Acinetobacter baumannii is not associated with osteomyelitis in a rat model: a pilot study
Stefan Collinet-Adler1, Carlos A Castro, Charles Gerald T Ledonio
1Division of Geographic Medicine and Infectious Diseases, Tufts Medical Center, Tufts University, Boston, MA, USA.
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.
Insights
Multidrug-resistant Acinetobacter baumannii (MDR AB) showed low virulence in rat bone defects, with Staphylococcus aureus (SA) dominating polymicrobial infections. MDR AB alone did not cause osteomyelitis, suggesting it may not contribute to bone infections.
Area of Science:
- Orthopedics
- Infectious Diseases
- Microbiology
Background:
- Multidrug-resistant Acinetobacter baumannii (MDR AB) is frequently found in infected segmental bone defects from combat trauma.
- While MDR AB poses challenges in visceral infections, its control in combat-related osteomyelitis is more common.
Purpose of the Study:
- To investigate the virulence of MDR AB in a rat model of segmental bone defects.
- To assess the impact of MDR AB alone and in combination with Staphylococcus aureus (SA) on bone defect infections.
Main Methods:
- Segmental defects were created in 60 rat femurs and inoculated with either MDR AB alone or MDR AB and SA.
- Bacteriology and radiographic assessments were performed at various time points to evaluate bacterial load and bone healing.
Main Results:
- MDR AB exhibited a significant decrease in bacterial load (3- to 5-log) regardless of inoculation type.
- In polymicrobial infections, SA predominated (59/60 animals), while MDR AB was rarely cultured (10/60 animals).
- MDR AB alone did not cause osteolysis; however, osteolysis was observed when SA was present. New bone formation occurred in 67% of defects with MDR AB alone.
Conclusions:
- MDR AB did not appear to cause or contribute to clinically significant osteomyelitis in this pilot study.
- The low virulence of MDR AB may explain the resolution of infections in combat-related bone defects.
- Further research is required to confirm the low virulence of MDR AB and its role in bone formation.
