Sensitive enzyme-amplified electrical immunoassay for protein A-bearing Staphylococcus aureus in foods.
An amperometric electrochemical immunoassay specific for protein A-bearing Staphylococcus aureus was developed. The method was based on a sandwich immunosorbent assay and incorporated an enzyme amplification step, using a NAD-specific redox cycle generating NADH (C. H. Stanley, A. Johannsson, and C. H. Self, J. Immunol. Methods 83:89-95, 1985). Reduction of the mediator, ferricyanide, was dependent on the initial concentration of antigen. The final potential was measured by using a Pt disk electrode polarized at +0.8 V to the Ag/AgCl reference electrode. The assay was rapid (4 h) and generated protein A- and cell (S. aureus)-dependent signals. The system was highly sensitive and could detect 10 pg of protein A ml-1 and less than 100 CFU of S. aureus ml-1. Similar sensitivities were observed with S. aureus cultures inoculated into beef and milk, but the sensitivity was reduced slightly (ca. 10(3) g-1) with samples of Cheddar cheese.
Brooks
J L
JL
Department of Microbiology, Agricultural and Food Research Council Institute of Food Research, Shinfield, Reading, United Kingdom.
Mirhabibollahi
B
B
Kroll
R G
RG
D003124:Colorimetry; D004563:Electrochemistry; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005506:Food Contamination; D005516:Food Microbiology; D013205:Staphylococcal Protein A / Q000032:analysis*; D013211:Staphylococcus aureus / Q000302:isolation & purification*
D013205:Staphylococcal Protein A