TRANSFER OF DRUG RESISTANCE BETWEEN ENTERIC BACTERIA INDUCED IN THE MOUSE INTESTINE. - Related Documents




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373601.0000TRANSFER OF DRUG RESISTANCE BETWEEN ENTERIC BACTERIA INDUCED IN THE MOUSE INTESTINE. Kasuya, Morimasa (Nagoya University School of Medicine, Nagoya, Japan). Transfer of drug resistance between enteric bacteria induced in the mouse intestine. J. Bacteriol. 88:322-328. 1964.-Transfer of multiple drug resistance in the intestines of germ-free and conventional mice was studied with strains of Shigella, Escherichia, and Klebsiella. The transfer experiment was carried out under antibiotic-free conditions to eliminate the production of drug-resistant bacteria by antibiotics. All resistance factors (chloramphenicol, streptomycin, tetracycline, and sulfathiazole) were transferred with ease in the intestinal tracts of mice, when donors and recipients multiplied freely, and acquired resistance was further transferred to other sensitive enteric bacteria in the intestinal tract. Bacteria to which resistance factors were transferred showed, in most of the experiments, exactly the same level and pattern of resistance as the donors. Based on the above, a hypothesis that the same process may possibly occur in the human intestine is presented.196414203347
358510.9996Effects of subtherapeutic concentrations of antimicrobials on gene acquisition events in Yersinia, Proteus, Shigella, and Salmonella recipient organisms in isolated ligated intestinal loops of swine. OBJECTIVE: To assess antimicrobial resistance and transfer of virulence genes facilitated by subtherapeutic concentrations of antimicrobials in swine intestines. ANIMALS: 20 anesthetized pigs experimentally inoculated with donor and recipient bacteria. PROCEDURES: 4 recipient pathogenic bacteria (Salmonella enterica serotype Typhimurium, Yersinia enterocolitica, Shigella flexneri, or Proteus mirabilis) were incubated with donor bacteria in the presence of subinhibitory concentrations of 1 of 16 antimicrobials in isolated ligated intestinal loops in swine. Donor Escherichia coli contained transferrable antimicrobial resistance or virulence genes. After coincubations, intestinal contents were removed and assessed for pathogens that acquired new antimicrobial resistance or virulence genes following exposure to the subtherapeutic concentrations of antimicrobials. RESULTS: 3 antimicrobials (apramycin, lincomycin, and neomycin) enhanced transfer of an antimicrobial resistance plasmid from commensal E coli organisms to Yersinia and Proteus organisms, whereas 7 antimicrobials (florfenicol, hygromycin, penicillin G, roxarsone, sulfamethazine, tetracycline, and tylosin) exacerbated transfer of an integron (Salmonella genomic island 1) from Salmonella organisms to Yersinia organisms. Sulfamethazine induced the transfer of Salmonella pathogenicity island 1 from pathogenic to nonpathogenic Salmonella organisms. Six antimicrobials (bacitracin, carbadox, erythromycin, sulfathiazole, tiamulin, and virginiamycin) did not mediate any transfer events. Sulfamethazine was the only antimicrobial implicated in 2 types of transfer events. CONCLUSIONS AND CLINICAL RELEVANCE: 10 of 16 antimicrobials at subinhibitory or subtherapeutic concentrations augmented specific antimicrobial resistance or transfer of virulence genes into pathogenic bacteria in isolated intestinal loops in swine. Use of subtherapeutic antimicrobials in animal feed may be associated with unwanted collateral effects.201323879845
490720.9995Mathematical 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
461330.9995Glycopeptide-resistance transferability from vancomycin-resistant enterococci of human and animal source to Listeria spp. AIMS: The glycopeptide-resistance transferability from vancomycin-resistant enterococci (VRE) of clinical and animal origin to different species of Listeria was investigated. METHODS AND RESULTS: Of 36 matings, performed on membrane filter, the glycopeptide resistance was successfully transferred in six attempts, five with donors of animal origin and only one with donors from clinical source. The acquired glycopeptide resistance in Listeria transconjugants was confirmed by the presence of the conjugative plasmid band and by the amplification of the 732-bp fragment of vanA gene in transferred plasmids. CONCLUSIONS: Despite the lower number of bacteria used in this study, the source of enterococci influenced the outcome of mating. Moreover transferred VanA plasmid induced a different expression in Listeria transconjugants, suggesting that gene expression might be influenced by species affiliation of recipients. SIGNIFICANCE AND IMPACT OF THE STUDY: Our data strengthen the opinion that enterococci are an important source of resistance genes for Listeria via the transfer of movable genetic elements. As these strains are commonly found in the same habitats, a horizontal spread of glycopeptide resistance in Listeria spp. could be possible.200415548299
