INTRODUCTION AND BACKGROUND
We propose to conduct a study on Pseudomonas aeruginosa biofilms using nanoparticles for
the treatment of human chronic infections and cystic fibrosis. Pseudomonas aeruginosa is a
human pathogen that causes major problems in number of clinical settings but largely in
patients that have wounds or burns, those with dwelling medical devices and victims of cystic
fibrosis (Hanlon et al.,2001). This bacterium can grow as a biofilm, which acts as its best defense
mechanism against human immunity and conventional antibiotic therapy (Costerton et al.,
1999). Pseudomonas aeruginosa’s biofilm is important because it secretes a large amount of
exopolysaccrides that surrounds the cells, and form a glycocalyx (extracellular polymeric
material) which act as a significant barrier to the penetration of antibiotics that could kill the
pathogen (Hanlon et al., 2001). Therefore we will develop a method using copper-oxide
nanoparticles to target the biofilms produced by Pseudomonas aeruginosa’s to help deliver
antibiotics through the biofilm’s protective layer to eradicate the bacteria residing inside the
biofilm.
A Nanoparticle is any microscopic particle approximately less than 100 nanometers.
Nanoparticles can reorganize into nanowires which are nanometer scale wires made of
materials that conduct electricity (Tang et al., 2002). Nanomedicine as a field of science that
combines nanotechnology and medicine has emerged (Roy et al., 2005). There has been an
increasing use of nanoparticles in nanomedicine; especially those made from metal oxides for
example copper oxide nanoparticles or nanowires (Roy et al., 2005). Metal oxide nanowires
have been used due to the following reasons, their outstanding optical, magnetic and electrical
properties, their large surface area, easy to prepare and good stability (Li et al., 2010).
Nanomedicine has used nanoparticles as platforms for diagnostic probes, and effective targeted
therapy (Roy et al., 2005). The involvement of nanoparticles in drug delivery, gives us an
assumption that it’s possible to use copper oxide nanowires to carry antibodies through the
biofilm for the treatment of Pseudomonas aeruginosa pathogen.
There have been several attempts to kill Pseudomonas aeruginosa pathogen, but among all
studies, the biofilm seemed to be a major barrier to their success. Many studies have used
diffusion as a way to enter the pathogen’s biofilm layer to kill it, which method will be used in
this study aswel. This is because Pseudomonas aeruginosa’s biofilm has an extracellular matrix
that consists of numerous pores and channels, which can be used for diffusion of oxygen and
other ions (Costerton et al., 1999).
Although past studies and this study use diffusion as a way to go through the Pseudomonas
aeruginos’s biofilm, there is a contradiction in the way agents or treatments are transported
through this biofilm layer. Previous studies have targeted Pseudomonas aeruginos’s biofilm
only with metal toxicity, use of bacteriophage, and direct use of antibodies whereas this
proposed study happens to use copper oxide nanowires to carry antibodies through the biofilm.
Metal toxicity was used to kill the pathogen by diffusing metal cations such as copper, lead,
nickel and many others individually through the Pseudomonas aeruginos’s biofilm, (Harrison et
al., 2005). This study found that high exposure of specific metals such as copper to the biofilm
helped kill the biofilm bacterial populations, although the method was ineffective when
exposed with other metal cations (Harrison et al., 2005). This is because metal cations were
observed to ionically interact with the negatively charged phosphodiester and other groups
outside the biofilm, thereby retarding their diffusion through the Pseudomonas aeruginosa’s
biofilm layer to kill the pathogen (Harrison et al., 2005). The use of bacteriophage as a method
of treatment was found successful in treating many infections even those proved to be
resistant to antibiotics initially, for example, biofilm associated infections such as Pseudomonas
aeruginosa (Hanlon et al., 2001). This treatment diffused phages or viruses into the biofilm to
directly kill the pathogen inside this biofilm. However found problematic due to the presence of
an extracellular polymeric material that acted as a barrier to the virus’s entry through the
biofilm (Hanlon et al., 2001). And finally in another study, there was direct use of antibodies
most susceptible to Pseudomonas aeruginosa pathogen such as Ciproflaxin and Tombramycin
antibiotics for the treatment of the bacterium (Walters 111 et al., 2003). Ciproflaxin antibiotic
was observed to diffuse more readily than Tombramyacin antibiotics. This slow penetration or
diffusion of Tombramycin was also because these antibiotics bound to the extracellular matrix
of Pseudomonas aeruginosa’s biofilm creating a diffusion barrier (Walters 111 et al., 2003).
