Morganella morganii is a gram-negative rod commonly found in the environment and in the intestinal tracts of humans, mammals, and reptiles as normal flora. Despite its wide distribution, it is an uncommon cause of community-acquired infection and is most often encountered in postoperative and other nosocomial settings. M morganii infections respond well to appropriate antibiotic therapy; however, its natural resistance to many beta-lactam antibiotics may lead to delays in proper treatment.
The genus Morganella belongs to the tribe Proteeae of the family Enterobacteriaceae. The Proteeae, which also include the genera Proteus and Providencia, are important opportunistic pathogens capable of causing a wide variety of nosocomial infections. Currently, Morganella contains only a single species, M morganii, with 2 subspecies, morganii and sibonii. M morganii was previously classified under the genus Proteus as Proteus morganii.
In the late 1930s, M morganii was identified as a cause of urinary tract infections. Anecdotal reports of nosocomial infections began to appear in the literature in the 1950s and 1960s. Tucci and Isenberg reported a cluster epidemic of M morganii infections occurring over a 3-month period at a general hospital in 1977.  Of these infections, 61% were wound infections and 39% were urinary tract infections.
In 1984, McDermott reported 19 episodes of M morganii bacteremia in 18 patients during a 5.5-year period at a Veterans Administration hospital.  Eleven of the episodes occurred in surgical patients. The most common source of bacteremia was postoperative wound infection, and most infections occurred in patients who had received recent therapy with a beta-lactam antibiotic. Other important epidemiological risk factors in these studies included the presence of diabetes mellitus or other serious underlying diseases and advanced age.
In 2011, Kwon et al reported a case of a 65-year-old man with an infected aortic aneurysm in which the pathogen was M morganii. Diagnosis requires a high index of suspicion and imaging tests. 
M morganii has been associated with urinary tract infections, sepsis, pneumonia, wound infections, musculoskeletal infections, CNS infections, pericarditis, chorioamnionitis, endophthalmitis, empyema, and spontaneous bacterial peritonitis.
M morganii is a rare cause of severe invasive disease. It accounts for less than 1% of nosocomial infections. M morganii is usually opportunistic pathogen in hospitalized patients, particularly those on antibiotic therapy.
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