Serratia marcescens (S.M.) is a rod-shaped, Gram-negative bacterium widely distributed in nature. It is best known for producing a distinctive reddish-pink pigment called prodigiosin. S.M. is classified primarily as an opportunistic pathogen, meaning it typically only causes infection when the immune system is weakened or natural defenses are bypassed. Although S.M. can cause genitourinary tract infections, it is not classified or treated as a sexually transmitted infection (STI).
Common Ways Serratia Marcescens Spreads
The primary habitats for Serratia marcescens are the natural environment, including soil, water, and plant surfaces. The pink or orange film sometimes observed in moist areas of a home, such as shower corners or sink drains, is often a biofilm formed by pigmented strains of this bacteria. This ubiquitous presence means exposure occurs frequently in daily life without resulting in disease for most healthy individuals.
A major concern involves S.M.’s role as a nosocomial, or hospital-acquired, pathogen. It accounts for a consistent percentage of infections acquired within healthcare settings, such as intensive care units. Transmission frequently occurs through contact with contaminated medical equipment or via the hands of healthcare personnel who have not followed proper hygiene protocols.
The bacteria thrive on moist surfaces and in devices like respiratory equipment, intravenous fluids, and catheters. Outbreaks have been linked to contaminated antiseptic solutions or inadequate sterilization of urological instruments. The presence of S.M. in a clinical setting is typically a sign of environmental colonization and subsequent opportunistic spread.
Genital Tract Infections Caused by Serratia Marcescens
Serratia marcescens is known to cause infections in the genitourinary system, most commonly presenting as urinary tract infections (UTIs). These infections are overwhelmingly opportunistic and are often associated with prior medical intervention. For example, a urinary catheter provides a direct physical pathway for the bacteria to enter the urinary tract, leading to colonization and infection.
S.M. has been identified as a rare cause of prostatitis, an inflammation of the prostate gland, in men. These cases are often seen in patients with underlying conditions or a history of urological procedures. S.M. has also been isolated in cases of chorioamnionitis, a severe infection of the membranes surrounding the fetus during pregnancy.
The crucial distinction is that S.M. colonizes the genitourinary tract incidentally, usually after a breach of the body’s defenses. When S.M. is found in the genital area, it is generally considered an infection that originated from the environment or the patient’s own gastrointestinal or urinary colonization, not a pathogen specifically adapted for sexual transmission.
Distinguishing S.M. from Classic STIs
The definition of a classic sexually transmitted infection requires the pathogen to be adapted for efficient transmission through sexual contact via mucosal surfaces. Organisms like Neisseria gonorrhoeae or Chlamydia trachomatis are evolved to survive and replicate within the genital tract and rely on sexual activity for propagation. Serratia marcescens lacks this specific adaptation.
S.M. is primarily an environmental organism, and its presence in the genitourinary system is considered incidental colonization from a non-sexual source. While close physical contact might theoretically transfer the bacteria, this mode is not its necessary route for survival and spread. Consequently, S.M. is not included in standard STI screening panels.
If an S.M. infection is diagnosed, it is treated as a complicated opportunistic infection, often requiring antibiotics based on susceptibility testing. Treatment focuses on addressing underlying risk factors, such as catheter removal or immune support. This approach differs from contact tracing of sexual partners, which is the hallmark of managing a true STI.