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Clinical significance and taxonomy of Actinobacillus hominis
A Friis-Møller1, J J Christensen, V Fussing
1Department of Clinical Microbiology, H:S Hvidovre Hospital, DK-2650 Hvidovre, Denmark.
Abstract:
Clinical findings in 36 immunosuppressed patients with lower respiratory tract infection or bacteremia with Actinobacillus hominis are described. Animal contact was only recorded for three patients; nine patients died despite appropriate antimicrobial treatment. Although infections with this microorganism seem to be rare, the fact that 37 of 46 strains characterized in this study have been found in Copenhagen indicates that under-reporting may occur. A. hominis is phenotypically relatively homogeneous but can be difficult to differentiate from other Actinobacillus species unless extensive biochemical testing is performed. Mannose-positive strains of A. hominis are especially difficult to differentiate from A. equuli. Attempts to identify A. hominis by automatic identification systems may lead to misidentifications. Ribotyping and DNA-DNA hybridization data show that A. hominis is a homogeneous species clearly separated from other species within the genus Actinobacillus.
Insights
Actinobacillus hominis infections can cause severe respiratory illness and bacteremia in immunosuppressed patients. Despite appropriate treatment, mortality remains high, and misidentification by automated systems is common, suggesting potential under-reporting.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Clinical Bacteriology
Background:
- Actinobacillus hominis is a bacterial species that can cause infections in humans.
- Immunosuppressed individuals are particularly vulnerable to severe outcomes from A. hominis infections, including lower respiratory tract infections and bacteremia.
Purpose of the Study:
- To describe the clinical findings in immunosuppressed patients with Actinobacillus hominis infections.
- To assess the difficulty in differentiating A. hominis from other Actinobacillus species using phenotypic and genotypic methods.
- To highlight potential under-reporting of A. hominis infections.
Main Methods:
- Clinical data from 36 immunosuppressed patients with A. hominis infection were reviewed.
- Phenotypic characterization of 46 A. hominis strains was performed.
- Genotypic methods, including ribotyping and DNA-DNA hybridization, were used to confirm species identification and assess homogeneity.
Main Results:
- 36 immunosuppressed patients experienced lower respiratory tract infection or bacteremia due to A. hominis.
- Nine patients died despite appropriate antimicrobial therapy.
- 37 out of 46 characterized strains were identified in Copenhagen, suggesting potential under-reporting.
- Phenotypic homogeneity of A. hominis makes differentiation from other species, like A. equuli, challenging, especially with mannose-positive strains.
- Automated identification systems may misidentify A. hominis.
- Ribotyping and DNA-DNA hybridization confirmed A. hominis as a distinct and homogeneous species within the Actinobacillus genus.
Conclusions:
- Actinobacillus hominis can cause severe, potentially fatal infections in immunosuppressed patients.
- Accurate identification of A. hominis requires extensive biochemical testing and can be problematic with automated systems.
- The prevalence of A. hominis infections may be underestimated due to identification challenges and potential under-reporting.