Serratia marcescens is a common bacterium found in diverse natural environments, including soil, water, and plants. It is recognized as an opportunistic pathogen, meaning it primarily causes infections in individuals whose immune systems are compromised or who are in healthcare settings. This bacterium can lead to various types of infections, making an understanding of its treatment important. Its ability to survive in moist environments contributes to its presence in clinical settings.
Understanding Serratia Infections
In healthcare environments, Serratia marcescens can be found in places like sinks and on medical equipment. As an opportunistic pathogen, it typically affects individuals who are hospitalized, have weakened immune systems, or possess medical devices like catheters.
The bacterium is responsible for a range of infections. These include urinary tract infections, respiratory tract infections such as pneumonia, and wound infections. It can also cause bloodstream infections (bacteremia) and infections associated with catheters. Eye infections, including keratitis, and meningitis are also reported.
Challenges in Treatment
Treating Serratia marcescens infections presents challenges due to the bacterium’s inherent and acquired resistance mechanisms. Serratia marcescens naturally produces enzymes called AmpC beta-lactamases, which provide intrinsic resistance to several common antibiotics, including ampicillin and first-generation cephalosporins.
Beyond natural resistance, Serratia marcescens can acquire additional resistance to a broader spectrum of antibiotics. This often occurs through the uptake of plasmids, small pieces of DNA that can carry genes for antibiotic resistance, leading to multidrug-resistant (MDR) strains. The formation of biofilms, communities of bacteria encased in a protective matrix, further complicates treatment by making it more difficult for antibiotics to reach and eliminate the bacteria.
Key Antibiotic Options
Several classes of antibiotics are effective against Serratia marcescens, though their efficacy can vary depending on the specific strain and its resistance profile. Carbapenems, such as meropenem and imipenem, are preferred for severe infections due to their broad activity against many Gram-negative bacteria, including those producing extended-spectrum beta-lactamases. Meropenem has demonstrated effectiveness in treating Serratia marcescens infections, even in cases like meningitis.
Aminoglycosides, including gentamicin and amikacin, are also used. Amikacin is particularly noted for its activity against gentamicin-resistant Serratia marcescens strains. Fluoroquinolones, such as ciprofloxacin and levofloxacin, are another class with activity against many Serratia strains.
Trimethoprim-sulfamethoxazole (TMP-SMX) is an effective option, especially for urinary tract infections caused by Serratia marcescens. For highly resistant strains, polymyxins, like colistin, can be considered. Newer agents, such as ceftazidime-avibactam and meropenem-vaborbactam, are used for treating highly resistant Serratia marcescens strains that produce specific carbapenemases or exhibit inducible AmpC beta-lactamases.
Guiding Treatment Decisions
Determining the most effective antibiotic for a Serratia marcescens infection relies on diagnostic testing, particularly antibiotic susceptibility testing (AST). Healthcare professionals collect samples, which can include blood, urine, or tissue, from the infected site. These samples are then cultured in a laboratory to identify the specific bacterial strain and assess its unique resistance profile to various antibiotics.
Treatment decisions are made by healthcare providers who consider these laboratory results in conjunction with the patient’s overall condition, the specific site of the infection, and local patterns of antibiotic resistance. This tailored approach helps ensure that the chosen antibiotic is most likely to be effective against the particular Serratia marcescens strain causing the infection. Adhering to appropriate antibiotic use is important in combating the ongoing challenge of antibiotic resistance.