Morganella morganii is a Gram-negative bacterium belonging to the Enterobacteriaceae family, commonly found in the intestines of humans and animals. It is primarily recognized as an opportunistic pathogen, causing infection when a host’s defenses are weakened or when the bacterium enters a normally sterile body site. The organism is a growing concern in clinical settings due to its capacity to cause serious infections, particularly in healthcare environments, combined with its increasing antibiotic resistance.
Where the Bacterium Is Found
Morganella morganii is ubiquitous, widely distributed in the natural world, inhabiting soil, water, and various food items. The bacterium is also part of the natural gut flora in a wide range of hosts, including humans, mammals, and reptiles. In healthy individuals, M. morganii typically exists as a harmless commensal organism within the gastrointestinal tract. Infection arises when the organism moves from this habitat to a different body location, such as the bloodstream or a wound, or when the host’s immune system is compromised.
How It Causes Disease
M. morganii is a cause of nosocomial, or hospital-acquired, infections, particularly in patients who are already unwell or undergoing medical procedures. Infections are varied and can be life-threatening, frequently manifesting as urinary tract infections, soft tissue infections, or wound infections. Bacteremia, the presence of bacteria in the bloodstream, is a serious manifestation often associated with a high mortality rate.
Infection begins when the organism gains entry through a breach in the body’s natural barriers. Primary risk factors include the use of medical devices, such as long-term indwelling urinary catheters, which provide a pathway into the body. Patients who have undergone recent surgery or who have underlying health issues are also at heightened risk. These issues include diabetes mellitus, kidney disease, advanced age, and general immunocompromised states. The bacterium also produces the enzyme urease, which enhances its capacity to infect the urinary tract.
Understanding Drug Resistance
The ability of Morganella morganii to evade antibiotic treatment is largely due to its sophisticated resistance mechanisms, which are often intrinsic to the species. The most significant mechanism involves the production of enzymes called beta-lactamases. These enzymes act by chemically breaking the beta-lactam ring structure found in many common antibiotics, such as penicillins and cephalosporins, thereby deactivating the drug.
M. morganii naturally possesses a chromosomally encoded beta-lactamase known as AmpC. This enzyme provides intrinsic resistance to drugs like ampicillin, amoxicillin, and most first- and second-generation cephalosporins. When this enzyme is “derepressed,” it can be produced in large quantities, leading to resistance even against certain third-generation cephalosporins.
A growing concern is the acquisition of other resistance genes, often carried on mobile genetic elements like plasmids, which allow for rapid transfer between bacteria. These include genes for Extended-Spectrum Beta-Lactamases (ESBLs), such as CTX-M and TEM types, which broaden the spectrum of drugs the bacteria can destroy. Furthermore, M. morganii can utilize other evasion methods, like efflux pumps, which are specialized protein channels that actively pump the antibiotic drug out of the bacterial cell before it can reach its target. The combined effect of these mechanisms allows the bacterium to resist multiple classes of antibiotics, leading to multidrug-resistant strains.
Treatment Strategies and Infection Control
The increasing antibiotic resistance in M. morganii makes treatment complex and dependent on precise laboratory information. Susceptibility testing is a crucial first step, as it tells clinicians exactly which antibiotics the specific bacterial strain can be successfully treated with. Treatment selection must account for the organism’s natural resistance to many common beta-lactam drugs.
For infections caused by strains susceptible to less potent drugs, third- or fourth-generation cephalosporins or fluoroquinolones may be effective. However, due to the prevalence of AmpC and ESBL production, more powerful agents are often required. Carbapenems, such as meropenem or imipenem, are frequently considered for multidrug-resistant M. morganii infections, although carbapenem resistance is also beginning to emerge in some isolates.
Infection control measures are equally important to prevent the spread of this opportunistic pathogen in healthcare settings. Strict adherence to hand hygiene protocols by all healthcare staff is paramount. Careful management and prompt removal of medical devices, particularly urinary catheters, when they are no longer needed, reduces the primary risk of infection. Isolation of infected patients and environmental cleaning protocols also help to contain outbreaks and limit the transmission of resistant strains.