Bile-Tolerant Gram-Negative Bacteria

Bile-tolerant gram-negative bacteria can survive in the human stomach (bile-tolerant) and they have a protective cell wall that causes them to turn red when subjected to the gram staining process (gram-negative). This combination of characteristics makes BTGN bacteria potentially harmful to humans.

Gram-negative bacteria thrive in virtually all environments that support life. They are an important medical challenge because the outer membrane that protects them from gram staining also protects them from many antibiotics, detergents, and anti-microbial enzymes produced by the immune system. When immune cells lyse gram-negative bacteria cells it can cause a toxic reaction that can include an increased respiratory rate, and low blood pressure — a life-threatening condition known as septic shock.

What organisms are classified as BTGN?

According to the United States Pharmacopeia’s website, “There is no strict definition of this group of micro-organisms. They are defined operationally as those micro-organisms that show growth in the stated conditions on Violet Red Bile Glucose Agar medium. They include, Gram-negative bacteria that grow in the presence of bile salts, non-lactose fermenting but able to utilize glucose, e.g., some Bile Tolerant Gram-Negative Bacteria includes members of the family Enterobacteriaceae, Pseudomonads and Aeromonas.”

Because there is no strict definition for BTGN, and the operational definition is based on growth in a specific medium, developing a DNA-based test is difficult. Therefore, research has concluded that the species covered in Total Enterobacteriaceae assay and the Pseudomonas aeruginosa assay sufficiently cover BTGN species.