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Isolation of Legionella pneumophila from blood with the BACTEC system: a prospective study yielding positive results
Abstract:
In a prospective study of 16 patients with Legionnaires disease confirmed by cultural isolation of Legionella pneumophila from the respiratory tract, 38% (6 of 16) had positive blood cultures. Daily subcultures were made onto buffered charcoal-yeast extract plates from 6B aerobic and 7C anaerobic BACTEC blood culture bottles (Johnston Laboratories, Inc., Towson, Md.). Isolation of L. pneumophila was achieved from both aerobic and anaerobic bottles. L. pneumophila growth indices failed to exceed the BACTEC threshold limits; thus, the organism would have been overlooked despite its presence in the blood culture bottles. Bacteremic patients had statistically significant higher quantities of L. pneumophila isolated from sputum and visualized on direct fluorescent antibody stains. Thus, the potential exists for improved diagnosis of Legionella infection by a relatively noninvasive procedure (blood culture) with an instrument already in use in many hospital laboratories.
Insights
Legionnaires disease diagnosis can be improved using blood cultures, even when the organism is not detected by standard growth indicators. This study found Legionella pneumophila in blood cultures of bacteremic patients, suggesting a valuable diagnostic approach.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Clinical Diagnostics
Background:
- Legionnaires disease is a severe pneumonia caused by Legionella pneumophila.
- Traditional diagnostic methods can be invasive or time-consuming.
- Early and accurate diagnosis is crucial for effective treatment.
Purpose of the Study:
- To evaluate the utility of blood cultures for diagnosing Legionnaires disease.
- To determine if Legionella pneumophila can be detected in blood cultures despite not meeting standard growth thresholds.
Main Methods:
- Prospective study of 16 patients with confirmed Legionnaires disease.
- Daily subcultures from aerobic and anaerobic BACTEC blood culture bottles.
- Analysis of L. pneumophila isolation and growth indices.
- Correlation with sputum analysis and direct fluorescent antibody stains.
Main Results:
- 38% of patients (6 of 16) had positive blood cultures for L. pneumophila.
- L. pneumophila was isolated from both aerobic and anaerobic bottles.
- Growth indices did not exceed BACTEC thresholds, indicating potential for missed detection.
- Bacteremic patients showed higher L. pneumophila quantities in sputum.
Conclusions:
- Blood cultures can aid in diagnosing Legionnaires disease, even with low bacterial loads.
- The BACTEC system may require adjusted thresholds or prolonged incubation for L. pneumophila detection.
- Blood culture offers a potentially improved, less invasive diagnostic method for Legionella infections.