Morganella morganii is a Gram-negative bacterium known as an opportunistic pathogen. While rarely causing illness in healthy people, it can cause severe and life-threatening infections under certain circumstances. The risk of fatality is concentrated among individuals whose defenses are compromised or when the bacteria enters normally sterile parts of the body.
The Nature of Morganella morganii
Morganella morganii is a rod-shaped bacterium belonging to the Enterobacteriaceae family, which includes organisms like E. coli. It is a facultative anaerobe, able to survive and grow in environments both with and without oxygen. The bacterium is mobile due to flagella, which allow it to move across surfaces and within the body.
This organism is widely distributed in the environment, commonly found in soil and water sources. It also exists as a normal part of the flora in the human gastrointestinal tract. It is termed an opportunistic pathogen because it typically causes disease only when it takes advantage of a host’s weakened state or breaches natural barriers, such as through injury or surgery.
Risk Factors and Vulnerable Populations
Infections caused by M. morganii are primarily known for causing nosocomial, or hospital-acquired, infections, often affecting patients receiving extended care. Elderly individuals and those with complex or long-standing medical issues are particularly susceptible.
Individuals with compromised immune systems face heightened danger from this opportunistic organism. Risk factors often involve chronic diseases or breaches in the body’s protective barriers, providing an entry point for the bacteria.
Primary Risk Factors
- Compromised immune systems
- Diabetes mellitus
- Congestive heart failure
- Renal or liver disease
- Long-term indwelling urinary catheters
- Recent surgery
- Severe traumatic injuries and burns
Clinical Manifestations and Severity
The spectrum of infections caused by M. morganii is broad, ranging from localized issues to severe, systemic disease. The most frequently reported sites of infection are the urinary tract, especially in catheterized patients, and surgical or traumatic wounds. Localized infections also include soft tissue abscesses and hepatobiliary tract infections.
The greatest threat occurs when the infection progresses to bacteremia, which is the presence of the bacteria in the bloodstream. Once in the blood, the infection can become systemic, leading to the life-threatening condition known as sepsis. Sepsis is a chain reaction where the body’s overwhelming response to the infection causes widespread inflammation and damage to its own tissues and organs.
This progression to sepsis is the mechanism by which M. morganii causes death, often resulting in multi-organ failure. Studies tracking outcomes for patients with M. morganii bloodstream infections report high mortality rates, ranging from approximately 21% to over 40% in different cohorts. The development of septic shock is a significant independent factor that increases the risk of death in affected patients.
Treatment and Antibiotic Resistance
Treatment of M. morganii infections requires the prompt administration of appropriate intravenous antibiotics. A major challenge is the bacterium’s natural and acquired resistance to many common drugs. M. morganii is intrinsically resistant to several classes of antibiotics, including penicillin, ampicillin, and first- and second-generation cephalosporins.
The organism frequently possesses mechanisms for acquired resistance, notably the production of certain enzymes like AmpC beta-lactamases. These enzymes can break down some third-generation cephalosporin antibiotics, further complicating the choice of treatment. Because of these resistance patterns, clinical laboratories must perform susceptibility testing on the isolated bacteria to determine which antibiotics will be effective against the specific strain.
For severe, multidrug-resistant infections, physicians may need to use potent agents such as carbapenems, which are often reserved as a last-line treatment option. Preventing the acquisition of M. morganii in high-risk settings, such as through strict hand hygiene and careful management of medical devices, remains the most direct way to reduce the risk of severe infection. Inappropriate initial antibiotic treatment is consistently identified as a major risk factor for death among patients with M. morganii bacteremia.