Evaluating targets for control of plasmid-mediated antimicrobial resistance in enteric commensals of beef cattle: a modelling approach. - Related Documents




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410801.0000Evaluating targets for control of plasmid-mediated antimicrobial resistance in enteric commensals of beef cattle: a modelling approach. Enteric commensal bacteria of food animals may serve as a reservoir of genes encoding antimicrobial resistance (AMR). The genes are often plasmidic. Different aspects of bacterial ecology can be targeted by interventions to control plasmid-mediated AMR. The field efficacy of interventions remains unclear. We developed a deterministic mathematical model of commensal Escherichia coli in its animate and non-animate habitats within a beef feedlot's pen, with some E. coli having plasmid-mediated resistance to the cephalosporin ceftiofur. We evaluated relative potential efficacy of within- or outside-host biological interventions delivered throughout rearing depending on the targeted parameter of bacterial ecology. Most instrumental in reducing the fraction of resistant enteric E. coli at steer slaughter age were interventions acting on the enteric E. coli and capable of either 'plasmid curing' E. coli, or lowering maximum E. coli numbers or the rate of plasmid transfer in this habitat. Also efficient was to increase the regular replacement of enteric E. coli. Lowering replication rate of resistant E. coli alone was not an efficient intervention target.201323339899
490710.9999Mathematical model of plasmid-mediated resistance to ceftiofur in commensal enteric Escherichia coli of cattle. Antimicrobial use in food animals may contribute to antimicrobial resistance in bacteria of animals and humans. Commensal bacteria of animal intestine may serve as a reservoir of resistance-genes. To understand the dynamics of plasmid-mediated resistance to cephalosporin ceftiofur in enteric commensals of cattle, we developed a deterministic mathematical model of the dynamics of ceftiofur-sensitive and resistant commensal enteric Escherichia coli (E. coli) in the absence of and during parenteral therapy with ceftiofur. The most common treatment scenarios including those using a sustained-release drug formulation were simulated; the model outputs were in agreement with the available experimental data. The model indicated that a low but stable fraction of resistant enteric E. coli could persist in the absence of immediate ceftiofur pressure, being sustained by horizontal and vertical transfers of plasmids carrying resistance-genes, and ingestion of resistant E. coli. During parenteral therapy with ceftiofur, resistant enteric E. coli expanded in absolute number and relative frequency. This expansion was most influenced by parameters of antimicrobial action of ceftiofur against E. coli. After treatment (>5 weeks from start of therapy) the fraction of ceftiofur-resistant cells among enteric E. coli, similar to that in the absence of treatment, was most influenced by the parameters of ecology of enteric E. coli, such as the frequency of transfer of plasmids carrying resistance-genes, the rate of replacement of enteric E. coli by ingested E. coli, and the frequency of ceftiofur resistance in the latter.201222615803
394320.9998Quinolone resistance in the food chain. Antimicrobials are used in pet animals and in animal husbandry for prophylactic and therapeutic reasons and also as growth promoters, causing selective pressure on bacteria of animal origin. The impact of quinolones or quinolone-resistant bacteria on the management of human infections may be associated with three different scenarios. (i) Quinolone-resistant zoonotic bacterial pathogens are selected and food is contaminated during slaughter and/or preparation. (ii) Quinolone-resistant bacteria non-pathogenic to humans are selected in the animal. When the contaminated food is ingested, the bacteria may transfer resistance determinants to other bacteria in the human gut (commensal and potential pathogens). And (iii) quinolones remain in residues of food products, which may allow the selection of antibiotic-resistant bacteria after the food is consumed. In this review, we analyse the abovementioned aspects, emphasising the molecular basis of quinolone resistance in Escherichia coli, Salmonella spp. and Campylobacter spp.200818308515
381830.9998A 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
