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PubMed1997

Rational approach to limiting emergence of antimicrobial drug resistance.

Microbial resistance to the available antimicrobial agents continues to be a major problem with regard to nosocomial and community acquired pathogens. The development of resistance to commonly used antimicrobials is of particular concern when it occurs in pathogenic organisms that cause invasive disease. This has implications on morbidity and mortality of infectious diseases, and will also result in escalated costs of care due to the use of alternative antimicrobials which are often more costly. The increasing frequency of drug resistance has been attributed to combinations of microbial characteristics, selective pressure of antimicrobial use and societal factors that enhance the transmission of drug resistant organisms. The emergence of antibiotic resistant bacteria has generally correlated with the rise and fall of specific antibiotic use in clinical practice. Although the discovery of a new drug temporarily confers therapeutic superiority over bacterial pathogens, the subsequent rapid evolution of resistance limits the duration of the effectiveness of specific agents against pathogens. Surveillance and the development of drug policies that encourage judicious use of antimicrobials will help to minimise the spread of resistant infections. This paper reviews how this dual strategy may be used to control antimicrobial resistance.

Bacterial Infections↗
PubMed2000

High frequency of hypermutable Pseudomonas aeruginosa in cystic fibrosis lung infection.

The lungs of cystic fibrosis (CF) patients are chronically infected for years by one or a few lineages of Pseudomonas aeruginosa. These bacterial populations adapt to the highly compartmentalized and anatomically deteriorating lung environment of CF patients, as well as to the challenges of the immune defenses and antibiotic therapy. These selective conditions are precisely those that recent theoretical studies predict for the evolution of mechanisms that augment the rate of variation. Determination of spontaneous mutation rates in 128 P. aeruginosa isolates from 30 CF patients revealed that 36% of the patients were colonized by a hypermutable (mutator) strain that persisted for years in most patients. Mutator strains were not found in 75 non-CF patients acutely infected with P. aeruginosa. This investigation also reveals a link between high mutation rates in vivo and the evolution of antibiotic resistance.

Adaptation, Physiological↗
PubMed2002

Characterization of a self-transferable plasmid from Salmonella enterica serotype typhimurium clinical isolates carrying two integron-borne gene cassettes together with virulence and drug resistance genes.

An unusual self-transferable virulence-resistance plasmid (pUO-StVR2) was found in nine multidrug-resistant (ACSSuT phenotype) Salmonella enterica serotype Typhimurium clinical isolates that were assigned to four different phage types and a single and distinctive XbaI pulsed-field gel electrophoresis profile. pUO-StVR2 is an IncFII plasmid of about 140 kb in length carrying the spvA, spvB, and spvC (Salmonella plasmid virulence) and rck (resistance to complement killing) genes. It also carries the oxa1/aadA1a (ampicillin resistance and streptomycin-spectinomycin resistance) gene cassette configuration located within a class 1 integron with qacEDelta1/sul1 (ammonium antiseptics resistance and sulfadiazine resistance); the transposon genes merA, tnpA, and tnpR (mercury resistance, transposase, and resolvase of Tn21, respectively); and the catA1 (chloramphenicol resistance) and tet(B) (tetracycline resistance) genes. The insertion of resistance genes into a Salmonella virulence plasmid constitutes a new and interesting example of plasmid evolution and presents a serious public health problem.

Bacteriophage Typing↗
PubMedDate not supplied

[Antibiograms in ambulatory medical practice. Results with a group of gram-negative bacilli strains isolated by uroculture].

During the April 1979--June 1978 period, 1161 tests were carried out on the sensitivity to antibiotics and chemotherapeutical agents of Gram-negative bacillus strains isolated from 7632 urocultures. Resistance was tested under qualitative control against 13 antimicrobial agents by the Kirby-Bauer diffusimetric method. The resistance sensitivity and the presence of intermediary strains is shown for E. coli Citrobacter, Enterobacter, Klebsiella, Proteus, Morganella, Providencia, and Pseudomonas. Attention is drawn to the fairly high proportion of intermediary strains. Their role from the therapeutical point of view is reduced, but epidemiologically, their role is important since their evolution towards resistance or sensitivity cannot be foreseen.

