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T Chakraborty

Publications and source records attributed to T Chakraborty.

178 records · Page 10Linked to original sources
PubMed1987

Marker exchange mutagenesis of the aerolysin determinant in Aeromonas hydrophila demonstrates the role of aerolysin in A. hydrophila-associated systemic infections.

We report here on the isolation of isogenic strains of Aeromonas hydrophila AB3 deleted for a segment of the aerolysin gene. All aer mutants obtained lacked the 49-kilodalton aerolysin gene product and were neither hemolytic for blood erythrocytes nor cytotoxic for Chinese hamster ovary tissue culture cells. One such mutant, AB3-5, was used in a mouse toxicity model to evaluate the role of aerolysin in the pathogenesis of A. hydrophila infections. The strain had a 50% lethal dose (LD50) of greater than 10(9) as compared with the parental strain which had an LD50 of 5 X 10(7). Reintegration of the deleted segment into AB3-5 resulted in an LD50 of 6 X 10(7) cells for this revertant. Furthermore, all mice injected with a sublethal dose of the parental strains developed necrotic lesions; this was never obtained with the aerolysin-deficient strain AB3-5. More importantly, specific neutralizing antibody to aerolysin was detected in mice surviving A. hydrophila infection, demonstrating that aerolysin is produced during the course of systemic A. hydrophila infections.

Aeromonas↗
PubMed1987

Mode of action of nitro-heterocyclic compounds on Escherichia coli.

The inhibitory and bactericidal activities of several different nitro-heterocyclic compounds, such as nitrofuran, nitronaphthofuran, nitrobenzofuran, nitroimidazole and nitrothiazole, were assessed in vitro. All these substances except nitroimidazole were active against Escherichia coli, though to different degrees. Under anaerobic test conditions the antibacterial activity increased slightly. Nitroreductase-deficient mutants, however, were highly resistant to all nitro-compounds, indicating that only when the nitro-group is reduced to these agents get into an active antibacterial form. SOS repair-deficient strains were much more susceptible to the nitro-containing substances than repair-proficient counterparts, indicating that damage to bacterial DNA is the essential mechanism of antibacterial activity of all nitro-heterocyclic compounds.

Escherichia coli↗
PubMed1986

Cloning, expression, and mapping of the Aeromonas hydrophila aerolysin gene determinant in Escherichia coli K-12.

DNA sequences corresponding to the aerolysin gene (aer) of Aeromonas hydrophila AH2 DNA were identified by screening a cosmid gene library for hemolytic and cytotoxic activities. A plasmid containing a 5.8-kilobase EcoRI fragment of A. hydrophila DNA was required for full expression of the hemolytic and cytotoxic phenotype in Escherichia coli K-12. Deletion analysis and transposon mutagenesis allowed us to localize the gene product to 1.4 kilobases of Aeromonas DNA and define flanking DNA regions affecting aerolysin production. The reduced hemolytic activity with plasmids lacking these flanking regions is associated with a temporal delay in the appearance of hemolytic activity and is not a result of a loss of transport functions. The aerolysin gene product was detected as a 54,000-dalton protein in E. coli maxicells harboring aer plasmids and by immunoblotting E. coli whole cells carrying aer plasmids. We suggest that the gene coding aerolysin be designated aerA and that regions downstream and upstream of aerA which modulate its expression and activity be designated aerB and aerC, respectively.

Aeromonas↗
PubMed1984

Cloning of enterotoxin gene from Aeromonas hydrophila provides conclusive evidence of production of a cytotonic enterotoxin.

Culture filtrates of two Aeromonas hydrophila strains which were isolated from patients with diarrhea and assumed to be causative agents of the infections were shown to contain enterotoxic, cytotoxic, and hemolytic activities. Modest heat treatment of the filtrates inactivated the cytotoxic and cytolytic activities, but not the enterotoxic activity. The construction of cosmid gene banks in Escherichia coli of DNA from both A. hydrophila strains demonstrated that the determinants of the three activities are located on three different segments of the A. hydrophila chromosome. Both heated culture filtrates of A. hydrophila and nonheated filtrates of an E. coli clone containing the A. hydrophila enterotoxin gene provoked fluid accumulation in the rabbit ileal loop and suckling mouse models and caused elongation of Chinese hamster ovary cells. Differences in the responses of the models to the A. hydrophila enterotoxin and to the heat-labile and heat-stabile toxins of E. coli indicated that the former is distinct from the latter two types of toxin. These results constitute conclusive evidence for the production by A. hydrophila of a cytotonic enterotoxin that is distinct from the A. hydrophila cytotoxin and hemolysin and known E. coli enterotoxins.

