E. cloacae: Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes


Enterobacter cloacae is a Gram-negative bacterium belonging to the Enterobacteriaceae family. It is a non-motile, facultative anaerobic, rod-shaped bacterium with a characteristic ability to ferment lactose. The name “cloacae” is derived from the Latin word “cloaca,” which means sewer or drain, indicating the bacterium’s presence in various environmental niches, including soil, water, and sewage.

E. cloacae is a normal part of the gut flora, it can also cause opportunistic infections, especially in healthcare settings. Its ability to develop antibiotic resistance highlights the importance of proper infection control measures and judicious use of antibiotics in medical practice.


The morphology of Enterobacter cloacae is typical of Gram-negative bacteria, and it can be described as follows:

Cell Shape: E. cloacae is a rod-shaped bacterium, also known as a bacillus. The cells are elongated and cylindrical in appearance.

Cell Arrangement: The cells can occur singly or form short chains when viewed under the microscope.

Gram Staining: When subjected to the Gram stain, E. cloacae appears as Gram-negative. This means that the bacterium does not retain the crystal violet stain during the staining process and takes up the counterstain (safranin), appearing pink or red in color.

Motility: E. cloacae is motile.

Capsule: Some strains of E. cloacae may produce a slimy protective layer called a capsule, which can aid in evading the host’s immune system and contribute to bacterial virulence.

E. cloacae mucoid growth on CLED agar of Urine Culture
Fig. E. cloacae mucoid growth on CLED agar of Urine Culture

Spores: E. cloacae is a non-spore-forming bacterium. Spores are specialized dormant structures that certain bacteria can produce to survive adverse environmental conditions, but E. cloacae lacks this ability.

Size: The average size of E. cloacae cells is around 0.5 to 0.8 micrometers in width and 1.5 to 3.0 micrometers in length.

Other Features: E. cloacae, like other members of the Enterobacteriaceae family, possesses a double-membrane structure with a thin peptidoglycan layer in the cell wall. It also has a peritrichous arrangement of pili or fimbriae on its surface, which are hair-like appendages that aid in adhesion to surfaces and can be involved in bacterial motility and the transfer of genetic material.


Enterobacter cloacae is considered an opportunistic pathogen, meaning it generally does not cause disease in healthy individuals but can become pathogenic under certain conditions. It is an important nosocomial (hospital-acquired) pathogen, often associated with infections in healthcare settings. The pathogenicity of E. cloacae is attributed to several factors, including its ability to colonize various surfaces and tissues, produce virulence factors, and develop resistance to antibiotics.

Factors contributing to the pathogenicity of E. cloacae include:

  1. Biofilm Formation: E. cloacae can adhere to surfaces and form biofilms. Biofilms are slimy, protective structures composed of bacterial cells and extracellular matrix. Within biofilms, bacteria are more resistant to host immune responses and antibiotics, making infections harder to treat.
  2. Antibiotic Resistance: It has the ability to acquire and express genes that confer resistance to a wide range of antibiotics. This characteristic allows the bacterium to survive and thrive in the presence of antimicrobial agents, leading to challenging treatment options for infections caused by multidrug-resistant strains.
  3. Production of Enzymes and Toxins: It can produce various enzymes and toxins that can contribute to tissue damage and evasion of the host’s immune system. For example, some strains produce extended-spectrum beta-lactamases (ESBLs) that can hydrolyze and inactivate certain beta-lactam antibiotics.
  4. Invasion and Colonization: It can invade and colonize different sites in the body, such as the urinary tract, respiratory tract, bloodstream, wounds, and surgical sites. Once established, it can cause localized infections or potentially spread to other parts of the body.
  5. Indwelling Medical Devices: It has a propensity to colonize and form biofilms on indwelling medical devices, such as urinary catheters, intravenous lines, and ventilators. This can lead to device-associated infections, which are difficult to treat due to the bacteria’s ability to resist antibiotics.

Clinical Infections caused by E. cloacae include:

  1. Urinary Tract Infections (UTIs): E. cloacae is a common cause of nosocomial UTIs, particularly in patients with urinary catheters.
  2. Bloodstream Infections (Bacteremia): It can enter the bloodstream, causing bacteremia, especially in patients with compromised immune systems or underlying health conditions.
  3. Respiratory Tract Infections: It can cause pneumonia and other respiratory infections, especially in ventilated patients.
  4. Wound Infections: It can be a cause of wound infections, particularly in post-surgical patients.
  5. Endocarditis and Meningitis: Though less common, E. cloacae has been associated with severe infections like endocarditis (inflammation of the heart valves) and meningitis (inflammation of the membranes covering the brain and spinal cord).

