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PubMed1988

[Comparative activity of habekacin and 4 other aminoglycosides against gram-negative bacilli. Evolution of resistance].

The activity of 5 aminoglycosides compounds (habekacin, amikacin, gentamicin, netilmicin and tobramycin) was studied by an agar dilution method, against 235 strains of Enterobacteriaceae and 146 other Gram negative bacilli. 79 to 98% of susceptible strains were observed, according to the aminoglycoside compound. Habekacin and amikacin were the most effective, specially against the more frequently resistant bacteria: Enterobacter, Serratia, Hafnia, Acinetobacter, Pseudomonas aeruginosa. In comparison with a previous study, no evolution was observed in the resistance to aminoglycosides.

Acinetobacter↗
PubMed1996

Independent evolution of the env and pol genes of HIV-1 during zidovudine therapy.

OBJECTIVE: To determine the effect that selection for antiviral resistance in the HIV-1 pol gene has on the level of variation and pattern of evolution in the V3 region of env. DESIGN: Proviral genomes obtained from two patients before, during and after the termination of zidovudine (ZDV) therapy (approximately 2 years) were amplified and sequenced in pol and env, and the evolution of the V3 hypervariable region compared with that of the reverse transcriptase domain of pol. METHODS: Gene fragments were polymerase chain reaction-amplified from patients' peripheral blood mononuclear cells. Nucleotide sequencing was carried out using T7 DNA polymerase and dye-labelled terminators on an automated DNA sequencer. Sequences were analysed using maximum likelihood phylogenetic techniques. RESULTS: Both patients showed multiple resistance-associated mutations after 1 year of ZDV therapy. Sequence diversity in V3 showed no reduction during the period of treatment. Substantial change continued to occur in this region and multiple lineages were present in both patients, in contrast to the single lineage observed in the pol gene of one (patient 74), a difference confirmed by likelihood ratio tests. CONCLUSIONS: There is no evidence from this study that selection due to antivirals has any significant impact on the evolution of the env gene. The independence in the evolution of these genes implies that recombination was occurring between the two genes during the study period. Such independent evolution should be allowed for in developing strategies for HIV therapy involving multiple target genes.

Amino Acid Sequence↗
PubMed2000

Environmentally directed mutations and their impact on industrial biotransformation and fermentation processes.

Microbial adaptation plays an important role in the selection of improved strains for biotechnological processes and for the maintenance and stability of the selected production strains. Most of the knowledge about adaptation processes and environmentally directed mutations originates from environmental microbiology and from studies on biological evolution. The increasing information on the molecular mechanisms of adapted mutations and on the development of methods frequently used in environmental and evolutionary microbiology, such as the selection in semi-continuous cultures or chemostats, can be used as input and tools for the improvement of industrial production organisms.

Bacteria↗
PubMed2005

[General and local risk factors in infectious keratitis].

PURPOSE: The paper presents a study of corneal ulcers at aged persons for the identification of etiologic and aggravates factors that may have a negative influence for the prognostic of the diseases. MATERIAL AND METHOD: We have performed a retrospective study using a lot of aged patients with corneal ulcers, hospitalized in 2002-2003 period. The data were obtained by both clinical examination (anamnesis and ocular examination) and by the laboratory exams (microbiologic exam). RESULTS AND DISCUSSIONS: We have analyzed by the epidemiological point of view, the distribution of cases with the age, sex, provenance area, and profession. We have demonstrated a predominant repartition of cases in the 7-th decade (45%) and for the masculine patients (in 60% of cases). The patients from rural area represented 75% of cases. In relationship with the etiology, the traumatic ulcers represent 25%, microbial keratitis 45% associated with local or general aggravating factors. Microbiological exam has revealed in principal non pathogen or pathogen germs in 10 cases (staphylococcus), moderate virulence germs in 5 cases (streptococcus) or very virulent germs (escherichia colli and pyocyanic bacillus) in 2 cases. CONCLUSIONS: The evolution of corneal ulcers at aged people is determined by etiologic and aggravating factors. The improvement of the evolution and of the prognosis depends on the most precocious application of local and general therapeutic measures.

Aged↗
PubMed1999

Resistance gene capture.

Integrons are the primary mechanism for antibiotic-resistance gene capture and dissemination among Gram-negative bacteria. The recent finding of super-integron structures in the genomes of several bacterial species has expanded their role in genome evolution and suggests that they are the source of mobile multi-resistant integrons.

Anti-Bacterial Agents↗
PubMed2002

Typing of Yersinia pestis isolates from the state of Ceará, Brazil.

AIMS: To investigate whether modifications in Yersinia pestis isolates from three plague foci from the state of Ceará, Brazil, had occurred over the years as a consequence of genetic adaptation to the environment. METHODS AND RESULTS: The isolates were studied with respect to susceptibility to antimicrobial drugs, plasmid and protein profiling, pigmentation on Congo red-agar plates, and the presence of some pathogenicity genes using PCR. Most of the expected virulence markers were detected in the cultures examined. There was no evidence of any alteration that could be associated with their origin (patients, rodents and fleas) or period of isolation (1971-1997). CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY: Phenotypic or genotypic changes were not detected in the cultures examined. However, the results obtained will serve as a reference to follow the evolution of Y. pestis in these foci.

