Morganella morganii

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Morganella morganii is a species of gram-negative bacteria. M. morganii has a commensal relationship within the intestinal tracts of humans, mammals, and reptiles as normal flora. Morganella morganii, is a member of the tribe Proteeae (normal fecal flora that often causes infection in patients whose normal flora have been disturbed by antibiotic therapy of the family Enterobacteriaceae, with two subspecies: M. morganii and M. sibonii. Although M. morganii has a wide distribution, it is considered an uncommon cause of community-acquired infection and it is most often encountered in postoperative and other nosocomial infections such as urinary tract infections.

Historical Perspective

Morganella morganii was first described by a British bacteriologist H. de R. Morgan in 1906 as Morgan's bacillus. Morgan isolated the bacteria from stools of infants who were noted to have had "summer diarrhea". Later in 1919 Winslow et al., named Morgan's bacillus, Bacillus morganii. However in 1936, Rauss renamed B. morganii as Proteus morganii. Fulton in 1943, showed that B. columbensis and P. morganii were the same and defined the genus Morganella, due to the DNA-DNA hybridization. Genus Morganella has two species M. morganii and M.columbensis. However in 1962, a review article by Ewing reported that M. columbensis had been reidentified as Escherichia coli, therefore removing that organism from the genus Morganella.

Microbiology

• Morganella morganii is facultative anaerobic and oxidase-negative. M.morganii are colonies, that appear off-white and opaque in color, when grown on agar plate M. morganii are straight rods, about 0.6-0.7 µm in diameter and 1.0-1.7 µm in length. This organism moves by way of peritrichous flagella, but some strains do not form flagella at 30 °C.
• M. morganii is catalase-positive (meaning it can produce the enzyme catalase), meaning it is able to convert hydrogen peroxide (H2O2) to water and oxygen. This is a common enzyme found in most living organisms. In addition M. morganii, is indole test-positive representing this organism can split tryptophan to indole, pyruvate and ammonium. Methyl red tests positive in M.morganii, indicator dye that turns red in acidic solutions.
• Although a rare human pathogen, M morganii has been reported as a cause of urinary tract infections, nosocomial surgical wound infections, peritonitis, CNS infection, endophthalmitis, pneumonia, chorioamnionitis, neonatal sepsis, pyomyositis, necrotizing fasciitis, and arthritis. Numerous cases of nosocomial infection have been described, usually as postsurgical wound infections or urinary tract infections. Patients in whom bacteremia develops are typically immunocompromised, diabetic, or elderly or have at least one serious underlying disease.

Clinical Manifestation

• Morganella morganii has been regarded as a harmless opportunistic pathogen, however there are strains that carry "antibiotic-resistant plasmids" and have been associated with nosocomial outbreaks of infections.
• There have been several reports that M. morganii causes sepsis, ecthyma, endophthalmitis, chorioamnionitis, however more commonly urinary tract infections, soft tissue infections, septic arthritis, meningitis and bacteremia often with fatal consequences.
• In a rare case published in 2003, a patient present with bilateral necrosis of both upper and lower eyelids. Upon microbial analysis the areas were shown to have heavy growth of M. morganii.

Treatment

• Treatment of M. morganii infections may include:
  • Ticarcillin
  • Piperacillin
  • Ciprofloxacin
  • Third-generation and Fourth-generation cephalosporins

• A study conducted at the University Hospital at Heraklion, Crete, Greece showed a 92% success rate in the use of these antibiotics.
• However, there are M. morganii strains are resistant to penicillin, ampicillin/sulbactam, oxacillin, first-generation and second-generation cephalosporins, macrolides, lincosamides, fosfomycin, colistin, and polymyxin B. The emergence of highly resistant strains of M. morganii have been associated with use of third-generation cephalosporins.
• Polymicrobial infections are most abundantly caused by this microbe which additionally damages the skin, soft tissues, and urogenital tract can be cured through use of the aforementioned antibiotics.

Antimicrobial regimen

• Morganella morganii

• Preferred regimen (1): Imipenem 500 mg IV q6h
• Preferred regimen (2): Meropenem 1.0 g IV q8h (adjust dose if necessary for renal function).
• Note (1): Carbapenems are considered first line therapy due to inducible cephalosporinases, and presence of extended-spectrum beta-lactamases in some isolates
• Note (2): Duration of treatment for UTI (generally complicated) is 7 days and duration of treatment for bacteremia is 14 days
• Note (3): Tigecycline is not reliably effective
• Alternative Regimen (1): Cefepime 2.0 g IV q8-12h
• Alternative Regimen (2): Ciprofloxacin 500 mg PO/400 mg IV q12h
• Alternative Regimen (3): Piperacillin 3 g IV q6h
• Alternative Regimen (4): Ticarcillin 3 g IV q4h
• Alternative Regimen (5): Gentamicin
• Alternative Regimen (6): Tobramycin 1 mg/kg IV q24h
• Alternative Regimen (7): Amikacin 3 mg/kg IV q24h
• Note: Aminoglycosides can be used alone for treatment of UTI