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PubMed1999

[Acquired antibiotic resistance in Madagascar: first evaluation].

The purpose of this study was to evaluate the incidence of acquired resistance to antibiotics in Madagascar. Testing was carried out on total of 1267 strains of medically significant bacteria isolated from specimens sent to the Pasteur Institute of Madagascar in Antananarivo between October 1997 and October 1998. Antibiograms were performed using the diffusion technique on gel media with antibiotic disks. Results were read according to the criteria of the Antibiogram Committee of the French Society of Microbiology. Preliminary findings documented a high incidence of resistance to widely available, low-price antibiotics including penicillin G and tetracycline for which 84 p. 100 and 65 p. 100 of Staphylococcus aureus respectively demonstrated resistance; tetracyclin to which 80 p. 100 of streptococcus were resistant; and ampicillin, cotrimoxazole, and phenicoles to which 60 p. 100, 60 p. 100 and 28 p. 100 of Escherichia coli respectively and 77 p. 100, 83 p. 100, and 71 p. 100 of Shigella sp. respectively were resistant. Second-line antibiotics including penicillin M, macrolides, nalidixic acid, and nitrofuranes were still relatively active, thus providing an effective alternative. Newly developed antibiotics such as fluoroquinolones and third-generation cephalosporines were highly effective but a few resistant strains were observed. Although not representative of Madagascar as a whole, the findings of this preliminary study indicate that acquired resistance must be taken into account in designing simplified decision charts for front-line laboratories, that appropriate information must be made available to health care workers, and that further testing is needed to monitor the evolution of antibiotic resistance.

Bacterial Infections↗
PubMed1985

Pefloxacin: evolution of in vitro activity during 18 months of use in an intensive care unit.

The MIC of pefloxacin against all the strains (3122) isolated in an intensive care unit during 18 months was studied. The MIC of pefloxacin was estimated by standard agar diffusion method in Mueller-Hinton agar. All the strains with a MIC lower than 2 mg/l were considered as sensitive, between 2 and 4 mg/l as "intermediary" and over 4 mg/l as resistant. Geometrical means of MICs were calculated for each month and for different species. The study continued for 18 months from the introduction of the drug which was in widespread and constant use as a first-choice antibiotic. No significant increase was detected in the incidence of resistant strains during the study; on the other hand, small, limited clusters of resistant strains were observed during minor nosocomial epidemics. The general features of quinolone activity, the spectrum of this new quinolone and the slow evolution of the bacterial population are discussed.

Bacteria, Aerobic↗
PubMedDate not supplied

[Microbial resistance: what is to be done? Information from the panel of experts].

This document represents the recommendations of a panel of Spanish experts on antibiotic use and resistance. In a Task Force, under the auspices of the Spanish Ministry of Health and Consumer Affairs that took place in 1994 in Madrid, the members were gravely concerned about the national increase in antibiotic resistance. They analysed the development, evolution and spread of antibiotic resistance among community-acquired human bacterial pathogens in Spain, its relation with antibiotic consumption, and they proposed future surveillance strategies for monitoring the patterns of antibiotic use and consumption. Success will require a collective action among the producers (pharmaceutical industry), prescribers (doctors, veterinarians), dispensers (pharmacists), and consumers (patients). Two similar documents have been recently published by the American Society of Microbiology and the World Health Organization showing the global concern about this topic.

Anti-Bacterial Agents↗
PubMed2004

Bacterial community profiles on feathers during composting as determined by terminal restriction fragment length polymorphism analysis of 16S rDNA genes.

Composting is one of the more economical and environmentally safe methods of recycling feather waste generated by the poultry industry, since 90% of the feather weight consists of crude keratin protein, and feathers contain 15% N. However, the keratin in waste feathers is resistant to biodegradation and may require the addition of bacterial inocula to enhance the degradation process during composting. Two keratin-degrading bacteria isolated from plumage of wild songbirds and identified as Bacillus licheneformis (OWU 1411T) and Streptomyces sp. (OWU 1441) were inoculated into poultry feather composts (1.13 x 10(8) cfu g(-1) feathers) and co-composted with poultry litter and straw in 200-l compost vessels. Composting temperatures, as well as CO(2) and NH(3) evolution, were measured in these vessels to determine the effects of inoculation on the rate and extent of poultry feather decomposition during composting. Terminal restriction fragment length polymorphisms of 16S rRNA genes were used to follow changes in microbial community structure during composting. The results indicated that extensive carbon conversion occurred in both treatments (55.5 and 56.1%). The addition of the bacterial inocula did not enhance the rate of waste feather composting. The microbial community structure over time was very similar in inoculated and uninoculated waste feather composts.

