For the Health of It
Biofilm-Associated Endometritis
Reprinted with permission from Equine Disease Quarterly, Volume 28, Number 1
Bacterial endometritis (infection of the uterine
mucosa) that is refractory to traditional antimicro-
bial treatment is a significant challenge to the equine
breeding industry. A common survival strategy em-
ployed by bacterial pathogens is the formation of a bio-
film, which is a complex and dynamic structure com-
posed 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 endometri-
tis, we have clearly identified the ability of the bacteri-
um 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 mi-
croscopic 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 sim-
ple 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 resid-
ing within the biofilm.
8 • Walking On
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 antibiot-
ics and non-antibiotic agents alone or in combination
against Gram-negative bacteria (E.coli, K.pneumoniae
and P.aeruginosa). Datawould 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 du-
ration, 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 dis-
rupted and bacterial killing ensued. Assessment of an-
tibiotic 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
the non-antibiotic compounds.
A recent in vivo study evaluated the intrauterine
treatment of a preformed Pseudomonas aeruginosa
biofilm with a combination of ceftiofur and tris-EDTA
or ceftiofur and tris-EDTA alone. Of five mares treat-
ed with a combination of ceftiofur and tris-EDTA, all
effectively cleared the infection. This contrasted with
only two of five mares treated with ceftiofur and one
of five mares with tris-EDTA. The findings confirmed
greater efficiency in killing preformed biofilm within
the uterus by using a combination of antibiotic (ceftio-
fur) and non-antibiotic (tris-EDTA) agents.
Advances in our understanding of the significance
of biofilms in human and veterinary medi- cine will in
time lead to improved diagnostics and more effective
treatment modalities. Fortunately several therapeutic
options are currently available to clinicians for the
treatment of biofilm-associated equine bacterial endo-
metritiss.
CONTACT:
Ryan A . Ferris, DVM, MS, Dipl . ACT
[email protected]
Summit Equine Inc
Newberg, Oregon