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Comparison of resistance genes from different sources support the hypothesis that the antibiotic-producing microorganisms are the source of resistant determinants present in clinical isolates. There is also evidence that Gram-positive cocci (staphylococci and streptococci) can serve as a reservoir of resistance genes for Gram-negative bacteria.
The authors studied the susceptibility to 5 aminoglycosides (amikacin, dibekacin, gentamicin, netilmicin and tobramycin) of 3,354 strains isolated at the Centre Hospitalier Sud in Bordeaux during 1987. The results are compared to those obtained in 1984 on 2,818 strains. Amikacin remains the most active aminoside against the Enterobacteriaceae and Acinetobacter; against Pseudomonas, tobramycin has become the best one at that time, as well as netilmicin against Staphylococcus aureus. Evolution: no significative increase of Enterobacteriaceae resistance to aminoglycosides was observed during the last 3 years except for Providencia and Serratia. For Acinetobacter and Pseudomonas, percentage of resistant strains is respectively two-fold and three-fold higher. Although resistance increased in that species, netilmicin and amikacin showed a still good activity against Staphylococcus aureus.
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Metchnikoff was one of the first to suggest the need for cooperation between phagocytes and therapeutic agents for the benefit of health. After the hopes raised by the discovery and the tremendous development of antimicrobials, there is now a creeping pessimism faced with the parallel evolution of resistance strategies in the microbial world. Interest has now turned to the use of immunomodulatory drugs, alone or combined with anti-infectious agents. Another tendency is based on the possibility that antimicrobials directly interfere with the host-microbe interplay. This review is aimed at summarizing our knowledge of the interactions between antimicrobial agents and the phagocyte, still a cornerstone in the natural defence system. Despite the problems inherent in the analysis and clinical relevance of effects observed in the test tube this developing area of research could provide new therapeutic solutions beyond the year 2000.
The value of the precious medical asset that antibiotics constitute is contimualby being eroded by the spread of resistance. For some time that bacterial world has been adapting itself to contend with the toxic assault of man-made poisons, antibiotics, by developing resistance in a very rapid process of evolutionary changes occurring before our very eyes. This evolutionary adaptation is an example of natural genetic engineering entailing an interchange between bacteria of genes conferring antibiotic resistance. Trimethoprim resistance is an example where numerous genes of unknown origin (some closely interrelated), expressing drug-resistant dihydrofolate reductases, move among human commensals and pathogens. They have been shown to move as gene cassettes in and out of the recently characterised integron structure occurring in many pathogens. They are also carried by various transposons such as Tn7, or Tn5393 originally observed in a plant pathogen, Erwinia amylovora. Betalactam resistance is another example of natural genetic engineering, where new betalactamases are continually emerging, and individual enzyme substrate specificity is modified by point mutation. At present, betalactamase mutants resistant to all commercially available betalactams, including clavulanic acid used in combination with betalactam antibiotics, are to be found in clinical isolates. Thus, currently bacteria seem to be triumphing in the running battle between the pharmaceutical industry and the bacterial world, the former introducing one new antibiotic variant after another, to which bacteria promptly develop resistance by manipulating their own genomes.
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The simplest conceivable event that can occur at the gene level can result in the development of efficacious resistance tot antibiotics. The bacterial world behaves as an enormous organism whose cells can exchange their genes very easily. Accordingly, opportunities for the exchange of genetic material in nature are probably unlimited. This knowledge cannot be ignored. It leads to the important conclusion that the antibiotics are societal drugs. A resistance gene which has appeared somewhere in the world can travel far and fast.
Blood sedimentation rate and balanced titration of immunoglobulins were studied in 59 patients presenting a ankylosing pelvispondylitis: in 30 of them, these examinations were repeated at an interval of 3-6 months. The sedimentation rate (Sed. rate) and the level of immunoglobulins G and A increased in the course of the disease, but an elective increase of the level of immunoglobulins A was not demonstrated. Neither the Sed. rate, nor the level of IgA are correlated to evolution criteria of the disease; a positive correlation is only found with the platelets number, in a vertical study of 59 patients. Nevertheless, the variations of the immunoglobulins A is positively correlated with alterations of the clinical condition as demonstrated in the longitudinal study carried out in 30 patients. This finding supports physiopathological hypothesis which incriminates microbial intestinal infections at the origin of evolutive bouts of ankylosing pelvispondylitis.
