Alcaligenes faecalis-Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes

Alcaligenes faecalis-Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes


Alcaligenes faecalis is a type of bacteria commonly found in the human intestinal tract and environment. It’s known for being Gram-negative and rod-shaped. This bacterium is often non-pathogenic but can be opportunistic, causing infections in immunocompromised individuals. Infections can range from urinary tract infections to respiratory issues. Alcaligenes faecalis is characterized by its ability to grow in both aerobic and anaerobic conditions, and it’s usually resistant to common antibiotics, making treatment of infections challenging.


Alcaligenes faecalis is a type of bacterium that is typically found in the human intestinal tract. It is a Gram-negative, rod-shaped bacterium. In terms of its morphology, it is generally small in size, typically around 0.5 to 0.8 µm in width and 1.0 to 3.0 µm in length. The cells can be found singly or in pairs and sometimes in short chains. They are motile due to the presence of peritrichous flagella, which are thin, hair-like structures that extend from the cell surface and aid in movement.

Alcaligenes faecalis is known for its ability to survive in a variety of environments, including soil and water, in addition to the human gut. It can utilize a wide range of organic compounds for energy and is often studied for its potential in bioremediation due to its ability to degrade various pollutants. However, it is important to note that while Alcaligenes faecalis is not typically pathogenic, it can be opportunistic in causing infections in individuals with compromised immune systems.


Alcaligenes faecalis is generally considered a low-virulence bacterium, but it can be an opportunistic pathogen, particularly in individuals with compromised immune systems or underlying health conditions. Its pathogenicity, or ability to cause disease, is not as pronounced or well-understood as in more notorious pathogenic bacteria, but there are several aspects to consider:

  1. Infection Sites: Alcaligenes faecalis has been associated with various types of infections, including respiratory tract infections, urinary tract infections, endocarditis (infection of the heart valves), and septicemia (bloodstream infection). It has also been reported in eye infections and in peritonitis (infection of the abdominal lining), especially in patients undergoing peritoneal dialysis.
  2. Opportunistic Nature: This bacterium more commonly affects individuals with a weakened immune system. This includes patients with chronic diseases, those undergoing certain medical treatments like chemotherapy, or patients with implanted medical devices. The presence of these devices, like catheters, can provide a surface for the bacteria to adhere to and form biofilms, which are communities of bacteria that are more resistant to antibiotics and the host’s immune response.
  3. Antibiotic Resistance: A significant concern with Alcaligenes faecalis is its potential resistance to multiple antibiotics. This resistance can make infections difficult to treat and control. The bacterium’s natural habitat in environments like water and soil exposes it to various antimicrobial agents, potentially contributing to this resistance.
  4. Virulence Factors: While the specific virulence factors of Alcaligenes faecalis are not as well characterized as in more common pathogens, like Staphylococcus aureus or Escherichia coli, it is known to possess mechanisms that contribute to its survival and pathogenicity. These may include biofilm formation, enzyme production, and mechanisms to evade the host immune response.
  5. Healthcare-Associated Infections: There have been reports of Alcaligenes faecalis being involved in healthcare-associated infections (HAIs), particularly in hospital settings where patients are more vulnerable due to weakened immune systems or invasive procedures.

Lab Diagnosis

The laboratory diagnosis of Alcaligenes faecalis infection involves several steps, focusing on the isolation and identification of the bacterium from clinical specimens. Here’s a general outline of the process:

  1. Sample Collection: The first step is the collection of appropriate clinical specimens, depending on the suspected site of infection. This could include urine, blood, sputum, or other bodily fluids. The samples should be collected under sterile conditions to avoid contamination.
  2. Culture: The collected specimens are cultured on appropriate media to promote the growth of bacteria. Alcaligenes faecalis can grow on common bacteriological media such as blood agar and MacConkey agar. It typically produces small, non-hemolytic (i.e., not producing a clear zone on blood agar), pale colonies on blood agar, and colorless colonies on MacConkey agar since it does not ferment lactose.
  3. Gram Staining: This is a preliminary test to classify bacteria into Gram-positive or Gram-negative groups based on their cell wall structure. Alcaligenes faecalis is Gram-negative, so it would appear pink or red under a microscope after this staining procedure.
  4. Microscopic Examination: The bacterium is observed under the microscope to identify its shape and arrangement. Alcaligenes faecalis is rod-shaped and can be found in pairs or short chains.
  5. Biochemical Tests: Various biochemical tests are used to further identify and differentiate Alcaligenes faecalis from other bacteria. These tests include oxidase test (Alcaligenes species are oxidase positive), catalase test, and tests for the utilization of different sugars. Alcaligenes faecalis is typically non-fermentative, meaning it does not produce gas from sugars.
  6. Antibiotic Susceptibility Testing: Given the concern of antibiotic resistance, testing the isolate for susceptibility to various antibiotics is a crucial step in guiding appropriate treatment.
  7. Molecular Methods: In some cases, more advanced techniques like PCR (Polymerase Chain Reaction) may be employed for identification, especially in complex cases or when rapid identification is necessary.
  8. Sensitivity to Disinfectants: Since Alcaligenes faecalis can be resistant to some disinfectants, testing the isolate’s sensitivity to these agents might be relevant in a healthcare setting to prevent nosocomial (hospital-acquired) infections.


