Long-term shifts in patterns of antibiotic resistance in enteric bacteria. - Related Documents




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465101.0000Long-term shifts in patterns of antibiotic resistance in enteric bacteria. Several mechanisms are responsible for the ability of microorganisms to tolerate antibiotics, and the incidence of resistance to these compounds within bacterial species has increased since the commercial use of antibiotics became widespread. To establish the extent of and changes in the diversity of antibiotic resistance patterns in natural populations, we determined the MICs of five antibiotics for collections of enteric bacteria isolated from diverse hosts and geographic locations and during periods before and after commercial application of antibiotics began. All of the pre-antibiotic era strains were susceptible to high levels of these antibiotics, whereas 20% of strains from contemporary populations of Escherichia coli and Salmonella enterica displayed high-level resistance to at least one of the antibiotics. In addition to the increase in the frequency of high-level resistance, background levels, conferred by genes providing nonspecific low-level resistance to multiple antibiotics, were significantly higher among contemporary strains. Changes in the incidence and levels of antibiotic resistance are not confined to particular segments of the bacterial population and reflect responses to the increased exposure of bacteria to antimicrobial compounds over the past several decades.200011097921
465010.9999Co-occurrence of resistance to different antibiotics among aquatic bacteria. BACKGROUND: Antibiotic resistance is not confined to pathogens, but is also widespread in various natural environments. In nature the microbes producing antibiotic compounds have been around for millions of years. Heavy use of antibiotics in medicine and veterinary practice may lead to the accumulation of resistance genes in microbial populations, followed by a rise in multiresistant bacteria. RESULTS: To test the extent of resistance among aquatic bacteria, we have collected 760 isolates resistant to at least one antibiotic. The phylogeny of the isolates covers a wide range of Proteobacteria, Actinobacteria and Bacteroidetes. In order to determine the extent of multiresistance, the isolates were tested on six antibiotics. As the growth rate of the different bacteria was highly variable, the classical medical resistance tests could not be used, and an alternative method considering the full growth curve was developed. In general, the overall resistances to different antibiotics could be explained by random, independent distribution. An exception to this was the resistances against tetracycline and chloramphenicol, which tended to occur in pairs. CONCLUSIONS: We conclude that there is no massive spread of multiresistance determinants in the studied environment, although some specific cases can be found, awaiting for molecular characterization of the resistance mechanisms.201223031674
383020.9999Resistance Gene Carriage Predicts Growth of Natural and Clinical Escherichia coli Isolates in the Absence of Antibiotics. Bacterial pathogens that carry antibiotic resistance alleles sometimes pay a cost in the form of impaired growth in antibiotic-free conditions. This cost of resistance is expected to be a key parameter for understanding how resistance spreads and persists in pathogen populations. Analysis of individual resistance alleles from laboratory evolution and natural isolates has shown they are typically costly, but these costs are highly variable and influenced by genetic variation at other loci. It therefore remains unclear how strongly resistance is linked to impaired antibiotic-free growth in bacteria from natural and clinical scenarios, where resistance alleles are likely to coincide with other types of genetic variation. To investigate this, we measured the growth of 92 natural and clinical Escherichia coli isolates across three antibiotic-free environments. We then tested whether variation of antibiotic-free growth among isolates was predicted by their resistance to 10 antibiotics, while accounting for the phylogenetic structure of the data. We found that isolates with similar resistance profiles had similar antibiotic-free growth profiles, but it was not simply that higher average resistance was associated with impaired growth. Next, we used whole-genome sequences to identify antibiotic resistance genes and found that isolates carrying a greater number of resistance gene types grew relatively poorly in antibiotic-free conditions, even when the resistance genes they carried were different. This suggests that the resistance of bacterial pathogens is linked to growth costs in nature, but it is the total genetic burden and multivariate resistance phenotype that predict these