranded DNA phages, VSK can integrate its genome into the chromosome of the host and enter into a lysogenic state. The double-stranded replicative form (RF) of the single-stranded phage DNA was isolated. A restriction map of the VSK RF DNA was constructed using HaeII, AvaII, ClaI and XbaI. By Southern blot analysis of the chromosomal DNA of the lysogen using labeled phage DNA as probe, the attachment site (attP) on the viral genome was also identified.

Bacteriophages↗
PubMed1996

The disposition kinetics and residues of fenvalerate in tissues following a single dermal application to black Bengal goats.

The disposition kinetics of fenvalerate were studied in goats after dermal application of 100 ml of 0.25% (w/v) solution. The insecticide persisted in the blood for 72 h. The mean (+/- SEM) Vd(area) and apparent t 1/2 (beta) were 9.92 +/- 1.44 L/kg and 17.51 +/- 2.65 h, while the AUC and ClB values were respectively 82.15 +/- 7.40 micrograms h/ml and 0.56 +/- 0.05 L/(kg h). Four days after the dermal application, the highest concentration of fenvalerate residues was found in the adrenal gland, followed by the biceps muscle, omental fat, liver, kidney, lung and cerebrum in that order. Fenvalerate caused hyperglycaemia but had no effect on serum protein and cholesterol levels. Serum acetylcholinesterase activities were increased after 24 h but were below the initial values from 48 to 120 h.

Acetylcholinesterase↗
PubMed1996

Strategies for production of a potential candidate vaccine for cholera.

First attempt at cholera vaccination was made by Jaime Ferran in 1884. Since then, a variety of strategies and methods have been evolved to create a safe, efficacious vaccine against cholera. For the first few years emphasis was on the development of parenteral vaccines. However, as a result of accumulation of a tremendous amount of knowledge, not only on Vibrio cholerae-the causative agent, but also on its interaction with the host, emphasis has shifted towards the development of oral vaccines. Two such vaccines, one killed, a whole cell/B subunit combination vaccine and the other a live attenuated one, have shown promise. The combination vaccine in its present state of development confers only a transient protection in young children, while the live attenuated one produces adverse reaction. To combat these, various strategies are being evolved. In one attempt, a potential candidate vaccine strain has been constructed from a non-reactogenic clinical isolate of V. cholerae, which is devoid of all known major virulence genes and is also a good colonizer. In animal studies this construct has shown considerable promise. This review discusses the various strategies that have been employed so far in the quest for an ideal cholera vaccine.

Administration, Oral↗
PubMed1995

Characterization of phage phi O139, a Vibrio cholerae O139 temperate bacteriophage with cohesive DNA termini.

A temperate bacteriophage isolated from Vibrio cholerae O139, the new epidemic strain of cholera, was found to have a polyhedral head 65 nm in diameter and a rigid contractile tail 120 nm in length. The phage chromosome was a double-stranded DNA of 35 kb, with unique cohesive ends and had a G + C content of 58.8%. A restriction map of the phage DNA was constructed using the restriction endonucleases AvaI and BstEII. The phage, whose presence could be detected in nine out of 13 V. cholerae O139 isolates tested, was found to have identical chromosomal integration sites in all the strains. The phage attachment site (attP) was found to be located very close to one end of the genome.

Bacteriophages↗
PubMed1995

Biotype traits and antibiotic susceptibility of Vibrio cholerae serogroup O1 before, during and after the emergence of the O139 serogroup.

Sixty-nine strains of Vibrio cholerae O1 isolated at different times were analysed to investigate if there were any differences among the O1 strains isolated before, during and after the advent of the O139 serogroup. Of the 69 O1 strains examined, 68 belonged to the Ogawa serotype while one belonged to the Inaba serotype. With the exception of one strain all other strains of V. cholerae O1 belonged to the eltor biotype. A single O1 strain isolated before the emergence of the O139 serogroup could not be classified as either eltor or classical biotype because it was resistant to both classical and eltor specific bacteriophages. Marked variations in the susceptibility to antibiotics of V. cholerae O1 isolated during the different periods were observed. In addition, strains of V. cholerae isolated after the epidemic of serogroup O139 in Calcutta showed an expanding R-type with resistance to a variety of drugs as compared to the O1 strains isolated before the advent of the O139 serogroup. From this study, it is clear that there is a substantial mobility in genetic elements of V. cholerae O1 which necessitates a continuous monitoring to keep abreast of the changing traits of the etiologic agent of cholera.

Agglutination Tests↗
PubMed1995

Presence of lysogenic phage in the outbreak strains of Vibrio cholerae O139.

Four outbreak strains of Vibrio cholerae O139 from endemic areas of India and Bangladesh were found to carry lysogenic phage(s). All of these phage(s) produced turbid plaques characteristic of lysogeny on V. cholerae MAK 757 (El Tor, Ogawa) cells as well as on their VcA-1 lysogens but were unable to infect V. cholerae 154 (classical) cells, the universal host for all classical phages. Colonies in the turbid plaques were O139 lysogens and these developed an auxotrophic requirement, mainly for purines suggesting the integration of the prophage into the host chromosome. The immunity profile of the O139 phage(s) was similar to that of phage alpha but differed in the sensitivity of the phage lysogen of V. cholerae MAK 757 to subsequent infection by phage beta.

Bacteriophages↗
PubMed1994

Unusual in vivo turnover of transfer RNA in Vibrio cholerae.

Two lines of evidence suggest that, unlike in other organisms, the transfer RNAs of Vibrio cholerae undergo rapid turnover in vivo. Firstly, the tRNA content of V. cholerae cells treated with rifampicin (an inhibitor of initiation of RNA synthesis) decreased rapidly and continuously. Secondly, the newly synthesized tRNAs were rapidly degraded even under normal conditions of growth; the average half life of tRNA was 11.8 min. The degradation is mediated by an enzyme(s), present in V. cholerae cytoplasm, that apparently degrades tRNA completely. Rapid turnover is balanced by an enhanced rate of tRNA biogenesis, which was calculated to be 2.5 times higher than that in Escherichia coli.

Cell-Free System↗
PubMed1989

The cloning and expression of transfer RNA gene cluster of Vibrio eltor phage e4.

Vibrio eltor phage e4 codes for five different tRNA species (S. Chattopadhyay and R. K. Ghosh, 1988, Virology, 165, 606-608). The tRNA genes contained in a 3.4-kb KpnI fragment (S. Chattopadhyay and R. K. Ghosh, 1988, Virology, 162, 337-345) have been cloned in pUC 19 at the KpnI site. Two recombinant plasmids, pSR216 and pSR112, produced four of the five tRNA species (arginine, isoleucine, tyrosine, and tryptophan) encoded in the phage genome. The tRNA genes were located on a 1.45-kb KpnI-HindIII subfragment.

Bacteriophages↗
PubMed1988

Localization of transfer RNA genes on the physical map of Vibrio eltor phage e4 genome.

Transfer RNAs were isolated from uninfected and phage e4-infected Vibrio eltor Mak 757 cells. These tRNAs were then aminoacylated with 3H-labeled amino acids and hybridized to DNA isolated from phage e4. Significant hybridization was observed only with tRNA isolated from phage e4-infected cells. Restriction enzyme digestion of phage e4 DNA followed by Southern blot using [32P]tRNA from infected cells revealed that tRNA genes were contained in a 3.4-kb Kpnl fragment. The tRNA genes were located on the physical map of the phage genome 19 kb from one of the termini.

Bacteriophages↗