Background: Multidrug resistant Acinetobacter baumannii (MDR AB) with and without Staphylococcus aureus (SA) is a commonly isolated organism in infected segmental bone defects in combat-related trauma in Iraq and Afghanistan. Although MDR AB in visceral infections is a therapeutic challenge, control of infection appears more common for combat-related osteomyelitis. Questions/purposes: Using a rat model, we explored the virulence of MDR AB in segmental bone defects alone and in combination with SA. Methods: Segmental defects in 60 rat femurs were created, stabilized, and inoculated with MDR AB alone and 60 with MDR AB and SA. We performed qualitative and quantitative bacteriology and radiographic assessments at 2, 4, and 8 weeks for MDR AB and at 1, 2, and 3 weeks for MDR AB and SA. Results: Quantitative bacteriology revealed a 3-to 5-log decrease in MDR AB from the initial inoculum. After polymicrobial inoculation, only 10 of 60 animals had positive cultures for MDR AB, whereas 59 of 60 animals had positive cultures for SA. Recovered SA were 2 to 5 log greater than the initial inoculum, while there again was a 3-to 5-log decrease in MDR AB. MDR AB alone did not cause bony lysis, but there was radiographic evidence of new bone formation in 67% of the segmental defects. Osteolysis was noted with MDR AB and SA. Conclusions: MDR AB did not appear to cause or contribute to clinically apparent osteomyelitis in this pilot study. Clinical Relevance: Resolution of infections in combat-related segmental bone defects inoculated with MDR AB may be attributable to low virulence. Additional studies are needed to confirm low virulence and bone formation with MDR AB.
Bibliographical noteFunding Information:
One or more of the authors (DTT) received funding from the US Army Medical Research and Material Command under Contract No. W81XWH-07-1-0195; one of the authors (SC-A) receives research support through the National Institutes of Health grant 2 T32 AI007329-16; one of the authors (CGTL) receives research support from Medtronic, the Scoliosis Research Society, and the Spinal Research Foundation. The views, opinions, and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy, or decision unless so designated by other documentation. Approval for all procedures involving animals was obtained through the Institutional Animal Care and Use Committee in accordance with the guidelines of the Association for the Assessment and Accreditation of Laboratory Animal Care. This work was performed at the Minneapolis Medical Research Foundation, Minneapolis, MN, USA.