Escherichia coli is a common gram-negative, rod-shaped bacterium that normally lives in the intestines of humans and animals. While most E. coli strains are harmless, some can cause intestinal illness. Pseudomonas aeruginosa is an opportunistic pathogen that is commonly found in soil, water, and hospitals. It can cause disease in immunocompromised or cystic fibrosis patients. Salmonella enterica serovar enteritidis is a gram-negative rod and facultative anaerobe often associated with egg-borne salmonellosis in humans. It can infect the ovaries of hens and some strains are antibiotic resistant.