Serratia marcescens: Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes

Introduction

• Classification: Belongs to the family Enterobacteriaceae.
• Habitat: Widely found in soil, water, plants, and damp environments (like bathrooms).
• Nature: Opportunistic pathogen that thrives in moist hospital environments.
• Significance: Frequently causes nosocomial (hospital-acquired) outbreaks.

Morphology

• Gram Stain: Gram-negative.
• Shape: Bacillus (rod-shaped).
• Motility: Motile via peritrichous flagella.
• Pigmentation: Some strains produce a dark red/pink pigment called prodigiosin.
• Temperature: Pigment production is optimal at room temperature (25°C) and decreases at 37°C.
• Spores: Non-spore-forming.

Pathogenicity

• Transmission: Spread via hand-to-hand contact by healthcare workers or contaminated medical devices.
• Infections: Cause urinary tract infections (UTIs), respiratory tract infections, wound infections, and sepsis.
• Vulnerable Groups: Affects intensive care unit (ICU) patients, newborns, and the immunocompromised.
• Biofilms: Forms strong biofilms on indwelling medical devices like catheters and intravenous lines.
• Virulence Factors: Secretes extracellular enzymes including DNase, lipase, and gelatinase.

Lab Diagnosis

• Specimen: Urine, sputum, blood, wound swabs, or intravenous catheter tips.

• Microscopy: Gram-negative rods with no specific structural arrangement.
• Culture: Grows well on Nutrient Agar and MacConkey Agar.
• Colony Appearance: Non-lactose-fermenting colonies on MacConkey; may show red/pink coloration if prodigiosin is produced.

• Biochemical Profile: Catalase positive, Oxidase negative, Citrate positive, and Indole negative.
• Key Differentiation: Rapidly hydrolyzes DNA (DNase positive), gelatin (gelatinase positive), and lipids (lipase positive).

Treatment

• Resistance: Intrinsic resistance to many common antibiotics, including ampicillin, first-generation cephalosporins, and macrolides.
• AmpC Beta-Lactamase: Carries inducible chromosomal AmpC genes that can lead to resistance during treatment.
• First Line: Fluoroquinolones (like ciprofloxacin), carbapenems (like meropenem), or fourth-generation cephalosporins (cefepime).
• Susceptibility: Strict reliance on culture and sensitivity testing due to multi-drug resistance (MDR) risks.

Prevention

• Hand Hygiene: Strict adherence to handwashing and sanitizing protocols in healthcare settings.
• Sterilization: Thorough disinfection of medical equipment, respirators, and endoscopes.
• Catheter Care: Timely removal and aseptic management of indwelling urinary and central venous catheters.
• Environmental Control: Keeping sinks, showers, and liquid soap dispensers clean, as bacteria thrive in damp areas.

Keynotes

• Red Pigment: Prodigiosin acts as a visual marker for environmental colonization, often resembling “pink mold” in bathrooms.
• Historical Fact: Once considered non-pathogenic, it was used in the 1950s biological warfare experiment “Operation Haze” to track aerosol dispersion.
• Serratia-Induced UTI: Often associated with long-term catheterization.
• Enzyme Triad: Uniquely positive for DNase, lipase, and gelatinase, differentiating it from most other Enterobacteriaceae.

Further Readings

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC12691863/
2. https://www.scribd.com/presentation/93977951/Serratia-marcescens
3. https://www.sciencedirect.com/topics/medicine-and-dentistry/serratia-infection
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC12290430/
5. https://www.researchgate.net/profile/Patrick_Grimont/publication/226092360_The_Genus_Serratia/links/0c960531489b4c2785000000/The-Genus-Serratia.pdf
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC3592283/
7. https://quiplabs.com/serratia-marcescens/
8. https://pmc.ncbi.nlm.nih.gov/articles/PMC4231636/
9. https://www.ijcmas.com/7-2-2018/K.%20Sharanya,%20et%20al.pdf
10. https://ispub.com/print/7865
11. https://biologyjournal.in/assets/archives/2022/vol7issue4/7-3-26-400.pdf
12. https://www.sciencephoto.com/media/10875/view/serratia-marcescens-bacteria
13. https://www.jmb.or.kr/journal/view.html?uid=6678&vmd=Full