Ammonia↗
PubMed2005

The evolution and function of blue and red light photoreceptors.

Photoreceptors allow living organisms to optimize perception of light in the natural environment and thus to gain information about their external world. In this review, we describe blue and red light photoreceptors in bacteria, plants, and animals in relation to their evolution. Analyses performed in different organisms have revealed wonderful examples of structural modifications of the light-sensing proteins themselves, as well as diversification of the signal transduction pathways they use in relation with their evolutionary history and function. In different organisms, the same photoreceptor may have a very conserved role (convergent evolution of function) or may modulate different responses (acquisition of new function). Multiple photoreceptors of the same family in the same organism indicate gene duplication events during evolution, with a consequent enhanced sensitivity to variations in ambient light. Conversely, two different photoreceptors may be involved in the control of the same physiological response. Genomic analysis in marine diatoms, combined with phylogenetic studies, has also revealed the presence of blue and red light photoreceptors in the marine environment. This discovery has intriguing implications for the understanding of light perception and its evolution in photosynthetic organisms. In addition, the characterization of these photoreceptors likely will add to our understanding of photoreceptor diversity as an adaptation to different habitats.

Animals↗
PubMed2002

Lipases for biotechnology.

Lipases constitute the most important group of biocatalysts for biotechnological applications. The high-level production of microbial lipases requires not only the efficient overexpression of the corresponding genes but also a detailed understanding of the molecular mechanisms governing their folding and secretion. The optimisation of industrially relevant lipase properties can be achieved by directed evolution. Furthermore, novel biotechnological applications have been successfully established using lipases for the synthesis of biopolymers and biodiesel, the production of enantiopure pharmaceuticals, agrochemicals, and flavour compounds.

Agrochemicals↗
PubMed1998

Microevolution of a standard strain of Cryptococcus neoformans resulting in differences in virulence and other phenotypes.

Cryptococcus neoformans is a major fungal pathogen for patients with debilitated immune systems. However, no information is available on the stability of virulence or of phenotypes associated with virulence for C. neoformans laboratory strains. A serendipitous observation in our laboratory that one isolate of C. neoformans ATCC 24067 (strain 52D) became attenuated after continuous in vitro culture prompted us to perform a comparative study of nine strain 24067 isolates obtained from six different research laboratories. Each isolate was characterized by DNA typing, virulence for mice, proteinase production, extracellular protein synthesis, melanin synthesis, carbon assimilation pattern, antifungal drug susceptibility, colony morphology, growth rate, agglutination titers, phagocytosis by murine macrophages, capsule size, and capsular polysaccharide structure. All isolates had similar DNA typing patterns consistent with their assignment to the same strain, although minor chromosome size polymorphisms were observed in the electrophoretic karyotypes of two isolates. Several isolates had major differences in phenotypes that may be associated with virulence, including growth rate, capsule size, proteinase production, and melanization. These findings imply that C. neoformans is able to undergo rapid changes in vitro, probably as a result of adaptation to laboratory conditions, and suggest the need for careful attention to storage and maintenance conditions. In summary, our results indicate that C. neoformans (i) can become attenuated by in vitro culture and (ii) is capable of microevolution in vitro with the emergence of variants exhibiting new genotypic and phenotypic characteristics.

Agglutination Tests↗
PubMed2006

The evolution of adaptive immunity.

Approximately 500 mya two types of recombinatorial adaptive immune systems appeared in vertebrates. Jawed vertebrates generate a diverse repertoire of B and T cell antigen receptors through the rearrangement of immunoglobulin V, D, and J gene fragments, whereas jawless fish assemble their variable lymphocyte receptors through recombinatorial usage of leucine-rich repeat (LRR) modular units. Invariant germ line-encoded, LRR-containing proteins are pivotal mediators of microbial recognition throughout the plant and animal kingdoms. Whereas the genomes of plants and deuterostome and chordate invertebrates harbor large arsenals of recognition receptors primarily encoding LRR-containing proteins, relatively few innate pattern recognition receptors suffice for survival of pathogen-infected nematodes, insects, and vertebrates. The appearance of a lymphocyte-based recombinatorial system of anticipatory immunity in the vertebrates may have been driven by a need to facilitate developmental and morphological plasticity in addition to the advantage conferred by the ability to recognize a larger portion of the antigenic world.