This review summarizes the recent discovery of the cupin superfamily (from the Latin term "cupa," a small barrel) of functionally diverse proteins that initially were limited to several higher plant proteins such as seed storage proteins, germin (an oxalate oxidase), germin-like proteins, and auxin-binding protein. Knowledge of the three-dimensional structure of two vicilins, seed proteins with a characteristic beta-barrel core, led to the identification of a small number of conserved residues and thence to the discovery of several microbial proteins which share these key amino acids. In particular, there is a highly conserved pattern of two histidine-containing motifs with a varied intermotif spacing. This cupin signature is found as a central component of many microbial proteins including certain types of phosphomannose isomerase, polyketide synthase, epimerase, and dioxygenase. In addition, the signature has been identified within the N-terminal effector domain in a subgroup of bacterial AraC transcription factors. As well as these single-domain cupins, this survey has identified other classes of two-domain bicupins including bacterial gentisate 1, 2-dioxygenases and 1-hydroxy-2-naphthoate dioxygenases, fungal oxalate decarboxylases, and legume sucrose-binding proteins. Cupin evolution is discussed from the perspective of the structure-function relationships, using data from the genomes of several prokaryotes, especially Bacillus subtilis. Many of these functions involve aspects of sugar metabolism and cell wall synthesis and are concerned with responses to abiotic stress such as heat, desiccation, or starvation. Particular emphasis is also given to the oxalate-degrading enzymes from microbes, their biological significance, and their value in a range of medical and other applications.
Microbial symbiosis underpins host adaptation, yet mechanisms of metabolic integration in holobionts remain unclear. Using metatranscriptomics, genomics, and metabolic assays, we investigated gut microbiome interactions in the European spruce bark beetle (Ips typographus). We observed metabolic complementarity among symbionts and host, forming cross-domain networks that support nutrient acquisition. Nitrogen recycling revealed strong interdependence: no single partner possessed a complete uric acid degradation pathway, but combined evidence supports a distributed pathway spanning beetle, Bacteria, and fungi. Additionally, bacterial nitrate reduction to ammonia indicates a potential nitrogen influx, making otherwise inaccessible inorganic nitrogen available to the host. Shaped by microbial interactions, symbionts also likely supply specific amino acids, while vitamin metabolism showed cross-domain co-metabolism, with Bacteria as main producers of B vitamins, while host and fungi modulated interconversion. Carbohydrate degradation was highly partitioned; bacteria target xylan and pectin, while fungi contribute to glucan breakdown. Crucially, our data provide indirect evidence that the beetle may contribute to complete cellulose degradation, highlighting an underappreciated host role in lignocellulose processing. In terms of enzymatic functional diversity, the bacteriome emerged as the most important microbiome component-an observation that contrasts with the traditional focus on fungi and underscores the need to consider bacterial contributions in insect symbioses. Despite life-stage variation, core metabolic functions remained stable. Overall, metabolic interdependence, rather than microbial composition alone, structures holobiont function. These results highlight functional redundancy and ecological resilience, emphasizing the importance of microbial cooperation and host-microbe metabolic evolution.
The practice of using antibiotics to treat and control microbial infections is a little more than 50 years old. Widespread administration of multiple classes of antibiotics over the years has had the unfortunate secondary effect of inducing the emergence of an increasing array of drug-resistant microbial strains. This article will discuss the evolution of certain forms of antibiotic resistance, as well as the mechanisms by which bacteria render numerous antimicrobials ineffective. Special emphasis is placed on emerging issues relating to organisms making up portions of the normal oral microflora.
Biodegradability screening tests of soil commonly measure 14CO2 evolution from radiolabeled test compounds, and glucose has often served as a positive control. When constant amounts of radiolabel were added to soil in combination with increasing amounts of unlabeled substrates, glucose and some related hexoses behaved in an anomalous manner. In contrast to that of formate, benzoate, n-hexadecane, or bis(2-ethylhexyl) phthalate, dilution of glucose radiocarbon with unlabeled glucose increased rather than decreased the rate and extent of 14CO2 evolution. [14C]glucose incorporation into biomass and Vmax values were consistent with the interpretation that application of relatively high concentrations of glucose to soil shifts the balance of the soil microbial community from the autochthonous (humus-degrading) to the zymogeneous (opportunistic) segment. The higher growth and turnover rates that define zymogeneous microorganisms, combined with a lower level of carbon incorporation into their biomass, result in the evolution of disproportionate percentages of 14CO2. When used as positive controls, glucose and related hexoses may raise the expectations for percent 14CO2 evolution to levels that are not realistic for other biodegradable compounds.
