Statistics for Occurrence and distribution of extended spectrum β-lactamase and AmpC-β-lactamase-producing Enterobacteriaceae and methicillin resistant Staphylococcus aureus in companion animals in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Microbiology, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand