What is Serratia marcescens?
Serratia marcescens is a Gram-negative opportunistic pathogen from the order Enterobacterales that has emerged as a significant cause of nosocomial infections, particularly in debilitated patients, newborns, and intensive care unit patients, with notable multidrug resistance patterns. 1
Microbiological Characteristics
- S. marcescens is a ubiquitous bacterium displaying high genetic plasticity that allows it to adapt and persist in multiple environmental niches including soil, water, plants, and hospital environments 1
- The organism was discovered by Italian pharmacist Bizio in 1819 and was historically thought to be nonpathogenic 2
- Many strains produce a characteristic red pigment called prodigiosin, which led to its use in military experiments in the mid-20th century when it was erroneously considered harmless 2, 3
- By the mid-1960s, S. marcescens was definitively recognized as a human pathogen 2
Clinical Significance and Infections
- S. marcescens causes an array of infections, most notably urinary tract infections and bloodstream infections 4
- The organism is particularly dangerous in hospital settings, causing numerous outbreaks and opportunistic infections often associated with medical devices and solutions given to hospitalized patients 2
- It represents one of the less frequent but more resistant bacterial species in urinary tract infections, alongside Klebsiella spp., Enterobacter spp., and P. aeruginosa 5
- Infections occur predominantly in immunocompromised individuals, with mortality rates reaching 31% in invasive infections 6
Antibiotic Resistance Profile
- S. marcescens isolates from clinical settings are frequently multidrug resistant, showing resistance to penicillin, cephalosporins, tetracycline, macrolides, nitrofurantoin, and colistin 6
- High levels of antibiotic resistance result from combined activity of intrinsic, acquired, and adaptive resistance elements 1
- The organism carries multiple antibiotic resistance determinants and is capable of acquiring additional resistance genes, including extended-spectrum and metallo beta-lactamases 4
- These resistance mechanisms pose a significant threat to public health worldwide 4
Recommended Treatment Approach
- Treatment should include carbapenems or aminoglycosides in combination with third-generation (and potentially fourth-generation) cephalosporins for invasive infections 6
- Amikacin shows excellent activity with no resistance reported among tested isolates 6
- Gentamicin demonstrates good activity with minimal resistance (3 of 26 isolates tested) 6
- Cotrimoxazole may be considered for uncomplicated urinary infections, though resistance is more common (10 of 27 isolates showed resistance) 6
Key Clinical Pitfalls
- The organism's environmental ubiquity means hospital personnel must remain vigilant in preventing nosocomial outbreaks 2
- Point source contamination from medical devices and hospital solutions is a striking feature of Serratia outbreaks 2
- Risk factors for infection include previous history of UTI, recent antibiotic therapy, hospitalization, indwelling catheters, or surgery 5