Drug resistance among infantile enteropathogenic Escherichia coli strains isolated in the United Kingdom.

Two hundred and thirty-two strains of Escherichia coli belonging to infantile enteropathogenic serotypes isolated in the United Kingdom during 1980 and 1981 were tested for resistance to 10 antimicrobial drugs. Resistance to one or more drugs was found in 134 (57.8%) of the strains, with resistance to sulphonamides, streptomycin, tetracycline, and ampicillin occurring most commonly. Resistance was transferable in 65 out of 104 resistant strains. These findings are a cause for concern because they indicate that the choice of treatment for severe illness is limited and suggest that a large pool of drug-resistant organisms exists in the community.     

Plasmid-encoded trimethoprim resistance in multiresistant epidemic Salmonella typhimurium phage types 204 and 193 in Britain.

Multiresistant strains of Salmonella typhimurium phage types 204 and 193 appeared in calves in 1977 and then spread epidemically in cattle. Food poisoning is the main route by which drug-resistant strains from cattle are spread to man, and by the end of 1979 these two multiresistant strains had been identified in 290 cases of human salmonellosis in Britain. Trimethoprim-resistant S typhimurium were rare until a strain of a new phage type, designated type 204c, spread in cattle in 1979. All isolations of type 204c were trimethoprim resistant. Trimethoprim had been used to treat cattle and this usage has probably contributed to the establishment of type 204c and the increased incidence of trimethoprim-resistant strains. The responsibility to prevent or control drug resistance in bovine S typhimurium lies with the veterinary profession, and more stringent regulatiions governing the use of antibiotics in animals bred for food may be necessary.     

Evidence of independent gene duplications during the evolution of archaeal and eukaryotic family B DNA polymerases

Eukaryotes and archaea both possess multiple genes coding for family B DNA polymerases. In animals and fungi, three family B DNA polymerases, alpha, delta, and epsilon, are responsible for replication of nuclear DNA. We used a PCR-based approach to amplify and sequence phylogenetically conserved regions of these three DNA polymerases from Giardia intestinalis and Trichomonas vaginalis, representatives of early-diverging eukaryotic lineages. Phylogenetic analysis of eukaryotic and archaeal paralogs suggests that the gene duplications that gave rise to the three replicative paralogs occurred before the divergence of the earliest eukaryotic lineages, and that all eukaryotes are likely to possess these paralogs. One eukaryotic paralog, epsilon, consistently branches within archaeal sequences to the exclusion of other eukaryotic paralogs, suggesting that an epsilon-like family B DNA polymerase was ancestral to both archaea and eukaryotes. Because crenarchaeote and euryarchaeote paralogs do not form monophyletic groups in phylogenetic analysis, it is possible that archaeal family B paralogs themselves evolved by a series of gene duplications independent of the gene duplications that gave rise to eukaryotic paralogs.      

Reevaluation of brush border motility: calcium induces core filament solation and microvillar vesiculation

The report that microvillar cores of isolated, demembranated brush borders retract into the terminal web in the presence of Ca(++) and ATP has been widely cited as an example of Ca(++)-regulated nonmuscle cell motility. Because of recent findings that microvillar core actin filaments are cross-linked by villin which, in the presence of micromolar Ca(++), fragments actin filaments, we used the techniques of video enhanced differential interference contrast, immunofluorescence, and phase contrast microscopy and thin-section electron microscopy (EM) to reexamine the question of contraction of isolated intestinal cell brush borders. Analysis of video enhanced light microscopic images of Triton- demembranated brush borders treated with a buffered Ca(++) solution shows the cores disintegrating with the terminal web remaining intact; membranated brush borders show the microvilli to vesiculate with Ca(++). Using Ca(++)/EGTA buffers, it is found that micromolar free Ca(++) causes core filament dissolution in membranated or demembranated brush borders, Ca(++) causes microvillar core solation followed by complete vesiculation of the microvillar membrane. The lengths of microvilli cores and rootlets were measured in thin sections of membranated and demembranated controls, in Ca(++)-, Ca(++) + ATP-, and in ATP-treated brush borders. Results of these measurements show that Ca(++) alone causes the complete solation of the microvillar cores, yet the rootlets in the terminal web region remain of normal length. These results show that microvilli do not retract into the terminal web in response to Ca(++) and ATP but rather that the microvillar cores disintegrate. NBD-phallicidin localization of actin and fluorescent antibodies to myosin reveal a circumferential band of actin and myosin in mildly permeabilized cells in the region of the junctional complex. The presence of these contractile proteins in this region, where other studies have shown a circumferential band of thin filaments, is consistent with the hypothesis that brush borders may be motile through the circumferential constriction of this “contractile ring,” and is also consistent with the observations that ATP-treated brush borders become cup shaped as if there had been a circumferential constriction.     