472040.9995Augmentation of antibiotic resistance in Salmonella typhimurium DT104 following exposure to penicillin derivatives. Antibiotic resistance in pathogenic bacteria has been a problem in both developed and developing countries. This problem is especially evident in Salmonella typhimurium, one of the most prevalent foodborne pathogens. While performing in vitro gentamicin protection-based invasion assays, we found that certain isolates of multiresistant S. typhimurium can be 'induced' to exhibit new resistance profiles. That is, bacteria become resistant to a wider range of antibiotics and they also exhibit quantitative increases in MIC values for antibiotics that were part of their pre-induction antibiograms. This 'induction' process involves growing the bacteria to stationary phase in the presence of antibiotics such as ampicillin, amoxicillin or ticarcillin. Since the isolates studied exhibited resistance to ampicillin, amoxicillin and ticarcillin prior to exposing the bacteria to these antibiotics, the observed phenomenon suggests that resistant Salmonella not only have a selective advantage over non-resistant Salmonella but their resistance phenotypes can be accentuated when an inappropriate antibiotic is used therapeutically.200010731615
379150.9994Horizontal transfer of Shiga toxin and antibiotic resistance genes among Escherichia coli strains in house fly (Diptera: Muscidae) gut. Whether the house fly, Musca domestica L., gut is a permissive environment for horizontal transfer of antibiotic resistance and virulence genes between strains of Escherichia coli is not known. House flies were immobilized and force fed suspensions of defined, donor strains of E. coli containing chloramphenicol resistance genes on a plasmid, or lysogenic, bacteriophage-born Shiga toxin gene stx1 (bacteriophage H-19B::Ap1). Recipient strains were E. coli lacking these mobile elements and genes but having rifampicin as a selectable marker. Plasmid transfer occurred at rates of 10(-2) per donor cell in the fly midgut and 10(-3) in the fly crop after 1 h of incubation postfeeding. Bacteriophage transfer rate was approximately 10(-6) per donor cell without induction, but induction with mitomycin C increased rates of transfer to 10(-2) per donor cell. These findings show that genes encoding antibiotic resistance or toxins will transfer horizontally among bacteria in the house fly gut via plasmid transfer or phage transduction. The house fly gut may provide a favorable environment for the evolution and emergence of pathogenic bacterial strains through acquisition of antibiotic resistance genes or virulence factors.200616619613
472160.9994Antimicrobial resistances do not affect colonization parameters of intestinal E. coli in a small piglet group. BACKGROUND: Although antimicrobial resistance and persistence of resistant bacteria in humans and animals are major health concerns worldwide, the impact of antimicrobial resistance on bacterial intestinal colonization in healthy domestic animals has only been rarely studied. We carried out a retrospective analysis of the antimicrobial susceptibility status and the presence of resistance genes in intestinal commensal E. coli clones from clinically healthy pigs from one production unit with particular focus on effects of pheno- and/or genotypic resistance on different nominal and numerical intestinal colonization parameters. In addition, we compared the occurrence of antimicrobial resistance phenotypes and genotypes with the occurrence of virulence associated genes typical for extraintestinal pathogenic E. coli. RESULTS: In general, up to 72.1% of all E. coli clones were resistant to ampicillin, chloramphenicol, kanamycin, streptomycin, sulfamethoxazole or tetracycline with a variety of different resistance genes involved. There was no significant correlation between one of the nominal or numerical colonization parameters and the absence or presence of antimicrobial resistance properties or resistance genes. However, there were several statistically significant associations between the occurrence of single resistance genes and single virulence associated genes. CONCLUSION: The demonstrated resistance to the tested antibiotics might not play a dominant role for an intestinal colonization success in pigs in the absence of antimicrobial drugs, or cross-selection of other colonization factors e.g. virulence associated genes might compensate "the cost of antibiotic resistance". Nevertheless, resistant strains are not outcompeted by susceptible bacteria in the porcine intestine.200919814790
