(From the August 2015 issue of Research Now)
Nearly half a million emergency room visits are the result of urinary tract infections (UTIs), according to the most recent national data on hospital discharges. UTIs can be caused by a number of different bacteria, but uropathogenic E. coli (UPEC) is a diverse group of E. coli strains known to cause more than 80% of UTIs. Recently, a team from the Center for Microbial Pathogenesis at The Research Institute at Nationwide Children’s Hospital discovered that UPEC biofilms, which possess protective antibiotic-resistant barriers, are maintained by DNABII proteins, an observation that could aid in the development of therapies to treat and even prevent bacterial infections.
“Biofilms are communities of bacteria that are adhered to a surface,” explains Steven D. Goodman, PhD, a principal investigator in the Center for Microbial Pathogenesis and lead author of the study, which was recently published in Molecular Microbiology. “When they are pathogenic or disease-causing, they are nearly impossible to eradicate because of the presence of an immune system and antibiotic-resistant extracellular matrix.”
According to Dr. Goodman, virtually all chronic and recurrent bacterial infections rely on the biofilm state as part of the disease course. The basis of this study revolves around a discovery from the laboratories of Lauren O. Bakaletz, PhD, director of the Center for Microbial Pathogenesis, and Dr. Goodman, who previously identified a linchpin protein – a member of the DNABII protein family – that binds extracellular DNA or eDNA, a common constituent of the extracellular matrix.
Previously, Drs. Bakaletz and Goodman demonstrated that using an antibody directed against these DNABII proteins resulted in the catastrophic collapse of bacterial biofilms and the release of the resident bacteria into a vulnerable form that was susceptible to the immune system and antimicrobials. This study examined what would happen if more DNABII proteins were supplemented to a growing biofilm.
Researchers built on work by Dr. Goodman and Sheryl Justice, PhD, co-author of the present study and a principal investigator in the Center for Microbial Pathogenesis, which showed that UPEC forms a formidable biofilm that is dependent on DNABII proteins in an in vivo animal model for urinary tract infections. Specifically, researchers formed UPEC biofilms in vitro in the presence or absence of added DNABII proteins that had been purified from not only UPEC, but from a variety of other bacterial pathogens as well. After the biofilms were grown for 24 hours, they were further tested for multiple attributes that are typical for biofilms and were examined by confocal laser scanning microscopy.
“We found that adding DNABII proteins from any bacterium doubled the size of UPEC biofilm, and this increase was reliant on eDNA being present,” explains Dr. Goodman. “Biofilms that had been pre-treated with an enzyme that degrades DNA failed to show this increase. Additionally, we found that the increased size of the biofilm was the result of driving free-floating bacteria into the biofilm matrix due to the presence of more of this critical structural material.”
Researchers tested these new biofilms and found that while they were larger, they were indistinguishable from the untreated UPEC biofilms.
“We concluded that not only was this essential protein limiting for biofilm production, but that the DNABII proteins were somewhat interchangeable,” says Dr. Goodman. “This indicated that when multi-species biofilms form, the eDNA-dependent matrix is likely conserved throughout the biofilm, allowing resident bacteria to interact productively while still protecting themselves from the outside world.”
Drs. Goodman, Bakaletz and their teams are very interested in expanding their knowledge of DNA structure to develop anti-DNABII protein-mediated approaches to disrupt biofilms that are better than the current ineffective therapeutic approaches. An understanding of the precise DNA structure could lead researchers to create simpler and more effective treatments for those who have chronic and recurrent bacterial infections.
Devaraj A, Justice SS, Bakaletz LO, Goodman SD. DNABII proteins play a central role in UPEC biofilm structure. Molecular Microbiology. 2015 April 16 [Epub ahead of print].
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].