Anti-Bacterial Agents↗
PubMed1997

The pneumococcal cell wall degrading enzymes: a modular design to create new lysins?

Autolysins are enzymes that degrade different bonds in the peptidoglycan and, eventually, cause the lysis and death of the cell. Streptococcus pneumoniae contains a powerful autolytic enzyme that has been characterized as an N-acetylmuramoyl-L-alanine amidase. We have cloned the lytA gene coding for this amidase and studied in depth the genetics and expression of this gene, which represented the first molecular analysis of a bacterial autolysin. Two observations have been fundamental in revealing further knowledge on the lytic systems of pneumococcus: (a) The well-documented dependence of the pneumococcal autolysin on the presence of choline in the cell wall for activity, and (b) the early observation that most pneumococcal phages also required the presence of this amino-alcohol in the growth medium to achieve a successful liberation of the phage progeny. We concluded that choline would serve as an element of strong selective pressure to preserve certain structures of the host and phage lytic enzymes which should lead to sequence homologies. We constructed active chimeras between the lytic enzymes of S. pneumoniae and its bacteriophages using genes that share sequence homology as well as genes that completely lack homologous regions. In this way, we demonstrated that the pneumococcal lytic enzymes are the result of the fusion of two independent functional modules where the carboxy-terminal domain might be responsible for the specific recognition of choline-containing cell walls whereas the active center of these enzymes should be localized in the N-terminal part of the protein. The modular design postulated for the pneumococcal lysins seems to be a widespread model for many types of microbial proteins and the construction of functional chimeric proteins between the lytic enzymes of pneumococcus and those of several gram-positive microorganisms, like Clostridium acetobutylicum or Lactococcus lactis, provided interesting clues on the modular evolution of proteins. The study of several genes coding for the lytic enzymes of temperate phages of pneumococcus also highlighted on some evolutionary relationships between microorganisms. We suggest that lysogenic relationships may represent a common mechanism by which pathogenic organisms like pneumococcus should undergo a rapid adaptation to an evolving environment.

Bacteriolysis↗
PubMed1998

Crucial crises in biology: life in the deep biosphere.

The origin and evolution of life on Earth are the result of a series of crises that have taken place on the planet over about 4500 millions of years since it originated. Biopoiesis (origin of life), ecopoiesis (origin of ecosystems) and the first ecosystems (stromatolites and microbial mats), as well as eukaryopoiesis (origin of nucleated cells) are revised. The paper then focuses on the study of the deep biosphere, describing ecosystems never found before, which are independent of solar radiation and have changed previous assumptions about the requirements of life; even the concept of biosphere, as Vernadsky defined it, has increased its scope. Since the discovery, in 1987, of bacteria growing in the crevices of rocks at 500 m deep, in boreholes drilled near the Savanna River, Aiken, South Carolina, other bacteria have been found in the deep subsurface reaching depths of about 3 km (e.g., in the Columbia River Basalt Group, near Richland, Washington state), in an anaerobic, hot, high-pressure environment. Some kinds of microorganisms can thrive at such depths, living in many cases a geochemical existence, by using very specialized metabolisms, which depend on the local environments. The existence of organisms independent from photosynthetic production is the most outstanding, novel feature of the deep biosphere. Living beings might not need other energy and chemical sources than those which occur in the development of all planetary bodies. Life, therefore, could even be an ineluctable outcome of planetary evolution and, as a corollary, a natural continuation of the usual development of physical phenomena in the universe.

Atmosphere↗
PubMed2004

Evolving protein functional diversity in new genes of Drosophila.

The mechanism by which protein functional diversity expands is an important evolutionary issue. Studies of recently evolved chimeric genes permit direct investigation of the origin of new protein functions before they become obscured by subsequent evolution. Found in several African Drosophila species, jingwei (jgw), a recently evolved gene with a domain derived from the still extant short-chain alcohol dehydrogenase (ADH) through retroposition, provides an opportunity to examine this previously undescribed process directly. We expressed JGW proteins in a microbial expression system and, after purification, investigated their enzymatic properties. We found that, unexpectedly, positive Darwinian selection for amino acid replacements outside the active site of JGW produced a novel dehydrogenase with altered substrate specificity compared with the ancestral ADH. Instead of detoxifying and assimilating ethanol like its Adh parental gene, we observe that JGW efficiently utilizes long-chain primary alcohols found in hormone and pheromone metabolism. These data suggest that protein functional diversity can expand rapidly under the joint forces of exon shuffling, gene duplication, and natural selection.