42070.9994Transferable nitrofuran resistance conferred by R-plasmids in clinical isolates of Escherichia coli. A high proportion of nitrofuran-resistant strains has been found in a collection of antibiotic-resistant Gram-negative bacteria isolated from patients with urinary tract infections. Some of the Escherichia coli carried R-plasmids that conferred resistance to nitrofurantoin and nitrofurazone. The mechanism of resistance is not clear; only in lactose non-fermenting recipients was there a decrease in the nitrofuran-reducing ability of whole-cell suspensions. One of the plasmids conferred enhanced resistance to UV light on DNA repair defective mutants but not on repair efficient strains. In some resistant strains, the total resistance was apparently the result of a combination of chromosomal and plasmid-borne genes. The presence of the plasmid may allow the development of higher resistance levels by mutation of chromosomal genes.19836368515
472380.9994Impact of Sublethal Disinfectant Exposure on Antibiotic Resistance Patterns of Pseudomonasaeruginosa. OBJECTIVE: The problem of hospital cross-infection due to contamination of disinfectants has been recognized elsewhere. The passage of bacteria through diluted disinfectants may not only bring about phenotypic changes in their antibiograms but also changes in phage susceptibility patterns. Contact with disinfectants in sublethal concentrations allows survival and multiplication of bacteria. METHODS AND MATERIALS: Serial passage, through disinfectants at subminimal inhibitory concentrations, induced antibiotic resistance in 18% of derived phenotypic variants of fifty strains of Pseudomonas aeruginosa which were isolated from diarrheal stools of infants in children's hospital. RESULTS: A proportion of these strains became susceptible to an increased number of antibiotics. The present study revealed that all the isolates were resistant to tetracycline and carbenicillin and 40% of these isolates became sensitive to both antibiotics after exposure to disinfectants. The exposure to disinfectants induced neomycin resistance among two isolates. The resistance patterns were three before disinfectants exposure which increased to be nine different patterns after exposure. No antibiotic resistance was transferred between P. aeruginosa and Escherichia coli K12 as a recipient strain. CONCLUSIONS: Almost 50% of the isolates tested became sensitive to tetracycline, carbenicillin and co-trimoxazole after exposure to disinfectants. The resistance patterns among the 50 isolates were three which changed to be nine different patterns after exposure to disinfectants. Unjustifiable use of disinfectants might give a chance for survival and multiplication of pathogenic bacteria to develop new resistance patterns to antibiotics in use with a short time. These new resistance variants of bacteria which multiply in hospital environment could lead to serious epidemic conflicts particularly the epidemiological reporting and management. OBJECTIVE: The problem of hospital cross-infection due to contamination of disinfectants has been recognized elsewhere. The passage of bacteria through diluted disinfectants may not only bring about phenotypic changes in their antibiograms but also changes in phage susceptibility patterns. Contact with disinfectants in sublethal concentrations allows survival and multiplication of bacteria. METHODS AND MATERIALS: Serial passage, through disinfectants at subminimal inhibitory concentrations, induced antibiotic resistance in 18% of derived phenotypic variants of fifty strains of Pseudomonas aeruginosa which were isolated from diarrheal stools of infants in children's hospital. RESULTS: A proportion of these strains became susceptible to an increased number of antibiotics. The present study revealed that all the isolates were resistant to tetracycline and carbenicillin and 40% of these isolates became sensitive to both antibiotics after exposure to disinfectants. The exposure to disinfectants induced neomycin resistance among two isolates. The resistance patterns were three before disinfectants exposure which increased to be nine different patterns after exposure. No antibiotic resistance was transferred between P. aeruginosa and Escherichia coli K12 as a recipient strain. CONCLUSIONS: Almost 50% of the isolates tested became sensitive to tetracycline, carbenicillin and co-trimoxazole after exposure to disinfectants. The resistance patterns among the 50 isolates were three which changed to be nine different patterns after exposure to disinfectants. Unjustifiable use of disinfectants might give a chance for survival and multiplication of pathogenic bacteria to develop new resistance patterns to antibiotics in use with a short time. These new resistance variants of bacteria which multiply in hospital environment could lead to serious epidemic conflicts particularly the epidemiological reporting and management.202539536720