991940.9998An In Vitro Chicken Gut Model Demonstrates Transfer of a Multidrug Resistance Plasmid from Salmonella to Commensal Escherichia coli. The chicken gastrointestinal tract is richly populated by commensal bacteria that fulfill various beneficial roles for the host, including helping to resist colonization by pathogens. It can also facilitate the conjugative transfer of multidrug resistance (MDR) plasmids between commensal and pathogenic bacteria which is a significant public and animal health concern as it may affect our ability to treat bacterial infections. We used an in vitro chemostat system to approximate the chicken cecal microbiota, simulate colonization by an MDR Salmonella pathogen, and examine the dynamics of transfer of its MDR plasmid harboring several genes, including the extended-spectrum beta-lactamase bla(CTX-M1) We also evaluated the impact of cefotaxime administration on plasmid transfer and microbial diversity. Bacterial community profiles obtained by culture-independent methods showed that Salmonella inoculation resulted in no significant changes to bacterial community alpha diversity and beta diversity, whereas administration of cefotaxime caused significant alterations to both measures of diversity, which largely recovered. MDR plasmid transfer from Salmonella to commensal Escherichia coli was demonstrated by PCR and whole-genome sequencing of isolates purified from agar plates containing cefotaxime. Transfer occurred to seven E. coli sequence types at high rates, even in the absence of cefotaxime, with resistant strains isolated within 3 days. Our chemostat system provides a good representation of bacterial interactions, including antibiotic resistance transfer in vivo It can be used as an ethical and relatively inexpensive approach to model dissemination of antibiotic resistance within the gut of any animal or human and refine interventions that mitigate its spread before employing in vivo studies.IMPORTANCE The spread of antimicrobial resistance presents a grave threat to public health and animal health and is affecting our ability to respond to bacterial infections. Transfer of antimicrobial resistance via plasmid exchange is of particular concern as it enables unrelated bacteria to acquire resistance. The gastrointestinal tract is replete with bacteria and provides an environment for plasmid transfer between commensals and pathogens. Here we use the chicken gut microbiota as an exemplar to model the effects of bacterial infection, antibiotic administration, and plasmid transfer. We show that transfer of a multidrug-resistant plasmid from the zoonotic pathogen Salmonella to commensal Escherichia coli occurs at a high rate, even in the absence of antibiotic administration. Our work demonstrates that the in vitro gut model provides a powerful screening tool that can be used to assess and refine interventions that mitigate the spread of antibiotic resistance in the gut before undertaking animal studies.201728720731
381950.9998Enhancement of bacterial competitive fitness by apramycin resistance plasmids from non-pathogenic Escherichia coli. The study of antibiotic resistance has in the past focused on organisms that are pathogenic to humans or animals. However, the development of resistance in commensal organisms is of concern because of possible transfer of resistance genes to zoonotic pathogens. Conjugative plasmids are genetic elements capable of such transfer and are traditionally thought to engender a fitness burden on host bacteria. In this study, conjugative apramycin resistance plasmids isolated from newborn calves were characterized. Calves were raised on a farm that had not used apramycin or related aminoglycoside antibiotics for at least 20 months prior to sampling. Of three apramycin resistance plasmids, one was capable of transfer at very high rates and two were found to confer fitness advantages on new Escherichia coli hosts. This is the first identification of natural plasmids isolated from commensal organisms that are able to confer a fitness advantage on a new host. This work indicates that reservoirs of antibiotic resistance genes in commensal organisms might not decrease if antibiotic usage is halted.200617148431
382160.9998Persistence of transferable extended-spectrum-β-lactamase resistance in the absence of antibiotic pressure. The treatment of infections caused by antibiotic-resistant bacteria is one of the great challenges faced by clinicians in the 21st century. Antibiotic resistance genes are often transferred between bacteria by mobile genetic vectors called plasmids. It is commonly believed that removal of antibiotic pressure will reduce the numbers of antibiotic-resistant bacteria due to the perception that carriage of resistance imposes a fitness cost on the bacterium. This study investigated the ability of the plasmid pCT, a globally distributed plasmid that carries an extended-spectrum-β-lactamase (ESBL) resistance gene (bla(CTX-M-14)), to persist and disseminate in the absence of antibiotic pressure. We investigated key attributes in plasmid success, including conjugation frequencies, bacterial-host growth rates, ability to cause infection, and impact on the fitness of host strains. We also determined the contribution of the bla(CTX-M-14) gene itself to the biology of the plasmid and host bacterium. Carriage of pCT was found to impose no detectable fitness cost on various bacterial hosts. An absence of antibiotic pressure and inactivation of the antibiotic resistance gene also had no effect on plasmid persistence, conjugation frequency, or bacterial-host biology. In conclusion, plasmids such as pCT have evolved to impose little impact on host strains. Therefore, the persistence of antibiotic resistance genes and their vectors is to be expected in the absence of antibiotic selective pressure regardless of antibiotic stewardship. Other means to reduce plasmid stability are needed to prevent the persistence of these vectors and the antibiotic resistance genes they carry.201222710119
