Phenol Coefficient: Standard Test Organism

The phenol coefficient is a measure used to compare the effectiveness of an antiseptic or disinfectant against a specific microorganism relative to phenol.

This coefficient is determined using a standardized laboratory test, often referred to as the phenol coefficient test.

Selecting the Test Organism

Historically, the standard organism designated for determining the phenol coefficient of disinfectants is Salmonella typhi (now often classified as *Salmonella enterica* serovar Typhi). This bacterium was chosen due to its relevance to public health (causing typhoid fever) and its consistent response to phenolic compounds.

• Salmonella typhi: The established standard organism for the phenol coefficient test. Its challenge allows for the comparison of disinfectant potency against phenol.
• Escherichia coli: While a common indicator organism, it is not the primary standard for the phenol coefficient.
• Candida albicans: This is a yeast, not a bacterium, and is typically used in antifungal testing, not for determining the phenol coefficient.
• Bacillus psychrophilus: This bacterium is known for its ability to grow at low temperatures and is not the standard for phenol coefficient testing.

Therefore, Salmonella typhi is the correct organism used for this determination.