ANTIBIOTIC RESISTANCE PROFILE OF ESCHERICHIA COLI ISOLATED FROM APPARENTLY HEALTHY DOMESTIC LIVESTOCK
CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Antibiotic usage is possibly the most important factor that promotes the emergence, selection and dissemination of antibiotic-resistant microorganisms in both veterinary and human medicine (Daniels et al., 2009). This acquired resistance occurs not only in pathogenic bacteria but also in the endogenous flora of exposed individuals (animals and humans). In intensively reared food animals, antibiotics may be administered to whole flocks rather than individual animals, and antimicrobial agents may be continuously fed to food animals such as poultry, goats, and cattle as growth promoters. Therefore, the antibiotic selection pressure for bacterial drug resistance in the animal is high and invariably their faecal flora contains a relatively high proportion of resistant bacteria (Whitworth et al., 2008; Literal et al., 2010).
The mechanism for spreading antibiotic resistance from animals to humans and vice versa remains controversial. Colonization of the intestinal tract with resistant Escherichia coli from chicken has been shown in human volunteers and there is historical evidence that animals are a reservoir for E. coli found in humans (Akwar et al., 2008; Kikuvi et al., 2010). Furthermore, 0spread of antibiotic resistance plasmids in E. coli from chickens to human handlers or of antibiotics – resistant microorganisms from animal to humans in various countries has been reported (Fang et al., 2008).
Resistance has been found in organisms common to both humans and animals, such as E. coli, Salmonella spp., Campylobacter spp. and Enterococcus among others (Davis et al., 2009). Due to the intricate balance of microflora of different habitats within the ecosystem, the transfer of resistance genes among bacteria occupying different habitats has the potential to occur frequently.
Resistance genes may be transferred vertically among bacteria of different genera and families or horizontally among different bacterial species within the same genus or family (Call et al., 2008). Widespread reliance on antimicrobials in food animal production has resulted in a considerable rise of antimicrobial-resistant strains of bacteria, complicating the treatment of infectious diseases in livestock, companion animals, and humans. This has led to important changes in the perceptions and priorities of regulatory agencies with regard to antimicrobial usage, particularly the use of antimicrobials as growth promoters and prophylactic agents. The selective pressure from the use of antimicrobial agents at sub therapeutic levels in dairy cattle could result in the selection of those strains that contain genes for antimicrobial resistance (Call et al., 2008).
1.2 Statement of problem
Molecular tools have been used to correlate animal associated pathogens with similar pathogens affecting humans and to clearly demonstrate transferable resistant genes carried by plasmids common to both animals and humans (Pitout et al., 2009; Ahmed et al., 2010). The possibility of antibiotic resistance genes circulating among humans, animals and the environment constitutes a direct threat to public health. This threat prompts research into emerging resistance mechanisms, novel approaches to antimicrobial efficacy and stringent control measures in the prudent use of antimicrobials in animal medicine.
In the developed world, the extensive use of antibiotics in agriculture, especially for prophylactic and growth promoting purposes, has generated much debate as to whether this practice contributes significantly to increased frequencies and dissemination of resistance genes into other ecosystems. In developing countries like Nigeria, antibiotics are used only when necessary, especially if the animals fall sick, and only the sick ones are treated in such cases. However, even in the absence of heavy use of antibiotics it is important to identify and monitor susceptibility profiles of bacterial isolates, particularly of commensal organisms. This, according to John and Fishman (1997), will provide information on resistance trends including emerging antibiotic resistance which are essential for clinical practice.
1.3 Aim of the study
The aim of this study is to investigate the antibiotic resistance profile of E. coli isolates from apparently healthy domestic livestock.
1.4 Objectives of the study
The specific objectives of the study include:
- To determine the antibiotic resistance profile for E. coli strains from the selected livestock
- To determine comparative resistance rates for E. coli strains from the different livestock
1.5 Scope of the Study
The scope of this study is limited to the investigation of antibiotics resistance profile of Eschirichia coli isolated from apparently healthy domestic livestock with particular interest in cattle, goats, swine and chicken in the absence of extensive use of antibiotics for both prophylaxis and growth promotion.