Novel Targets for Treatment of Pseudomonas aeruginosa Biofilms - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 255

5 DNase

As stated earlier in this chapter, the matrix of the biofilm plays a very important role
in the tolerance to antimicrobials. In addition to its vital stabilizing effect
(Montanaro et al. 2011 ), eDNA has been shown to chelate cations in the biofilm
(i.e., aminoglycosides). Hence,

targeting eDNA seems to be an important

antibiofilm target.
In 2002, cleaving DNA with DNases was demonstrated to be effective in
preventing biofilm formation of P. aeruginosa in vitro in flow cells (Whitchurch
et al. 2002 ). However, DNase treatment of already existing biofilms only had an
effect on immature biofilms younger than 84 h. Older biofilms seemed to be
independent of the stability offered by DNA (e.g., more polysaccharide) or able
to inactivate the DNase (Whitchurch et al. 2002 ). Similar results were shown by
(Tetz et al. 2009 ), who also showed that coadministration of DNase together with
ʲ

-lactam antibiotics to a 24-h-old P. aeruginosa biofilm, significantly reduced the
biomass as compared to the control (Tetz et al. 2009 ).
DNases are thus promising drugs against biofilm formation and are already
administered to chronically infected CF patients with significant result (Frederiksen
et al. 2006 ; Alipour et al. 2009 ; Kaplan 2009 ). It has been shown that necrotic
PMNs release F-actin and DNA that via filament bundles enhance P. aeruginosa
biofilm formation in vitro (Walker et al. 2005 ; Parks et al. 2009 ). As in the case
without the presence of PMNs, inhibition of biofilm formation in the presence of
DNase was observed, but only in young biofilms. Interestingly, it was found that the
mature biofilms could be disrupted with a combination of the DNase and polyvalent
anion polyaspartat (Tang et al. 2005 ; Parks et al. 2009 ). It was hypothesized that the
bundles of F-actin and DNA are stabilized by multivalent cations (i.e., histones and
antimicrobial peptides) and are dissolved by multivalent anions such as
polyaspartate. The dissociation of the bundles increases the access of DNase to
cleavage sites and thus facilitates biofilm disruption (Tang et al. 2005 ; Tolker-
Nielsen and Hoiby 2009 ).
These finding might explain the efficacy of inhaled DNase in CF, which is
associated with a reduction in infectious burden and incidences of pulmonary
exacerbations (Robinson 2002 ; Frederiksen et al. 2006 ). The potential of DNase
treatment can be enhanced by the addition of anionic polymers to disrupt biofilms
in vivo. However, Tolker-Nielsen and Høiby foresee several problems with
polyvalent anions that need to be addressed before CF patients can be treated.
First, they speculate that the anions will either bind to or struggle to diffuse into the
sputum. Second, they point out that biofilms that give rise to PMN accumulation
and lung tissue damage are located in the respiratory part of the airways, where
inhalation therapy (i.e., DNase and polyaspartate) is out of reach (Tolker-Nielsen
and Hoiby 2009 ). If the above problems can be solved, this treatment will help
thousands of patients with CF, but it also seems to be promising for other biofilm
infections.