Animals↗
PubMed1970

Comparative studies with tox plus and tox minus corynebacteriophages.

The characteristics of nine inducible temperate corynebacteriophages designated alpha(tox+), beta(tox+), P(tox+), gamma(tox-), pi(tox+), K(tox-), rho(tox-), L(tox+), and delta(tox+) have been compared. Virion morphology and ability to recombine genetically with the well-studied phage beta(tox+) have been correlated with other properties of the phages, and the distribution of the genetic marker tox+ among related and relatively unrelated corynebacteriophages has been analyzed. The immunity specificity, host range, and plaque morphology of each phage were determined. The phages can be separated into five groups with different immunity specificities. Each type of host range previously recognized in mutants of phage beta(tox+) was present in one or more of the phages included in the present study, and the phages were found to produce plaques of several different morphological types. Representative phages with each of the five types of immunity specificity were further characterized with respect to virion morphology, ability to recombine with phage beta(tox+), latent period, average burst size, and neutralization by homologous and heterologous antiphage sera. All of these phages have polyhedral heads and long slender tails, but two distinct morphological types were distinguished by the sizes and proportions of the components of the virions. Only phages of the same morphological type as beta(tox+) were capable of genetic recombination with beta(tox+), but morphological similarity between phages was not sufficient to insure interfertility. The phages which recombined with beta(tox+) resembled one another in plaque morphology, latent period, and average burst size, whereas phages which failed to recombine with beta(tox+) differed in these characteristics. The phages capable of genetic recombination with beta(tox+) were found to differ from each other in immunity specificity, host range, neutralization by antiphage sera, and toxinogenicity. Thus, these latter characteristics are of limited value in establishing the extent of relatedness between corynebacteriophages. The genetic marker tox+ was not consistently correlated with any other property of the corynebacteriophages analyzed in this study. The most striking finding regarding the distribution of the tox+ marker is its presence both in beta(tox+) and delta(tox+), phages which fail to recombine genetically and which differ in virion morphology. The presence of the tox+ marker in genetically unrelated corynebacteriophages poses many questions concerning the origin(s) of tox+ and the evolution of the phage-host interactions which determine the ability of corynebacteria to synthesize diphtherial toxin.

Animals↗
PubMedDate not supplied

Multiple-drug resistant enterococci: the nature of the problem and an agenda for the future.

Enterococci, leading causes of nosocomial bacteremia, surgical wound infection, and urinary tract infection, are becoming resistant to many and sometimes all standard therapies. New rapid surveillance methods are highlighting the importance of examining enterococcal isolates at the species level. Most enterococcal infections are caused by Enterococcus faecalis, which are more likely to express traits related to overt virulence but--for the moment--also more likely to retain sensitivity to at least one effective antibiotic. The remaining infections are mostly caused by E. faecium, a species virtually devoid of known overt pathogenic traits but more likely to be resistant to even antibiotics of last resort. Effective control of multiple-drug resistant enterococci will require 1) better understanding of the interaction between enterococci, the hospital environment, and humans, 2) prudent antibiotic use, 3) better contact isolation in hospitals and other patient care environments, and 4) improved surveillance. Equally important is renewed vigor in the search for additional drugs, accompanied by the evolution of new therapeutic paradigms less vulnerable to the cycle of drug introduction and drug resistance.

Anti-Bacterial Agents↗
PubMed2006

Two faces of the prokaryote concept.

Bacteria had remained undefined when, in 1962, Roger Y. Stanier and C.B. van Niel published their famed paper ''The concept of a bacterium.'' The articulation of the prokaryote-eukaryote dichotomy was a vital moment in the history of biology. This article provides a brief overview of the context in which the prokaryote concept was successfully launched in the 1960s, and what it was meant to connote. Two concepts were initially distinguished within the prokaryote-eukaryote dichotomy at that time. One was organizational and referred to comparative cell structure; the other was phylogenetic and referred to a ''natural'' classification. Here, I examine how the two concepts became inseparable; how the prokaryotes came to signify a monophyletic group that preceded the eukaryotes, and how this view remained unquestioned for 15 years, until the birth of molecular evolutionary biology and coherent methods for bacteria phylogenetics based on 16S rRNA. Today, while microbial phylogeneticists generally agree that the prokaryote is a polyphyletic group, there is no agreement on whether the term should be maintained in an organizational sense.

Archaea↗
PubMed1990

Evolution of enzymatic mechanisms of resistance among beta-lactam antibiotics.

Resistance to third-generation cephalosporins occurs as a result of either the production of high concentrations of chromosomal cephalosporinase or, increasingly, the presence of broad-spectrum plasmid-mediated beta-lactamases. Both cases represent the response of bacteria in the hospital setting to the selection pressure brought to bear by the use of these antibiotics. Continued evolution of the plasmid-mediated enzymes is occurring as new antibiotics are introduced, probably reflecting the process that began when the first beta-lactamase apparently evolved from the penicillin-binding proteins. beta-Lactamase inhibitors offer one approach to dealing with the evolution of resistance to previously beta-lactamase-stable antibiotics.

