Lateral Flow Immunoassay Evaluated for Respiratory Samples

A rapid S. aureus–specific lateral flow immunochromatography (LFI) test has been developed using a specific monoclonal antibody to the S. aureus cell-wall peptidoglycan.

Scientists at King's College London (UK) used a LFI strip and modified the antigen target and capture/detection antibody to achieve greater sensitivity and specificity. They used an affinity-purified mouse monoclonal anti-S. aureus antibody that was raised specifically against S. aureus cell-wall peptidoglycan and conjugated with gold colloid. They used samples from six volunteers with severe asthma as well as spiked sputum and bronchial lavage specimens.

The LFI test was shown to be specific for S. aureus with no signal development for other Staphylococcal species or common respiratory pathogens. Evaluation of S. aureus isolates spiked into induced sputum and bronchoalveolar lavage samples derived from severe asthmatic patients showed a detection limit of 106 colony forming units (CFU)/mL for the LFI. The LFI test strips positively detected methicillin-sensitive S. aureus (MSSA), methicillin-resistant S. aureus (MRSA). The test was also shown to successfully detect S. aureus in one sample independently determined to be S. aureus positive by quantitative polymerase chain reaction.

The authors concluded that that an LFI detection limit of equal to or greater than 106 CFU/mL may be sufficiently sensitive to screen for preliminary information in a number of applications, but LFI tests with lower detection limits of less than 104 CFU/mL would be more clinically relevant. Further studies are currently ongoing to lower the detection limits of the LFI test and evaluate the robustness of the assay for a number of different applications. The ability of the LFI test to rapidly detect S. aureus in clinical respiratory samples suggests that it might be a useful platform for further development of point-of-care diagnostic applications. The study was published in the January 2013 edition of the journal Diagnostic Microbiology & Infectious Diseases.

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