What Is The Difference between Actinomycosis and Actinobacillosis?

What is the difference between actinomycosis and actinobacillosis? Actinomycosis is caused by various species of the Actinomyces genus with Actinomyces israelii being the most common culprit. Actinobacillosis is caused by various species within the Actinobacillus genus, such as Actinobacillus lignieresii and Actinobacillus equuli.

Actinomycosis and actinobacillosis are both bacterial infections caused by different species within the Actinomyces and Actinobacillus genera, respectively. Although they share some similarities in their names and are both associated with the Actinobacteria phylum.

Difference between Actinomycosis and Actinobacillosis (With Table)

Basic Terms Actinomycosis Actinobacillosis
Causative Agent Actinomyces species, often A. israelii Actinobacillus species, e.g., A. lignieresii, A. equuli
Gram Stain Gram-positive Gram-negative
Bacterial Structure Branched filaments resembling fungi Bacillary or coccobacillary
Aerobic/Anerobic Anaerobic or microaerophilic Facultatively anaerobic
Normal Flora Part of normal flora in humans and animals Often found in the respiratory and gastrointestinal tracts of animals
Clinical Presentation Chronic suppurative infections, abscess formation, sulfur granules “Wooden tongue,” “lumpy jaw,” respiratory infections in animals
Hosts Humans and animals Mainly affects animals, particularly livestock
Transmission Endogenous (not typically contagious) Direct contact, contaminated feed and water in animals
Common Sites of Infection Cervicofacial, thoracic, abdominal regions Tongue, jaw, respiratory tract in animals
Prevalence in Humans Primarily affects humans Mainly seen in animals, less common in humans

What Is Actinomycosis?

Actinomycosis is a chronic bacterial infection that is primarily caused by various species of the Actinomyces genus. Actinomyces bacteria are gram-positive, anaerobic or microaerophilic, and they normally inhabit the mucous membranes of the mouth, throat, digestive tract, and urogenital tract in humans. The most common species associated with actinomycosis is Actinomyces israelii.

Actinomycosis typically occurs when the bacteria invade the surrounding tissues, leading to the formation of abscesses, chronic inflammatory lesions, and the development of characteristic sulfur granules. These granules are composed of bacterial colonies and cellular debris.

The infection often presents as a slowly progressing, chronic condition and can affect various parts of the body, with common sites including the cervicofacial region (head and neck), thoracic region (lungs), and abdominal region. Actinomycosis can cause localized swelling, pain, and the formation of draining sinuses.

Risk factors for actinomycosis include dental infections, dental procedures, poor oral hygiene, and conditions that compromise the mucous membranes, allowing the bacteria to enter and establish infection.

Diagnosis is usually based on clinical presentation, imaging studies, and microbiological cultures. Treatment typically involves prolonged courses of antibiotics, often including penicillin or other beta-lactam antibiotics.

It’s important to note that actinomycosis is not considered highly contagious between individuals. The infection usually arises endogenously, meaning it originates from the person’s own flora, and it is not typically spread from person to person. Early diagnosis and appropriate antibiotic therapy are crucial for the successful management of actinomycosis.

What Is Actinobacillosis?

Actinobacillosis is a bacterial infection caused by various species within the Actinobacillus genus. Actinobacillus bacteria are gram-negative, facultatively anaerobic organisms that can infect a variety of animals, particularly livestock. The most common species associated with actinobacillosis include Actinobacillus lignieresii and Actinobacillus equuli.


The clinical presentation of actinobacillosis can vary depending on the species involved and the affected animal. In cattle, it is often associated with conditions known as “wooden tongue” or “lumpy jaw.”

“Wooden tongue” is characterized by swelling and inflammation of the tongue, leading to a firm and woody consistency. “Lumpy jaw” involves the formation of abscesses in the jaw, resulting in visible lumps.

In other animals, such as horses, pigs, and sheep, actinobacillosis can manifest as respiratory infections, septicemia, or other localized lesions.

Transmission of actinobacillosis can occur through direct contact between animals or through the ingestion of contaminated feed and water. The bacteria can enter the body through breaks in the mucous membranes or skin.

Diagnosis is typically based on clinical signs, bacterial culture, and sometimes histopathological examination of affected tissues. Treatment involves the administration of appropriate antibiotics, often including beta-lactam antibiotics.