Adaptation, Physiological↗
PubMed2002

The highest priority: what microbial genomes are telling us about immunity.

Study of microbial genomes has provided new insight into the functions that pathogens require for survival in the animal host. Small genome bacterial pathogens, defined as those < or = 1/3 the size of Escherichia coli, include chlamydiae, rickettsiae and ehrlichiae, mycoplasmas, and spirochetes. The small genome size is believed to result from reductive evolution, a process of initial mutation with loss of function followed by progressive accumulation of mutations and eventual gene deletion. This is most notable in the 1.1 Mb genome of Rickettsia prowazekki in which 24% of the genome is non-coding, as compared to approximately 10% in the 4.4 Mb E. coli. Consequently, these pathogens are thus presumed to retain only the most important functions for survival and propagation. There is consistent evidence from small genomes that the genetic deletion is primarily related to the loss of metabolic function and especially reduction of multiple overlapping pathways and duplicated genes. Thus, these pathogens undergo progressive reduction in their genomes yet maintain the ability to infect, survive within, and cause disease in animals. In the face of this reductive process, what genes and associated functions are maintained? Strikingly, these pathogens devote a high percentage of their genomes to paralogous families of polymorphic surface molecules. This retention suggests that evasion of the immune response is the highest priority of obligate microbial pathogens and provides a strategy for identifying protective antigens for vaccine development to control disease.

Adaptation, Physiological↗
PubMed2005

Perspective: Sign epistasis and genetic constraint on evolutionary trajectories.

Epistasis for fitness means that the selective effect of a mutation is conditional on the genetic background in which it appears. Although epistasis is widely observed in nature, our understanding of its consequences for evolution by natural selection remains incomplete. In particular, much attention focuses only on its influence on the instantaneous rate of changes in frequency of selected alleles via epistatic contribution to the additive genetic variance for fitness. Thus, in this framework epistasis only has evolutionary importance if the interacting loci are simultaneously segregating in the population. However, the selective accessibility of mutational trajectories to high fitness genotypes may depend on the genetic background in which novel mutations appear, and this effect is independent of population polymorphism at other loci. Here we explore this second influence of epistasis on evolution by natural selection. We show that it is the consequence of a particular form of epistasis, which we designate sign epistasis. Sign epistasis means that the sign of the fitness effect of a mutation is under epistatic control; thus, such a mutation is beneficial on some genetic backgrounds and deleterious on others. Recent experimental innovations in microbial systems now permit assessment of the fitness effects of individual mutations on multiple genetic backgrounds. We review this literature and identify many examples of sign epistasis, and we suggest that the implications of these results may generalize to other organisms. These theoretical and empirical considerations imply that strong genetic constraint on the selective accessibility of trajectories to high fitness genotypes may exist and suggest specific areas of investigation for future research.

Biological Evolution↗
PubMed1980

Construction of a physical map of a kanamycin (Km) transposon, Tn5, and a comparison to another Km transposon, Tn903.

A cleavage map of Tn5, a kanamycin (Km) transposon from plasmid JR67, was constructed from pMKI, a composite plasmid of ColE1 and Tn5, and compared to that of Tn903, a Km transposon from plasmid R6-5. The two transposons showed marked heterogeneity in both the structural gene for Km resistance and the inverted repeat regions as evidenced by their distinctly different restriction maps. This result suggests separate paths of evolution for the two Km transposons.

Base Sequence↗
PubMed1989

Mutagenic DNA repair genes on plasmids from the 'pre-antibiotic era'.