Aeromonas↗
PubMed1982

Purification of the E. coli dnaA gene product.

The product of the dnaA gene of Escherichia coli was isolated in a highly enriched form. The purification product binds specifically to DNA containing the E. coli chromosomal origin of replication, oriC.

Bacterial Proteins↗
PubMed1978

The DNA . tyrocidine complex and its dissociation in the presence of gramicidin D.

The peptide antibiotic tyrocidine affects transcription in vitro by interfering with the initiation process. The complex formed between tyrocidine and native DNA is stable against nucleolytic enzymes. It is sensitive to variations in the salt concentration. Protection of DNA as a function of the tyrocidine concentration follows a curve suggesting cooperative binding of tyrocidine to DNA. The complex formation at low tyrocidine concentrations is accompanied by the presence of single stranded regions of unknown length. With single-stranded DNA, tyrocidine forms a complex which is relatively insensitive to high salt concentrations. Both native and single-stranded DNAs of the complexes become digestible in the presence of gramicidin D, another peptide antibiotic. Breakdown of the complex as a function of the gramicidin D concentration follows a curve which is the reverse of cooperative binding. Gramicidin D acts more effectively on single-stranded rather than on double-stranded DNA . tyrocidine complexes. The DNA . tyrocidine complex, which is broken down by formamide and dimethyl sulfoxide is stabilized by gramicidin D. The implications of these results are discussed with respect to a possible recognition of DNA sequences by tyrocidine and the interaction between DNA, tyrocidine and gramicidin D.

Bacillus↗
PubMedDate not supplied

Molecular control of myogenesis: antagonism between growth and differentiation.

Insight into the molecular mechanisms that control establishment of the skeletal muscle phenotype has recently been obtained through cloning of a family of muscle-specific regulatory factors that can activate myogenesis when transfected into non-muscle cells. This family of factors, which includes MyoD, myogenin, myf-5, and MRF4, can bind DNA and transactivate muscle-specific genes in collaboration with ubiquitous cellular factors. Growth factors play an antagonistic role in myogenesis by suppressing the actions of the myogenic regulatory factor family. This review will focus on the regulation and mechanism of action of this family of myogenic regulatory factors and on the central role of peptide growth factors in modulating their expression and biological activities.

Animals↗
PubMedDate not supplied

Molecular analysis of bacterial cytolysins.

Results of molecular and pathogenic studies of three different bacterial hemolysins (cytolysins) are presented. These exoproteins derive from the two gram-negative bacteria Escherichia coli and Aeromonas hydrophila and from the gram-positive pathogen Listeria monocytogenes. The hemolysin of E. coli is determined by an 8-kilobase (kb) region that includes four clustered genes (hlyC, hlyA, hlyB, and hlyD). This hemolysin determinant is part either of large transmissible plasmids or of the chromosome. The genes located chromosomally are found predominantly in E. coli strains that can cause pyelonephritis and/or other extraintestinal infections. A detailed analysis of the chromosomal hyl determinants of one nephropathogenic E. coli strain revealed the existence of specific, large chromosomal insertions 75 kb and 100 kb in size that carry the hly genes but that also influence the expression of other virulence properties, i.e., adhesion and serum resistance. The direct involvement of E. coli hemolysin in virulence could be demonstrated in several model systems. The genetic determinants for hemolysin (cytolysin) formation in A. hydrophila (aerolysin) and L. monocytogenes (listeriolysin) are less complex. Both cytolysins seem to be encoded by single genes, although two loci (aerB and aerC) that affect the expression and activity of aerolysin have been identified distal and proximal to the structural gene for aerolysin (aerA). Cytolysin-negative mutants of both bacteria were obtained by site-specific deletion and/or transposon mutagenesis. These mutants show a drastic reduction in the virulence of the respective bacteria.

Aeromonas↗
PubMedDate not supplied

Musculoskeletal problems in the separation of ischiopagus tetrapus twins.

A pair of ischiopagus tetrapus twins were successfully separated in Calcutta in 1986. The gastrointestinal tracts were separated at a preliminary operation, and the definitive operation was performed 3 months later. Four iliac osteotomies, division of symphysis pubes, and reconstruction of individual pelves with dissection and separation of pelvic organs alloted to individual twins were the procedures performed in the definitive operation. The musculoskeletal results have been excellent in the present case.

Female↗