Lab Diagnosis

The laboratory diagnosis of Enterobacter cloacae involves a series of tests and procedures to identify and differentiate the bacterium from other members of the Enterobacteriaceae family and to determine its antimicrobial susceptibility. The following are the key steps involved in the laboratory diagnosis of E. cloacae:

  1. Sample Collection: A clinical specimen (e.g., urine, blood, sputum, wound swab) is collected from the patient suspected of having an infection caused by E. cloacae.
  2. Sample Processing: The collected specimen is processed to isolate the bacteria. This involves streaking the specimen onto specific culture media that support the growth of Gram-negative bacteria, such as MacConkey agar.
  3. Culture and Identification: After an incubation period (usually 18-24 hours), colonies of bacteria should have grown on the culture media. E. cloacae colonies typically appear as pink to dark pink on MacConkey agar due to their ability to ferment lactose. These colonies can then be subjected to further identification tests.
  4. Gram Staining: A Gram stain is performed on the isolated colonies to determine their Gram nature. E. cloacae will stain as Gram-negative rods.
  5. Biochemical Tests: Several biochemical tests are performed to identify E. cloacae based on its characteristic reactions. Some common tests include:
    • Triple Sugar Iron (TSI) agar test: E. cloacae typically produces an alkaline slant and acid butt with gas production and no H2S (hydrogen sulfide) production.
    • Citrate utilization test: E. cloacae can utilize citrate as a sole carbon source, causing the pH indicator to change in the media.
    • Urease test: E. cloacae is negative for urease production.
    • Indole test: E. cloacae is typically indole-negative.
  6. API Test Strips (optional): Commercial identification systems like API (Analytical Profile Index) can be used for rapid and accurate identification of E. cloacae.
  7. Antimicrobial Susceptibility Testing: The isolated E. cloacae strains are subjected to antimicrobial susceptibility testing to determine which antibiotics are effective in treating the infection. This is crucial due to the bacterium’s ability to develop antibiotic resistance.
  8. Confirmation: All the obtained results from biochemical tests and API strips are combined to confirm the identification of E. cloacae.


The treatment of Enterobacter cloacae infections can be challenging due to the bacterium’s ability to develop antibiotic resistance and its association with healthcare-associated infections. The choice of treatment depends on the severity of the infection, the site of infection, and the susceptibility of the bacterium to specific antibiotics. It is crucial to perform antimicrobial susceptibility testing to guide appropriate therapy. Empirical treatment is often started while waiting for the susceptibility results, and adjustments can be made based on the test results.

General treatment principles for E. cloacae infections include:

  1. Antibiotics: It is often resistant to multiple antibiotics, including commonly used broad-spectrum antibiotics like cephalosporins and fluoroquinolones. Therefore, the choice of antibiotics should be based on local susceptibility patterns and individual patient factors.
  2. Combination Therapy: In severe infections, combination therapy with two or more antibiotics may be considered, especially when dealing with multidrug-resistant strains. However, this approach should be carefully managed to prevent the emergence of further resistance.
  3. Antibiotic Sensitivity: The choice of antibiotics should be guided by the results of antimicrobial susceptibility testing, whenever possible. This ensures that the selected antibiotics are effective against the specific strain causing the infection.
  4. Intravenous Administration: In critically ill patients or those with severe infections, intravenous administration of antibiotics may be necessary to achieve sufficient drug levels quickly.
  5. Duration of Treatment: The duration of antibiotic therapy depends on the site and severity of the infection. It is generally advised to complete the full course of treatment to ensure eradication of the bacterium and prevent relapses.
  6. Infection Control Measures: In healthcare settings, strict infection control measures should be implemented to prevent the spread of E. cloacae infections among patients. This includes proper hand hygiene, isolation of infected patients, and appropriate disinfection of medical equipment.
  7. Antibiotic Stewardship: Given the prevalence of antibiotic resistance, judicious use of antibiotics is essential. This involves using antibiotics only when necessary, choosing the right drug, dose, and duration, and minimizing the risk of antibiotic resistance.


Preventing infections caused by Enterobacter cloacae involves a combination of infection control measures, antibiotic stewardship, and hygiene practices. Since it is often associated with healthcare settings, specific preventive strategies target healthcare-associated infections (HAIs). Additionally, general preventive measures can help reduce the risk of community-acquired infections. Here are some key prevention strategies:

1. Infection Control Measures in Healthcare Settings:

  • Hand Hygiene: Strict adherence to hand hygiene protocols is essential for healthcare workers and visitors to prevent the transmission of E. cloacae and other pathogens. Proper handwashing with soap and water or using alcohol-based hand sanitizers should be practiced.
  • Isolation Precautions: Infected patients should be placed in appropriate isolation precautions to prevent the spread of E. cloacae to other patients. Standard, contact, and droplet precautions may be necessary depending on the nature of the infection.
  • Sterilization and Disinfection: Proper cleaning, disinfection, and sterilization of medical equipment and surfaces are essential to prevent the transmission of E. cloacae. Regular cleaning protocols should be followed, and reusable medical equipment should be appropriately sterilized.
  • Personal Protective Equipment (PPE): Healthcare workers should use appropriate PPE, such as gloves, gowns, masks, and eye protection, when caring for patients with E. cloacae infections to protect themselves and prevent cross-contamination.
  • Environmental Hygiene: Keeping the healthcare environment clean and free from contamination is critical to reducing the spread of infections. Regular cleaning and disinfection of patient care areas and shared facilities should be maintained.