costs, rather than individual alleles or mean resistance across antibiotics.IMPORTANCE Managing the spread of antibiotic resistance in bacterial pathogens is a major challenge for global public health. Central to this challenge is understanding whether resistance is linked to impaired bacterial growth in the absence of antibiotics, because this determines whether resistance declines when bacteria are no longer exposed to antibiotics. We studied 92 isolates of the key bacterial pathogen Escherichia coli; these isolates varied in both their antibiotic resistance genes and other parts of the genome. Taking this approach, rather than focusing on individual genetic changes associated with resistance as in much previous work, revealed that growth without antibiotics was linked to the number of specialized resistance genes carried and the combination of antibiotics to which isolates were resistant but was not linked to average antibiotic resistance. This approach provides new insights into the genetic factors driving the long-term persistence of antibiotic-resistant bacteria, which is important for future efforts to predict and manage resistance.201930530714
992230.9999De novo acquisition of antibiotic resistance in six species of bacteria. Bacteria can become resistant to antibiotics in two ways: by acquiring resistance genes through horizontal gene transfer and by de novo development of resistance upon exposure to non-lethal concentrations. The importance of the second process, de novo build-up, has not been investigated systematically over a range of species and may be underestimated as a result. To investigate the DNA mutation patterns accompanying the de novo antibiotic resistance acquisition process, six bacterial species encountered in the food chain were exposed to step-wise increasing sublethal concentrations of six antibiotics to develop high levels of resistance. Phenotypic and mutational landscapes were constructed based on whole-genome sequencing at two time points of the evolutionary trajectory. In this study, we found that (1) all of the six strains can develop high levels of resistance against most antibiotics; (2) increased resistance is accompanied by different mutations for each bacterium-antibiotic combination; (3) the number of mutations varies widely, with Y. enterocolitica having by far the most; (4) in the case of fluoroquinolone resistance, a mutational pattern of gyrA combined with parC is conserved in five of six species; and (5) mutations in genes coding for efflux pumps are widely encountered in gram-negative species. The overall conclusion is that very similar phenotypic outcomes are instigated by very different genetic changes. The outcome of this study may assist policymakers when formulating practical strategies to prevent development of antimicrobial resistance in human and veterinary health care.IMPORTANCEMost studies on de novo development of antimicrobial resistance have been performed on Escherichia coli. To examine whether the conclusions of this research can be applied to more bacterial species, six species of veterinary importance were made resistant to six antibiotics, each of a different class. The rapid build-up of resistance observed in all six species upon exposure to non-lethal concentrations of antimicrobials indicates a similar ability to adjust to the presence of antibiotics. The large differences in the number of DNA mutations accompanying de novo resistance suggest that the mechanisms and pathways involved may differ. Hence, very similar phenotypes can be the result of various genotypes. The implications of the outcome are to be considered by policymakers in the area of veterinary and human healthcare.202539907470
381840.9999A study of the transfer of tetracycline resistance genes between Escherichia coli in the intestinal tract of a mouse and a chicken model. Experiments to demonstrate the transfer of genes within a natural environment are technically difficult because of the unknown numbers and strains of bacteria present, as well as difficulties designing adequate control experiments. The results of such studies should be viewed within the limits of the experimental design. Most experiments to date have been based on artificial models, which only give approximations of the real-life situation. The current study uses more natural models and provides information about tetracycline resistance as it occurs in wild-type bacteria within the environment of the normal intestinal tract of an animal. Tetracycline sensitive, nalidixic acid resistant Escherichia coli isolates of human origin were administered to mice and chicken animal models. They were monitored for acquisition of tetracycline resistance from indigenous or administered donor E. coli. Five sets of in vivo experiments demonstrated unequivocal transfer of tetracycline resistance to tetracycline sensitive recipients. The addition of tetracycline in the drinking water of the animals increased the probability of transfer between E. coli strains originating from the same animal species. The co-transfer of unselected antibiotic resistance in animal models was also demonstrated.200616930278
