Equine Disease Quarterly | EQUINE
The third quarter of 2018 saw cases of Eastern equine
encephalomyelitis confirmed in Canada (9) and the
USA (39), the majority of which were in unvaccinated
horses. Florida and Georgia were the most severely
affected states in the USA.
West Nile virus infection was reported by Canada (14
cases), France (6 cases), Greece (one case), Germany
(one case), Italy (105 cases), Romania (one case), RSA
(one case), and the USA (140 cases, many in the state
of Ohio). Australia confirmed one case of Hendra virus
infection in an unvaccinated horse on a premises in New
South Wales. A single case of equine encephalosis was
diagnosed in a horse in the RSA Province of Gauteng.
Biofilm-Associated Endometritis
Bacterial endometritis (infection of the uterine mucosa)
that is refractory to traditional antimicrobial treatment
is a significant challenge to the equine breeding
industry. A common survival strategy employed by
bacterial pathogens is the formation of a biofilm,
which is a complex and dynamic structure composed
of aggregates of bacteria surrounded by a thick
protective layer of exopolysaccharide. Biofilms confer
resistance to immune mediated clearance by reducing
the host’s ability to recognize infection. Additionally,
biofilms protect bacteria from antibiotics by providing
a diffusion barrier and creating a microenvironment
that slows down bacterial metabolism and replication,
which makes them more tolerant to antimicrobial
agents. Using a model of equine infectious
endometritis, we have clearly identified the ability
of the bacterium Pseudomonas aeruginosa to form
a biofilm within the uterus of the mare. The biofilm
forms in multiple locations with the greatest amount of
adherent bacteria occurring between the tissue folds
and in the uterine horns. This suggests that a traditional
guarded culture swab may not be ideal for detecting
biofilm-associated infections and a low volume lavage
may be a better diagnostic tool. The bacteria are in
greater numbers deep within the endometrial glands as
compared to the luminal surface. To be successful in
clearing these infections, treatment options will need
to be capable of penetrating deeper into the glands
and tissue. For microscopic visualization of biofilms
within endometrial biopsies, Bouin’s solution provides
significantly better preservation of the biofilm matrix
on the surface of the endometrium as compared to
traditional formalin fixation.
Bacteria residing in a biofilm can be up to 1,000
times more refractive to treatment with antibiotics
as compared to free-living (planktonic) bacteria. The
simple administration of more or a higher concentration
of antibiotics has failed to eliminate chronic biofilm
infections in both human and veterinary medicine.
The goal in treating a biofilm-associated infection is
to disrupt the biofilm material and kill the bacteria
residing within the biofilm.
A series of in vitro (within a laboratory setting, such as
in a test tube) studies were conducted to assess biofilm
dispersal and/or bacterial killing by antibiotics and
non-antibiotic agents alone or in combination against
Gram-negative bacteria (E. coli, K. pneumoniae and
P. aeruginosa). Data would indicate that antibiotics
and non-antibiotic agents are more effective against
biofilms if administered concurrently. When dealing
with bacterial infections protected in biofilms, the
treatment period should be at least 72 hours in
duration, with repeated treatments every 24 hours (i.e.
a uterine infusion of the selected combination once
every 24 hours for three consecutive days). Following
this treatment protocol, the biofilm was completed
disrupted and bacterial killing ensued. Assessment of
antibiotic sensitivity of the offending pathogen(s) is still
important as inherent genetic resistance of the bacteria
involved will not be overcome solely by the addition of
• Volume 21 Issue 1 | March 2019 •
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