410770.9998Modeling the infection dynamics of bacteriophages in enteric Escherichia coli: estimating the contribution of transduction to antimicrobial gene spread. Animal-associated bacterial communities are infected by bacteriophages, although the dynamics of these infections are poorly understood. Transduction by bacteriophages may contribute to transfer of antimicrobial resistance genes, but the relative importance of transduction among other gene transfer mechanisms is unknown. We therefore developed a candidate deterministic mathematical model of the infection dynamics of enteric coliphages in commensal Escherichia coli in the large intestine of cattle. We assumed the phages were associated with the intestine and were predominantly temperate. Model simulations demonstrated how, given the bacterial ecology and infection dynamics, most (>90%) commensal enteric E. coli bacteria may become lysogens of enteric coliphages during intestinal transit. Using the model and the most liberal assumptions about transduction efficiency and resistance gene frequency, we approximated the upper numerical limits ("worst-case scenario") of gene transfer through specialized and generalized transduction in E. coli by enteric coliphages when the transduced genetic segment is picked at random. The estimates were consistent with a relatively small contribution of transduction to lateral gene spread; for example, generalized transduction delivered the chromosomal resistance gene to up to 8 E. coli bacteria/hour within the population of 1.47 × 10(8) E. coli bacteria/liter luminal contents. In comparison, the plasmidic blaCMY-2 gene carried by ~2% of enteric E. coli was transferred by conjugation at a rate at least 1.4 × 10(3) times greater than our generalized transduction estimate. The estimated numbers of transductants varied nonlinearly depending on the ecology of bacteria available for phages to infect, that is, on the assumed rates of turnover and replication of enteric E. coli.201424814786
421080.9998Epidemiology of resistance to antibiotics. Links between animals and humans. An inevitable side effect of the use of antibiotics is the emergence and dissemination of resistant bacteria. Most retrospective and prospective studies show that after the introduction of an antibiotic not only the level of resistance of pathogenic bacteria, but also of commensal bacteria increases. Commensal bacteria constitute a reservior of resistance genes for (potentially) pathogenic bacteria. Their level of resistance is considered to be a good indicator for selection pressure by antibiotic use and for resistance problems to be expected in pathogens. Resistant commensal bacteria of food animals might contaminate, like zoonotic bacteria, meat (products) and so reach the intestinal tract of humans. Monitoring the prevalence of resistance in indicator bacteria such as faecal Escherichia coli and enterococci in different populations, animals, patients and healthy humans, makes it feasible to compare the prevalence of resistance and to detect transfer of resistant bacteria or resistance genes from animals to humans and vice versa. Only in countries that use or used avoparcin (a glycopeptide antibiotic, like vancomycin) as antimicrobial growth promoter (AMGP), is vancomycin resistance common in intestinal enterococci, not only in exposed animals, but also in the human population outside hospitals. Resistance genes against antibiotics, that are or have only been used in animals, i.e. nourseothricin, apramycin etc. were found soon after their introduction, not only in animal bacteria but also in the commensal flora of humans, in zoonotic pathogens like salmonellae, but also in strictly human pathogens, like shigellae. This makes it clear that not only clonal spread of resistant strains occurs, but also transfer of resistance genes between human and animal bacteria. Moreover, since the EU ban of avoparcin, a significant decrease has been observed in several European countries in the prevalence of vancomycin resistant enterococci in meat (products), in faecal samples of food animals and healthy humans, which underlines the role of antimicrobial usage in food animals in the selection of bacterial resistance and the transport of these resistances via the food chain to humans. To safeguard public health, the selection and dissemination of resistant bacteria from animals should be controlled. This can only be achieved by reducing the amounts of antibiotics used in animals. Discontinuing the practice of routinely adding AMGP to animal feeds would reduce the amounts of antibiotics used for animals in the EU by a minimum of 30% and in some member states even by 50%.200010794955
