A Rapid Agar-Based Screening Method for Acyl Homoserine Lactone (AHL) Production in Clinical Isolates of Acinetobacter baumannii
Saipriya Kamaraju
Global Medical Education and Research Foundation, Lakdikapul, Telangana, India and Centre for Biotechnology, Institute of Science and Technology, Jawaharlal Nehru Technological University, Kukatpally, Telangana, India.
Venkataraman Sritharan *
Global Medical Education and Research Foundation, Lakdikapul, Telangana, India.
Archana Giri
Centre for Biotechnology, Institute of Science and Technology, Jawaharlal Nehru Technological University, Kukatpally, Telangana, India.
*Author to whom correspondence should be addressed.
Abstract
Background: The rapid emergence and dissemination of resistant pathogens threatens to compromise the effectiveness of conventional antimicrobial therapies, thereby increasing morbidity, mortality, and healthcare burden worldwide.
Aim: This study aims to evaluate a rapid agar-based phenotypic method for detecting acyl homoserine lactone (AHL) production in clinical isolates of Acinetobacter baumannii and to examine its distribution among carbapenem-resistant and carbapenem-sensitive isolates.
Place and Duration of Study: Department of Molecular Diagnostics and Biomarkers, Gleneagles Global Hospitals, Hyderabad, India.
Methodology: Seventy-two clinical isolates of A. baumannii were subjected to antimicrobial susceptibility testing against imipenem and meropenem using the Kirby–Bauer disk diffusion method and categorised as carbapenem-resistant (CRAB, n = 58) or carbapenem-sensitive (CSAB, n = 14). AHL production was screened using a rapid agar cross-streak biosensor assay employing Chromobacterium violaceum CV026 for short-chain AHL detection and Agrobacterium tumefaciens NTL4 (pZLR4) for long-chain AHL detection. Genotypic confirmation of the quorum-sensing synthase gene abaI was performed using PCR.
Results: None of the isolates produced short-chain AHLs detectable by CV026. However, all 72 isolates induced blue-green pigmentation in A. tumefaciens, indicating production of long-chain AHLs. Based on visual intensity scoring, 80% of isolates were categorised as strong AHL producers and 20% as weak producers. The abaI gene was detected in all isolates. Long-chain AHL production was observed in both CRAB and CSAB isolates without discrimination based on carbapenem resistance status.
Conclusion: The rapid agar-based biosensor method enables simple and effective detection of quorum-sensing signal molecules in clinical isolates of A. baumannii within 24 hours. Long-chain AHL production was universally observed among both carbapenem-resistant and carbapenem-sensitive isolates, indicating that quorum-sensing activity is a common phenotypic feature of clinical strains. Although AHL production did not distinguish carbapenem resistance status, this screening approach may serve as a practical tool for studying quorum–sensing–associated virulence and persistence mechanisms in routine microbiology laboratories.
Keywords: Antimicrobial resistance, quorum sensing, acyl homoserine lactone, antimicrobial susceptibility testing, Acinetobacter baumannii