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Genetic characterisation of resistance markers in sentinel E coli and Enterococcus in farm animals - OD2007

Description
Extensive use of antibiotics in the latter half of the 20th Century in both human medicine and animal husbandry has left a legacy of resistant bacteria that seriously threaten the continued efficacy of sntibacterial chemotherapy. Since the main driver of the evolution of these resistant strains in use of antibiotics, any action taken to reverse the seemingly inexorable increase in the numbers of resistant bacteria must include more sparing use of antibiotics. However, there is insufficient information to allow a confident prediction as to the consequences on resistant populations of bacteria limiting the use of antibiotics. The project is designed to reduce the paucity of information. An animal model (the pig) will ve used to investigate the persistence (or lack of) of resistance genes and their expression in marked strains of Escherichia coli and Enterococcus faecium (sentinel enteric bacteria). Marked strains will be established in experimental animals by use of one antibiotic (rifampicin). The stability of a selection of other, unrelated antibiotic resistance genes will be determined both during and following withdrawal of the selective antibiotic. Marked strains will carry a variety of resistance genes on a variety of genetic elements (plasmid, transposon, integron, gene cassette). Isolates that have appently lost a resistance determinant, as identified by reversion to a drug-sensitive phenotype, will be investigated by PCR analysis for carriage of he resistance gene. A positive PCR result will indicate carriage of a silences resistance gene. Sequencing will be used to determine whether loss of a resistance phenotype is due to gene mutation or some other form of gene silencing. In addition to the animsl model, bacterial samples from pig and poultry farms, obtained before, during and after antibiotic use will be sreened for expression of drug resistance and for the presence of particular resistance gened by PCR analysis. Strains failing to display a resistant phenotype but yielding a posistive PCR reaction will be analysed further, as for similar strains obtained from the animal mode, bacterial samples from pig and poultry farms, obtained before, during and after antibiotic use will be screened for expression of drug resistance and for the presence of particular resistance genes by PCR analysis. Strains failing to display a resistant phenotype but yielding a positive PCR reaction will be analysed further, as for similar strains obtained from the animal model.

The objectives of the work are:
1. To assess the longitudinal effects of antibiotic administration and subsequent withdrawal on the stability of expression of antibiotic resistance genes;
2. To determine what types of resistance determinants show the great genetic stability.
3. To determine to what extent loss of resistance phenotype can be attributed to silencing rather than loss of the resistance gene; and
4. To monitor the longitudinal effects of antibiotic administration and withdrawal on the expression of antibiotic resistance and the carriage of resistance determinants in the natural flora of arm animals.

The outcomes will be:
1. acquisition of knowledge of the distribution of resistance genes, irrespecitive of expression, among sentinel faecal bacteria obtained from farm animals (pigs and poultry);
2. quantitation of the level of carriage of silent resistance genes in sentinel bacteria of the GI tract of farm animals;
3. An understanding of the likely fates of antibiotic resistance genes and their carrier elements following discontinuation of antibiotic use in an animal model;
4. An understanding of the dynamics (persistance/loss/silencing) of resistance genes, selected and unselected, in populations of bacteria in animals;
5. Mathematic modelling that will predict likely trends with regard to fitness and persistence of antibiotic resistance bacteria once drug use has ceased.
Objective
01: To assess the longitudinal effects of antibiotic administration and withdrawal on the expression of antibiotic resistance related to the carriage of specific resistance genes.

02: To determine what types of resistantt determine what types of resistant determinants are the most genetically stable and model this data in terms of fitness, persistence and therapeutic outcome.

3. To determine to what extent loss of resistance phenotype may reflect silencing of the resistance gene rather than its physical loss or destruction.

4. To monitor the longitudinal effects of antibiotic administration and withdrawal on the expression of antibiotic resistance and the carriage of resistance determinants in the normal flora.
Project Documents
• Final Report : Genetic characterisation of resistance markers in sentinel E coli and Enterococcus in farm animals   (358k)
Time-Scale and Cost
From: 2001

To: 2005

Cost: £303,393
Contractor / Funded Organisations
University - Bristol
Keywords
Animal Diseases              
Animal Health              
Antimicrobial Resistance              
Bacteria              
Biotechnology              
E.coli O157              
Modelling              
Pigs              
Plants and Animals              
Fields of Study
Animal Health