These three past studies are significant to our study because they all faced a diffusion barrier in
some way when trying to diffuse through Pseudomonas aeruginosa’s biofilm to kill the
pathogen. But neither of the treatments used copper oxide nanowires, which brings in the
importance of the use of nanowires in our proposed study hoping to be more successful than
the above treatments. The challenges found in past studies and the new discoveries in
nanomedicine, has led us to a new scientific question that will be addressed in the above
proposal as, Can copper oxide nanowires carrying antibiotics diffuse through the porous
structure of Pseudomonas aeruginosa’s biofilm? This question predicts that copper oxides
nanowires will help carry antibiotics susceptible to Pseudomonas aeruginosa’s pathogen
through the biofilm to kill the pathogen. Therefore the use of copper oxide nanowires in this
study, is supposed to reduce or remove the diffusion barrier through the biofilm that was found
in previous studies. And if these copper oxide nanowires diffuse through the biofilm successful,
this study predicts that, the antibodies attached to the nanowires will be released to kill the
pathogen inside the biofilm. Some of the alternate hypothesis to this proposed research
question could be, can copper oxide nanowires alone without antibiotics kill Pseudomonas
aeruginosa pathogen when it successfully diffuses through the biofilm? This hypothesis predicts
that there is no need to attach antibiotics to the nanowires if nanowires themselves are able to
get rid of the infection. Another alternate hypothesis could be, do copper oxide nanowires
attached to antibiotics diffuse right through the Pseudomonas aeruginosa’s biofilm without
killing the pathogen inside? This assumption could be possible because of the nature of the
biofilm’s extracellular layer, that is, they contain of in and out end pores and also because
infected bacterial cells mostly reside between these pores (Hanlon et al., 2001). Therefore
because of these reasons, this hypothesis predicts that these copper oxide nanowires carrying
antibiotics might diffuse right through the biofilm pores before releasing the antibiotics to kill
the pathogen. The above alternate hypotheses will be answered when the proposed research
question is applied and successfully carried out as below. And if successful, we will have found a
solution or treatment to many biofilm associated infections in all species such as cystic fibrosis.
Citations
Costerton JW, Stewart PS, Greenberg EP. 1999. Bacterial biofilms: A common cause of persistent
infections. Science. 284: 1318-22.
Hanlon WG, Denyer Ps, Olliff JC, Ibrahim JL. 2001. Reduction in exopolysaccharide viscosity as an aid to
bacteriophage penetration through Pseudomonas aeruginosa biofilms. American society for microbiology.
67: 2746-53.
Harrison JJ, Turner JR, Ceri H. 2005. Persister cells, the biofilm matrix and tolerance to metal cations in
biofilm and planktonic Pseudomonas aeruginosa. Biofilm research group. University of Calgary. 7: 98194.
Li Y, Zhang Q, Li J. 2010. Direct electrochemistry of hemoglobin immobilized in Cuo Nanowire bundles.
Talanta. 83: 162-66.
Tang Z, Kotov AN, Giersig M. 2002. Spontaneous organization of single ctde nanoparticles into
Luminescent nanowires. Science, new series. 297: 237-40.
Roy I, Ohulchanskyy YT, Bharali JD, Pudavar EH, Mistretta AR, Kaur N, Prasad NP, Rentzepis MP. 2005.
Optical tracking of organically modified silica nanoparticles as DNA carries. A nonviral, Nanomedicine
approach for Gene delivery. National academy of science of the United States of America. 102: 279-84.
Walters 111 CM, Roe F, Bugnicourt A, Franklin MJ, Stewart SP. 2003. Contributions of antibiotic
penetration, oxygen limitation, and low metabolic activity to tolerance of Pseudomonas aeruginosa
biofilms to Ciprofloxacin and Tobramyacin. American society for microbiology. 47: 317-23.