Abstract
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.
Highlights
Escherichia coli (E. coli) belong to a group of pathogenic bacteria called gram-negative enterobacteria that includes Salmonella and Pseudomonas
Using the anti-LPS test strip we developed, the presences of purple color of the PVDF membrane-block would indicate the presence of LPS (Figure 1, inset)
When the color intensity was plotted against the concentrations of LPS, we found that the test strip can readily detect as low as 0.025 μg/mL of LPS from both E. coli and Salmonella while maintaining a dynamic range up to 200 μg/mL (Figure 1)
Summary
Escherichia coli (E. coli) belong to a group of pathogenic bacteria called gram-negative enterobacteria that includes Salmonella and Pseudomonas. E. coli and Salmonella found in contaminated foods can cause diarrhea, and even death in severe cases. E. coli and Salmonella account for more than 33% of all food-borne deaths [1]. E. coli causes a battery of diseases in which bacteria cause bloody diarrhea, or it leaves the intestine causing hemolytic uremic syndrome or thrombotic thrombocytopenic purpora (caused by E. coli O157:H7). E. coli and Salmonella contamination is especially common with certain household food products. These food items include but are not limited to: undercooked ground beef, vegetables, fruit that was fertilized with cow manure or has been washed with E. coli contaminated water, and fruit juices that have not been pasteurized. E. coli contaminated food can cause watery diarrhea. Other more severe and rare diseases are kidney failure, blindness, paralysis, Necrotizing Entero Colitis (NEC) and even death [2]
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