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    Is the family pet a risk for multidrug resistant infections? : thesis presented in fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2019) Toombs-Ruane, Leah
    Risk factors for community-acquired urinary tract infections (UTI) caused by extended-spectrum beta-lactamase-(ESBL) and AmpC beta-lactamase-(ACBL) producing Enterobacteriaceae were investigated in a prospective case-control study conducted between August 2015 and September 2017. Both cases and controls were from the Auckland and Northland regions of New Zealand. A telephone questionnaire was delivered to participants, and the results analysed for putative risk factors for human infections. Analysis was performed using regression models, including factors around pet ownership and any other animal contact. Faecal samples were submitted from some households; this included samples from both people and companion animals. Isolates collected from index case urine samples and ESBL- or ACBL-producing faecal samples were sequenced and subsequently analysed through a bioinformatics pipeline. Pet ownership was not found to be a risk for human ESBL- or AmpC-producing infections in this study. Another important finding of this research was that E. coli ST-131 was the most commonly found bacteria associated with the UTI from people recruited into the case-control study. The strains of this sequence type were likely to have entered New Zealand in multiple introductions over the last 20 years. Transmission of ESBL-/ACBLproducing E. coli was also suspected to have occurred within households where a person had been recently infected with the same bacteria (in the form of a UTI) caused by an ESBL-/ACBL-producing Enterobacteriaceae. The results of this study as a whole indicate that while pets may not be a major risk for acquisition of ESBL/ACBL-producing bacteria, they are likely to play a role in the transmission of bacteria within homes and the community, and therefore warrant attention in future work.
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    Epidemiological investigations of Shiga toxin-producing Escherichia coli (STEC) O157 And STEC O26 in New Zealand slaughter cattle, and the source attribution of human illness : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2014) Jaros, Patricia
    Shiga toxin-producing Escherichia coli O157:H7 (STEC O157) and related non-O157 STEC strains are enteric pathogens of significant public health concern worldwide, including New Zealand, causing clinical diseases ranging from diarrhoea and bloody diarrhoea to the life-threatening haemolytic uraemic syndrome. Cattle are considered the principal hosts and have been shown to be a source of STEC infection for both foodborne and environmental outbreaks of human diarrhoeal disease overseas. A series of observational studies were conducted to gain knowledge on the epidemiology of STEC O157 and STEC O26 in New Zealand slaughter cattle and assess the relative importance of cattle as a source of domestically-acquired STEC infections in humans. A repeated cross-sectional study conducted on four selected New Zealand beef slaughter plants provided detailed data on the prevalence and concentration of faecal shedding of STEC O157 and STEC O26 in 695 very young calves (4–7 days-old) and 895 adult cattle post-slaughter, identifying calves as more prevalent carriers of STEC. Findings of a subsequent cohort study, the first of its kind, provided evidence that for the 60 calves examined, transportation and lairage was not associated with increase of faecal shedding of E. coli O157 and O26 (STEC and non-STEC) but increase of cross-contamination of hides and carcasses post-slaughter. In a national prospective case-control study, 113 STEC cases and 506 random controls were interviewed for risk factor evaluation. The study findings implicate that environmental and animal contact, but not food, as significant exposure pathways for sporadic STEC infections in humans in New Zealand, and suggest ruminants as the most important source of infection. The molecular analysis of bovine and human STEC O157 isolates provided evidence for the historical introduction of a subset of the globally-circulating STEC O157 strains into New Zealand and ongoing localised transmission of STEC between cattle and humans. These findings will contribute to the development of a risk management strategy for STEC, similar to those already implemented for Campylobacter, Salmonella, and Listeria, which pose a high risk to public health and New Zealand’s access to international markets. Furthermore, risk factors identified in the case-control study will contribute to the design of public health interventions to reduce the incidence of STEC infections in New Zealand.
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    The host specificities of the lysogenic phage of Escherichia coli strain W and of phage Mu : a thesis presented in partial fulfilment of the requirements for the degree of M.Sc. in Microbiology at Massey University
    (Massey University, 1975) Rice, Malcolm
    Investigation of the bacteriophages present in the supernant of broth cultures of E.coli strain W have demonstrated a phage which plates on E.coli strain C, designated W.C, and another phage which plates on E.coli strain K, designated W.K. Both phages are very closely related. Differences were observed in the ability of their respective lysogens to exclude phage Plv. By available criteria, the phage W.K was found to be indistinguishable from phage Mu. As such, E.coli W may be a natural reservoir for phage Mu. Antisera were prepared against the phage W.C, W.K and Mu.K respectively. Neutralisation tests have demonstrated that the W phages and Mu phage may express one of several tail forms with respect to their tail components associated with host adsorption and therefore host specificity; the 'C' form is recognised by neutralising antibodies in the W.C antiserum, and the 'K' form is recognised by neutralising antibodies in the W.K and Mu.K antisera. Failure of any of these antisera to neutralise phage Mu propogated on Citrobacter freundii support the proposal for a third tail form 'F'. Observation of the plating behaviour of these phages, W.C, W.K and Mu.K, together with their neutralisation characteristics established that the phages can vary their host range specificities in two different ways: either they behave as host range mutants, plating on E.coli strains C and K with approximately equal frequencies - extended host range mutants; or they exhibit an alternate host-specificity type of behaviour, plating efficiently, only on the host in which they were last propogated. In this latter mode, a distinct event, or possibly two events, are required at the genome level to permit the observed change in the host range phenotype. As phages W.K and Mu.K appear identical, and phage W.C is very closely related to phage W.K, the events required for this phenotypic change to occur may as postulated include inversion of the G region of the phage DNA. Recent studies overseas, and as presented here, demonstrate that induced phage Mu (or phage W.K) are of two type, a G(+) form and a G(-) form, which differ in the orientation of their G region. The G(+) form is the form of the phage adsorbing to, and propogating lytically on the host bacterium E.coli K, the G(-) form has been found to adsorb to and propogate on a restrictionless strain of C. freundii. The G(-) form of phage Mu was not neutralised by the W.C or the Mu.K antisera. As such, it represents a third tail form that the phage Mu is capable of expressing. Evidence is also presented that all these phage, W.C, W.K and Mu.K, and their derivatives may express a mom-like function.