Final answer:
The only gram-negative bacteria among the lab samples can be identified by its red or pink color after Gram staining, thin peptidoglycan layer, and outer membrane containing lipopolysaccharides, unlike gram-positive bacteria which appear violet.
Step-by-step explanation:
To identify the gram-negative bacteria among four samples provided in the lab, it is necessary to understand the distinct characteristics that differentiate gram-negative bacteria from gram-positive ones. Gram-negative bacteria, by definition, are those that stain red with Gram stain due to their thin cell wall structure and a unique outer membrane containing lipopolysaccharides. One can recognize them by the red or pink color they exhibit after the Gram staining process, in contrast to gram-positive bacteria, which appear violet due to their thick peptidoglycan layer and lack of an outer membrane.
An example of a gram-negative bacterium is Escherichia coli, which appears as small, pink cells. Another identifying feature of gram-negative bacteria like Salmonella is their outer membrane that distinguishes them from gram-positive bacteria in the staining process. The cell-wall differences not only affect staining but are also indicative of the bacteria's structural and chemical composition, which can be crucial for determining the appropriate treatment in clinical settings. For example, the presence of lipopolysaccharides (LPS) in gram-negative bacteria is known for eliciting a strong immune response in humans.