490690.9998Factors that affect transfer of the IncI1 β-lactam resistance plasmid pESBL-283 between E. coli strains. The spread of antibiotic resistant bacteria worldwide presents a major health threat to human health care that results in therapy failure and increasing costs. The transfer of resistance conferring plasmids by conjugation is a major route by which resistance genes disseminate at the intra- and interspecies level. High similarities between resistance genes identified in foodborne and hospital-acquired pathogens suggest transmission of resistance conferring and transferrable mobile elements through the food chain, either as part of intact strains, or through transfer of plasmids from foodborne to human strains. To study the factors that affect the rate of plasmid transfer, the transmission of an extended-spectrum β-lactamase (ESBL) plasmid from a foodborne Escherichia coli strain to the β-lactam sensitive E. coli MG1655 strain was documented as a function of simulated environmental factors. The foodborne E. coli isolate used as donor carried a CTX-M-1 harboring IncI1 plasmid that confers resistance to β-lactam antibiotics. Cell density, energy availability and growth rate were identified as factors that affect plasmid transfer efficiency. Transfer rates were highest in the absence of the antibiotic, with almost every acceptor cell picking up the plasmid. Raising the antibiotic concentrations above the minimum inhibitory concentration (MIC) resulted in reduced transfer rates, but also selected for the plasmid carrying donor and recombinant strains. Based on the mutational pattern of transconjugant cells, a common mechanism is proposed which compensates for fitness costs due to plasmid carriage by reducing other cell functions. Reducing potential fitness costs due to maintenance and expression of the plasmid could contribute to persistence of resistance genes in the environment even without antibiotic pressure. Taken together, the results identify factors that drive the spread and persistence of resistance conferring plasmids in natural isolates and shows how these can contribute to transmission of resistance genes through the food chain.201525830294
3832100.9998A population genomics approach to exploiting the accessory 'resistome' of Escherichia coli. The emergence of antibiotic resistance is a defining challenge, and Escherichia coli is recognized as one of the leading species resistant to the antimicrobials used in human or veterinary medicine. Here, we analyse the distribution of 2172 antimicrobial-resistance (AMR) genes in 4022 E. coli to provide a population-level view of resistance in this species. By separating the resistance determinants into 'core' (those found in all strains) and 'accessory' (those variably present) determinants, we have found that, surprisingly, almost half of all E. coli do not encode any accessory resistance determinants. However, those strains that do encode accessory resistance are significantly more likely to be resistant to multiple antibiotic classes than would be expected by chance. Furthermore, by studying the available date of isolation for the E. coli genomes, we have visualized an expanding, highly interconnected network that describes how resistances to antimicrobials have co-associated within genomes over time. These data can be exploited to reveal antimicrobial combinations that are less likely to be found together, and so if used in combination may present an increased chance of suppressing the growth of bacteria and reduce the rate at which resistance factors are spread. Our study provides a complex picture of AMR in the E. coli population. Although the incidence of resistance to all studied antibiotic classes has increased dramatically over time, there exist combinations of antibiotics that could, in theory, attack the entirety of E. coli, effectively removing the possibility that discrete AMR genes will increase in frequency in the population.201728785420
3831110.9998The distribution of fitness effects of plasmid pOXA-48 in clinical enterobacteria. Antimicrobial resistance (AMR) in bacteria is a major public health problem. The main route for AMR acquisition in clinically important bacteria is the horizontal transfer of plasmids carrying resistance genes. AMR plasmids allow bacteria to survive antibiotics, but they also entail physiological alterations in the host cell. Multiple studies over the last few years have indicated that these alterations can translate into a fitness cost when antibiotics are absent. However, due to technical limitations, most of these studies are based on analysing new associations between plasmids and bacteria generated in vitro, and we know very little about the effects of plasmids in their native bacterial hosts. In this study, we used a CRISPR-Cas9-tool to selectively cure plasmids from clinical enterobacteria to overcome this limitation. Using this approach, we were able to study the fitness effects of the carbapenem resistance plasmid pOXA-48 in 35 pOXA-48-carrying isolates recovered from hospitalized patients. Our results revealed that pOXA-48 produces variable effects across the collection of wild-type enterobacterial strains naturally carrying the plasmid, ranging from fitness costs to fitness benefits. Importantly, the plasmid was only associated with a significant fitness reduction in four out of 35 clones, and produced no significant changes in fitness in the great majority of isolates. Our results suggest that plasmids produce neutral fitness effects in most native bacterial hosts, helping to explain the great prevalence of plasmids in natural microbial communities.202337505800