Alcohol Dehydrogenase↗
PubMed2003

Mechanistic diversity of fosfomycin resistance in pathogenic microorganisms.

Microbial resistance to the antibiotic fosfomycin [(1R,2S)-epoxypropylphosphonic acid, 1] is known to be mediated by thiol transferase enzymes FosA and FosB, which catalyze the addition of glutathione and l-cysteine to C1 of the oxirane, respectively. A probe of the microbial genome database reveals a related group of enzymes (FosX). The genes mlr3345 from Mesorhizobium loti and lmo1702 from Listeria monocytogenes were cloned and the proteins expressed. This heretofore unrecognized group of enzymes is shown to catalyze the Mn(II)-dependent addition of water to C1 of the oxirane. The ability of each enzyme to confer resistance in Escherichia coli is correlated with their catalytic efficiency, such that the M. loti protein confers low resistance while the Listeria enzyme confers very robust resistance. The crystal structure of the FosX from M. loti was solved at a resolution of 1.83 A. The structure reveals an active-site carboxylate (E44) located about 5 A from the expected position of the substrate that appears to be poised to participate in catalysis. Single turnover experiments in H218O and kinetic analysis of the E44G mutant of the FosX enzymes indicate that the carboxylate of E44 acts as a general base in the direct addition of water to 1. The FosX from M. loti also catalyzes the addition of glutathione to the antibiotic. The catalytic promiscuity and low efficiency of the M. loti protein suggest that it may be an intermediate in the evolution of clinically relevant fosfomycin resistance proteins such as the FosX from Listeria monocytogenese.

Bacterial Proteins↗
PubMed1996

HLA-B27 and bacteria.

Most HLA-B27 positive individuals live without noticing the risk factor they carry. Only when certain bacteria come into play, usually in the form of intestinal or genital infection, some of the HLA-B27 positive individuals will develop a reactive disease. Such an association is so well established that it has formed a basis to study the relation of autoimmune reactions to microbial infections. Early epidemiological investigations have been followed by studies on immunological cross-reactivity and recently by studies on presentation of bacterial peptides by the HLA-B27 molecule. This introductory review briefly summarizes the evolution of the research, the goal of which still remains to clarify the etiopathogenetic mechanisms of HLA-B27 associated diseases.

Bacterial Infections↗
PubMed2005

Dynamics of sulfate-reducing microorganisms (dsrAB genes) in two contrasting mudflats of the Seine estuary (France).

By combining molecular biology and biochemical approaches, the dynamics of sulfate-reducing microorganisms (SRM) was investigated in the sediments of the Seine estuary (France). Both intertidal mixing-zone and freshwater mudflats were sampled during a 1-year period; the quantification of SRM was realized by using competitive polymerase chain reaction (PCR) based on dsrAB gene amplification, previously described by Leloup et al. (2004), and sulfate reduction rate (SRR) was determined via the SO4(2-) radiotracer method. Throughout the year, abundance of dsrAB genes and SRR were predominantly high in the top 15 cm of the sediment. A seasonal dynamic was observed; a predominance of activity was noted during the early summer, and seems to be mainly controlled by physical-chemical parameters (temperature and dissolved organic carbon concentration) and topographic evolution of the mudflat (erosion/deposit erosion).

Bacteria↗
PubMed1994

Mutagenesis of the b'-subunit of Synechocystis sp. PCC 6803 ATP-synthase.

We investigated the F0F1 ATP synthase of the cyanobacterium, Synechocystis sp. PCC 6803. The gene for the F0-subunit b', a peptide probably located at the interface between F0 and F1, has been partially or completely evicted from the bacterial genome. We found that the complete deletion of the subunit was lethal to the cells. However, the subunit could be truncated down to its hydrophobic N-terminal stretch without much harm. Since the gene for b' probably shares a common ancestor with the gene for subunit b and emerged by gene duplication, we propose that b' gathered a new role during evolution, perhaps in the regulation of photophosphorylation.

