The Bacterium: Serratia marcescens

Serratia marcescens is a Gram-negative bacterium belonging to the family Enterobacteriaceae. It is a common environmental bacterium found in various habitats, including soil, water, plants, and animals. While S. marcescens is generally considered an opportunistic pathogen, it can cause infections in humans, particularly in healthcare settings. 

1. Morphology and Characteristics: Serratia marcescens is a rod-shaped bacterium that appears pinkish-red in color on agar plates due to the production of a red pigment called prodigiosin. It is facultatively anaerobic, motile, and non-spore-forming. It has the ability to grow at a wide range of temperatures and pH levels.
2. Pathogenicity: Serratia marcescens is an opportunistic pathogen, meaning it primarily affects individuals with weakened immune systems or those who have underlying medical conditions. It can cause a variety of infections, including urinary tract infections, respiratory tract infections, wound infections, bacteremia, and meningitis. It is often associated with healthcare-associated infections, particularly in intensive care units and among immunocompromised patients.
3. Antibiotic Resistance: Serratia marcescens has shown a propensity for developing antibiotic resistance. It can acquire resistance genes through horizontal gene transfer, leading to multidrug-resistant strains. Some strains of Serratia marcescens have been found to be resistant to commonly used antibiotics, such as cephalosporins, fluoroquinolones, and aminoglycosides, making treatment challenging.
4. Biofilm Formation: Serratia marcescens has the ability to form biofilms, which are complex microbial communities encased in a self-produced extracellular matrix. Biofilms can attach to surfaces, such as medical devices and indwelling catheters, leading to persistent infections and increased resistance to antibiotics.
5. Prodigiosin Pigment: Serratia marcescens is known for its production of prodigiosin, a red pigment that gives the bacterium its characteristic color. Prodigiosin has attracted attention due to its potential applications in various fields, including medicine, as it has shown anti-tumor and immunosuppressive properties.
6. Environmental Role: Serratia marcescens is widely distributed in the environment and plays a role in nutrient cycling. It has been found in soil, water, plants, and insects. In nature, it can also exhibit beneficial interactions with plants, including biocontrol of plant pathogens.
7. Research and Industrial Applications: Serratia marcescens has been studied extensively in research laboratories due to its ease of cultivation and genetic tractability. It has served as a model organism for studying various biological processes, including antibiotic resistance, biofilm formation, and pigment production. Additionally, some strains of Serratia marcescens have been explored for their potential use in biotechnological applications, such as the production of enzymes and biodegradable polymers.
8. Infection Control Measures: Given its association with healthcare-associated infections, proper infection control measures are crucial to prevent the spread of S. marcescens in healthcare settings. These measures include hand hygiene, environmental cleaning, adherence to aseptic techniques, and prudent use of antibiotics.

S. marcescens is a versatile bacterium with both clinical significance and ecological importance. While it can cause infections in vulnerable individuals, further research is needed to understand its complex interactions with the environment and its potential for beneficial applications.