Serratia marcescens is a bacterium frequently encountered in both household settings and healthcare environments. This microorganism often manifests as a pink or reddish discoloration on surfaces, particularly in damp areas. While commonly recognized as a household nuisance, it also possesses the capacity to cause infections in certain populations.
What is Serratia Marcescens?
Serratia marcescens is a type of rod-shaped, Gram-negative bacterium belonging to the Enterobacteriaceae family. A distinctive characteristic of many S. marcescens strains is their ability to produce a bright red or pink pigment called prodigiosin, especially when growing at room temperature, typically between 20 to 30°C.
This pigment is responsible for the “pink slime” often observed in moist areas, though not all pathogenic strains produce this color.
This bacterium thrives in damp, humid environments, making places like bathrooms, sinks, shower curtains, and toilet bowls ideal breeding grounds. It can also be found in soil, water, and even on plants and insects.
S. marcescens often feeds on fatty substances or phosphorus-containing materials, such as soap residue and shampoo, contributing to its prevalence in domestic settings. While its presence in homes is primarily a nuisance, Serratia marcescens is also recognized as an opportunistic pathogen. It poses a concern in healthcare settings, where it can cause infections, particularly in vulnerable individuals.
Eliminating Serratia Marcescens in Your Environment
Eliminating Serratia marcescens from household surfaces requires a combination of physical cleaning and disinfection. Initial physical removal involves scrubbing affected surfaces with a brush and a household cleanser, such as dish soap and water, to effectively remove the slimy biofilm. Thoroughly rinsing the cleaned surfaces with water and drying them completely helps prevent moisture buildup, which is essential for controlling bacterial growth.
Chemical disinfectants are highly effective against S. marcescens. Household bleach, which contains sodium hypochlorite, is a widely used option. A common dilution for disinfection is about 1/3 cup of bleach per gallon of water, or approximately 4 teaspoons per quart of room temperature water. Surfaces should remain visibly wet for a contact time of at least 6 minutes, or up to 10-20 minutes for thorough disinfection, before being rinsed. Always ensure proper ventilation and wear gloves when using bleach.
Hydrogen peroxide is another effective disinfectant against S. marcescens due to its oxidative properties. A 3% hydrogen peroxide solution can be sprayed directly onto affected areas and allowed to sit for at least 10 minutes before wiping clean. While effective, some studies suggest that organisms with high catalase activity, like S. marcescens, may require longer exposure times, potentially 30-60 minutes, for a significant reduction in cell counts.
Isopropyl alcohol, typically at concentrations of 70% or higher, also effectively kills S. marcescens by disrupting cellular functions. For surface disinfection, the alcohol should be applied to cover the area and allowed to remain wet for at least 10 seconds, or preferably 30 seconds to a minute, to ensure maximum effectiveness. As with other chemical agents, ensure good ventilation when using isopropyl alcohol.
Heat can also be used to eliminate S. marcescens on certain items. Hot water or steam cleaning is effective for sanitizing surfaces where it commonly grows, such as shower curtains or pet dishes. Regularly washing shower curtains in hot water with laundry detergent can help prevent growth. Regularly wiping down wet surfaces, improving bathroom ventilation, and ensuring items like pet dishes are cleaned and dried frequently can significantly reduce the conditions favorable for S. marcescens to thrive.
Addressing Serratia Marcescens Infections
Addressing actual infections caused by this bacterium requires medical intervention. Although typically a harmless environmental bacterium for healthy individuals, S. marcescens can act as an opportunistic pathogen, particularly affecting vulnerable populations. These include hospitalized patients, individuals with weakened immune systems, and those with medical devices such as catheters or ventilators.
Serratia marcescens is known to cause various types of infections. Common sites of infection include the urinary tract, leading to urinary tract infections (UTIs), and the respiratory tract, causing pneumonia. It can also cause wound infections, eye infections, and, in more severe cases, bloodstream infections (bacteremia) or meningitis. Symptoms vary depending on the infection site but may include fever, pain, and localized swelling.
Diagnosing an S. marcescens infection typically involves a healthcare provider taking samples from the affected area, such as urine, blood, or wound fluid, for laboratory culture. Treatment for Serratia marcescens infections relies on antibiotics, but selecting the appropriate medication can be challenging due to the bacterium’s tendency to develop antibiotic resistance. Some strains of S. marcescens are naturally resistant to several antibiotics, including certain penicillins and first-generation cephalosporins.
Medical professionals often consider carbapenems, aminoglycosides, or certain third- and fourth-generation cephalosporins for treatment, sometimes in combination. Tobramycin and ciprofloxacin may also be considered, with meropenem being a preferred option for severe infections. Susceptibility testing is crucial to determine which antibiotics will be effective against a specific strain. Self-treatment is not an option; medical diagnosis and prescribed antibiotic therapy are necessary for effective management of these infections.