2. Antibiotic Stewardship:

  • Judicious use of Antibiotics: Healthcare providers should follow antibiotic stewardship principles, prescribing antibiotics only when necessary and using the most appropriate antibiotic based on susceptibility testing. Unnecessary or incorrect use of antibiotics can lead to antibiotic resistance.
  • Multidrug-Resistant Organism (MDRO) Screening: Active surveillance for MDROs, including E. cloacae, among high-risk patients can help identify carriers and implement infection control measures promptly.

3. General Preventive Measures:

  • Hygiene Practices: In the community, practicing good hygiene, including regular handwashing, can help reduce the risk of infection. Proper food handling and preparation can also prevent foodborne infections.
  • Immunization: Vaccination against vaccine-preventable diseases can protect individuals from certain infections and reduce the overall burden of disease.
  • Avoiding Close Contact: Avoid close contact with individuals who have symptoms of infection to minimize the risk of transmission.


  • Microbial Classification: Enterobacter cloacae is a Gram-negative bacterium belonging to the Enterobacteriaceae family. It is a non-motile, rod-shaped bacterium that ferments lactose.
  • Habitat: E. cloacae can be found in various environments, including soil, water, sewage, and the gastrointestinal tracts of humans and animals.
  • Opportunistic Pathogen: It is considered an opportunistic pathogen, meaning it typically does not cause disease in healthy individuals but can lead to infections, especially in immunocompromised or hospitalized patients.
  • Healthcare-Associated Infections:It is a significant cause of healthcare-associated infections (HAIs), often found in healthcare settings, such as hospitals and long-term care facilities.
  • Clinical Infections: It can cause a range of infections, including urinary tract infections (UTIs), bloodstream infections (bacteremia), respiratory tract infections, wound infections, and more rarely, severe infections like endocarditis and meningitis.
  • Antibiotic Resistance: It has a remarkable ability to develop resistance to multiple antibiotics, including broad-spectrum antibiotics like cephalosporins and fluoroquinolones. Multidrug-resistant strains are a growing concern in clinical settings.
  • Biofilm Formation: It can produce biofilms, which are slimy protective structures that allow the bacterium to evade the host’s immune system and resist antimicrobial treatment.
  • Laboratory Diagnosis: Identification of E. cloacae involves culturing clinical specimens on specific media, Gram staining, and performing biochemical tests to distinguish it from other bacterial species.
  • Treatment: The choice of antibiotics for E. cloacae infections should be based on susceptibility testing. Combination therapy and proper antibiotic stewardship are crucial in managing infections caused by multidrug-resistant strains.
  • Prevention: Preventive measures include strict infection control protocols, hand hygiene, appropriate use of personal protective equipment (PPE), and antibiotic stewardship. These practices can help reduce the spread of E. cloacae and other healthcare-associated infections.

Further Readings

  1. “Enterobacter cloacae – An Emerging Nosocomial Pathogen” (2018) by Sarita Mohapatra et al. – This review article discusses the epidemiology, clinical relevance, and antibiotic resistance of Enterobacter cloacae as an emerging nosocomial pathogen.
  2. “Multidrug-Resistant Enterobacter cloacae: A Systematic Review of Epidemiology and Risk Factors” (2016) by Youjiang Zhang et al. – This systematic review provides insights into the epidemiology and risk factors associated with multidrug-resistant Enterobacter cloacae infections.
  3. “Molecular Mechanisms of Antibiotic Resistance in Clinical Enterobacter Cloacae Isolates” (2020) by Min Yee et al. – This research article delves into the molecular mechanisms underlying antibiotic resistance in clinical Enterobacter cloacae isolates.
  4. “Biofilm Formation by Multidrug-Resistant Enterobacter cloacae Isolates: A Study on Association with Resistance Phenotype and Phenotypic Characteristics” (2020) by Elsadek et al. – This study explores the relationship between biofilm formation and multidrug resistance in Enterobacter cloacae isolates.
  5. “Virulence Factors and Antimicrobial Resistance of Klebsiella pneumoniae and Enterobacter cloacae Produced by ESBL-Producing Klebsiella pneumoniae (KPC-Kp) and E. cloacae (KPC-Ec) Causing Infection in Intensive Care Units of a Critical Area in Rio de Janeiro, Brazil” (2018) by Patrícia Sampaio Tavares Veras et al. – This research article investigates the virulence factors and antibiotic resistance profiles of ESBL-producing Enterobacter cloacae in critical care settings.
  6. “Epidemiology of Carbapenem-Resistant Enterobacteriaceae Infections: A Study in Northern Italy” (2021) by Vito G. D’Andrea et al. – This study provides insights into the epidemiology of carbapenem-resistant Enterobacteriaceae (CRE) infections, including Enterobacter cloacae, in Northern Italy.

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