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B S Drasar

Publications and source records attributed to B S Drasar.

At least 19 recordsLinked to original sources
PubMed1992

Association of Vibrio cholerae with fresh water amoebae.

An investigation was undertaken to determine whether Acanthamoeba polyphaga SHI and Naegleria gruberi 1518/1e could affect the survival of various strains of Vibrio cholerae in laboratory microcosms. In microcosms pre-inoculated with trophozoites of amoebae, all six strains of V. cholerae tested survived and multiplied during 24 h. In control microcosms without trophozoites of amoebae, survival of the V. cholerae strains was much decreased. Two strains of V. cholerae were used to determine whether V. cholerae might survive ingestion within amoebae and subsequent encystment. Strain 152 was re-isolated from encysting N. gruberi 1518/1e but not from A. polyphaga SHI. Strain 9112 could not be isolated from cysts of either species of amoebae.

Acanthamoeba↗
PubMed1992

Pathogenesis and ecology: the case of cholera.

The way in which the results of various studies of cholera have influenced the understanding of the disease are discussed. Attention is given to the outcomes of medical research, targeted on problems of cholera and biological research focused on understanding Vibrio cholerae. The contrast between these approaches has produced a new understanding of the ecological nature of disease. The importance of the environmental reservoir of V. cholerae as the engine for the generation of diversity is highlighted.

Cell Line↗
PubMed1992

Detection of Brucella melitensis and Brucella abortus by DNA amplification.

Suitable reaction conditions and oligonucleotide primers were sought for the detection of Brucella melitensis and Brucella abortus by the polymerase chain reaction. Primers were chosen from within the coding sequence of a gene encoding a 31 kDa B. abortus antigen. The test was shown to be sensitive, and specificity was demonstrated using DNA derived from a panel of Gram-negative pathogens. There was no detectable difference between B. melitensis and B. abortus in the sensitivity of the reaction or in the size of the amplification product. The technique should be applicable in the diagnosis of brucellosis.

Base Sequence↗
PubMed1991

Molecular epidemiology of plasmid patterns in Shigella flexneri types 1-6.

A total of 123 drug-resistant and drug-sensitive Shigella flexneri types 1-6, and their Escherichia coli K12 transconjugants were used for plasmid profile analysis by agarose gel electrophoresis. Resistance factors (R-factors) were further characterized by incompatibility testing. The overall distribution of small plasmids in S. flexneri showed that a cryptic plasmid of about 4.6 Kb was found in all serotypes, and a plasmid of about 4.2 Kb was found in serotypes 1-4. Shigella flexneri types 2, 4 and 6 showed a 6.5 Kb plasmid which correlated with SSu-resistance. All S. flexneri serotypes harboured large plasmids of about 217 Kb. Plasmid profile analysis of S. flexneri in Ethiopia showed a high degree of uniformity within individual serotypes. However, there was a limited variability which, at times, could be useful for epidemiological investigation. Shigella flexneri serotypes 1-6 harboured resistance plasmids with diverse molecular weights but mostly belonging to incompatibility groups N and X.

Anti-Bacterial Agents↗
PubMed1991

Antimicrobial effect of fermented Ghanaian maize dough.

Unhygienic conditions of a typical rural community in a developing country were simulated in the laboratory by inoculating fermented maize dough porridge with Shigella flexneri and enterotoxigenic Escherichia coli (ETEC). The antimicrobial effects of the different processes involved in the preparation of fermented maize dough porridge were assessed. The soaking process reduced the pH but no antimicrobial effect against shigella and ETEC was noted. Unfermented maize dough did not inhibit any of the test strains. When the fermentation process had become established, half of the strains tested were inhibited by the fermented maize dough when examined 8 h after inoculation. Cooking the fermented maize dough into porridge reduced the antimicrobial effect but there was still significant inhibition of pathogens. This suggests that the antimicrobial effect of fermented maize dough is not due to pH per se. Fermentation of maize dough appears to be a useful strategy for reducing contamination of weaning foods by Sh. flexneri and ETEC. The possible nature of the antimicrobial agent(s) produced during the fermentation of maize dough is discussed.

Escherichia coli↗
PubMed1990

Fermentation of cereals for reduction of bacterial contamination of weaning foods in Ghana.

Unfermented and fermented maize dough weaning foods prepared by mothers in a Ghanaian village were examined for gram-negative bacilli (GNB) immediately after preparation and during storage to assess the antimicrobial effect of fermentation. GNB were cultured from all samples of unfermented dough (51) and from 16 of 51 samples of fermented dough. The extent of contamination was significantly higher in the unfermented dough than in fermented dough (5.9 [SEM 0.1] vs 4.0 [0.4] log10 colony forming units/g). After 6 h and 12 h storage, a higher proportion of samples of porridge made from unfermented dough contained GNB than did those made with fermented dough (45/51 vs 22/55; 49/51 vs 20/51, respectively) and levels of GNB were significantly higher in the porridge made from unfermented dough after 6 h (4.2 [0.2] vs 3.8 [0.2]). Fermentation of maize dough is an effective method to reduce contamination of maize dough weaning foods with GNB.

