Gram-positive bacilli —————————–
>Actinomyces israelii 
>Arcanobacterium haemolyticum (formerly known as Corynebacterium haemolyticum)
>Bacillus species:
1] Bacillus anthracis
2] Bacillus cereus
3] Bacillus subtilis
>Clostridium species:
1] Clostridium difficile
2] Clostridium perfringens
3] Clostridium tetani
>Corynebacterium species:
1] Corynebacterium diphtheria
2] Corynebacterium jeikeium
3] Corynebacterium urealyticum
>Erysipelothrix rhusiopathiae
>Listeria monocytogenes
>Lactobacillus species (several e.g. L. acidophilus,L. brevis, L. buchneri, L. casei,
L. fermentum, L. gallinarum , L. gasseri)
>Nocardia species:
1] Nocardia asteroides
2] Nocardia brasiliensis
>Propionibacterium acnes
>Rhodococcus equi (formerly Prescottia equi, Corynebacterium equi)
Actinomyces:
- Genus of the actinobacteria class of bacteria.
- Gram-positive, rod-shaped, non-spore-forming, non-acid-fast, facultative anaerobe.
- Actinomyces are facultatively anaerobic (except A. meyeri, a strict anaerobe).
- Actinomyces species do not form endospores
- Actinomyces colonies form fungus-like branched networks of hyphae.
- Actinomyces are known for causing disease in humans and are normally present in the gums and are the most common cause of infection in dental procedures and oral abscesses.
- Many Actinomyces species are opportunistic pathogens particularly in the oral cavity.
Actinomyces israelii:
- Gram-positive rod-shaped bacteria within the Actinomyces.
- Known to live commensally on and within humans (A. israelii is a normal colonizer of the vagina, colon, and mouth).
- Opportunistic pathogen and a cause of actinomycosis. Infection is established first by a breach of the mucosal barrier during various procedures (dental, GI), aspiration, or pathologies such as diverticulitis.
- Many physiologically diverse strains of the species are known to exist, though all are strict anaerobes.
- Manifestations of disease: Oral-cervicofacial disease is the most common form of actinomycosis. Another form of actinomycosis is thoracic disease, which is often misdiagnosed as a neoplasm, as it forms a mass that extends to the chest wall. Abdominal disease is another manifestation of actinomycosis.
- Actinomycosis may be considered when a patient has chronic progression of disease across tissue planes that is mass-like at times, sinus tract development that may heal and recur, and refractory infection after a typical course of antibiotics.
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