| dc.description.abstract | Internal parasitism, a major cause of production losses in sheep, is routinely
controlled by anthelmintic drenches, however, alternative control strategies are
needed to combat the increasing resistance to these chemicals. [sic] A possible novel
method of controlling abomasal nematodes, such as Haemonchus contortus, is
manipulation of their essential resident bacteria, as is currently used to control
filarial nematodes. For the first time, bacteria have been identified in the
reproductive tract, as well as in the gut, of H contortus, using genetic
fingerprinting, light and electron microscopy and fluorescence in situ
hybridisation (FISH).
PCR-DGGE analysis showed that adult worms had less complex bacterial
profiles than did abomasal contents. L3, eggs and adult worms had similar
bacterial profiles; 16S rRNA sequences obtained from seven major common
DGGE bands were dominated by lactic acid bacterial and Proteobacterial
sequences. PCR-DGGE short sequences and clone libraries of nearly full length
sequences from all three life-cycle stages contained sequences belonging to
Weissella, Lactococcus, Leuconostoc and Streptococcus. Clone library
sequences were used to design group-, class- and species-specific FISH probes
to locate bacteria in the parasites.
The gut lumen of adult worms contained a mixed population of Grampositive
and Gram-negative bacteria, which appeared to be multiple
morphotypes in TEM images. The FISH probe (EUB338), which targets most
bacteria, hybridised with the gut bacteria, but only some of these were targeted
by Strc493, which targets most Streptococcus sp. and some Lactococcus sp.
Neither the lactic acid bacterial group- nor the Weissella species-specific probes
targeted any bacteria in the gut.
A single morphotype of Gram-positive bacteria was seen in large numbers in
the distal uterus of female H contortus in the TEM. They were close relatives of
either Lactococcus sp. or Streptococcus sp., as they were targeted by the FISH
probe Strc493. These bacteria seemed to be non-pathogenic to the nematodes, as adult female worms appeared to be healthy (nonnal in size and active) and carry
normal eggs within them. Their roles in worm biology are unknown.
A smaller number of bacteria were seen in the TEM in eggs within female
wom1s. They were closely related to Weissella confusa, as all were targeted by
lactic acid bacterial group- and Weissella species-specific probes, as well as by
EUB338. These bacteria were dispersed throughout the eggs, as they could be
seen at different focal panels in confocal microscopy. DNA fingerprinting and
visualisation of these bacteria in eggs strongly suggest they are maternally
transmitted endosymbionts.
As this study was carried out on a parasite strain which has been maintained
in the laboratory, practical applications of this research would depend on these
bacteria being present in field strains of H. contortus. | en |
