Is E. coli ornithine positive or negative?

E. coli is ornithine positive.

Understanding E. coli and Ornithine Decarboxylase

Escherichia coli (E. coli) is a well-known bacterium often studied in microbiology. When it comes to specific biochemical tests used for bacterial identification, E. coli exhibits a distinct characteristic regarding its ability to decarboxylate certain amino acids.

Ornithine Decarboxylase Activity

Based on microbiological studies, E. coli possesses and expresses the enzyme ornithine decarboxylase. This enzyme is responsible for the removal of a carboxyl group from the amino acid ornithine, converting it into a diamine called putrescine. The production of putrescine increases the alkalinity (pH) of the growth medium, which is detected in laboratory tests.

According to a reference from September 2, 2015, "E. coli is arginine, lysine, and ornithine decarboxylase positive." This directly confirms that E. coli tests positive for ornithine decarboxylase activity.

Significance in Bacterial Identification

The ability of a bacterium to produce specific decarboxylase enzymes is a crucial characteristic used in diagnostic microbiology for the identification and differentiation of various bacterial species.

• Positive Result: Indicates the presence of the specific enzyme (e.g., ornithine decarboxylase).
• Negative Result: Indicates the absence of the enzyme or its lack of expression under the test conditions.

For E. coli, being ornithine positive, along with its other biochemical profiles, helps distinguish it from other Gram-negative bacteria that may be ornithine negative.

Key Decarboxylase Characteristics of E. coli

Beyond ornithine, E. coli is also known to be positive for other decarboxylase enzymes, which further aids in its identification.

These enzymatic activities play roles in the bacterium's metabolism and survival, often by helping to counteract acidic environments, thus making them valuable markers in clinical and environmental microbiology.