Diarrhea, Infantile↗
PubMed1990

Evidence for a DNA inversion system in Bordetella pertussis.

The expression of virulence-associated genes in Bordetella pertussis can be lost in three ways: phase variation, antigenic modulation, or serotype conversion. The mechanism(s) of these alterations in gene expression is unclear. B. pertussis chromosomal DNA was probed with cloned pin genes from Escherichia coli and cloned hin genes from Salmonella typhimurium. DNA duplex melting temperature experiments indicated significant homology between B. Pertussis chromosomal DNA and both DNA inversion genes. Southern blots using the hin gene probe showed homology with a 15 kb EcoRI fragment of B. pertussis chromosomal DNA. We postulate here that B. pertussis contains a DNA inversion system which may be responsible for serotype conversion or virulence phase change in this organism.

Blotting, Southern↗
PubMed1990

Plasmid profiles of antibiotic-resistant Shigella dysenteriae types 2, 3, 4, 6 and 7 isolated in Ethiopia during 1976-85.

Plasmid profile analysis by agarose gel electrophoresis was carried out on 37 drug-resistant strains of Shigella dysenteriae types 2, 3, 4, 6 and 7. These strains were collected between 1976 and 1985 in Addis Ababa, Ethiopia. The plasmid profile of S. dysenteriae type 2 strains with R-type CSSuT did not show middle-sized plasmids likely to code for CSSuT resistance. All strains contained a large plasmid of about 120 megadaltons (MDa), and a cryptic plasmid of about 2.2 MDa. The plasmid profiles of S. dysenteriae type 3 with R-types ACSSuT, SSuT and SSu showed a 4.2 MDa SSu-determinant, which was demonstrated in Escherichia coli K12 recipients resulting from triparental crosses. The ACT determinant in S. dysenteriae type 3 with R-type ACSSuT is probably chromosomally mediated. Cryptic plasmids of about 3.0 and 2.2 MDa were found in all S. dysenteriae type 3 isolates. The 4.2 MDa plasmid featured prominently in the plasmid profiles of S. dysenteriae types 4, 6 and 7 with R-types SSuT and SSu. However, this plasmid was not mobilizable by triparental crosses. There was a relative paucity of transferable plasmids in non-Shiga bacillus isolates. However, incompatibility group N plasmids, coding for tetracycline resistance, were detected.

DNA, Bacterial↗
PubMed1990

Plasmid profiles of Shigella dysenteriae type 1 isolates from Ethiopia with special reference to R-plasmids.

Plasmid profiles of 80 Shigella dysenteriae type 1 (Shiga's bacillus) strains, collected between 1974 and 1985 in Ethiopia, were examined. Strains with the dominant antibiotic-resistance (R-) type--resistance to ampicillin (A), chloramphenicol (C), streptomycin (S), sulphadiazine (Su) and tetracycline (T)--showed two distinct plasmid profiles (PP). Six plasmid bands were demonstrated in "Ethiopian strains" with PP-1A isolated between 1974 and 1982. In mating experiments with these strains, Escherichia coli K12 recipients showed plasmids pYH10a (72 Mda, atypical Inc FIme, coding for ACSSuT resistance). Eight plasmid bands were demonstrated in strains with PP-2A. These strains were first isolated in 1980 and carried plasmid pYH11a (40 Mda, Inc X, coding for ACT resistance). Strains with PP-2A were identical with a "Zairian strain" described elsewhere. Strains with R-type ACT were "Zairian strains" lacking the 5.1- and 4.2-Mda plasmids. Those with R-type CSSuT were temporally clustered in 1978-1980 and carried plasmid pYH12 (58 Mda, Inc B, coding for the same R-type). A trimethoprim-resistant strain (Gimira strain) had a pattern of small plasmids similar to those of the "Zairian strain" and is probably a subclone of the latter. The fact that a limited number of plasmid profiles have remained constant over many years shows the limitation of plasmid profile analysis as an epidemiological tool. However, when the usual profile is known for a given area, identification of a distinctly different pattern becomes easy and epidemiologically useful.

DNA Replication↗
PubMed1990

Vibrio cholerae HlyA hemolysin is processed by proteolysis.

