[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other clinically important bacteria](https://durgical.com/en/microbiology/groups/other-clinically-important-bacteria/) › Enterobacter, Serratia and Citrobacter

[Microbiology](https://durgical.com/en/microbiology/) · [Other clinically important bacteria](https://durgical.com/en/microbiology/groups/other-clinically-important-bacteria/)

# Enterobacter, Serratia and Citrobacter

- Bacterium
- Gram-negative
- Contact
- For completeness

Hospital Enterobacterales that infect patients with urinary catheters, lines or ventilators and pile up antibiotic resistance.

Updated 2026-11-01

Also called: hospital Enterobacterales

## Key points

- Enterobacter, Citrobacter freundii and Serratia carry chromosomal AmpC: ceftriaxone can fail during treatment.
- Serratia marcescens: red pigment, hospital urinary and respiratory infections.
- KPC: a carbapenemase common in Colombia; NDM is a metallo-beta-lactamase.
- Patient colonised or infected with a multidrug-resistant organism: contact precautions.

## At a glance

**Gram**
Gram-negative

**Shape**
Rod

**Oxygen**
Facultative anaerobe

**Family**
Order Enterobacterales (Enterobacteriaceae, Yersiniaceae)

**Stain**
Gram-negative rods; Serratia marcescens may form a red pigment

## Morphology

- Motile Gram-negative rods, glucose fermenters, oxidase negative
- Enterobacter and Citrobacter ferment lactose; Serratia does so slowly or not at all
- Some Serratia strains produce red colonies

## Transmission

- Healthcare workers' hands, contaminated equipment and solutions
- The patient's own gut flora, selected by antibiotics
- Urinary catheters, venous lines and mechanical ventilation

**Reservoir:** Human and animal gut, water, soil and damp hospital surfaces

### Isolation precautions

What the care team adds to standard precautions.

**Contact**
Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

## Virulence factors

- Chromosomal AmpC beta-lactamase (Enterobacter, Citrobacter freundii, Serratia): can rise during treatment with third-generation cephalosporins
- Plasmid-borne ESBLs and carbapenemases (KPC, NDM)
- Biofilms on catheters and lines
- Lipopolysaccharide (endotoxin) that triggers sepsis

## Diseases it causes

- Catheter-associated urinary tract infection [Urinary tract infection (acute cystitis) →](https://durgical.com/en/conditions/urinary-tract-infection/)
- Line-associated bacteraemia and sepsis [Sepsis and septic shock →](https://durgical.com/en/conditions/sepsis-and-septic-shock/)
- Ventilator-associated pneumonia
- Citrobacter koseri: meningitis and brain abscesses in newborns

## Clinical picture

- Fever in an ICU patient with a catheter, line or ventilator
- Surgical wound infections
- Outbreaks in neonatal units

## Diagnosis

- Culture with identification and susceptibility testing
- Phenotypic or molecular carbapenemase tests (KPC, NDM, OXA-48)
- Rectal swab screening during outbreaks of carbapenem-resistant Enterobacterales

## Treatment

Guided by susceptibility testing. Because of AmpC, third-generation cephalosporins are avoided in serious Enterobacter infections; cefepime or carbapenems are used. For KPC producers there are newer inhibitor combinations (ceftazidime-avibactam, meropenem-vaborbactam); metallo-beta-lactamases (NDM) need other options.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Cefepime](https://durgical.com/en/pharmacology/cefepime/)
- [Meropenem](https://durgical.com/en/pharmacology/meropenem/)
- [Ceftazidime + avibactam](https://durgical.com/en/pharmacology/ceftazidime-avibactam/)

## Prevention

- Hand hygiene and contact precautions for multidrug-resistant organisms
- Early removal of catheters and lines that are no longer needed
- Antimicrobial stewardship programmes

## In Colombia

KPC-producing Enterobacterales are endemic in Colombian hospitals, and the INS conducts surveillance of antimicrobial resistance in healthcare-associated infections.

## Memory aid

"Red hospital": Serratia paints the plate red and, with Enterobacter and Citrobacter, hides behind AmpC once ceftriaxone is started.

## Test yourself

Think of the answer, then tap the question to see it.

## Why are third-generation cephalosporins avoided in serious Enterobacter infections?

It carries a chromosomal AmpC beta-lactamase that can rise during treatment and cause failure.

## Which Enterobacterales member can produce red colonies?

Serratia marcescens.

## Which Enterobacterales carbapenemase is especially common in Colombia?

KPC (Klebsiella pneumoniae carbapenemase).

## Which isolation precautions apply to a patient with carbapenem-resistant Enterobacterales?

Standard precautions plus contact precautions.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/enterobacter-serratia-and-citrobacter/)

## Related

- [Klebsiella pneumoniae](https://durgical.com/en/microbiology/klebsiella-pneumoniae/)
- [Escherichia coli](https://durgical.com/en/microbiology/escherichia-coli/)
- [Pseudomonas aeruginosa](https://durgical.com/en/microbiology/pseudomonas-aeruginosa/)
- [Acinetobacter baumannii](https://durgical.com/en/microbiology/acinetobacter-baumannii/)

## Related conditions

- [Urinary tract infection (acute cystitis)](https://durgical.com/en/conditions/urinary-tract-infection/)
- [Sepsis and septic shock](https://durgical.com/en/conditions/sepsis-and-septic-shock/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

**Contact**
Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

**Droplet**
Surgical mask within about a metre; single room.

**Airborne**
N95 respirator and a negative-pressure room.

[← Back to the group: Other clinically important bacteria](https://durgical.com/en/microbiology/groups/other-clinically-important-bacteria/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Klebsiella, Enterobacter, and Serratia Infections - Infectious Disease - MSD Manual Professional Edition](https://www.msdmanuals.com/professional/infectious-diseases/gram-negative-bacilli/klebsiella-enterobacter-and-serratia-infections) (MSD Manual Professional Edition, 2025); [About Carbapenem-resistant Enterobacterales (CRE) | CRE | CDC](https://www.cdc.gov/cre/about/index.html) (CDC, 2025).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/microbiology/enterobacter-serratia-and-citrobacter/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/enterobacter-serratia-and-citrobacter/