Morganellaceae

Three Proteus species P. vulgaris, P. mirabilis, and P. penneri are opportunistic human pathogens, most commonly resulting in urinary tract infections.[2] Proteus vulgaris is commonly found in the intestine in various animals, and is shed into manure and soil.

About 10–15% of kidney stones are struvite stones, caused by alkalinization of the urine by the action of the urease enzyme of Proteus (and other) bacterial species.[3]

Providencia rettgeri is a common cause of traveller's diarrhea.[4]

Arsenophonus are endosymbiotic bacteria of various insects. In Nasonia parasitic wasps, Arsenophonus nasoniae acts as a reproductive manipulator by killing developing male wasps. This promotes an increased frequency of females in the population, which are the only biological sex that transmits Arsenophonus to the next generation. This type of interaction is referred to as "male-killing or son-killing."[5]

In flies and Lice, Arsenophonus-like bacteria act as primary symbionts faithfully transmitted from generation to generation.[5] In such relationships, the primary endosymbiont commonly supplements the host's metabolism by providing essential vitamins and nutrients that the host cannot synthesize itself.[6]

Photorhabdus and Xenorhabdus are bacterial associates of entomopathogenic nematodes. These nematodes infect insects and regurgitate their Photorhabdus or Xenorhabdus bacteria into the insect blood (also called hemolymph). The bacteria then suppress the insect's immune response, increasing the success of the nematode parasite. As a result of this highly effective evolutionary strategy, entomopathogenic nematodes are commonly used as biological control agents against insect pests like corn rootworms.[7]

Providencia are common bacterial species in the microbiome of Drosophila fruit flies.[8] In Drosophila melanogaster, Providencia rettgeri is a common pathogen isolated from wild-caught flies.[9] The fly immune system defends against this infection using a highly specific antimicrobial peptide that is required for defence against P. rettgeri, but not other Providencia species.[9][10]