Actinomyces & Nocardia (Ditki Notes)

• Gram-positive filamentous rods cause infections in humans

Actinomyces Israelii

• Anerobic, slow-growing, and has low virulence
• Opportunistic pathogen: common colonizer of the oral cavity and upper respiratory tract, and sometimes present in the gastrointestinal and urogenital tracts
• Morphology: Branching, fungus-like; forms colonies called sulfur granules, which comprise bacteria and calcium phosphate, and have a dimpled, molar-like appearance, do not contain sulfur
• Infections occur when the bacteria invade deeper tissues of the oral cavity, infections can spread
• Chronic, slow forming granulomatous lesions that become abscesses that drain pus with sulfur granules
• Cervicofacial infection most commonly occurs in the cervicofacial region following dental trauma
• Produces localized swelling, often in the mandibular region resulting in "lumpy jaw"
• Abscesses may form sinus tracts that erupt on the face
• Central nervous system infection can manifest as a single abscess with headache and focal neurological signs
• Thoracic infection produces nonspecific symptoms such as fever and non-productive cough, and lung abscesses may form
• Abdominal cavity infection can affect any organ, and can produce fever and fatigue
• Abdominal cavity infection may be mistaken for signs of Crohn's diseases, and masses have been mistaken for tuberculosis and cancerous tumors
• Pelvic actinomycosis has been associated with long-term use of intra-uterine devices; masses can easily be mistaken for tumors
• Prevention: includes good oral hygiene, and, in the case of dental procedures, prophylactic antibiotics
• Treatment: includes drainage or surgical debridement when necessary and administration of penicillin
• Other species of Actinomcyes are also associated with actinomcyosis.

Nocardia

• Includes several species that can infect and cause nocardiosis
• Nocardia nomenclature and classification has changed dramatically over the years
• Some isolates that were once commonly associated with nocardiosis no longer are
• Microbiology: Weakly acid-fast, with a delicate "beaded" appearance
• Aerobic and catalase-positive, with slow growth. Unique aerial hyphae, with filaments that grow upward from the colony
• Not considered part of the normal human microflora, found in soil, gain entry to human hosts via inhalation and aspiration
• Individuals with defective cellular immunity are particularly susceptible to infection
• Pathogenic Nocarida avoid phagocytic destruction, which is key to innate immunity
• Enzymes catalase and superoxide dismustase protect them from the harmful effects of phagocytic reactive oxygen species
• Cord factor: Prevents phagosome-lysosome fusion, which means the bacteria avoid bactericidal molecules; Nocardia can survive and replicate within macrophages, which travel throughout the body

Infections: Nocardiosis

• Overall, Nocardiosis is rare, and manifests as non-specific symptoms, ruled out early to avoid delayed diagnosis and treatment
• Weakly acid-fast nature and aerial hyphae make it easy to identify
• Lung infection is most common; illness onset is associated with nonspecific symptoms
• Lung abscesses and necrosis can develop, and dissemination to other organs can occur
• CNS infection is the most serious form of nocardiosis, and results in abscesses with non-specific symptoms (such as fever and headache); meningitis is possible but infrequent
• Cutaneous infections manifest as granulomas, ulcers, or cellulitis, and may involve nearby lymphatics
• Infection can be primary or secondary
• Treatment: Nocardia response to antibiotics varies, so testing for antimicrobial susceptibility is crucial
• Pulmonary infections are treated with trimethoprim-sulfamethoxazole (TMP-SMX) and amikacin
• CNS infections are treated with trimethoprim-sulfamethoxazole and imipenem or cephalosporin
• Prolonged antibiotic treatment is recommended to avoid relapse