Synthesis of plastoquinone-9 and phytylplastoquinone from homogentisate in lettuce chloroplasts

Chloroform-soluble extracts of unpurified chloroplast preparations of lettuce, pea and spinach and of class I lettuce chloroplasts that have been incubated in the light with [methylene-³H]homogentisate contain ³H-labelled plastoquinones-9 and -8 (minor homologue), 2-demethylplastoquinones-9 and -8 (minor homologue), pytylplastoquinone and 2-demethylphytylplastoquinone.. The absence of demethylquinols, the presumed precursors of the dimethylquinones, from the extracts to the fact that no precautions were taken in the extraction procedure to present their oxidation to the corresponding quinones.In unpurified lettuce chloroplasts the synthesis of these compounds from [methylene-³H]homogentisate is Mg²⁺-dependent and it is stimulated by light. The addition of isopentenyl pyrophosphate to the incubation mixtures increases the amounts of both groups of quinones (polyprenyl quinones and phytyl quinones) synthesised in the light and the amounts of polyprenyl quinones synthesised in the dark. Replacement of isopentenyl pyrophosphate with a source of preformed polyrenyl pyrophosphates brings about a marked rise in the amounts of polyprenyl quinones synthesized. This rise in polyprenyl quinone synthesis is further increased if the chloroplats are subjects to osmotic shock. The presence of S-adenosylmethionine increases the amounts of dimethylquinones synthesized at the expense of the demethylquinones. The implied precursor-product relationships between 2-demethylphytylplastoquinone (quinol?) and phytylplastoquinone and between the 2-demethylplastoquinones (quinols) and plastoquinones were verified in a pulse-labelling experiment. Confirmation that these quinones, or their corresponding quinols, are synthesized.     

Formation of 3-hexaprenyl-4-hydroxybenzoate by matrix-free mitochondrial membrane-rich preparations of yeast.

It has been shown that a 10 000 x g matrix-free mitochondrial membrane-rich preparation from commercial bakers' yeast is able to synthesize 3-all-transhexaprenyl-4-hydroxybenzoate from 4-hydroxybenzoate and isopentenyl pyrophosphate. The synthesis is Mg2+ dependent and is stimulated markedly by the primer for polyprenylpyrophosphate synthesis of 3-hexaprenyl-4-hydroxybenzoate from 4-hydroxybenzoate, isopentenyl pyrophosphate and 3,3-dimethylallyl pyrophosphate the priming function of 3,3-dimethylallyl pyrophosphate can be performed by either geranyl pyrophosphate (most efficient) or farnesyl pyrophosphate. At high Mg2+ concentrations, however, geranyl pyrophosphate and farnesyl pyrophosphate act mainly as sources of preformed side chains and 3-diprenyl- and 3-tripenyl-4-hydroxybenzoate, respectively, are produced. In the presence of a source of preformed polyprenyl pyrophosphates the membrane preparations catalysed the polyprenylation of methyl-4-hydroxybenzoate, 4-hydroxybenzaldehyde, 4-hydroxybenzylalcohol and 4-hydroxycinnamate. No evidence was obtained for the involvement of either 4-hydroxybenzoyl CoA or 4-hydroxybenzoyl-S-protein in the formation of 3-polyprenyl-4-hydroxybenzoates.