Advanced Dental Admission Test (ADAT)

Which type of bacteria are characterized by an outer membrane containing Lipid A?

1. Actinobacteria

2. Gram-negative bacteria

3. Staphylococci

4. Mycobacteria

The correct answer is: Gram-negative bacteria

The answer is accurate because Gram-negative bacteria are defined by their unique cell wall structure, which is composed of a thin layer of peptidoglycan surrounded by an outer membrane. This outer membrane contains Lipid A, which is a component of lipopolysaccharide (LPS). Lipid A is a key molecule that contributes to the structural integrity of the bacterial cell wall and plays a critical role in the immune response of the host. When Gram-negative bacteria are subject to certain conditions, such as antibiotic treatment, Lipid A can be released into the host's bloodstream, potentially triggering a strong inflammatory response. This characteristic is not found in other types of bacteria listed, as they lack an outer membrane or have differing structural components in their membranes. For example, Actinobacteria and Mycobacteria have different cell wall structures that do not include Lipid A, and Staphylococci are classified as Gram-positive bacteria that do not possess an outer membrane at all. Understanding these structural differences is crucial for comprehending the behavior and pathogenic potential of various bacterial types.