4216120.9997Antimicrobial Resistance in the Food Chain in the European Union. Consumers require safety foods but without losing enough supply and low prices. Food concerns about antimicrobial residues and antimicrobial-resistant (AMR) bacteria are not usually appropriately separated and could be perceived as the same problem. The monitoring of residues of antimicrobials in animal food is well established at different levels (farm, slaughterhouse, and industry), and it is preceded by the legislation of veterinary medicines where maximum residues limits are required for medicines to be used in food animal. Following the strategy of the World Health Organization, one of the proposed measures consists in controlling the use of critical antibiotics. The European Union surveillance program currently includes the animal species with the highest meat production (pigs, chickens, turkeys, and cattle) and the food derived from them, investigating antimicrobial resistance of zoonotic (Salmonella and Campylobacter) and indicator (Escherichia coli and enterococci) bacteria. AMR mechanisms encoded by genes have a greater impact on transfer than mutations. Sometimes these genes are found in mobile genetic elements such as plasmids, transposons, or integrons, capable of passing from one bacterium to another by horizontal transfer. It is important to know that depending on how the resistance mechanism is transferred, the power of dissemination is different. By vertical transfer of the resistance gene, whatever its origin, will be transmitted to the following generations. In the case of horizontal transfer, the resistance gene moves to neighboring bacteria and therefore the range of resistance can be much greater.201830077219
3896130.9997Antimicrobial resistance genes in bacteria from animal-based foods. Antimicrobial resistance is a worldwide public health threat. Farm animals are important sources of bacteria containing antimicrobial resistance genes (ARGs). Although the use of antimicrobials in aquaculture and livestock has been reduced in several countries, these compounds are still routinely applied in animal production, and contribute to ARGs emergence and spread among bacteria. ARGs are transmitted to humans mainly through the consumption of products of animal origin (PAO). Bacteria can present intrinsic resistance, and once antimicrobials are administered, this resistance may be selected and multiply. The exchange of genetic material is another mechanism used by bacteria to acquire resistance. Some of the main ARGs found in bacteria present in PAO are the bla, mcr-1, cfr and tet genes, which are directly associated to antibiotic resistance in the human clinic.202032762867
3935140.9997Removal of antimicrobial prophylaxis and its effect on swine carriage of antimicrobial-resistant coliforms. The use of antimicrobials in the food animal industry has caused an increased prevalence of antimicrobial-resistant bacteria and antimicrobial resistance genes, which can be transferred to the microbiota of humans through the food chain or the environment. To reduce the development and spread of antimicrobial resistance, restrictions on antimicrobial use in food animals have been implemented in different countries. We investigated the impact of an antimicrobial restriction intervention during two generations of pigs. Fecal samples were collected in five growth phases. The frequency of antimicrobial-resistant coliforms and antimicrobial-resistant bacteria or antimicrobial resistance genes was analyzed. No differences in the richness or abundance of antimicrobial-resistant coliforms or antimicrobial resistance genes were found when animals fed with or without prophylactic antimicrobials were compared. Withholding antimicrobial supplementation did not negatively affect weight gain in pigs. Withdrawal of prophylactic antimicrobial consumption during two generations of pigs was not enough to reduce the prevalence of antimicrobial resistance genes, as measured by richness and abundance markers. This study indicates that the fitness costs associated with bacterial carriage of some antimicrobial resistance genes are low.202134872396
4156150.9997Antibiotic resistance genes in Escherichia coli - literature review. Antimicrobial resistance threatens humans and animals worldwide and is recognized as one of the leading global public health issues. Escherichia coli (E. coli) has an unquestionable role in carrying and transmitting antibiotic resistance genes (ARGs), which in many cases are encoded on plasmids or phage, thus creating the potential for horizontal gene transfer. In this literature review, the authors summarize the major antibiotic resistance genes occurring in E. coli bacteria, through the major antibiotic classes. The aim was not only listing the resistance genes against the clinically relevant antibiotics, used in the treatment of E. coli infections, but also to cover the entire resistance gene carriage in E. coli, providing a more complete picture. We started with the long-standing antibiotic groups (beta-lactams, aminoglycosides, tetracyclines, sulfonamides and diaminopyrimidines), then moved toward the newer groups (phenicols, peptides, fluoroquinolones, nitrofurans and nitroimidazoles), and in every group we summarized the resistance genes grouped by the mechanism of their action (enzymatic inactivation, antibiotic efflux, reduced permeability, etc.). We observed that the frequency of antibiotic resistance mechanisms changes in the different groups.202540249005