Treatment of infections caused by Alcaligenes faecalis can be challenging due to its intrinsic resistance to many commonly used antibiotics. However, the specific treatment regimen should be guided by the results of antibiotic susceptibility testing. Here are some general considerations:

  1. Antibiotic Therapy: The choice of antibiotics should be based on the susceptibility profile of the isolated strain of Alcaligenes faecalis. Commonly, the bacterium is resistant to many penicillins and first-generation cephalosporins. However, it may be susceptible to:
    • Aminoglycosides (e.g., gentamicin, tobramycin)
    • Quinolones (e.g., ciprofloxacin)
    • Carbapenems (e.g., imipenem, meropenem)
    • Extended-spectrum cephalosporins
    • Colistin
    • Trimethoprim-sulfamethoxazole
  2. Combination Therapy: In severe infections, especially in cases of resistance to multiple drugs, combination antibiotic therapy might be necessary. The exact combination should be determined based on susceptibility testing and clinical judgment.
  3. Treatment Duration: The duration of antibiotic therapy depends on the site and severity of the infection, as well as the patient’s response to treatment. It’s important to complete the full course of antibiotics to ensure the eradication of the infection and to reduce the risk of developing resistance.
  4. Supportive Care: Alongside antibiotic therapy, supportive care is crucial, especially in severe infections. This may include fluid and electrolyte management, oxygen therapy for respiratory infections, and other supportive measures as needed.
  5. Management of Underlying Conditions: It’s important to manage any underlying conditions that may have predisposed the patient to infection with Alcaligenes faecalis. This includes optimizing control of chronic diseases, reviewing and possibly removing indwelling medical devices (such as catheters) that may be a source of infection, and ensuring good infection control practices.
  6. Monitoring and Follow-up: Regular monitoring during treatment for signs of improvement or any adverse reactions to antibiotics is important. Follow-up cultures may be necessary to confirm the eradication of the infection.


Preventing infections caused by Alcaligenes faecalis primarily involves good hygiene practices, especially in healthcare settings, and proper management of underlying health conditions. Here are some key strategies for prevention:

  1. Hand Hygiene: Proper hand washing is crucial in preventing the spread of many infections, including those caused by Alcaligenes faecalis. Healthcare workers, patients, and visitors should regularly wash their hands with soap and water or use alcohol-based hand sanitizers.
  2. Sterilization and Disinfection: Regular and thorough cleaning and disinfection of hospital and laboratory equipment are essential. This includes sterilizing medical instruments and ensuring that areas such as operating rooms, patient rooms, and laboratories are kept clean.
  3. Use of Personal Protective Equipment (PPE): In healthcare settings, the use of appropriate PPE such as gloves, gowns, and masks can help prevent the spread of infections.
  4. Proper Catheter Care: Since Alcaligenes faecalis can be associated with infections in patients with catheters, proper insertion, maintenance, and timely removal of catheters are important. This includes using aseptic techniques during catheter insertion and regular monitoring for any signs of infection.
  5. Antibiotic Stewardship: Judicious use of antibiotics in healthcare settings can help prevent the development of antibiotic-resistant strains of bacteria. This means prescribing antibiotics only when necessary and ensuring the correct dosage and duration of treatment.
  6. Isolation Precautions: If a patient is known to be infected with a multi-drug resistant strain of Alcaligenes faecalis, implementing isolation precautions can help prevent the spread to other patients, particularly in a hospital setting.
  7. Monitoring Water Systems: Since Alcaligenes faecalis can be found in water systems, regular monitoring and maintenance of these systems, especially in healthcare facilities, can help reduce the risk of waterborne infections.
  8. Education and Training: Healthcare workers should be educated and trained about infection control practices and the importance of adhering to these practices to prevent the spread of infections.
  9. Managing Chronic Conditions: Patients with chronic conditions or those who are immunocompromised should be regularly monitored and their health conditions managed effectively to reduce the risk of opportunistic infections.
  10. Surveillance: Implementing surveillance systems in healthcare settings to quickly identify and respond to infections can help in early detection and containment of outbreaks.


