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R Virgilio

Publications and source records attributed to R Virgilio.

15 recordsLinked to original sources
PubMed1996

Evolution of drug resistance in Salmonella panama isolates in Chile.

In a search for Salmonella isolates in the environment in Chile in 1975, drug-susceptible strains of Salmonella panama were recovered for the first time from river water and vegetables in the vicinity of Santiago. Two to 3 years later, antibiotic-resistant S. panama began to appear in a variety of sources (meat, animals, vegetables, etc.), giving rise to a human epidemic that involved the entire nation. Of 139 clinical isolates studied, 7 were drug susceptible, 11 were resistant only to nitrofurans, and 3 were streptomycin, spectinomycin, and nitrofuran resistant; none of these 21 isolates harbored plasmid DNA. Most isolates (n = 107) were resistant to nitrofurans (chromosomal) and to streptomycin, spectinomycin, sulfonamides, tetracycline, and mercuric and tellurite salts; this multidrug resistance was encoded on a 218-kb plasmid classified in a number of strains as being in the IncHI2 group. From 1982 to 1993, 11 isolates acquired an additional self-transferable plasmid coding for resistance to any one of ampicillin (61 kb), ampicillin and trimethoprim (65 kb), ampicillin, trimethoprim, streptomycin, and sulfonamides (71 kb), ampicillin, gentamicin, kanamycin, and tetracycline (120 kb), or a nontransferable plasmid of approximately 6 kb encoding resistance to ampicillin or kanamycin. With the exception of ampicillin or ampicillin and trimethoprim resistance, S. panama isolates from foodstuffs, mainly pork meat products, and animals had resistance patterns that were the same as those found in clinical specimens. Remarkably, strains from goats and goat cheese and from shellfish isolated in particular rural regions were either drug susceptible or resistant only to streptomycin-spectinomycin encoded on a mobile genetic element and to nitrofurans. The report describes the arrival of a susceptible S. panama strain, its spread all over the country, and the evolution of progressively complex resistance patterns.

Chile↗
PubMed1981

Naturally occurring prototrophic strains of Salmonella typhi.

In a survey of the nutritional requirements of Salmonella typhi it was found that 3.2% of 560 recent clinical isolates were able to grow in a minimal medium consisting of phosphates, ammonium and magnesium sulfates, and glucose; the remainder required tryptophan. Both groups grew slowly and rather poorly in these media due to a deficient utilization of sulfur from sulfate. Addition of cysteine or sodium sulfide or thiosulfate promoted rapid and profuse growth. Minimal medium containing thiosulfate as a source of sulfur allowed for an easy and sharp differentiation of prototrophic variants needing none of the amino acids, and tryptophan auxotrophs. The prototrophic phenotype is not the result of the presence of rare prototrophic mutants, since these strains were able to develop in minimal medium from very small inocula (10(2)), all colonies were prototrophic in replica plating experiments, and the cultures gave comparable colony counts when seeded simultaneously in nutrient and on minimal agar plates.

Culture Media↗
PubMed1977

Pharmacokinetic study of intravenous rifampicin.

The time course of the serum and urine concentrations of rifampicin were evaluated during and after administration of an intravenous preparation of the antibiotic. 300, 450 and 600 mg dose levels of the antibiotic were evaluated, all being given as intravenous infusion after solution in 500 ml of glucose, the infusion lasting 3 h. The results have shown that the serum level curves and the kinetic parameters calculated on them do not differ to any major extent from those corresponding to the same doses given orally. No changes of relevance in the half-life values were observed between doses. Changes in serum bilirubin levels were observed with a pattern similar to that commonly seen with oral administration of rifampicin.

Administration, Oral↗
PubMed1966

Electron microscopy of Staphylococcus aureus cell wall lysis.

Virgilio, Rafael (Escuela de Química y Farmacia, Universidad de Chile, Santiago, Chile), C. González, Nubia Muñoz, and Silvia Mendoza. Electron microscopy of Staphylococcus aureus cell wall lysis. J. Bacteriol. 91:2018-2024. 1966.-A crude suspension of Staphylococcus aureus cell walls (strain Cowan III) in buffer solution was shown by electron microscopy to lyse slightly after 16 hr, probably owing to the action of autolysin. The lysis was considerably faster and more intense after the addition of lysozyme. A remarkable reduction in thickness and rigidity of the cell walls, together with the appearance of many irregular protrusions in their outlines, was observed after 2 hr; after 16 hr, there remained only a few recognizable cell wall fragments but many residual particulate remnants. When autolysin was previously inactivated by trypsin, there was a complete inhibition of the lytic action of lysozyme; on the other hand, when autolysin was inactivated by heat and lysozyme was added, a distinct decrease in the thickness of the cell walls was observed, but there was no destruction of the walls. The lytic action of lysozyme, after treatment with hot 5% trichloroacetic acid, gave rise to a marked dissolution of the structure of the cell walls, which became lost against the background, without, however, showing ostensible alteration of wall outlines. From a morphological point of view, the lytic action of autolysin plus lysozyme was quite different from that of trichloroacetic acid plus lysozyme, as shown by electron micrographs, but in both cases it was very intense. This would suggest different mechanisms of action for these agents.

Bacteriolysis↗