Adaptation of Amoeba Plate Test To Recover Legionella Strains from Clinical Samples

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Diagnostic Bacteriology

Background:

• Legionella isolation from respiratory samples is crucial for diagnosing Legionnaires' disease (LD).
• Current methods include axenic culture and liquid-based amoebic coculture (LAC).
• Optimizing recovery and turnaround time for Legionella diagnostics is essential.

Purpose of the Study:

• To adapt and evaluate the amoeba plate test (APT) for Legionella recovery from respiratory samples.
• To compare APT performance against axenic culture and LAC.
• To assess the impact of APT on diagnostic turnaround time.

Main Methods:

• Prospective study involving 133 respiratory samples from patients with LD.
• Comparison of three culture techniques: axenic culture, LAC, and APT.
• Evaluation of sensitivity and time to result for each method.

Main Results:

• Legionella was isolated from 46.6% of samples using the combined techniques.
• APT showed a sensitivity of 36.1%, comparable to axenic culture (42.9%) and superior to LAC (30.1%).
• APT significantly reduced median identification time to 4 days versus 7 days for LAC (P < 0.0001).

Conclusions:

• The amoeba plate test (APT) is a viable alternative to LAC for Legionella isolation.
• APT is particularly useful for samples with microbial overgrowth, such as sputum.
• APT can be implemented as a second-line technique to improve Legionella diagnostic yield and speed.