Development of a high-throughput method to evaluate serum bactericidal activity using bacterial ATP measurement as survival readout

PLoS One. 2017 Feb 13;12(2):e0172163. doi: 10.1371/journal.pone.0172163. eCollection 2017.

Abstract

Serum Bactericidal Activity (SBA) assay is the method of choice to evaluate the complement-mediated functional activity of both infection- and vaccine-induced antibodies. To perform a typical SBA assay, serial dilutions of sera are incubated with target bacterial strains and complement. The conventional SBA assay is based on plating on agar the SBA reaction mix and counting the surviving bacterial colony forming units (CFU) at each serum dilution. Even with automated colony counting, it is labor-intensive, time-consuming and not amenable for large-scale studies. Here, we have developed a luminescence-based SBA (L-SBA) method able to detect surviving bacteria by measuring their ATP. At the end of the SBA reaction, a single commercially available reagent is added to each well of the SBA plate, and the resulting luminescence signal is measured in a microplate reader. The signal obtained is proportional to the ATP present, which is directly proportional to the number of viable bacteria. Bactericidal activity is subsequently calculated. We demonstrated the applicability of L-SBA with multiple bacterial serovars, from 5 species: Citrobacter freundii, Salmonella enterica serovars Typhimurium and Enteritidis, Shigella flexneri serovars 2a and 3a, Shigella sonnei and Neisseria meningitidis. Serum bactericidal titers obtained by the luminescence readout method strongly correlate with the data obtained by the conventional agar plate-based assay, and the new assay is highly reproducible. L-SBA considerably shortens assay time, facilitates data acquisition and analysis and reduces the operator dependency, avoiding the plating and counting of CFUs. Our results demonstrate that L-SBA is a useful high-throughput bactericidal assay.

MeSH terms

  • Adenosine Triphosphate / immunology*
  • Adenosine Triphosphate / metabolism
  • Animals
  • Bacteria / immunology*
  • Bacteria / metabolism
  • Blood Bactericidal Activity / immunology*
  • Citrobacter freundii / immunology
  • Citrobacter freundii / metabolism
  • High-Throughput Screening Assays / methods*
  • Immune Sera / blood
  • Immune Sera / immunology*
  • Linear Models
  • Mice
  • Microbial Viability / immunology
  • Neisseria meningitidis / immunology
  • Neisseria meningitidis / metabolism
  • Reproducibility of Results
  • Salmonella enterica / immunology
  • Salmonella enterica / metabolism
  • Shigella flexneri / immunology
  • Shigella flexneri / metabolism
  • Shigella sonnei / immunology
  • Shigella sonnei / metabolism
  • Species Specificity

Substances

  • Immune Sera
  • Adenosine Triphosphate

Grants and funding

This study was sponsored by Novartis Vaccines Institute for Global Health, now acquired by the GSK group of companies. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.