Enterotube

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The Enterotube is an example of a rapid, multi test system used in identification of unknown oxidase- negative, gram- negative, rod shaped bacteria of the family Enterobacteriaceae. It consists of a tube with a flat side and contains 12 compartments for different biochemical tests. Although the manufacturer is continuously improving the accuracy of this system, it is worth noting that this system may sometimes yield false results.

Methods and Procedure

The Enterotube is used by first removing the caps from both ends to expose the inoculation wire. The wire is sterile and need not be flamed. The Enterotube is inoculated by touching the wire to a well isolated colony from a Petri plate. The wire is pulled and rotated from the other end to inoculate all the compartments and pushed all the way back in to reinoculate the compartments. The wire is then pulled until it reaches the indole compartment and is broken off using a pair of pliers. The perforation on the aerobic compartments must be punctured using a flamed inoculation needle or a similar device. The tube is finally recapped and incubated at 37 degrees Celsius for 24 hours.Methods and Procedure

Reading the Enterotube Results

After 24 hours of incubation, any color change is recorded in the ID card provided by the manufacturer or from a separate vendor. The appropriate reagents are added to the indole and Voges-Proskauer compartments and their results are recorded in the same ID card. The numerical values of the positive tests are added in their appropriate sections to yield a 5-digit ID for the organism being tested. This 5-digit number is looked up in a reference book or computer software to determine the identity of the bacteria.

Accuracy and Limitations

Although the manufacturer has improved on the accuracy of the Enterotube since it was first produced in the early 1970’s, it must be noted that the identification results is not always correct and may require retesting. In one study, the first testing of the Enterotube correctly identified only 90.6% of the unknown bacterial cultures. Repeat testing using the Enterotube identified 97.9% of the bacterial cultures. (a total of 235 organisms were used). Above all, the Enterotube™ II system is considered an acceptable method of identifying pathogens from the family Enterobacteriaceae in a clinical lab setting.

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Burhan Ahmed, is currently the Editor-in-Chief at Medicalopedia.org.
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