4314160.9997Cephalosporin resistance among animal-associated Enterobacteria: a current perspective. Beta-lactam antimicrobials are an important class of drugs used for the treatment of infection. Resistance can arise by several mechanisms, including the acquisition of genes encoding beta-lactamases from other bacteria, alterations in cell membrane permeability and over expression of endogenous beta-lactamases. The acquisition of beta-lactamase resistance genes by both Salmonella and Escherichia coli appears to be on the rise, which may pose potential problems for the treatment of infections in both human and animal medicine. The prudent use of clinically important antimicrobials is therefore critical to maintain their effectiveness. Where possible, the use of newer generation cephalosporins should be limited in veterinary medicine.200515954857
4148170.9997Plasmids 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
6631180.9997Antibiotic Resistance in Escherichia coli from Farm Livestock and Related Analytical Methods: A Review. The indiscriminate use of antibiotics for the treatment of human and animal infections has led to the rise of resistance in pathogens and in commensal bacteria. In particular, farm animals may act as vectors for the dissemination of drug-resistant genes because of the intensive use of antibiotics in animal production, enabling resistance to a wide range of antimicrobial agents, including those normally used in human medicine. Escherichia coli, being a widespread commensal, is considered a good indicator of antibiotic use. Ultimately, it is emerging as a global threat, developing dramatically high levels of antibiotic resistance to multiple classes of drugs. Its prevalence in food animals is hence alarming, and more studies are needed in order to ascertain the spread dynamics between the food chain and humans. In this context, great attention should be paid to the accurate detection of resistance by conventional and molecular methods. In this review, a comprehensive list of the most widely used testing methods is also addressed.201829554996
3938190.9997Human health hazards associated with the administration of antimicrobials to slaughter animals. Part II. An assessment of the risks of resistant bacteria in pigs and pork. Risks for the consumer regarding the acquisition of resistant bacteria and/or resistance genes via the consumption of pork are discussed. In general, Salmonella spp. and Escherichia coli that originate from animals do not easily transfer their resistance genes to the resident intestinal flora of humans. The prevalence of resistant E. coli in humans seems more associated with being a vegetarian (odds ratio (OR) 1.89) than with the consumption of meat and meat products. Other risk factors are treatment with antimicrobials (OR 2-5), becoming hospitalized (OR 5.93), or working in a health setting (OR 4.38). In the Netherlands, annually an estimated 45,000 people (0-150,000) become a carrier of resistant E. coli and/or resistance genes that ori ginate from pigs, while an estimated 345,000 persons (175,000-600,000) become a carrier of resistant E. coli and/or resistance genes that originate from hospitals, e.g. other patients. Any problems with resistant Salmonella spp. that stem from pigs are, in fact, an integral part of the total problem of food-borne salmonellosis. Sometimes there are outbreaks of a specific multi-resistant clone of S. typhimurium that causes problems in both farm animals and humans. The probability that in the next 30 years there is no or maximally one outbreak of a specific clone that originates from pig herds is estimated at about 75%. Antimicrobials used as a growth promoter can have a measurable influence on the prevalence of resistant bacteria. The likely chain of events regarding avoparcin and the selection and dissemination of resistance against vancomycin in the enterococci gives the impression that the impact of the use of antimicrobials in animals on the prevalence of resistance in humans is largely determined by whether resistance genes are, or become, located on a self-transferable transposon. Furthermore, consumer health risks of antimicrobials used in slaughter pigs are mainly determined by the selection and dissemination of bacterial resistance and much less by the toxicological properties of any residues in pork. It is also concluded that most of the problems with resistant bacteria in humans are associated with the medical use of antimicrobials, and that the impact of particularly the veterinary use of antimicrobials is limited. However, the impact of antimicrobials used as a feed additive appears to be much greater than that of antimicrobials used for strictly veterinary purposes. The use of antimicrobials as a feed additive should therefore be seriously reconsidered.200111205995