358490.9994Risk assessment of transmission of capsule-deficient, recombinant Actinobacillus pleuropneumoniae. Actinobacillus pleuropneumoniae is the etiologic agent of swine pleuropneumonia. Live, non-encapsulated vaccine strains have been shown to be efficacious in preventing acute disease in pigs. Recombinant DNA technology has the advantage of generating defined mutants that are safe, but maintain critical immunoprotective components. However, some recombinant strains have the disadvantage of containing antibiotic resistance genes that could be transferred to the animal's normal bacterial flora. Using DNA allelic exchange we have constructed attenuated, capsule-deficient mutants of A. pleuropneumoniae that contain a kanamycin resistance (Kn(R)) gene within the capsule locus of the genome. Following intranasal or intratracheal challenge of pigs the encapsulated parent strains colonized the challenge pigs, and were transmitted to contact pigs. In contrast, the capsule-deficient mutants were recovered only from the challenged pigs and not from contact pigs. Each kanamycin-resistant colony type recovered from the respiratory or gastrointestinal tracts of pigs challenged with the recombinant strain was screened with a probe specific for the Kn(R) gene. All probe-positive colonies were assayed for the specific Kn(R) gene by amplification of a 0.9 kb fragment of the antibiotic resistance gene by PCR. The 0.9 kb fragment was amplified from the recombinant A. pleuropneumoniae colonies, but not from any of the heterologous bacteria, indicating there was no evidence of transmission of the Kn(R) gene to resident bacteria. Following aerosol exposure of 276 pigs with recombinant, non-encapsulated A. pleuropneumoniae the recombinant bacteria were not recovered from any nasal swabs of 75 pigs tested or environmental samples 18 h after challenge. Statistical risk analysis, based on the number of kanamycin-resistant colonies screened, indicated that undetected transmission of the Kn(R) gene could still have occurred in at most 1.36% of kanamycin-resistant bacteria in contact with recombinant A. pleuropneumoniae. However, the overall risk of transmission to any resident bacteria was far lower. Our results indicate there was little risk of transmission of capsule-deficient, recombinant A. pleuropneumoniae or its Kn(R) gene to contact pigs or to the resident microflora.200415530740
3818100.9994A 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
3580110.9994Transfer of plasmid-mediated resistance to tetracycline in pathogenic bacteria from fish and aquaculture environments. The transferability of a large plasmid that harbors a tetracycline resistance gene tet(S), to fish and human pathogens was assessed using electrotransformation and conjugation. The plasmid, originally isolated from fish intestinal Lactococcus lactis ssp. lactis KYA-7, has potent antagonistic activity against the selected recipients (Lactococcus garvieae and Listeria monocytogenes), preventing conjugation. Therefore the tetracycline resistance determinant was transferred via electroporation to L. garvieae. A transformant clone was used as the donor in conjugation experiments with three different L. monocytogenes strains. To our knowledge, this is the first study showing the transfer of an antibiotic resistance plasmid from fish-associated lactic bacteria to L. monocytogenes, even if the donor L. garvieae was not the original host of the tetracycline resistance but experimentally created by electroporation. These results demonstrate that the antibiotic resistance genes in the fish intestinal bacteria have the potential to spread both to fish and human pathogens, posing a risk to aquaculture and consumer safety.200919236483
3575120.9994Susceptibility of Lactobacillus spp. to antimicrobial agents. Bacteria used as probiotics or in starter cultures may serve as hosts of antibiotic resistance genes, which can be transferred to pathogenic bacteria. Before launching a starter culture or a probiotic product into the market, it is therefore important to verify that the single bacterial isolates (strains) do not contain transferable resistance genes. A study has been undertaken to establish the levels of susceptibility of Lactobacillus spp. to various antimicrobial agents. This is a prerequisite for differentiating putative transferable resistance from natural resistance. A selection of 62 strains has been screened with the use of the Etest (ABBiodisk, Stockholm, Sweden) for their susceptibility to 25 antimicrobial agents. The strains belonged to the following species: Lactobacillus plantarum/pentosus, L. rhamnosus, L. paracasei, L. sakei, L. curvatus and species of the L. acidophilus group: L. johnsonii, L. crispatus, L. gasseri, and L. acidophilus. The results from the Etests have shown that the level of susceptibility to the antimicrobial agents is species-dependent. For the following antimicrobial agents, susceptibility varied several folds between species: vancomycin, teicoplanin, tetracycline, norfloxacin, ciprofloxacin, fusidic acid, and clindamycin. The differences between the species were more subtle for the rest of the tested antimicrobial agents. On the basis of the result, it was possible to suggest minimal inhibition concentrations (MICs) for the individual Lactobacillus species to be used as a microbiological breakpoint when screening strains for transferable resistance genes.200312505455