Amino Acid Sequence↗
PubMed1994

A new class of DNA photolyases present in various organisms including aplacental mammals.

DNA photolyase specifically repairs UV light-induced cyclobutane-type pyrimidine dimers in DNA through a light-dependent reaction mechanism. We have obtained photolyase genes from Drosophila melanogaster (fruit fly), Oryzias latipes (killifish) and the marsupial Potorous tridactylis (rat kangaroo), the first photolyase gene cloned from a mammalian species. The deduced amino acid sequences of these higher eukaryote genes show only limited homology with microbial photolyase genes. Together with the previously cloned Carassius auratus (goldfish) gene they form a separate group of photolyase genes. A new classification for photolyases comprising two distantly related groups is proposed. For functional analysis P.tridactylis photolyase was expressed and purified as glutathione S-transferase fusion protein from Escherichia coli cells. The biologically active protein contained FAD as light-absorbing cofactor, a property in common with the microbial class photolyases. Furthermore, we found in the archaebacterium Methanobacterium thermoautotrophicum a gene similar to the higher eukaryote photolyase genes, but we could not obtain evidence for the presence of a homologous gene in the human genome. Our results suggest a divergence of photolyase genes in early evolution.

Amino Acid Sequence↗
PubMed2000

Effects of hexanal, trans-2-hexenal, and storage temperature on shelf life of fresh sliced apples.

In this paper, the effects of hexanal and trans-2-hexenal, which are both natural molecules characterizing apple aroma, on the microbial population and on color retention of fresh sliced apples were evaluated. In particular, a central composite design (CCD) was developed to assess the individual and interactive effects of the chosen volatile molecules and storage temperatures on (i) the growth of the naturally occurring microflora, (ii) the evolution over time of an inoculated spoilage yeast (Pichia subpelliculosa), and (iii) the enzymatic browning reaction in minimally processed apples. The inclusion of hexanal and trans-2-hexenal in the storage atmosphere of apple slices determined a significant extension of shelf life also when P. subpelliculosa was inoculated at levels of 10(3) colony-forming units/g and abusive storage temperatures were used. In fact, the presence of these molecules in the packaging atmospheres considerably prolonged the lag phases of the inoculated yeast and reduced the growth potential of naturally occurring bacteria. Moreover, the addition to the modified atmosphere of low levels of the hexanal increased the color stability of the products up to 16 days.

Aldehydes↗
PubMed1991

A constant rate of spontaneous mutation in DNA-based microbes.

In terms of evolution and fitness, the most significant spontaneous mutation rate is likely to be that for the entire genome (or its nonfrivolous fraction). Information is now available to calculate this rate for several DNA-based haploid microbes, including bacteriophages with single- or double-stranded DNA, a bacterium, a yeast, and a filamentous fungus. Their genome sizes vary by approximately 6500-fold. Their average mutation rates per base pair vary by approximately 16,000-fold, whereas their mutation rates per genome vary by only approximately 2.5-fold, apparently randomly, around a mean value of 0.0033 per DNA replication. The average mutation rate per base pair is inversely proportional to genome size. Therefore, a nearly invariant microbial mutation rate appears to have evolved. Because this rate is uniform in such diverse organisms, it is likely to be determined by deep general forces, perhaps by a balance between the usually deleterious effects of mutation and the physiological costs of further reducing mutation rates.

Bacteriophage lambda↗
PubMed1984

The stratified microbial community at Laguna Figueroa, Baja California, Mexico: a possible model for prephanerozoic laminated microbial communities preserved in cherts.

The microbial mat community of the evaporite flat at North Pond, Laguna Figueroa (Baja California, Mexico) was actively involved in the production of laminated sediments prior to 1978. Heavy rains in 1979 and 1980 flooded the mat with 1 and 3 meters of meteoric water respectively. The flooding deposited up to 10 cm of silicoclastic sediment over the Microcoleus-dominated mat and resulted in the cessation of laminated sediment deposition. In 1982, the surface had been recolonized by species of cyanobacteria (Spirulina, Oscillatoria) and purple photosynthetic bacteria (Chromatium, Thiocapsa). The silicoclastic sediments and residual evaporites, which overlaid the laminated sediment, had been reworked into an anaerobic, sulfide-rich mud and contained well preserved sheaths of filamentous and coccoid bacteria. The Swaziland Sequence in the Barberton mountain land (which includes the Onverwacht and Fig Tree Group as well as the Swartkoppie zone between them) contains laminated sediments and carbon-rich chert. Structurally preserved microfossils have been found in the smooth black chert but not in the laminae. We concur with others who suggested that the laminated sediments from the Swaziland Sequence were deposited by an active stratified microbial community. However, we propose that these organisms which were preserved were originally buried in the associated sulfide-rich muds and were subsequently silicified.

Bacteria↗