Morganella morganii: Morphology, Pathogenesis, Diagnosis, and Resistance

Morganella morganii is a gram-negative bacterium frequently found in the environment and as part of the normal flora in human intestines. While often considered opportunistic, it can be responsible for serious infections, particularly in immunocompromised individuals.

Its clinical significance has surged due to its growing resistance to multiple antibiotics, posing challenges in treatment. Understanding this pathogen’s characteristics and behavior is crucial for effective medical intervention.

Morphology and Identification

Morganella morganii exhibits distinct morphological characteristics that aid in its identification. This bacterium is rod-shaped and measures approximately 0.6 to 1.0 micrometers in width and 1.0 to 2.5 micrometers in length. It is motile, possessing peritrichous flagella that enable movement. When cultured on standard laboratory media, such as MacConkey agar, it forms smooth, opaque colonies that are typically non-lactose fermenting, distinguishing it from other Enterobacteriaceae.

The identification process often begins with a Gram stain, revealing its gram-negative nature. Further biochemical tests are employed to confirm its identity. Morganella morganii is oxidase-negative and catalase-positive, and it produces urease, which can be detected using urea agar. Additionally, it is capable of producing hydrogen sulfide, a trait that can be observed on triple sugar iron (TSI) agar. These biochemical properties are crucial for differentiating it from other closely related bacteria.

Molecular techniques have also become invaluable in the identification of Morganella morganii. Polymerase chain reaction (PCR) and sequencing of specific genetic markers, such as the 16S rRNA gene, provide precise identification. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) is another advanced tool that has streamlined the identification process, offering rapid and accurate results.

Pathogenic Mechanisms

Morganella morganii employs a variety of mechanisms to facilitate infection and overcome host defenses. Central to its pathogenicity is its ability to produce a range of virulence factors. One notable example is the urease enzyme, which not only aids in nitrogen metabolism but also contributes to urinary tract infections by hydrolyzing urea, leading to ammonia production. This raises the pH of the urine, creating a favorable environment for the bacterium and potentially leading to the formation of struvite stones.

Another important factor is its capability to adhere to and invade host tissues. This is mediated through the expression of various adhesins and pili, which enable the bacterium to firmly attach to epithelial cells. Once attached, Morganella morganii can invade and replicate within host cells, evading immune detection. This intracellular lifestyle, combined with its motility, allows the pathogen to disseminate to different tissues, complicating the infection.

The secretion of toxins is another significant aspect of Morganella morganii’s pathogenic arsenal. Hemolysins, for instance, can lyse red blood cells, providing the bacterium with access to iron, a nutrient critical for its growth. Additionally, cytotoxins can damage host cells and tissues, leading to inflammatory responses that further exacerbate the infection.

Biofilm formation is an adaptive strategy that enhances Morganella morganii’s resilience. Within biofilms, the bacteria embed themselves in a protective extracellular matrix, which shields them from antibiotics and immune responses. Biofilms are particularly problematic in medical settings, where they can form on indwelling devices such as catheters and prosthetic implants, leading to chronic infections that are difficult to eradicate.

Antibiotic Resistance

The issue of antibiotic resistance in Morganella morganii presents a formidable challenge in clinical settings. This bacterium has developed resistance mechanisms that render many conventional antibiotics ineffective. One primary method is the production of beta-lactamases, enzymes that degrade beta-lactam antibiotics such as penicillins and cephalosporins. Extended-spectrum beta-lactamases (ESBLs) are particularly concerning, as they can hydrolyze a wider range of beta-lactam antibiotics, complicating treatment options.

Additionally, Morganella morganii can acquire resistance genes through horizontal gene transfer. Plasmids, transposons, and integrons often carry these resistance determinants, which can be transferred between bacteria, sometimes even across different species. This genetic exchange accelerates the spread of resistance, making it a public health concern. The bacterium’s intrinsic resistance to certain antibiotics, such as colistin, further narrows the therapeutic arsenal available to clinicians.

Efflux pumps are another mechanism that contributes to antibiotic resistance. These membrane proteins actively expel a variety of antibiotics from the bacterial cell, reducing their intracellular concentrations and thus their efficacy. Overexpression of efflux pumps can lead to multidrug resistance, complicating the selection of effective treatments. The regulation of these pumps is often complex, involving multiple genetic pathways that can be upregulated in response to antibiotic exposure.

The clinical implications of this resistance are profound. Infections caused by resistant Morganella morganii strains require alternative therapeutic strategies, often involving the use of combination therapies or newer antibiotics like carbapenems. However, the emergence of carbapenem-resistant strains underscores the need for ongoing surveillance and the development of novel antimicrobial agents. The rise of resistance also emphasizes the importance of antimicrobial stewardship programs aimed at optimizing antibiotic use to slow the spread of resistance.

Clinical Manifestations

Morganella morganii, while often part of the normal gut flora, can become pathogenic under certain conditions, leading to a variety of infections. Its clinical manifestations are diverse, reflecting its ability to infect multiple body systems. One of the most common presentations is urinary tract infections (UTIs), especially in hospitalized patients or those with underlying urological abnormalities. Symptoms can include dysuria, hematuria, and fever, often necessitating prompt medical intervention.

Beyond UTIs, Morganella morganii can also cause wound infections, particularly in surgical sites or trauma cases. These infections can be characterized by purulent discharge, erythema, and local pain. The pathogen’s ability to form biofilms on medical devices further complicates these infections, often requiring both antimicrobial therapy and device removal for resolution. Invasive procedures or compromised skin integrity serve as entry points, facilitating the spread of the bacterium.

In more severe cases, Morganella morganii can lead to bacteremia, where the bacteria enter the bloodstream, causing systemic infection. This condition is often marked by high fever, chills, and hypotension, and can progress to septic shock if not promptly treated. Immunocompromised individuals, including those with diabetes, malignancies, or those on immunosuppressive therapy, are particularly vulnerable to such systemic infections. The bacterium’s ability to evade the immune system and its multidrug-resistant nature make these cases particularly challenging to manage.

Diagnostic Techniques

Accurately diagnosing Morganella morganii infections is vital for effective treatment. The diagnostic process typically involves several steps, beginning with clinical examination and patient history. Given its association with hospital-acquired infections, a detailed medical history can provide clues regarding potential exposure and infection risk factors. Laboratory testing is essential for confirming the diagnosis and guiding treatment.

Microbiological cultures are a cornerstone of diagnosis. Samples from suspected infection sites, such as urine, blood, or wound exudates, are cultured on differential media to isolate the bacterium. Once isolated, a series of biochemical tests, including carbohydrate fermentation profiles and enzyme activities, are performed to identify the organism. These tests are crucial for distinguishing Morganella morganii from other gram-negative bacteria.

Molecular methods have become increasingly important in identifying and characterizing this pathogen. Polymerase chain reaction (PCR) assays targeting specific genetic sequences, such as the 16S rRNA gene, offer precise identification and can detect low bacterial loads. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) is another advanced technique that provides rapid and accurate microbial identification by analyzing protein profiles. These methods enhance diagnostic accuracy and speed, facilitating timely and appropriate treatment interventions.

Conclusion