415350.9999Amino acid variation in the GyrA subunit of bacteria potentially associated with natural resistance to fluoroquinolone antibiotics. In studies of genetic diversity in natural microbial populations, we have analyzed nucleotide sequences in the quinolone resistance-determining region of the bacterial gyrA gene in ciprofloxacin-resistant and nonselected soil bacteria obtained from the environment. It is apparent that this sequence is highly variable, and resistance to fluoroquinolone antibiotics occurring in environmental populations of bacteria is due at least in part to natural sequence variation in this domain. We suggest that the development of new antimicrobial agents, including completely synthetic antimicrobials such as the fluoroquinolones, should incorporate the analysis of resistance mechanisms among microbes in natural environments; these studies could predict potential mechanisms of resistance to be encountered in subsequent clinical use of the agents and would guide chemical modification designed to evade resistance development.19979420056
414660.9999Aquatic Environments as Hotspots of Transferable Low-Level Quinolone Resistance and Their Potential Contribution to High-Level Quinolone Resistance. The disposal of antibiotics in the aquatic environment favors the selection of bacteria exhibiting antibiotic resistance mechanisms. Quinolones are bactericidal antimicrobials extensively used in both human and animal medicine. Some of the quinolone-resistance mechanisms are encoded by different bacterial genes, whereas others are the result of mutations in the enzymes on which those antibiotics act. The worldwide occurrence of quinolone resistance genes in aquatic environments has been widely reported, particularly in areas impacted by urban discharges. The most commonly reported quinolone resistance gene, qnr, encodes for the Qnr proteins that protect DNA gyrase and topoisomerase IV from quinolone activity. It is important to note that low-level resistance usually constitutes the first step in the development of high-level resistance, because bacteria carrying these genes have an adaptive advantage compared to the highly susceptible bacterial population in environments with low concentrations of this antimicrobial group. In addition, these genes can act additively with chromosomal mutations in the sequences of the target proteins of quinolones leading to high-level quinolone resistance. The occurrence of qnr genes in aquatic environments is most probably caused by the release of bacteria carrying these genes through anthropogenic pollution and maintained by the selective activity of antimicrobial residues discharged into these environments. This increase in the levels of quinolone resistance has consequences both in clinical settings and the wider aquatic environment, where there is an increased exposure risk to the general population, representing a significant threat to the efficacy of quinolone-based human and animal therapies. In this review the potential role of aquatic environments as reservoirs of the qnr genes, their activity in reducing the susceptibility to various quinolones, and the possible ways these genes contribute to the acquisition and spread of high-level resistance to quinolones will be discussed.202236358142
380770.9999Antimicrobial drug resistance genes do not convey a secondary fitness advantage to calf-adapted Escherichia coli. Maintenance of antimicrobial drug resistance in bacteria can be influenced by factors unrelated to direct selection pressure such as close linkage to other selectively advantageous genes and secondary advantage conveyed by antimicrobial resistance genes in the absence of drug selection. Our previous trials at a dairy showed that the maintenance of the antimicrobial resistance genes is not influenced by specific antimicrobial selection and that the most prevalent antimicrobial resistance phenotype of Escherichia coli is specifically selected for in young calves. In this paper we examine the role of secondary advantages conveyed by antimicrobial resistance genes. We tested antimicrobial-susceptible null mutant strains for their ability to compete with their progenitor strains in vitro and in vivo. The null mutant strains were generated by selection for spontaneous loss of resistance genes in broth supplemented with fusaric acid or nickel chloride. On average, the null mutant strains were as competitive as the progenitor strains in vitro and in newborn calves (in vivo). Inoculation of newborn calves at the dairy with antimicrobial-susceptible strains of E. coli did not impact the prevalence of antimicrobial-resistant E. coli. Our results demonstrate that the antimicrobial resistance genes are not responsible for the greater fitness advantage of antimicrobial-resistant E. coli in calves, but the farm environment and the diet clearly exert critical selective pressures responsible for the maintenance of antimicrobial resistance genes. Our current hypothesis is that the antimicrobial resistance genes are linked to other genes responsible for differential fitness in dairy calves.200616391076