The leukocidal activity of the Vibrio cholerae hemolysin (HlyA) was utilized to detect, enrich, and clone hybridoma cells expressing neutralizing monoclonal antibody in a new survivor selection protocol. A bank of 550 hybridoma clones was obtained from a mouse immunized with hemolysin by using standard techniques. The hybridoma bank was treated with a dose of HlyA hemolysin lethal to nonimmune clones. Five surviving hybridoma clones (X1 through X5) which possessed anti-HlyA activity were obtained. Western immunoblot analysis of V. cholerae culture supernatants with monoclonal antibody from clone X1 identified proteins with Mrs of 83,200, 71,600, and 60,300. Amino-terminal sequence analysis of the 71,600-Mr and 60,300-Mr forms showed homology with the published predicted sequence of HlyA. Our data indicate that proteolytic cleavage occurs between residues 120 and 121 (Glu-Leu) of the 83,200-Mr form, producing the 71,600-Mr form with the terminus NH2-L-L-F-T-P-F-D-Q-A-E-E-. Cleavage between residues 150 and 151 (Gly-Phe) releases the 60,300-Mr form with the terminus NH2-F-A-S-P-A-P-A-N-S-E-. Calculations based on the DNA sequence and the N termini indicated that the actual molecular masses of the 83,200-, 71,600-, and 60,300-Mr forms were, respectively, 79.4 kilodaltons (kDa), 68.6 kDa, and 65.3 kDa. Survivor selection and amino-terminal microsequencing offer powerful tools for the analysis of leukotoxic agents.

Amino Acid Sequence↗
PubMed1990

Long-term persistence of toxigenic Vibrio cholerae 01 in the mucilaginous sheath of a blue-green alga, Anabaena variabilis.

Cholera epidemics occur twice a year in the endemic area of Bangladesh. Vibrio cholerae 01 can be isolated from the environment only during the epidemics and the question of possible interepidemic environmental reservoirs of V. cholerae remains open. The present laboratory-based studies investigate the role of an aquatic alga, Anabaena variabilis, as a possible reservoir. Persistence of V. cholerae inside the mucilaginous sheath of A. variabilis was observed by phase-contrast and fluorescent microscopy for more than 15 months after inoculation.

Cholera Toxin↗
PubMed1989

Enterotoxigenic Escherichia coli in the domestic environment of a Malaysian village.

The membrane-filter assay, GM1-ELISA, and DNA-DNA hybridization assay, were used to detect enterotoxigenic Escherichia coli (ETEC) in samples of water, weaning food, food preparation surface swabs, fingerprints of mothers, and the fingerprints and stools of children under 5 years of age, in 20 households in a Malaysian village. Weaning food and environmental samples were frequently contaminated by faecal coliforms, including ETEC. The membrane-filter assay detected and enumerated faecal coliforms and LT-ETEC in all types of water and weaning food samples. Highest concentrations of faecal coliforms and LT-ETEC were found in weaning food, followed by well-water, stored water and stored drinking water. The GM1-ELISA detected LT-ETEC in weaning food, food preparation surfaces, fingerprints and stool samples. The DNA-DNA hybridization assay detected a larger proportion of STa2-ETEC than the other toxotypes, either singly or in combination. All the assays in combination detected the presence of ETEC in all types of samples on at least one occasion in each household. It was not possible to classify households as consistently more or less contaminated with ETEC. On individual occasions it was possible to show a significant association of the presence of LT-ETEC between the fingerprints of children and their stools, fingerprints of mothers and children, and weaning food and the stools of the child consuming the food.

Child, Preschool↗
PubMed1989

Attachment of toxigenic Vibrio cholerae 01 to various freshwater plants and survival with a filamentous green alga, Rhizoclonium fontanum.

In Bangladesh, cholera epidemics occur twice a year. V. cholerae 01 are readily isolated from the environment only during epidemics. The interepidemic reservoirs or sites of survival and multiplication of V. cholerae are still unknown. Investigations were carried out with various fresh-water plants as possible reservoirs of V. cholerae in the environment. Attachment to and acute population changes of V. cholerae on various plant surfaces was used as a screening technique to screen a particular plant species for survival studies. Five plant species, Anabaena variabilis, Rhizoclonium fontanum, Cladophora sp., Fontinalis antipyretica and Elodea canadensis were used for attachment experiments. Among these plants, R. fontanum showed the best attachment. On the basis of attachment results, survival experiments were carried out with R. fontanum. At 0.05% salinity toxigenic V. cholerae 01 survive longer in the presence of R. fontanum than in medium without algae.

Chlorophyta↗
PubMed1989

Plasmid DNA analysis by agarose gel electrophoresis on an epidemic-associated strain of trimethoprim resistant Shiga's bacillus from Gimira Wereda (Keffa administrative region, southwest Ethiopia).

A combination of genetic mating experiments and plasmid DNA analysis by gel electrophoresis was carried out on an epidemic-associated Shiga's bacillus with resistance type ACSSuTTp, isolated in 1983 from Gimira Wereda, Keffa Administrative Region, South West Ethiopia. The donor strain contained 9 plasmid species. Their sizes in megadaltons (Mdal) were: 120, 40, 35, 12.5, 6.0, 5.1, 4.3, 2.5 and 1.7. Analysis of Escherichia coli K12 transconjugants revealed that the 40, 35, and 4.3 Mdal plasmids coded for tetracyline-trimethoprim, ampicillin -chloramphenicol and streptomycin-sulphadiazine resistance respectively.

DNA, Bacterial↗