Laboratory Safety: *

The bacterial host used in most molecular biology and teaching laboratories is Escherichia coli. Since E. coli is often associated with outbreaks of disease, concern may arise over its safety. Unfortunately, media reports on E. coli disease do not contain the background information necessary for understanding this issue. There are many naturally occurring strains of E. coli. They inhabit the lower intestinal tracts of many animals, including humans, cattle, and swine. The strains found in different animals vary genetically, and can even vary between individuals of the same species.

However, some genetic variants of E. coli do cause disease. These variants contain genes not found in the harmless organisms. These genes encode toxins and proteins that enable the organism to invade cells within the body. The nature of the disease gene varies; E. coli strains with different disease genes have been associated with several diseases. Some E. coli have genes for enterotoxin, which causes the travelers' diarrhea often called "Montezuma's revenge." The E. coli that causes the sometimes fatal hemolytic-uremic syndrome have genes that encode a toxin different from the travelers' diarrhea toxin, and additionally have genes that enable them to invade and disrupt cells lining in the intestinal tract.

Laboratory strains of E. coli used in molecular biology research do not contain any of these disease genes and are harmless under normal conditions. If introduced into a cut or into the eye, laboratory strains could conceivably cause infection, so standard safety precautions should be taken when handling the organisms. Every day, hundreds of scientists and their students handle these organisms (many in a rather cavalier manner) without any notable consequences. We do not recommend cavalier handling of any strain of E. coli, but the history of scientists with the organism should be reassuring.

Tips for Handling E. coli:

When transferring liquid suspension cultures, keep nose and mouth away from the tube to avoid inhaling aerosol that might be created.

Wipe down lab bench with a 10% bleach solution, soapy water, or disinfectant at the end of laboratory sessions.

Wash hands before leaving laboratory.

Collect for treatment bacterial cultures, as well as tubes, pipettes, and any other materials that have come into contact with cultures. Disinfect these materials in one of two ways:

Treat with 10% bleach solution for 15 min or more before disposing in the regular garbage.

Autoclave at 121 °C for 15 min. Dispose of sterilized materials in the regular garbage.

*Adapted from the Teacher's Manual accompanying #21-1078 Petrifilm Transformation Kit, Carolina Biological Supply Co.

Chemical safety is a serious concern and great care has been taken to ensure that the chemicals used in this experiment pose as little health threat as possible. The chemicals included in this experiment are not toxic in the amounts used. For instance, compound A1, 2-nitrobenzaldehyde, is toxic to a typical adult when 18 g (18,000 mg) are consumed orally. In this lab, 54 mg of this compound will be used for the entire class. Despite the lack of toxicity, some of the compounds are irritating to the skin and eyes so standard laboratory safety procedures should be followed. Hands should be washed when leaving the laboratory, and any spills should be reported and cleaned up immediately. Material Safety Data Sheets (MSDS) for each compound used in this experiment have been provided.