465280.9999Antibiotic-resistant soil bacteria in transgenic plant fields. Understanding the prevalence and polymorphism of antibiotic resistance genes in soil bacteria and their potential to be transferred horizontally is required to evaluate the likelihood and ecological (and possibly clinical) consequences of the transfer of these genes from transgenic plants to soil bacteria. In this study, we combined culture-dependent and -independent approaches to study the prevalence and diversity of bla genes in soil bacteria and the potential impact that a 10-successive-year culture of the transgenic Bt176 corn, which has a blaTEM marker gene, could have had on the soil bacterial community. The bla gene encoding resistance to ampicillin belongs to the beta-lactam antibiotic family, which is widely used in medicine but is readily compromised by bacterial antibiotic resistance. Our results indicate that soil bacteria are naturally resistant to a broad spectrum of beta-lactam antibiotics, including the third cephalosporin generation, which has a slightly stronger discriminating effect on soil isolates than other cephalosporins. These high resistance levels for a wide range of antibiotics are partly due to the polymorphism of bla genes, which occur frequently among soil bacteria. The blaTEM116 gene of the transgenic corn Bt176 investigated here is among those frequently found, thus reducing any risk of introducing a new bacterial resistance trait from the transgenic material. In addition, no significant differences were observed in bacterial antibiotic-resistance levels between transgenic and nontransgenic corn fields, although the bacterial populations were different.200818292221
464990.9999Factors affecting the measurement of antibiotic resistance in bacteria isolated from lake water. It is more difficult to obtain a reliable assessment of antibiotic resistance in populations of aquatic bacteria than in those populations which are well characterized (e.g. bacteria of medical and veterinary significance). Factors which influence the results include the bacterial taxa involved, their site of origin and the methods and media used to isolate and subculture the bacteria, and to perform the sensitivity tests. Examples of these effects are provided. The resistance profiles obtained with populations of aquatic pseudomonads depend on the species composition of the population. Resistance patterns in aquatic bacteria varied with the site from which they were isolated; a higher incidence of resistance was recorded along shorelines and in sheltered bays than in the open water. The inclusion of antibiotics in the media employed for primary isolation increased the number of individual and multiple resistances recorded. A similar effect was observed with increased inoculum size in the sensitivity disc method but this could be reversed by raising the incubation temperature. The medium used to conduct the test also affected the results and many aquatic bacteria failed to grow on media such as Iso-Sensitest Agar. It is recommended that the sensitivity disc method is adopted for aquatic bacteria because it permits interpretation of a wider range of response. Comparison of the incidence of antibiotic resistance in different habitats will remain meaningless, however, until comprehensive methods for the identification of bacteria are developed and the techniques used for sensitivity testing are standardized.19863636321
4573100.9999High pressure processing, acidic and osmotic stress increased resistance to aminoglycosides and tetracyclines and the frequency of gene transfer among strains from commercial starter and protective cultures. This study analyzed the effect of food-related stresses on the expression of antibiotic resistance of starter and protective strains and resistance gene transfer frequency. After exposure to high-pressure processing, acidic and osmotic stress, the expression of genes encoding resistance to aminoglycosides (aac(6')Ie-aph(2″)Ia and aph(3')-IIIa) and/or tetracyclines (tetM) increased. After cold stress, a decrease in the expression level of all tested genes was observed. The results obtained in the gene expression analysis correlated with the results of the phenotype patterns. After acidic and osmotic stresses, a significant increase in the frequency of each gene transfer was observed. To the best of the authors' knowledge, this is the first study focused on changes in antibiotic resistance associated with a stress response among starter and protective strains. The results suggest that the physicochemical factors prevailing during food production and storage may affect the phenotype of antibiotic resistance and the level of expression of antibiotic resistance genes among microorganisms. As a result, they can contribute to the spread of antibiotic resistance. This points to the need to verify strains used in the food industry for their antibiotic resistance to prevent them from becoming a reservoir for antibiotic resistance genes.202235953184
