Citrobacter freundii

1. What is Citrobacter freundii?

Citrobacter freundii is a species of facultative anaerobic Gram-negative bacteria belonging to the family Enterobacteriaceae. It is rod-shaped and typically measures 1-5 μm in length. This bacterium is commonly found in soil, water, sewage, food, and the intestinal tracts of animals and humans¹².

2. Transmission of Citrobacter freundii

Citrobacter freundii can be transmitted through:

• Direct contact: With contaminated surfaces or materials.
• Ingestion: Of contaminated food or water.
• Nosocomial transmission: In healthcare settings, particularly affecting immunocompromised patients².

3. Epidemiology of Citrobacter freundii

Citrobacter freundii is widely distributed in the environment and is a common component of the gut flora. It is considered an opportunistic pathogen, primarily causing infections in immunocompromised individuals, the elderly, and those with prolonged hospital stays². The bacterium has been increasingly recognized for its multidrug-resistant (MDR) strains².

4. Pathology, Disease, and Infection Caused by Citrobacter freundii

Citrobacter freundii can cause a variety of infections, including:

• Urinary tract infections (UTIs)
• Respiratory tract infections
• Sepsis
• Meningitis
• Wound infections
• Gastroenteritis²

5. Laboratory Tests for Citrobacter freundii

• Gram stain: Gram-negative.
• Cell shape: Rod-shaped.
• Cell arrangement: Single or in pairs.
• Culture media: Grows on standard media like MacConkey agar.
• Selective culture media: XLD agar, Hektoen enteric agar.
• Biochemical tests: Positive for citrate utilization, hydrogen sulfide production, and lactose fermentation¹².

6. List of Specimen Types for Citrobacter freundii

• Blood
• Urine
• Sputum
• Stool
• Wound swabs
• Cerebrospinal fluid (CSF)²

7. List of Specimen Collection Sites for Citrobacter freundii Isolation

• Blood samples
• Urinary tract samples (urine)
• Respiratory tract samples (sputum)
• Gastrointestinal tract samples (stool)
• Wound swabs
• Cerebrospinal fluid (CSF)²

8. Colony Morphology of Citrobacter freundii

• Edge: Entire
• Elevation: Raised
• Surface: Smooth
• Size: Medium
• Form: Circular
• Opacity: Opaque
• Colour: Pale or colorless
• Consistency: Moist
• Effect on the media: No significant effect
• Pigment: Non-pigmented¹²

If you need more detailed information or have any other questions, feel free to ask!

¹: Wikipedia - Citrobacter freundii ²: GIDEON - Citrobacter freundii

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9. Treatment Guidelines for Citrobacter freundii

Citrobacter freundii is a Gram-negative bacterium that can cause various infections, including urinary tract infections (UTIs), respiratory tract infections, and bacteremia. Here are the key treatment guidelines:

Empiric Therapy

1. Severe Infections:

   • Carbapenems (e.g., meropenem, imipenem) are often used for severe infections, especially if resistance is suspected.
   • Cefepime or piperacillin-tazobactam can also be considered.

2. Moderate Infections:

   • Ceftriaxone or ciprofloxacin are commonly used if the strain is susceptible.
   • Levofloxacin is another option for oral therapy.

Definitive Therapy

• Based on Susceptibility Testing: Once culture and sensitivity results are available, therapy should be adjusted accordingly. Common options include:
  • Cefepime
  • Ertapenem
  • Ciprofloxacin
  • Levofloxacin
  • Trimethoprim-sulfamethoxazole (TMP-SMX)

Special Considerations

• AmpC Beta-Lactamase Production: Citrobacter freundii can produce AmpC beta-lactamase, leading to resistance to many beta-lactam antibiotics. In such cases, carbapenems or cefepime are preferred¹².
• Duration of Therapy: Typically, 7-14 days depending on the severity and site of infection².

Consultation

• Infectious Disease Specialist: For complicated cases or multidrug-resistant strains, consulting an infectious disease specialist is recommended.

Would you like more detailed information on any specific aspect of the treatment?

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10. Antimicrobial Susceptibility Testing (AST) for  Citrobacter freundii

Citrobacter freundii is known for its ability to develop resistance to multiple antibiotics, making AST crucial for effective treatment. Here are the key points:

Testing Methods

1. Kirby-Bauer Disc Diffusion:

   • Commonly used for initial screening.
   • Involves placing antibiotic-impregnated discs on an agar plate inoculated with the bacterium¹.

2. Broth Microdilution:

   • Determines the Minimum Inhibitory Concentration (MIC) of antibiotics.
   • Provides quantitative results, making it a preferred method for detailed analysis².

3. Automated Systems:

   • Systems like VITEK 2 and BD Phoenix offer rapid and standardized results.
   • Useful for high-throughput testing in clinical laboratories³.

Resistance Mechanisms

• AmpC Beta-Lactamase Production:

  • Confers resistance to many beta-lactam antibiotics.
  • Detected using specific screening tests like the double-disk synergy test (DDST)¹.

• Extended-Spectrum Beta-Lactamases (ESBLs):

  • Detected using combination disk tests or molecular methods.
  • ESBL-producing strains show resistance to third-generation cephalosporins¹.

Commonly Tested Antibiotics

• Beta-Lactams: Cefepime, Piperacillin-Tazobactam
• Carbapenems: Meropenem, Imipenem
• Fluoroquinolones: Ciprofloxacin, Levofloxacin
• Aminoglycosides: Gentamicin, Amikacin
• Sulfonamides: Trimethoprim-Sulfamethoxazole (TMP-SMX)⁴.

Interpretation of Results

• Susceptible (S): Likely to respond to treatment with the antibiotic.
• Intermediate (I): May respond to higher doses or if the infection is at a site where the drug is physiologically concentrated.
• Resistant ®: Unlikely to respond to treatment with the antibiotic³.

Would you like more details on any specific testing method or resistance mechanism?

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