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- Model II - Rapid E. coli O157 Strip Test

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The SMART-II Rapid E. coli O157 Strip Test is an immunochromatographic assay for the qualitative detection of E. coli O157 antigen in food. The test is designed to be used as an aid to the diagnosis of E. coli O157 and as an adjunct to culture methodology.

Test Summary:

E. coliis part of the healthy bowel fecal flora of both humans and lower animals; however, some strains of E. coli can cause severe and life-threatening diarrhea. Enterohemorrhagic E. coli (EHEC) O157:H7 was first identified as a pathogenic agent of human hemorrhagic colitis in the United States in 1982. Since then, outbreaks of human hemorrhagic colitis and hemolytic uremic syndrome (HUS) in association with E coli O157:H7 infections have been reported in Europe, Asia, and other continents including North America. EHEC strains are water and foodborne (1). They are most commonly ingested in undercooked ground beef contaminated at slaughterhouses where it has come into contact with bovine feces (2). Outbreaks associated with E. coli O157 have also occurred from unpasteurized fruit juices and apple cider (3). Person-to-person transmission is by the oral-fecal route.E. coliO157:H7 was also responsible for a major outbreak in 1993 in the Western United States. This was later traced to uncooked fast-food hamburgers. More recently in October 1996, outbreaks were reported due to unpasteurized apple juice (4). Recent studies have shown that beef and dairy cattle are natural reservoirs of E. coli O157:H7. The organism has been isolated from feces of asymptomatic cattle, raw milk, poultry, pork and lamb (5).

Because cattle frequently are colonized with verotoxic E coli (VTEC), foods of bovine origin are an important source of human infection’. During the slaughter of cattle, intestinal VTEC can contaminate the surface of meat. These surface contaminants can then be distributed throughout the meat when it is ground; and can survive to cause human disease if cooking time and temperature are inadequate (2). Investigations using assays for verotoxin have shown prevalence rates for VTEC of 36.4% in retail ground beef and 10.6% in retail ground pork specimens (3). Most reported epidemics of O157:H7 gastroenteritis have occurred after ingestion of undercooked ground beef. but outbreaks have also been linked to unpasteurized milk, cheese, yogurt, cold cuts, potatoes, contaminated water, fresh apple juice, unpasteurized apple cider, and person-to-person spread (4). Preparation of food on a surface that has been contaminated (e.g. by juices from thawing meat) can increase the risk of VTC infection.

Early and rapid detection of Escherichia coli O157:H7, the etiological agent of food poisoning associated diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome (HUS), is of high epidemiological and clinical importance for a number of reasons:

  1. Severity of the disease process in infants.
  2. Identification of colonized individuals, and
  3. Identification and control of the original source of the outbreak (6),(7),(8),(9).

Traditionally, isolation and Identification of this organism from clinical specimens is performed by standard culture methods using Sorbitol/MacConkey medium. Cultures are observed for the presence of non-sorbitol fermenting bacterial colonies which are subcultured to a non-selective medium and screened with a specific E. coli O157 antisera. The entire procedure may require more than 72 hours to complete.

E. coli O157:H7 contains a lipopolysaccharide (LPS) specific (O157) and a flagellar protein specific {H7} antigen as well as many other antigens. The LPS O157 antigen is the most important cellular target antigen in detection for identification studies. It is the major pathogenic antigen (so called endotoxin), elicits the most antigenic response and is the most predominant component on the cell surface {3-4% of the total bacterial cell weight). It is the most useful diagnostic approach to identify E. coli O157:H7 infection in humans, animals, and/or contaminated foods.

A strip test has been developed for detection of E. coli O157 in food specimens10. The test is run after incubating a food sample with a growth medium selective for E. coli O157. This test strip is comprised of colloidal gold particle-labeled anti-E. coli O157:H7 antibodies dried in a binding zone and immobilized antibodies in a capture zone. In this one-step procedure, the test strip is added to a test tube containing several drops of enriched specimen. The specimen migrates up the test strip and within minutes, the test strip is read. A POSITIVE result is indicated by a colored band at the test zone.

Introduction:Expected Values:

The SMART-II RapidE. coliO157 Strip Test is expected to show a Positive test result on those samples that exhibit a POSITIVE culture result forE. coliO157. The incidence of isolation may vary according to the geographical area.

Performance Characteristics:

Analytical Sensitivity:

The minimum number of cells detectable (analytical sensitivity of the test) is 3.3 x 104 cfu/mL.

Sensitivity:

The SMART-II Rapid E. coli O157 Strip Test can detect 1 cfu/25 g of sample when enriched for 8 hours at 42°C.

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