Final answer:
The pathogens E. coli, Shigella sonnei, and Salmonella enterica are part of the Gammaproteobacteria, a diverse class of gram-negative bacteria responsible for various human diseases.
Step-by-step explanation:
The group of gram-negative bacteria that includes the pathogens E. coli, Shigella sonnei, and Salmonella enterica fall into the category of Gammaproteobacteria. This class of Proteobacteria consists of a diverse collection of organisms, many of which are known to cause diseases in humans. Among these, E. coli is notable for its presence in the normal microbiota of the colon, although certain strains can become pathogenic and cause significant health issues.