Serratia marcescens is a common bacterium found in various environments. First recognized in Italy in 1819 by Bartolomeo Bizio, it is known for producing a vibrant red pigment, which historically led to mistaken interpretations of “bloody” phenomena on foods like bread. This unique color and widespread presence make it a notable microorganism.
Understanding Serratia marcescens
Serratia marcescens is a Gram-negative bacterium, meaning it does not retain the purple stain used in the Gram staining procedure, appearing pink or red instead. It is rod-shaped and motile, possessing flagella that enable its movement. A distinctive feature of some strains is their ability to produce a red pigment called prodigiosin, especially when grown at temperatures between 20 to 30 degrees Celsius. This pigment production can vary in color from dark red to pale pink, influenced by factors like temperature and the age of the bacterial colonies.
This bacterium is commonly found in a variety of natural habitats, including soil, water, and plants. It can also thrive in the digestive tracts of different animals. In human environments, Serratia marcescens is frequently encountered in damp places such as bathrooms, often appearing as a pink, orange, or reddish discoloration on shower corners, tile grout, and basins. This growth occurs as it feeds on phosphorus-containing materials or fatty substances like soap residue. While not a regular part of human fecal flora, it may be present in the human gut.
Infections Caused by the Bacteria
Serratia marcescens is an opportunistic pathogen, causing infections in individuals with weakened or compromised immune systems. It is a significant contributor to healthcare-associated infections, accounting for about 1-2% of cases in hospitals. These infections affect vulnerable populations, including newborns, the elderly, and individuals with underlying medical conditions or those using medical devices like catheters and ventilators.
The bacterium can lead to a range of infections in humans. Common sites of infection include the urinary tract (UTIs) and the respiratory tract, leading to pneumonia. It can also cause wound infections, bloodstream infections (sepsis), and more severe conditions like meningitis, endocarditis, and osteomyelitis. Outbreaks have been reported in neonatal intensive care units, often linked to contaminated medical equipment or insufficient infection control practices.
Identifying and Treating Infections
Diagnosing Serratia marcescens infections involves laboratory culture of samples from the infected site. Healthcare providers may collect samples such as urine, blood, sputum, fluid or tissue from a wound, or cerebrospinal fluid. These samples are then grown in a lab to identify the presence of Serratia marcescens bacteria.
Once the bacterium is identified, antibiotic susceptibility testing is performed to determine which antibiotics will be most effective against the specific strain causing the infection. This step is important because Serratia marcescens can exhibit resistance to several antibiotics, including ampicillin, amoxicillin, and first-generation cephalosporins. Treatment involves specific antibiotics, with carbapenems like meropenem effective, especially for severe infections. Third and fourth-generation cephalosporins, aminoglycosides, and fluoroquinolones may also be used, sometimes in combination to enhance effectiveness. Surgical drainage may also be necessary for purulent collections like abscesses.
Preventing Serratia marcescens Infections
Preventing Serratia marcescens infections relies on adherence to hygiene practices and infection control measures. Thorough handwashing is important, particularly for healthcare workers and individuals caring for those with weakened immune systems. Maintaining clean environments is also important, with regular cleaning of surfaces, especially in damp areas like bathrooms, using bleach-based disinfectants.
In healthcare settings, strict infection control protocols are implemented to minimize spread. This includes proper sterilization of medical devices and ensuring that all equipment, food, and water sources are monitored for contamination. Isolation of infected patients can also help prevent transmission to others. Avoiding scratching surfaces during cleaning is advisable, as abrasions can create favorable breeding grounds for the bacteria.