Overlays of histograms for the Alexa Fluor® 647 Plus fluorescence of (A) Staphylococcus epidermis albus, (B) S. capitis, (C) S. aureus NCTC 8325, (D) S. hyicus (E) S.aureus pepper isolate and (F) S. xylosus stained with one of three primary anti-Bacillus endospore commercial antibodies combined with Alexa Fluor® 647 Plus-conjugated anti-rabbit secondary antibody or Alexa Fluor® 647 Plus-conjugated anti-rabbit secondary antibody alone. The colour codes for each of the histograms are: black – Bacillus cereus ensdospores stained with Genway primary and secondary antibodies; red – test species stained with Genway primary and secondary antibodies; blue – test species stained with EastCoast Bio primary and secondary antibodies; purple – test species stained with ViroStat primary and secondary antibodies; green – B. cereus stained with secondary antibody only;yellow – test species stained with secondary antibody only.
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This study was carried out by Dr Ultan Cronin and Dr Elaine O'Meara with the assistance of Ms Laura Girardeaux and supervised by Prof Martin Wilkinson. The project studied the factors influencing the binding of Staphylococcus protein A (SpA) of commercial antibodies raised against other microbial species. It was found that SpA-mediated antibody binding was strain-, growth-phase- and food matrix-dependent and influenced by simulated food processing treatments and cell adherence. After testing a number of ways to block protein A-mediated antibody binding, it was found that a product used for preventing the binding of antibodies to Fc receptors in mammalian cells also worked to block the SpA reaction.
This research points the way towards reducing an important source of false negatives in antibody-based assays for microbial detection.
The full paper is available here.