This small, straight Gram negative rod is motile by peritrichous flagella. Some strains produce gas from glucose. Growth is often nonpigmented at 35-37 C but can exhibit pigments (typically orange or red) at 25 C. Once thought to be harmless, it is now known to be an opportunistic pathogen that can cause pneumonia and urinary infections in compromised individuals. It can be isolated from many natural environments, from plants to soil to water, and is a frequent component of gut microflora of animals.