Preventive measures for actinobacillosis in livestock include maintaining good hygiene, providing proper nutrition, and promptly treating any injuries or infections that could serve as entry points for the bacteria.

It’s important to note that actinobacillosis primarily affects animals, and human cases are relatively rare. However, when humans are affected, it is usually associated with occupational exposure to infected animals.

Main Difference between Actinomycosis and Actinobacillosis

  1. Causative Agents:
    • Actinomycosis: Caused by various species of the Actinomyces genus, commonly Actinomyces israelii.
    • Actinobacillosis: Caused by various species within the Actinobacillus genus, such as Actinobacillus lignieresii and Actinobacillus equuli.
  2. Gram Stain:
    • Actinomycosis: Gram-positive bacteria.
    • Actinobacillosis: Gram-negative bacteria.
  3. Bacterial Structure:
    • Actinomycosis: Branched filaments resembling fungi.
    • Actinobacillosis: Bacillary or coccobacillary.
  4. Aerobic/Anerobic:
    • Actinomycosis: Anaerobic or microaerophilic.
    • Actinobacillosis: Facultatively anaerobic.
  5. Normal Flora:
    • Actinomycosis: Part of normal flora in humans and animals.
    • Actinobacillosis: Often found in the respiratory and gastrointestinal tracts of animals.
  6. Clinical Presentation:
    • Actinomycosis: Chronic suppurative infections, abscess formation, sulfur granules.
    • Actinobacillosis: “Wooden tongue,” “lumpy jaw,” respiratory infections in animals.
  7. Hosts:
    • Actinomycosis: Humans and animals.
    • Actinobacillosis: Mainly affects animals, particularly livestock.
  8. Transmission:
    • Actinomycosis: Endogenous (not typically contagious).
    • Actinobacillosis: Direct contact, contaminated feed, and water in animals.
  9. Common Sites of Infection:
    • Actinomycosis: Cervicofacial, thoracic, abdominal regions.
    • Actinobacillosis: Tongue, jaw, respiratory tract in animals.
  10. Prevalence in Humans:
    • Actinomycosis: Primarily affects humans.
    • Actinobacillosis: Mainly seen in animals, less common in humans.

Similarities between Actinomycosis and Actinobacillosis

  1. Both are bacterial infections within the Actinomycetes phylum.
  2. Both exhibit a chronic and slowly progressive nature, forming abscesses and causing tissue inflammation.
  3. Both involve bacterial invasion of surrounding tissues, leading to localized lesions.
  4. Actinomycosis affects both humans and animals, while Actinobacillosis primarily affects animals, especially livestock.
  5. Risk factors for both include compromised barriers and breaks in mucous membranes.
  6. Diagnosis relies on clinical evaluation, imaging, and microbiological cultures.
  7. Antibiotics are commonly used for treatment, with specific choices based on the causative agent’s susceptibility.


The difference between Actinomycosis and Actinobacillosis sheds light on the unique challenges posed by these bacterial infections. While both fall under the umbrella of the Actinomycetes phylum, they diverge significantly in terms of causative agents, clinical manifestations, and host preferences.


Actinomycosis, arising from various Actinomyces species, is a versatile gram-positive infection that impacts both humans and animals. Its chronic nature, propensity for abscess formation, and the presence of sulfur granules distinguish it from Actinobacillosis. This condition often emerges from the individual’s own flora, underlining the importance of recognizing its endogenous origin.

On the other hand, Actinobacillosis, linked to Actinobacillus species, predominantly affects animals, particularly livestock. The gram-negative nature of these bacteria and their facultative anaerobic characteristics set the stage for varied clinical presentations. From “wooden tongue” and “lumpy jaw” in cattle to respiratory infections in other animals, Actinobacillosis poses unique challenges in the veterinary realm.

The differences in transmission are notable as well – Actinomycosis is not highly contagious, typically arising from internal sources, while Actinobacillosis can spread through direct contact or contaminated feed and water sources among animals.

In navigating these distinctions, healthcare professionals, veterinarians, and researchers gain valuable insights into tailored diagnostic and treatment strategies. From clinical evaluations and imaging studies to targeted antibiotic therapies, recognizing the nuances between these infections is pivotal for successful management.

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