3820110.9999Selection of a multidrug resistance plasmid by sublethal levels of antibiotics and heavy metals. How sublethal levels of antibiotics and heavy metals select for clinically important multidrug resistance plasmids is largely unknown. Carriage of plasmids generally confers substantial fitness costs, implying that for the plasmid-carrying bacteria to be maintained in the population, the plasmid cost needs to be balanced by a selective pressure conferred by, for example, antibiotics or heavy metals. We studied the effects of low levels of antibiotics and heavy metals on the selective maintenance of a 220-kbp extended-spectrum β-lactamase (ESBL) plasmid identified in a hospital outbreak of Klebsiella pneumoniae and Escherichia coli. The concentrations of antibiotics and heavy metals required to maintain plasmid-carrying bacteria, the minimal selective concentrations (MSCs), were in all cases below (almost up to 140-fold) the MIC of the plasmid-free susceptible bacteria. This finding indicates that the very low antibiotic and heavy metal levels found in polluted environments and in treated humans and animals might be sufficiently high to maintain multiresistance plasmids. When resistance genes were moved from the plasmid to the chromosome, the MSC decreased, showing that MSC for a specific resistance conditionally depends on genetic context. This finding suggests that a cost-free resistance could be maintained in a population by an infinitesimally low concentration of antibiotic. By studying the effect of combinations of several compounds, it was observed that for certain combinations of drugs each new compound added lowered the minimal selective concentration of the others. This combination effect could be a significant factor in the selection of multidrug resistance plasmids/bacterial clones in complex multidrug environments. Importance: Antibiotic resistance is in many pathogenic bacteria caused by genes that are carried on large conjugative plasmids. These plasmids typically contain multiple antibiotic resistance genes as well as genes that confer resistance to biocides and heavy metals. In this report, we show that very low concentrations of single antibiotics and heavy metals or combinations of compounds can select for a large plasmid that carries resistance to aminoglycosides, β-lactams, tetracycline, macrolides, trimethoprim, sulfonamide, silver, copper, and arsenic. Our findings suggest that the low levels of antibiotics and heavy metals present in polluted external environments and in treated animals and humans could allow for selection and enrichment of bacteria with multiresistance plasmids and thereby contribute to the emergence, maintenance, and transmission of antibiotic-resistant disease-causing bacteria.201425293762
4640120.9999Genome analysis of probiotic bacteria for antibiotic resistance genes. To date, probiotic bacteria are used in the diet and have various clinical applications. There are reports of antibiotic resistance genes in these bacteria that can transfer to other commensal and pathogenic bacteria. The aim of this study was to use whole-genome sequence analysis to identify antibiotic resistance genes in a group of bacterial with probiotic properties. Also, this study followed existing issues about the importance and presence of antibiotic resistance genes in these bacteria and the dangers that may affect human health in the future. In the current study, a collection of 126 complete probiotic bacterial genomes was analyzed for antibiotic resistance genes. The results of the current study showed that there are various resistance genes in these bacteria that some of them are transferable to other bacteria. The tet(W) tetracycline resistance gene was more than other antibiotic resistance genes in these bacteria and this gene was found in Bifidobacterium and Lactobacillus. In our study, the most numbers of antibiotic resistance genes were transferred with mobile genetic elements. We propose that probiotic companies before the use of a micro-organism as a probiotic, perform an antibiotic susceptibility testing for a large number of antibiotics. Also, they perform analysis of complete genome sequence for prediction of antibiotic resistance genes.202234989942