4572130.9994Effect of high pressure processing on changes in antibiotic resistance genes expression among strains from commercial starter cultures. This study analyzed the effect of high-pressure processing on the changes in resistance phenotype and expression of antibiotic resistance genes among strains from commercial starter cultures. After exposure to high pressure the expression of genes encoding resistance to aminoglycosides (aac(6')Ie-aph(2″)Ia and aph(3')-IIIa) decreased and the expression of genes encoding resistance to tetracyclines (tetM and tetW), ampicillin (blaZ) and chloramphenicol (cat) increased. Expression changes differed depending on the pressure variant chosen. The results obtained in the gene expression analysis correlated with the results of the phenotype patterns. To the best of the authors' knowledge, this is one of the first studies focused on changes in antibiotic resistance associated with a stress response among strains from commercial starter cultures. The results suggest that the food preservation techniques might affect the phenotype of antibiotic resistance among microorganisms that ultimately survive the process. This points to the need to verify strains used in the food industry for their antibiotic resistance as well as preservation parameters to prevent the further increase in antibiotic resistance in food borne strains.202336462825
3574140.9994Antibiotic resistances of starter and probiotic strains of lactic acid bacteria. The antibiotic resistances of 45 lactic acid bacteria strains belonging to the genera Lactobacillus, Streptococcus, Lactococcus, Pediococcus, and Leuconostoc were investigated. The objective was to determine antibiotic resistances and to verify these at the genetic level, as is currently suggested by the European "qualified presumption of safety" safety evaluation system for industrial starter strains. In addition, we sought to pinpoint possible problems in resistance determinations. Primers were used to PCR amplify genes involved in beta-lactam antibiotic, chloramphenicol, tetracycline, and erythromycin resistance. The presence of ribosomal protection protein genes and the ermB gene was also determined by using a gene probe. Generally, the incidences of erythromycin, chloramphenicol, tetracycline, or beta-lactam resistances in this study were low (<7%). In contrast, aminoglycoside (gentamicin and streptomycin) and ciprofloxacin resistances were higher than 70%, indicating that these may constitute intrinsic resistances. The genetic basis for ciprofloxacin resistance could not be verified, since no mutations typical of quinolone resistances were detected in the quinolone determining regions of the parC and gyrA genes. Some starter strains showed low-level ampicillin, penicillin, chloramphenicol, and tetracycline resistances, but no known resistance genes could be detected. Although some strains possessed the cat gene, none of these were phenotypically resistant to chloramphenicol. Using reverse transcription-PCR, these cat genes were shown to be silent under both inducing and noninducing conditions. Only Lactobacillus salivarius BFE 7441 possessed an ermB gene, which was encoded on the chromosome and which could not be transferred in filter-mating experiments. This study clearly demonstrates problems encountered with resistance testing, in that the breakpoint values are often inadequately identified, resistance genes may be present but silent, and the genetic basis and associated resistance mechanisms toward some antibiotics are still unknown.200717122388
4722150.9994Ciprofloxacin, amoxicillin, and aminoglycosides stimulate genetic and phenotypic changes in uropathogenic Escherichia coli strains. Antibiotic therapy and its consequences in bacterial and human aspects are widely investigated. Despite this, the emergence of new multidrug resistant bacteria is still a current problem. The scope of our work included the observation of changes among uropathogenic Escherichia coli strains after the treatment with a subinhibitory concentration of different antibiotics. The sensitive strains with or without virulence factors were incubated with amoxicillin, ciprofloxacin, gentamycin, or tobramycin. After each passage, the E. coli derivatives were compared to their wild types based on their susceptibility profiles, virulence genes, biofilm formations and the fingerprint profiles of PCR products amplified with using the (N)(6)(CGG)(4) primer. It turned out that antibiotics caused significant changes in the repertoire of bacterial virulence and biofilm formation, corresponding to acquired cross-resistance. The genomic changes among the studied bacteria were reflected in the changed profiles of the CGG-PCR products. In conclusion, the inappropriate application of antibiotics may cause a rapid rise of Multidrug Resistant (MDR) strains and give bacteria a chance to modulate their own pathogenicity. This phenomenon has been easily observed among uropathogenic E. coli strains and it is one of the main reasons for recurrent infections of the urinary tract.201930938219
