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At least 685 records · Page 38Linked to original sources
PubMed1981

[Salmonellal sensitivity to antibiotics in 1975-1979 and its characteristics in S. typhimurium].

Sensitivity of 314 Salmonella strains of 16 serotypes of the main groups ABCDE isolated from patients with salmonellosis in 1975-1979 was studied with the method of standard paper disks with respect to levomycetin, streptomycin, tetracycline, monomycin, erythromycin, oleandomycin and in a part of the cultures to kanamycin, ristomycin, ampicillin, carbenicillin and polymyxin. 78 per cent of the strains fell within S. typhimurium. It was found that S. typhimurium had higher resistance levels to the above antibiotics and the so called "hospital" strains of the pathogens were mainly resistant simultaneously to 4-12 antibiotics. The Salmonella strains of the other serotypes isolated mainly in 1975-1977 preserved sufficient sensitivity to the antibiotics used for the most prolonged periods and most widely in therapy.

Anti-Bacterial Agents↗
PubMed1995

[Resistance to its own antibiotic nigericin and macromolecular synthesis in Streptomyces hygroscopicus 155].

The influence of nigericin (nandavir) on the organism producing it (Streptomyces hygroscopicus 155) was studied with respect to the synthesis of protein, RNA and DNA. The resistance of the mycelium of different ages to the exogenic antibiotic was investigated. Exogenic nigericin had a more marked inhibitory effect on the macromolecular synthesis in a nonproductive variant of the strain. The antibiotic sensitivity of the mycelium in both the variants (productive and nonproductive) depended on the culture age. It was suggested that there were not less than two mechanisms of the protection from the own antibiotic in the organism.

Drug Resistance, Microbial↗
PubMed1970

Studies on resistance transfer factor deoxyribonucleic acid in Escherichia coli.

A variant of the derepressed R factor, R1, which does not contain any of the drug resistance markers, and represents, in large part, the resistance transfer factor (RTF) was studied in Escherichia coli. RTF deoxyribonucleic acid (DNA) was specifically labeled in a female cell after conjugation. Physical characterization of the molecule showed that RTF possessed an average molecular weight of 50 x 10(6) daltons and a buoyant density of 1.709 g/cm(3). By comparison to R1, we calculate that the region of DNA carrying the drug resistance genes is therefore about 20% of the R1 molecule and has a buoyant density of approximately 1.716 g/cm(3). These results support the hypothesis that the single species of R-factor DNA observed in E. coli represents a composite of the 1.709 and 1.716 g/cm(3) replicons seen in Proteus.

Carbon Isotopes↗
PubMed1982

Genetic interactions between mixed microbial populations.

Of the various mechanisms by which DNA has been shown to be transferred between bacteria in the laboratory, the combination of promiscuous plasmids and transposable DNA seems the most likely means by which this occurs in Nature. Not only can this lead to the direct transmission of the associated genes, but it can also lead to various structural and genetic changes in other DNA, particularly chromosomal, which might play an important role in microbial evolution. The changes in the DNA in a Pseudomonas strain that has evolved to degrade a novel substrate are considered in this context.

Bacteria↗
PubMed1970

Hemin-deficient mutants of Salmonella typhimurium.

Nine hemin-deficient mutants of Salmonella typhimurium LT2 were isolated as neomycin-resistant colonies. Five of these mutants could be stimulated by Delta-aminolevulinic acid (Delta-ALA), thus representing hemA mutants. Since S. typhimurium LT2 is not able to incorporate hemin, the identification of the mutants not stimulated by Delta-ALA was made on the basis of the simultaneous loss of catalase activity and cytochromes. The hemA gene was mapped by conjugation in the trp region, probably in the order purB-pyrD-hemA-trp; the episome FT(71)trp does not carry the hemA gene. Transductional intercrosses by phage P22 indicate that hemA 11, 12, 13, and 37 are at very closely linked sites, whereas hemA14 is at a more distant site in the same or an adjacent gene. No joint transduction was detected between hemA and trp or pyrF. The loci affected in the other hemin-deficient mutants were linked in conjugation to the pro(+) marker (frequency of linkage, 88 to 97%), but cotransduction of the two markers could not be obtained. The episome F lac hem purE, which originates from Escherichia coli K-12, could complement these hemin-deficient mutants of S. typhimurium LT2. As a result, the sequence of the markers on the chromosome of S. typhimurium LT2 is probably pro heme purE, analogous to the sequence found in E. coli K-12. Thus, the chromosome of S. typhimurium also possesses two hem regions, with a location similar to that described in E. coli K-12.

Amino Acids↗
PubMed1999

Genetics and engineering of microbial exopolysaccharides for food: approaches for the production of existing and novel polysaccharides.

Microbial exopolysaccharides (EPSs) are used in the food industry for their unique properties as viscosifiers, stabilisers, emulsifiers or gelling agents. In recent years, significant progress in the understanding of the genetics and biochemistry of microbial EPS synthesis by both Gram-negative and Gram-positive bacteria has been made. Biosynthesis pathways have been elucidated, and several of the genes involved have been characterised. This knowledge can now be applied to start EPS engineering or to improve EPS production.

Amino Acid Sequence↗
PubMed1992

Evaluation of methods for detecting ecological effects from genetically engineered microorganisms and microbial pest control agents in terrestrial systems.

This report summarizes and evaluates research from several laboratories that deals with the detection of ecological effects induced through exposure of microbes or plants to genetically engineered microorganisms (GEMs) and microbial pest control agents (MPCAs). Some 27 potential endpoints for measuring effects have been studied. Perturbations induced by GEMs have been detected in about one-half of these endpoints. Detectable effects have been recorded for over half of the 16 species of bacteria and fungi studied. The effects caused by GEMs and MPCAs include inhibition of beneficial mycorrhizal fungi growing on Douglas fir seedling roots, depression in plant root and shoot growth, inhibition of predatory soil protozoa, accumulation of a toxic metabolite during biodegradation that inhibits soil fungi, increased microbial community respiration due to rapid lignin breakdown in soil, and the displacement of a broad group of gram-negative bacteria that inhabit the root surface of cereal crops. These effects were usually, but not always, of short duration. However, some of the changes were irreversible during the observation time of days, weeks, or in one case, months.

Journal Article↗