3793130.9999Physicochemical Factors That Favor Conjugation of an Antibiotic Resistant Plasmid in Non-growing Bacterial Cultures in the Absence and Presence of Antibiotics. Horizontal gene transfer (HGT) of antibiotic resistance genes has received increased scrutiny from the scientific community in recent years owing to the public health threat associated with antibiotic resistant bacteria. Most studies have examined HGT in growing cultures. We examined conjugation in growing and non-growing cultures of E. coli using a conjugative multi antibiotic and metal resistant plasmid to determine physiochemical parameters that favor horizontal gene transfer. The conjugation frequency in growing and non-growing cultures was generally greater under shaken than non-shaken conditions, presumably due to increased frequency of cell collisions. Non-growing cultures in 9.1 mM NaCl had a similar conjugation frequency to that of growing cultures in Luria-Bertaini broth, whereas those in 1 mM or 90.1 mM NaCl were much lower. This salinity effect on conjugation was attributed to differences in cell-cell interactions and conformational changes in cell surface macromolecules. In the presence of antibiotics, the conjugation frequencies of growing cultures did not increase, but in non-growing cultures of 9.1 mM NaCl supplemented with Cefotaxime the conjugation frequency was as much as nine times greater than that of growing cultures. The mechanism responsible for the increased conjugation in non-growing bacteria was attributed to the likely lack of penicillin-binding protein 3 (the target of Cefotaxime), in non-growing cells that enabled Cefotaxime to interact with the plasmid and induce conjugation. Our results suggests that more attention may be owed to HGT in non-growing bacteria as most bacteria in the environment are likely not growing and the proposed mechanism for increased conjugation may not be unique to the bacteria/plasmid system we studied.201830254617
3800140.9999Alterations of Salmonella enterica Serovar Typhimurium Antibiotic Resistance under Environmental Pressure. Microbial horizontal gene transfer is a continuous process that shapes bacterial genomic adaptation to the environment and the composition of concurrent microbial ecology. This includes the potential impact of synthetic antibiotic utilization in farm animal production on overall antibiotic resistance issues; however, the mechanisms behind the evolution of microbial communities are not fully understood. We explored potential mechanisms by experimentally examining the relatedness of phylogenetic inference between multidrug-resistant Salmonella enterica serovar Typhimurium isolates and pathogenic Salmonella Typhimurium strains based on genome-wide single-nucleotide polymorphism (SNP) comparisons. Antibiotic-resistant S Typhimurium isolates in a simulated farm environment barely lost their resistance, whereas sensitive S Typhimurium isolates in soils gradually acquired higher tetracycline resistance under antibiotic pressure and manipulated differential expression of antibiotic-resistant genes. The expeditious development of antibiotic resistance and the ensuing genetic alterations in antimicrobial resistance genes in S Typhimurium warrant effective actions to control the dissemination of Salmonella antibiotic resistance.IMPORTANCE Antibiotic resistance is attributed to the misuse or overuse of antibiotics in agriculture, and antibiotic resistance genes can also be transferred to bacteria under environmental stress. In this study, we report a unidirectional alteration in antibiotic resistance from susceptibility to increased resistance. Highly sensitive Salmonella enterica serovar Typhimurium isolates from organic farm systems quickly acquired tetracycline resistance under antibiotic pressure in simulated farm soil environments within 2 weeks, with expression of antibiotic resistance-related genes that was significantly upregulated. Conversely, originally resistant S Typhimurium isolates from conventional farm systems lost little of their resistance when transferred to environments without antibiotic pressure. Additionally, multidrug-resistant S Typhimurium isolates genetically shared relevancy with pathogenic S Typhimurium isolates, whereas susceptible isolates clustered with nonpathogenic strains. These results provide detailed discussion and explanation about the genetic alterations and simultaneous acquisition of antibiotic resistance in S Typhimurium in agricultural environments.201830054356
