Gram-negative bacteria are a group of bacteria characterized by their thin peptidoglycan cell wall and an outer membrane containing lipopolysaccharides. This structure makes them more resistant to certain antibiotics compared to Gram-positive bacteria. They are often identified using a staining technique called the Gram stain, which reveals their pink color under a microscope. These bacteria are commonly found in various environments, including soil, water, and the human gut. Some Gram-negative bacteria, such as Escherichia coli and Salmonella, can cause infections and diseases in humans. Understanding their structure and behavior is crucial for developing effective treatments and preventing infections.