4473160.9994The genetics of bacterial trimethoprim resistance in tropical areas. Resistance to trimethoprim in Gram-negative bacteria is largely manifested by two trimethoprim resistant dihydrofolate reductases (types I and II) encoded by genes originally located on resistance plasmids. Although trimethoprim resistance increased markedly after the clinical introduction of trimethoprim in the West, its spread has slowed and, in Edinburgh at least, has actually been declining. This reduction has been accompanied by the migration of a transposon, encoding the type I plasmid resistance gene, into the bacterial chromosome. In tropical areas, the incidence of trimethoprim resistance is very much higher. In Tanzania, it has spilled over into other bacteria outside the Enterobacteriaceae, but it was in India where the major problem existed. The majority (64%) of the Indian Enterobacteriaceae studied were resistant to the drug and most of the resistance genes were located on very large plasmids which also conferred resistance to many other antibacterial drugs. Some Indian plasmids carried a new trimethoprim resistance gene which is not detectable by conventional sensitivity tests and may be spreading unnoticed elsewhere. The proportion of trimethoprim resistance has been related to the volume of antibacterial drugs used.19873318025
4605170.9994Self-transmissible multidrug resistance plasmids in Escherichia coli of the normal intestinal flora of healthy swine. The resistance genes and their surroundings on three self-transmissible plasmids found in Escherichia coli of the enteric normal flora of healthy pigs have been characterized. The resistance elements found are similar to those commonly found in clinical isolates, like the transposon Tn1721 including the Tet A tetracycline resistance determinant, Tn10 with the Tet B determinant, Tn21 including a class 1 integron with the aadA1a cassette inserted, sulII encoding sulfonamide resistance, and the strA-strB genes responsible for streptomycin resistance. The plasmids were able to mobilize into various recipients, including swine pathogens, zoonotic bacteria, and commensals when conjugation experiments were carried out. Transfer of plasmids did not require optimal conditions concerning nutrition and temperature as plasmids were transferred in 0.9% saline at room temperature, suggesting that in vivo transfer might be possible. This study shows that transferable resistance elements appearing in normal flora bacteria from animals are similar to those commonly found in clinical isolates of human origin. The results indicate a probable communication between pathogens and the normal flora with respect to exchange of resistance factors.200111442346
3807180.9994Antimicrobial 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
3392190.9994Coselection for resistance to multiple late-generation human therapeutic antibiotics encoded on tetracycline resistance plasmids captured from uncultivated stream and soil bacteria. AIMS: Transmissible plasmids captured from stream and soil bacteria conferring resistance to tetracycline in Pseudomonas were evaluated for linked resistance to antibiotics used in the treatment of human infections. METHODS AND RESULTS: Cells released from stream sediments and soils were conjugated with a rifampicin-resistant, plasmid-free Pseudomonas putida recipient and selected on tetracycline and rifampicin. Each transconjugant contained a single 50-80 kb plasmid. Resistance to 11 antibiotics, in addition to tetracycline, was determined for the stream transconjugants using a modification of the Stokes disc diffusion antibiotic susceptibility assay. Nearly half of plasmids conferred resistance to six or more antibiotics. Resistance to streptomycin, gentamicin, and/or ticarcillin was conferred by a majority of the plasmids, and resistance to additional human clinical use antibiotics such as piperacillin/tazobactam, ciprofloxacin and aztreonam was observed. MICs of 16 antibiotics for representative sediment and soil transconjugants revealed large increases, relative to the Ps. putida recipient, for 11 of 16 antibiotics tested, including the expanded spectrum antibiotics cefotaxime and ceftazidime, as well as piperacillin/tazobactam, lomefloxacin and levofloxacin. CONCLUSIONS: Resistance to multiple antibiotics-including those typically used in clinical Pseudomonas and enterobacterial infections-can be conferred by transmissible plasmids in streams and soils. SIGNIFICANCE AND IMPACT OF STUDY: Selective pressure exerted by the use of one antibiotic, such as the common agricultural antibiotic tetracycline, may result in the persistence of linked genes conferring resistance to important human clinical antibiotics. This may impact the spread of resistance to human use antibiotics even in the absence of direct selection.201424797476