4127150.9999The Perfect Condition for the Rising of Superbugs: Person-to-Person Contact and Antibiotic Use Are the Key Factors Responsible for the Positive Correlation between Antibiotic Resistance Gene Diversity and Virulence Gene Diversity in Human Metagenomes. Human metagenomes with a high diversity of virulence genes tend to have a high diversity of antibiotic-resistance genes and vice-versa. To understand this positive correlation, we simulated the transfer of these genes and bacterial pathogens in a community of interacting people that take antibiotics when infected by pathogens. Simulations show that people with higher diversity of virulence and resistance genes took antibiotics long ago, not recently. On the other extreme, we find people with low diversity of both gene types because they took antibiotics recently-while antibiotics select specific resistance genes, they also decrease gene diversity by eliminating bacteria. In general, the diversity of virulence and resistance genes becomes positively correlated whenever the transmission probability between people is higher than the probability of losing resistance genes. The positive correlation holds even under changes of several variables, such as the relative or total diversity of virulence and resistance genes, the contamination probability between individuals, the loss rate of resistance genes, or the social network type. Because the loss rate of resistance genes may be shallow, we conclude that the transmission between people and antibiotic usage are the leading causes for the positive correlation between virulence and antibiotic-resistance genes.202134065307
4148160.9999Plasmids in the environment. Bacterial plasmids existed in bacteria before the antibiotic era but their presence was brought into prominence by the use of antibiotics which selected for antibiotic resistant strains. Subsequently, the range of genes carried on plasmids was shown to extend far beyond those coding for antibiotic resistance. Any consideration of plasmids in the environment, therefore, must include all plasmids whether or not they are genetically linked with antibiotic resistance. Antibiotic resistant bacteria may be found in the environment either by contamination with excreta from man and animals in which the strains were selected, or by their selection within the environment by antibiotics synthesized in situ or reaching the environment in an undegraded form in sewage from man and animals, or from industry. Other agents, also contaminating the environment, exert a selective pressure such as heavy metals in industrial effluents which select for metal resistance. This paper reviews the incidences and role of plasmids in various habitats including natural waters, soil, pastures, farm wastes, and human sewage from both hospitalised and other populations. Aspects of plasmid ecology, their biological role, and the transmissibility of genetic material between bacteria within the environment are considered. Two recent studies in Bristol, UK, are reported. The first was a genetic study on Escherichia coli isolates from calf slurry. Various DNA probes were used to determine the extent of gene exchange between the various serotypes within the natural environment. The second was a preliminary study to determine the stability of a recombinant plasmid, in a wild strain of Escherichia coli of pig origin, after its release into a semi-contained farm situation. It is now recognized that plasmids are widely distributed in bacterial populations in terrestrial and aquatic environments. Many have been detected by their carriage of genes coding for antibiotic or heavy metal resistance. Others, mainly cryptic in nature, have been demonstrated by plasmid profile studies on isolates from various habitats. Plasmids were shown to be present in a relatively few bacteria deposited in culture collections prior to the antibiotic era. Subsequently, the increased prevalence of R plasmids in bacteria in most ecosystems were due mainly to the selective pressure imposed by the use of antibiotics. This pressure may have been exerted either in the environment in which the strains were found or elsewhere, the environment subsequently being contaminated by antibiotic resistant bacteria.(ABSTRACT TRUNCATED AT 400 WORDS)19883074480
3724170.9999A phenotypic study of the resistome in a peri-urban ecosystem. Since the discovery of antibiotics, the dispersion of resistance genes has increased exponentially, leading to the current state in which it has become increasingly difficult to achieve an effective treatment for infectious diseases. The enormous capacity for genetic exchange between microorganisms is causing resistance genes to be able to reach all environments, even those where there is no anthropogenic impact or exposure to these drugs. In this work, a phenotypic study of the resistome has been conducted in a peri-urban ecosystem (Granada, Spain), wherein the resistance to 32 antibiotics of 710 bacterial strains isolated from 70 samples from different ecological niches with varying levels of exposure to antibiotics and anthropic