(From the October 2014 Research Now)
A new study published in Molecular Microbiology offers insight into the mechanisms by which bacterial biofilms — densely packed communities often containing disease-causing microbes that, when present, are critical in almost every known bacterial infection — can be disrupted or collapsed, rendering them susceptible to the immune system and antibiotics. The research, led by investigators in the Center for Microbial Pathogenesis in The Research Institute at Nationwide Children’s Hospital, determined how newly developed antibodies attach to a particular protein made by the bacteria and induce the biofilm to collapse.
Bacterial biofilms grow on living or inanimate surfaces and are found in virtually every infection of the body, from the middle ear (a condition called otitis media) to the teeth and the lungs. These biofilms secrete and surround themselves with a sticky substance called extracellular polymeric substance (EPS). EPS protects bacteria against the host’s immune response, such as antibodies, as well as therapeutics like antibiotics.
“Previously, we developed an antibody to the protein that secures the EPS scaffolding in biofilms,” says Lauren O. Bakaletz, PhD, co-lead author of the study and director of the Center for Microbial Pathogenesis. “Our recent work shows that the antibody causes the structural and catastrophic collapse of the biofilm by ‘capturing’ the scaffolding protein.”
Dr. Bakaletz, along with co-lead author Steven D. Goodman, PhD, also a principal investigator in the Center for Microbial Pathogenesis, grew lab-based biofilms of the model organism non-typeable Haemophilus influenza, since the bacterium causes multiple diseases of the upper and lower respiratory tracts, including middle ear infections, sinusitis and exacerbations of both cystic fibrosis and chronic obstructive pulmonary diseases. They then examined how antibodies to the key scaffolding protein worked and induced the biofilm to collapse.
“By taking images of the biofilms — which were stained to tell us if the bacteria were alive or dead — over time and during treatment with antibodies, we were able to figure out that the biofilm collapse was rapid, occurring within six hours,” Dr. Bakaletz explains. “We also determined that the effect was specific to the protein we were targeting, and that the antibodies worked to disrupt the biofilm even if they were not in direct contact with the biofilm.”
Prior studies had shown that the scaffolding protein, known as Integration Host Factor (IHF), stabilized the biofilm matrix and held it together, thereby protecting the bacteria. The researchers knew the antibody could bind IHF, but they wanted to know more about how this led to the collapse of the biofilm. Their data showed that the antibodies were able to induce disruption of the biofilm indirectly by capturing IHF protein that was “free” in the environment surrounding the biofilm. Specifically, as the dose of antibodies increased, they captured more “free” IHF and made the environment less ideal for the biofilm to remain intact. This caused the biofilm to collapse, releasing the bacteria and making them susceptible to antibiotics, other targeted antibodies and therapeutics.
Along with other investigators, Drs. Bakaletz and Goodman previously showed that biofilms formed by other important human bacterial pathogens could also be disrupted by antibodies targeted against IHF, in a variety of model organisms. Until these data were generated, however, there was a healthy amount of skepticism among the research community regarding any biofilm disruption method that appeared to have broad efficacy against so many different types of bacteria, the researchers say. But this recent publication in Molecular Microbiology enabled Drs. Bakaletz and Goodman to answer questions that other investigators had posed with respect to how the antibody worked, demonstrating the rapid capture and collapse mechanisms with key model organisms.
“We are currently conducting preclinical testing of this approach, using a number of model systems,” Dr. Bakaletz adds. “Our goal is to try to demonstrate real clinical feasibility in the not-too-distant future.” If these antibodies can be activated in patients’ bodies during an infection, it is possible that they can indirectly cause the microbial biofilms to collapse, allowing the body to defeat the invader and recover from the disease.
Brockson ME, Novotny LA, Mokrzan EM, Malhotra S, Jurcisek JA, Akbar R, Devaraj A, Goodman SD, Bakaletz LO. Evaluation of the kinetics and mechanism of action of anti-integration host factor-mediated disruption of bacterial biofilms.Molecular Microbiology. 2014 July 29. [Epub ahead of print].
Goodman SD, Obergfell KP, Jurcisek JA, Novotny LA, Downey JS, Ayala EA, Tjokro N, Li B, Justice SS, Bakaletz LO. Biofilms can be dispersed by focusing the immune system on a common family of bacterial nucleoid-associated proteins.Mucosal Immunology. 2011. 4:625-637.