Here are some keynotes on Alcaligenes faecalis:

  1. Classification: Alcaligenes faecalis is a Gram-negative, rod-shaped bacterium. It is non-fermentative and oxidase positive.
  2. Habitat: This bacterium is commonly found in the environment, including soil and water, and it can also be isolated from the human gastrointestinal tract.
  3. Opportunistic Pathogen: While not a major pathogen, Alcaligenes faecalis can cause opportunistic infections, particularly in individuals with weakened immune systems or those with underlying health conditions.
  4. Infection Types: It is associated with various types of infections, including urinary tract infections, respiratory tract infections, endocarditis, and occasionally, septicemia. It can also cause infections in patients with indwelling medical devices.
  5. Antibiotic Resistance: Alcaligenes faecalis exhibits intrinsic resistance to many common antibiotics, including certain penicillins and cephalosporins, making its infections challenging to treat.
  6. Diagnosis: Laboratory diagnosis involves culturing the organism from clinical specimens, Gram staining, and conducting various biochemical tests for its identification. Antibiotic susceptibility testing is crucial for guiding treatment.
  7. Treatment: Treatment typically involves antibiotics to which the isolate is susceptible, with aminoglycosides, quinolones, carbapenems, and extended-spectrum cephalosporins being potential options. Antibiotic therapy should be based on susceptibility testing results.
  8. Prevention: Preventative measures include good hygiene practices, especially in healthcare settings, proper sterilization and disinfection of medical equipment, judicious use of antibiotics, and managing underlying health conditions.
  9. Environmental Resilience: The bacterium’s ability to survive in various environments, including water systems, underscores the need for regular monitoring in healthcare facilities to prevent nosocomial infections.
  10. Clinical Significance: While Alcaligenes faecalis is not one of the most common causes of hospital-acquired infections, its potential for antibiotic resistance and the ability to cause infections in vulnerable populations make it a bacterium of clinical interest.

Further Readings

  1. Scientific Journals and Articles: Look for articles in peer-reviewed journals like the Journal of Clinical Microbiology, Infection and Immunity, or the American Journal of Infectious Diseases. Platforms like PubMed, Google Scholar, and JSTOR can be great places to search for scholarly articles.
  2. Microbiology Textbooks: Standard microbiology textbooks often have sections on various bacteria, including their characteristics, pathogenicity, and clinical significance. Textbooks like “Medical Microbiology” by Patrick R. Murray or “Brock Biology of Microorganisms” could be useful.
  3. Infectious Disease Reference Books: Books specifically focusing on infectious diseases can provide detailed insights into the pathogenicity, diagnosis, and treatment of infections caused by Alcaligenes faecalis. “Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases” is a comprehensive resource.
  4. Clinical Guidelines and Reviews: Look for clinical guidelines or review articles that focus on the management of infections caused by non-fermenting Gram-negative bacteria, including Alcaligenes faecalis.
  5. Healthcare and Research Institution Websites: Websites of major healthcare institutions like the Centers for Disease Control and Prevention (CDC), World Health Organization (WHO), and the National Institutes of Health (NIH) often have educational resources and updates on various pathogens.
  6. Online Medical Databases: Databases like UpToDate, Medscape, and the Merck Manual provide up-to-date information on various medical conditions, including those caused by bacteria like Alcaligenes faecalis.
  7. University Websites: Many universities that have microbiology or medical departments often publish resources, lecture notes, or articles about different microorganisms.
  8. Conferences and Workshops: Attending conferences or workshops on microbiology and infectious diseases can offer insights from experts in the field and the latest research findings.
  9. Public Health Journals: Journals focusing on public health can provide a broader context on the impact of bacteria like Alcaligenes faecalis on public health and healthcare systems.
  10. Case Studies and Clinical Reports: Reading case studies and clinical reports can provide real-world insights into the diagnosis, treatment, and management of infections caused by Alcaligenes faecalis.
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