Download Abstract

Plasmid profiles of Moraxella bovis and the development of a model of infectious
bovine keratoconjunctivitis
Master of Philosophy in Veterinary Science
1995
Kelly-Maree Jordan Edens
Abstract
Ninety-four isolates of Moraxella bovis were examined on the basis of their plasmid
profile after chromosomal DNA had been removed. They were grouped according to
their country of origin, which included strains from New Zealand, Australia, America
and Britain. The extraction of plasmids was based on that used by McDonald et al
(1986). The molecular size of the plasmids was demonstrated by the electrophoretic
mobility of plasmid DNA on agarose gel (0.05%). All New Zealand isolates contained
1-4 plasmids, most contained 4 plasmids ranging from small (1-10kb) to large
(>23kb). In those isolates which contained a single plasmid, it was usually very large.
Australian isolates generally carried less plasmids with large plasmids commonly
observed. A single American isolate and a number of British isolates did not contain
any plasmids and this was confirmed by a second method of extraction (Marshall et
al, 1985). No plasmid profiles were distinctively unique to their country of origin,
subtle differences could be seen. Isolates from the same outbreak demonstrated
identical plasmid profiles. Isolates from recurrent outbreaks in the same group of
cattle also had identical isolates obtained from unrelated geographically separated
outbreaks.
The development of an in vitro model of infectious bovine keratoconjunctivitis (IBK)
was investigated by inflicting damage on corneas, collected from the freezing works,
followed by inoculation of M. bovis broth culture. With the eyeball in the frame the
corneal epithelium was physically damaged with an artist’s 10 mm oil brush using a
range of protocols. The most efficient method was found to be turning the brush once
while the tip rested on the corneal surface. Scanning electron microscopy illustrated
the damage caused by M. bovis when the surface was damaged prior to inoculation
and the extent to which M. bovis adhered and/or penetrated. This method was then
applied to an animal model (in vivo). A group of 10 animals had their right eyes
abraded with a brush and inoculated with M. bovis, while their left eye only had
M. bovis inoculated. The control animals (5) had their right eyes abraded and their left
eyes left untreated. For animal welfare reasons, topical treatment was administered to
eyes which developed clinical signs of IBK. After two weeks observation, 8 of 10
eyes which had been abraded and received inoculation with M. bovis had shown the
initial signs of infection. M. bovis was re-isolated from 9 of 10 eyes. It is suggested
that this model could be used to evaluate the efficacy of vaccines or treatments for
IBK because it is reproducible. Quick, relatively simple to carry out and cheaper than
the methods previously and presently used.