Gram-negative bacteria are a group of bacteria characterized by their thin peptidoglycan layer and an outer membrane containing lipopolysaccharides. This structure makes them more resistant to certain antibiotics compared to Gram-positive bacteria, which have a thicker peptidoglycan layer. The outer membrane also acts as a barrier to many harmful substances, contributing to their survival in various environments. These bacteria can be found in diverse habitats, including soil, water, and the human body. Some Gram-negative bacteria are harmless or even beneficial, while others can cause serious infections, such as Escherichia coli and Salmonella. Understanding their structure and behavior is crucial for developing effective treatments.