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

Gram-negative rods(GNRs) of Serratia marcescens at a magnification of 1000x with 8x optical zoom

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.
Fig. Serratia marcescens colony morphology on MacConkey medium

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.
Fig. Gram-negative rods(GNRs) of Serratia marcescens at a magnification of 1000X
  • 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.
Fig. Gram-negative rods(GNRs) of Serratia marcescens at a magnification of 1000x with 8x optical zoom
  • 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
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Tags: AmpC beta-lactamaseBacillusBacteriaBiofilm formationCarbapenemsCatalase positiveCefepimecitrate positivecontaminated medical devicesDamp environmentsDNase positiveEnterobacteriaceaeEnzyme triad.FluoroquinolonesGelatinase positiveGram-negativeHand hygieneHealthcare-associatedindole negativeIndwelling cathetersIntrinsic resistanceLipase positiveMacConkey agarMedicallabnotesMedlabsolutions9MicrohubMotilemruniverseimulti-drug resistantNeonatal sepsisnon-lactose fermenterNon-spore-formingNosocomial infectionOperation HazeOpportunistic pathogenoxidase negativeperitrichous flagellaPink bathroom moldProdigiosinRed pigmentRespiratory infectionRod-shapedRoom temperature pigmentSerratia marcescensUniverse84aUrinary tract infection
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