Preview

PDF (Whole thesis) whole_SoltaniMe...pdf | Download (11MB) Available under University of Tasmania Standard License. | Preview

Abstract

The physiological requirements of Australian isolates of four species of
Cytophaga!Flexibacter-like bacteria(CFLB), namely Cytophaga johnsonae (CJ),
Cytophaga psychrophila (CP), Flexibacter columnaris (FC) and Ffexibacter
maritimus (FM) were studied. Also, the pathogenesis and chemotherapy of some
diseases caused by these bacteria were investigated.
In vitro responses of the organisms to environmental conditions, including
temperature, salinity and pH, showed that all species have psychrotrophic
tendencies with CJ and CP growing at the lowest temperature, FC the highest and
CP having the narrowest range of temperature for growth. FM preferred full salinity
(seawater) for growth with no growth in the presence of NaCl alone, whereas' the
other three strains preferred no salinity for growth. All species grew well over a
similar pH range.
In vivo assessment of susceptibility of a number of freshwater species of fish
including barramundi (Lates calcarifer), goldfish (Carassius auratus), guppy
(Poecilia reticulata) and rainbow trout ( Oncorhynchus mykiss) to infections by CJ
and CP resulted in occurrence of infection by CJ only in barramundi. This occurred
during bath exposure of fish to the organism when it was coupled with thermal
stress and was achieved by rapidly reducing the maintenance temperature. No
infection could be induced in the other species tested.
Barramundi were more susceptible to FC infection than goldfish and the
disease was more severe at higher water temperatures than at lower ones.
Pathological features were similar in both species with acute necrosis of epithelial
surfaces.
Experimentally, FM induced infection in Atlantic salmon (Salmo salal),
rainbow trout and greenback flounder (Rhombosolea tapirina) only by bath
immersion at full or 15‰ salinity. Distribution of lesions, level of susceptibility and
temporal pattern of infection were similar in both salmonids, and larger Atlantic
salmon were more resistant to infection than smaller sizes. There was a great
consistency in histopathological features of experimental infection in salmonids and
in natural outbreaks in a number of captured species, including striped trumpeter
(Latris lineata), flounder, yellow-eyed mullet (Aldrichetta forsten) and commercial
salmonids. A remarkable lack of inflammatory response, consistent fragmentation
and degeneration of the epithelium, with infiltration of amorphous protein-like
materials and occasional intra-epithelial inflammatory cells, congestion and
haemorrhage were also observed, with invading bacterial cells colonizing dense
connective tissue and occasionally the underlying musculature. Scale loss, odema
and low degree of inflammation in scale pockets were evident, but the remaining
scales were intact.
In vitro antimicrobial activity of skin mucus obtained from naive fish against
these organisms gave variable results.
In vitro and in viva efficacies of commonly-used chemotherapeutants were
determined for these pathogens. Treatment of barramundi with oxolinic acid (OA)
as a bath (50 ppm) or by mouth (10 mg/kg b w) resulted in serum levels above the
minimum inhibitory concentration (MIG) for FC and produced significant clinical
efficacy (P<0.05). Amoxycillin (AM) was found to produce adequate serum levels
against FM, when used as a bath (200 ppm) or given orally (80 mg/kg b w) to
Atlantic salmon and rainbow trout, respectively. At these dose rates this antibiotic
was also clinically efficacious against this pathogen (P<0.05). Trimethoprim (TMP)
produced more than adequate serum levels for the control of FM when given as a
bath (50 ppm) or orally (10 mg/kg b w) to Atlantic salmon and rainbow trout,
respectively. TMP was significantly more protective than AM when tested in viva
(P<0.05). For CJ and CP the MIG values for OA and oxytetracycline were low,
whereas that for TMP was high. MIG values indicated CP strains were more
sensitive to AM and norfloxacin than was CJ.

Item Type:	Thesis - PhD
Authors/Creators:	Soltani, M
Keywords:	Bacteria, Bacterial diseases in fishes, Fishes
Copyright Information:	Copyright 1995 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (Ph.D.)--University of Tasmania, 1995. Includes bibliographical references (p. 149-175)
Item Statistics:	View statistics for this item

Actions (login required)

Item Control Page