action has been determined. The study of resistances using phenotypic procedures constitutes a very useful and complementary alternative to genomic methods. The obtained results show a high percentage of resistance in all the subsystems analysed, stating high multi-resistance profiles. Vancomycin and erythromycin were the antibiotics to which the highest levels of resistance were observed, whereas the lowest levels were obtained in chloramphenicol. Regarding the environments studied, the highest percentages of resistance were found in wastewater, farms and food. It should be noted that in natural soil samples (not exposed to antibiotics or anthropogenic activities), worrying levels of resistance to practically all the groups of antibiotics analysed were detected. These results support the generally accepted conclusion that an appropriate control and management of wastewater and solid waste that may contain antibiotics or resistant bacteria is really important to prevent the wide propagation of the resistome in the environment.202539557147
4111180.9999Antibiotic resistance in oral commensal streptococci from healthy Mexicans and Cubans: resistance prevalence does not mirror antibiotic usage. Antibiotic resistance genes might be maintained by selection pressures different from those which are responsible for initially selecting resistant bacteria. This possibility was suggested from a comparison of oral commensal streptococci isolated from healthy people not taking antibiotics. Resistance frequencies were similar for organisms from Mexico and Cuba despite significant differences in antibiotic usage in these two countries. Resistance to > or = 4 drugs was far more common in Mexico, the only detectable trend that can be related to the higher use of antibiotics in Mexico. If resistance is not uniquely maintained by antibiotics, then other environmental factors must also be at work. These need to be identified if a strategy to control antibiotic resistance is to be successful.200212480100
8927190.9999Changes in Intrinsic Antibiotic Susceptibility during a Long-Term Evolution Experiment with Escherichia coli. High-level resistance often evolves when populations of bacteria are exposed to antibiotics, by either mutations or horizontally acquired genes. There is also variation in the intrinsic resistance levels of different bacterial strains and species that is not associated with any known history of exposure. In many cases, evolved resistance is costly to the bacteria, such that resistant types have lower fitness than their progenitors in the absence of antibiotics. Some longer-term studies have shown that bacteria often evolve compensatory changes that overcome these tradeoffs, but even those studies have typically lasted only a few hundred generations. In this study, we examine changes in the susceptibilities of 12 populations of Escherichia coli to 15 antibiotics after 2,000 and 50,000 generations without exposure to any antibiotic. On average, the evolved bacteria were more susceptible to most antibiotics than was their ancestor. The bacteria at 50,000 generations tended to be even more susceptible than after 2,000 generations, although most of the change occurred during the first 2,000 generations. Despite the general trend toward increased susceptibility, we saw diverse outcomes with different antibiotics. For streptomycin, which was the only drug to which the ancestral strain was highly resistant, none of the evolved lines showed any increased susceptibility. The independently evolved lineages often exhibited correlated responses to the antibiotics, with correlations usually corresponding to their modes of action. On balance, our study shows that bacteria with low levels of intrinsic resistance often evolve to become even more susceptible to antibiotics in the absence of corresponding selection.IMPORTANCE Resistance to antibiotics often evolves when bacteria encounter antibiotics. However, bacterial strains and species without any known exposure to these drugs also vary in their intrinsic susceptibility. In many cases, evolved resistance has been shown to be costly to the bacteria, such that resistant types have reduced competitiveness relative to their sensitive progenitors in the absence of antibiotics. In this study, we examined changes in the susceptibilities of 12 populations of Escherichia coli to 15 antibiotics after 2,000 and 50,000 generations without exposure to any drug. The evolved bacteria tended to become more susceptible to most antibiotics, with most of the change occurring during the first 2,000 generations, when the bacteria were undergoing rapid adaptation to their experimental conditions. On balance, our findings indicate that bacteria with low levels of intrinsic resistance can, in the absence of relevant selection, become even more susceptible to antibiotics.201930837336