Earth's early history may have been characterized by coevolution of microbial metabolism and atmospheric composition. Metabolic developments affected the composition of the atmosphere and the resultant changes in the atmosphere stimulated the evolution of new metabolic capabilities. The first organisms were presumably fermenting heterotrophs, exploiting organic molecules abiotically synthesized. These organisms multiplied, developing new biosynthetic capabilities to overcome deficiencies in the abiotic supply of particular compounds, until their growth was limited by the energy source provided by abiotic synthesis of fermentable organic compounds. Further growth required a new energy source, which may have been the chemical energy represented by the mixture of carbon dioxide and hydrogen in the primitive atmosphere. Chemotrophic organisms resembling methane bacteria may have evolved to exploit this source. They would have flourished, along with the heterotrophs that fed on them, until they had decreased the level of atmospheric hydrogen to the point where further extractions of chemical energy from the atmosphere was not possible. Once again, the expansion of life was limited by the availability of energy. The origin of bacterial photosynthesis overcame the second energy crisis. Photosynthetic bacteria could exploit the abundant energy of sunlight while using atmospheric hydrogen and reduced compounds derived from it only as electron donors. Life flourished again, drawing atmospheric hydrogen (replenished only by volcanoes) down to levels so low as to limit even bacterial photosynthesis. Before the full potential of photosynthesis could be exploited the evolution of the metabolic apparatus to process an electron donor of unlimited abundance was necessary. This donor, of course, was water, and the new metabolic process was algal photosynthesis. The oxygen released changed the world from anaerobic to aerobic and made possible the last great advance in energy-yielding metabolism, aerobic respiration.
Investigations were done to determine whether the replication kinetics of human immunodeficiency virus (HIV)-1 were altered when the virus acquired a set or subsets of five mutations (A62V, V75I, F77L, F116Y, and Q151M) in the pol gene conferring resistance to multiple dideoxynucleosides. In the absence of drugs, the replication rate of all infectious clones generated was comparable to that of wild type HIV-1. However, in the presence of zidovudine or didanosine, the comparative order for replication was HIV-1(62/75/77/116/151) > HIV-1(77/116/151) > HIV-1(75/77/116/151) approximately HIV-1(151), whereas that for drug resistance was HIV-1(75/77/116/151) > HIV-1(62/75/77/116/151) > or = HIV-1(77/116/151) > HIV-1(151). The virologic features of these infectious mutants suggest that HIV-1 develops drug resistance through one or more mutations, which, however, sacrifice replicative capability; then it finally acquires optimal replication competence by additional mutations when the multi-dideoxynucleoside-resistant mutant emerges.
As an approach in the study of the evolution of threonine biosynthetic pathways throughout various organisms, the sequences of three enzymes, namely homoserine dehydrogenase, homoserine kinase and threonine synthase, originating from six organisms, namely Escherichia coli, Bacillus subtilis, Corynebacterium glutamicum, Brevibacterium lactofermentum, Pseudomonas aeruginosa and Saccharomyces cerevisiae, were compared. As a general trend all three enzymatic activities were carried out by proteins sharing sequence relatedness (except for the homoserine kinase of P aeruginosa). Unexpectedly however, for each step one or two enzymes stood out of the main stream: i) for homoserine dehydrogenase, the yeast protein is atypically similar to the E coli enzyme; ii) for homoserine kinase, the P aeruginosa protein shares no similarity with any other species; and iii) for threonine synthase, the B subtilis protein is far distant from the enzymes of other species. Hence in contrast to other biosynthetic pathways such as the tryptophan one, the threonine pathway seems not to have evolved as a whole throughout different organisms but rather each step seems to have been subjected to multiple constraints including substrate-mediated ones and host-specific ones.
Antimicrobial agents are approaching the end of their effectiveness. The prevailing drug development strategy is based on a presumption that results in resistance: that disease can be cured by exploitation of the vulnerabilities in microbial reproduction. Although some did predict the evolution of resistance to such drugs, the mechanisms by which genes conferring resistance have spread was not predicted. The author argues that the mechanism of spread is a consequence of the chemotherapeutics themselves acting on the evolution of pathogens, and that for future drugs to remain effective they must avoid such effects.It is thus not the individual who forms language; it is the language which forms the individual. -Alberto to Sophie in Sophie's World [Gaarder, J. (1995) Phoenix House, London]