Resistance transfer factors are natural conjugative plasmids encoding antibiotic resistance. Some also encode mutagenic DNA repair genes giving resistance to DNA damage and induced mutagenesis. It has been shown that antibiotic resistance has been acquired by recent transposition events; however, we show here that mutagenic repair genes existed much earlier on these types of plasmids. Conjugative plasmids from eight incompatibility groups from the Murray collection of 'pre-antibiotic era' enterobacteria were tested for complementation of mutagenic repair-deficient Escherichia coli umuC36. Although none of these plasmids carry transposon-encoded drug resistance genes, IncI1 and IncB plasmids were identified which restored ultraviolet resistance and induced mutability to umuC36 mutants. Furthermore they increased the UV resistance and induced mutability of wild-type E. coli, Klebsiella aerogenes and Citrobacter intermedius, thus showing that they could confer a general selective advantage to a variety of hosts. Like known mutagenic repair genes, complementation by these plasmid genes required the SOS response of the host cell. Nucleotide hybridisation showed that these plasmids harboured sequences similar to the impCAB locus, the mutagenic repair operon of modern-day IncI1 plasmids. The evolution of mutagenic repair genes is discussed.

DNA Repair↗
PubMed1981

Physical and functional mapping of Tn2603, a transposon encoding ampicillin, streptomycin, sulfonamide, and mercury resistance.

A map of cleavage sites for restriction endonuclease EcoRI, BamHI, HindIII, and SalI on Tn2603, a transposon encoding resistance to ampicillin, streptomycin, sulfonamide, and mercury, was constructed by an analysis of restriction cleavage patterns of plasmid pMK1.::Tn2603 and its deletion derivative. By cloning the fragments generated from pMK1.::Tn2603 with these restriction endonucleases to a pACYC184 plasmid vehicle, the regions necessary for expression of resistance were located on the restriction cleavage map of Tn2603. Ampicillin, streptomycin, and sulfonamide-resistance genes were mapped in a cluster on the region between the center and the right and the mercury-resistance gene was located to the left of the map. The final functional map of Tn2603 was compared with those of Tn4 and Tn21 and the evolutional relationships between them were discussed.

Chromosome Mapping↗
PubMed1993

Origins of species: acquired genomes and individuality.

Entire genomes with their accompanying protein synthetic systems are transferred throughout the biosphere primarily as bacteria and protists which become symbionts as they irreversibly integrate into pre-existing organisms to form more complex individuals. Individualization is stabilized by simultaneous transmission of once-separate heterologous genetic systems. The origin of new species is hypothesized to correlate with the acquisition, integration and subsequent inheritance of such acquired microbial genomes. These processes were recognized by Mereschkovsky ("Symbiogenesis" in Russian, 1909) and by Wallin ("Symbionticism", see p. 181, this issue).

Animals↗
PubMed2004

Methane oxidation and formation of EPS in compost: effect of oxygen concentration.

Oxygen concentration plays an important role in the regulation of methane oxidation and the microbial ecology of methanotrophs. However, this effect is still poorly quantified in soil and compost ecosystems. The effect of oxygen on the formation of exopolymeric substances (EPS) is as yet unknown. We studied the effect of oxygen on the evolution of methanotrophic activity. At both high and low oxygen concentrations, peak activity was observed twice within a period of 6 months. Phospholipid fatty acid analysis showed that there was a shift from type I to type II methanotrophs during this period. At high oxygen concentration, EPS production was about 250% of the amount at low oxygen concentration. It is hypothesized that EPS serves as a carbon cycling mechanism for type I methanotrophs when inorganic nitrogen is limiting. Simultaneously, EPS stimulates nitrogenase activity in type II methanotrophs by creating oxygen-depleted zones. The kinetic results were incorporated in a simulation model for gas transport and methane oxidation in a passively aerated biofilter. Comparison between the model and experimental data showed that, besides acting as a micro-scale diffusion barrier, EPS can act as a barrier to macro-scale diffusion, reducing the performance of such biofilters.

Animals↗
PubMed1997

What clinicians need to know about antiviral drugs and viral resistance.

The development of safe and effective antiviral therapies for the management of a variety of viral infections has expanded tremendously in recent years. Treatment is now possible for serious and potentially life-threatening infections with herpesviruses, respiratory viruses such as influenza A and respiratory syncytial virus, and the human immunodeficiency virus. The increased availability and use of antiviral drugs, however, has led to the emergence of drug-resistant viruses, especially in immunocompromised hosts. With this review, the major antiviral agents are presented with a description of the mechanisms of action, the evolution of drug resistance, and the need for in vitro antiviral susceptibility testing.

Anti-HIV Agents↗