Amino Acid Sequence↗
PubMed2004

Adaptation to the deleterious effects of antimicrobial drug resistance mutations by compensatory evolution.

Compensatory mutations, due to their ability to mask the deleterious effects of another mutation, are important for the adaptation and evolution of most organisms. Resistance to antibiotics, antivirals, antifungals, herbicides and insecticides is usually associated with a fitness cost. As a result of compensatory evolution, the initial fitness costs conferred by resistance mutations (or other deleterious mutations) can often be rapidly and efficiently reduced. Such compensatory evolution is potentially of importance for (i) the long-term persistence of drug resistance, (ii) reducing the rate of fitness loss associated with the accumulation of deleterious mutations in small asexual populations, and (iii) the evolution of complexity of cellular processes.

Amino Acid Sequence↗
PubMed2006

Natural products from plant-associated microorganisms: distribution, structural diversity, bioactivity, and implications of their occurrence.

A growing body of evidence suggests that plant-associated microorganisms, especially endophytic and rhizosphere bacteria and fungi, represent a huge and largely untapped resource of natural products with chemical structures that have been optimized by evolution for biological and ecological relevance. A diverse array of bioactive small molecule natural products has been encountered in these microorganisms. The structures of over 230 metabolites isolated and characterized from over 70 plant-associated microbial strains during the past four years are presented with information on their hosts, culture conditions, and biological activities. Some significant biological and ecological implications of their occurrence are also reviewed.

Bacteria↗
PubMed1995

RTM1: a member of a new family of telomeric repeated genes in yeast.

We have isolated a new yeast gene called RTM1 whose overexpression confers resistance to the toxicity of molasses. The RTM1 gene encodes a hydrophobic 34-kD protein that contains seven potential transmembrane-spanning segments. Analysis of a series of industrial strains shows that the sequence is present in multiple copies and in variable locations in the genome. RTM loci are always physically associated with SUC telomeric loci. The SUC-RTM sequences are located between X and Y' subtelomeric sequences at chromosome ends. Surprisingly RTM sequences are not detected in the laboratory strain X2180. The lack of this sequence is associated with the absence of any SUC telomeric gene previously described. This observation raises the question of the origin of this nonessential gene. The particular subtelomeric position might explain the SUC-RTM sequence amplification observed in the genome of yeasts used in industrial biomass or ethanol production with molasses as substrate. This SUC-RTM sequence dispersion seems to be a good example of genomic rearrangement playing a role in evolution and environmental adaptation in these industrial yeasts.

Amino Acid Sequence↗
PubMed1993

Tn5-mediated bleomycin resistance in Escherichia coli requires the expression of host genes.

The transposon Tn5 expresses a gene, ble, whose product increases the viability of Escherichia coli and also confers resistance to the DNA-cleaving antibiotic bleomycin and the DNA-alkylating agent ethylmethanesulphonate. We find that the Ble protein induces expression of an alkylation inducible gene, aidC, and that both the AidC gene product and DNA polymerase I are required for Ble to confer bleomycin resistance. These findings support models in which Ble enhances DNA repair and suggest that Tn5 confers a fitness advantage to the host bacterium by increasing the repair of spontaneous DNA lesions. Such co-operation between a transposon and its host suggests that Tn5 is a symbiotic rather than a selfish DNA element.

Bacterial Proteins↗
PubMed2005

Host-bacterial mutualism in the human intestine.

The distal human intestine represents an anaerobic bioreactor programmed with an enormous population of bacteria, dominated by relatively few divisions that are highly diverse at the strain/subspecies level. This microbiota and its collective genomes (microbiome) provide us with genetic and metabolic attributes we have not been required to evolve on our own, including the ability to harvest otherwise inaccessible nutrients. New studies are revealing how the gut microbiota has coevolved with us and how it manipulates and complements our biology in ways that are mutually beneficial. We are also starting to understand how certain keystone members of the microbiota operate to maintain the stability and functional adaptability of this microbial organ.

Anaerobiosis↗