Journal of Microbial & Biochemical Technology

Abstract

Anti-LPS Test Strip for the Detection of Food Contaminated with Salmonella and E. coli

Alvin Wang, Gabriel Molina, Victor Prima and Kevin K.W. Wang

Enterobacteria such as E. coli and Salmonella release an endotoxin, or lipopolysaccharide (LPS) that contributes to food poisoning symptoms. We hypothesize that LPS could be detected by a simple strip test, thus detecting the presence of enterobacteria in food. Here we described the development of a novel Anti-LPS detection strip test. Flexible polystyrene test strips with an absorbent poly (vinylidene fluoride) membrane adhered onto one end were exposed to various dilutions of food or bacterial sources. This was followed by the sequential incubation with a primary anti-LPS antibody, biotinylated secondary antibody, and streptavidin-linked enzyme alkaline phosphatase. The test strip was then developed with substrate 5-bromo-4-chloro-3-indolyl phosphate/nitroblue tetrazolium. Thus, the presence of purple precipitate product would indicate the presence of LPS and enterobacteria. The intensity or darkness of the color was quantified densitometrically and compared to LPS standard curve. The test strip assay was shown to readily detect as low as 25 ng/mL of purified LPS. In addition, theanti-LPS test strip assay can sensitively detect and quantify LPS released by live E. coli into culture media. Finally, three food groups (strawberry slices, spinach leaves and ground beef) were inoculated with E. coli for two time points at room temperature and then rinse water from each food preparation was subjected to the anti-LPS test strip assay. For all three food groups, the test strip assay can readily detect and quantify both 8 h and 24 h bacteria contamination over their respective uncontaminated controls. In conclusion, a simple prototype anti-LPS strip test was developed to readily detect enterobacteria contamination of common food.