| الوصف: |
The use of antimicrobials in Australian beef feedlots is essential for preventing disease, as well as for modifying the rumen for grain-based diets to reduce greenhouse gases. The purpose of regular monitoring of antimicrobial resistance through surveillance is to maintain the lifespan of currently registered antimicrobial classes, and in particular, shared drug classes (i.e. those registered for both human and animal treatment). In contrast, new antimicrobial drug classes are only being developed for the human market. It is critical that the Australian feedlot industry understands and embraces antimicrobial stewardship guidelines to continue to effectively treat and prevent bacterial infections in cattle. Bovine Respiratory Disease (BRD) is the major cause of morbidity and mortality in feedlot cattle, both in Australia and internationally. BRD has been described as a composite of infections involving the respiratory system of cattle. The main bacterial causes of BRD are Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni, and antimicrobial agents used to treat BRD in Australia include tulathromycin, tetracycline, tilmicosin, and ceftiofur. Internationally, antimicrobial resistance (AMR) has rapidly developed in BRD pathogens in North America due to the widespread dissemination of mobile genetic elements referred to as Integrative Conjugative Elements (ICEs) containing multiple resistance genes. Unfortunately, there is very little research on antimicrobial resistance in BRD pathogens in Australian feedlots, and only two previous studies (1993 and 2014). The main aim of this thesis was to determine the antimicrobial susceptibility of Australian BRD isolates obtained between 2004-2019, determine the genetic basis of resistance, and undertake a molecular epidemiological investigation. A preliminary investigation on the susceptibility of a small collection of BRD pathogens, obtained from diagnostic submissions to veterinary diagnostic laboratories (VDLs) between 2004 and 2016, to gamithromycin, a ... |