923. Evaluation of Gene Disruption Mutants of Enterococcus faecalis in a Rat Model of Foreign Body Osteomyelitis
Session: Poster Abstract Session: Bacterial Pathogenesis
Saturday, October 22, 2011
Room: Poster Hall B1

Background: The importance of biofilm formation is being increasingly recognized in the pathogenesis of enterococcal infections. We previously performed screens to identify genetic determinants in the core genome of Enterococcus faecalis OG1RF (wild-type strain) that contribute to in vitro biofilm formation. We evaluated the following gene disruption mutants in a rabbit model of native aortic valve endocarditis: ΩahrC (transposon insertion in EF0983, a transcriptional regulator), ΩatlA (transposon insertion in EF0799, an autolysin), and Δeep (in-frame deletion of EF2380, a metalloprotease). ΩahrC and Δeep had significantly lower mean vegetation bacterial loads compared to the wild-type strain. We further tested these mutants in an osteomyelitis model.

Methods: Experimental chronic foreign body osteomyelitis was established in male Wistar rats. The proximal left tibia was surgically exposed, and a 3-mm hole was drilled into the medullary cavity. 108 colony forming units (CFU) of each isolate in 50 μL of sterile saline was injected into the bone. A 5-mm by 1-mm titanium wire was implanted. Four weeks after establishing infection, the rats were sacrificed. Pulverized bone and wire from each rat were placed separately in trypticase soy broth, vortexed and sonicated. Quantitative cultures of the bone and wire were performed. For statistical comparisons, we used the Wilcoxon rank sum test and Fisher's exact test.

Results: Cultures from rats infected with OG1RF (n=16), ΩahrC (n=10), ΩatlA (n=9), and Δeep (n=13) revealed 5.63, 5.40, 5.76, 5.68 log10 CFU/g of bone, and 3.93, 3.38, 4.57, 3.50 log10 CFU/g of wire, respectively (median values are reported). There was growth of enterococci from all wires in the OG1RF and Δeep groups. There was no growth of enterococci from 3/10 wires in the ΩahrC group (p=0.04), and 1/7 wires in the ΩatlA group (p=0.37).

Conclusion: In a rat model of osteomyelitis with retention of the foreign body, median enterococcal counts were not significantly different in animals infected with genetic mutants compared to E. faecalis OG1RF. Four weeks after establishing infection, a larger number of wires were negative for enterococci among animals infected with the ΩahrC mutant compared to the wild-type strain.

Subject Category: B. Bacterial pathogenesis, studies in animal models, molecular pathogenicity

Paschalis Vergidis1, Kristi L. Frank2, Gary M. Dunny2, Kerryl E. Greenwood Quaintance1, Patrick M. Schlievert2, Melissa J. Karau1, Suzannah M. Schmidt1, Jayawant N. Mandrekar1 and Robin Patel1, (1)Mayo Clinic, Rochester, MN, (2)University of Minnesota, Minneapolis, MN


P. Vergidis, None

K. L. Frank, None

G. M. Dunny, None

K. E. Greenwood Quaintance, None

P. M. Schlievert, None

M. J. Karau, None

S. M. Schmidt, None

J. N. Mandrekar, None

R. Patel, Pfizer: Grant Investigator, Research grant
Astellas: Grant Investigator, Research grant
Pocared: Grant Investigator, Research grant
Tornier: Grant Investigator, Research grant
Unlicensed US patent: Dr. Patel reports having an unlicensed U.S. patent pending for a method and an apparatus for sonication , Dr. Patel reports forgoing her right to receive royalties in the event that the patent is licensed

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.