Microbiology · 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
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) →
- Line-associated bacteraemia and sepsis 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:
Prevention
- Hand hygiene and contact precautions for multidrug-resistant organisms
- Early removal of catheters and lines that are no longer needed
- Antimicrobial stewardship programmes
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.
Related
Related conditions
← Back to the group: 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 (MSD Manual Professional Edition, 2025); About Carbapenem-resistant Enterobacterales (CRE) | CRE | CDC (CDC, 2025).
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Representative model, for educational purposes only.