ACTINOMYCETES OF MEDICAL IMPORTANCE

Actinomycetes (including Mycobacterium) A. They are Gram positive bacteria that have a DNA with greater than 60%G+C content (Historically this group was restricted to include branching filamentous bacteria only, now it includes some cocci in the genus Micrococcus). The term Actinomycete literally means “ray-fungus”. ALL Actinomycetes are true bacteria and NOT fungi B. Actinomycetes can be divided into 2 broad categories: (a) STRICTLY AEROBIC ACTINOMYCETES (b) ANAEROBIC (MICROAEROPHILIC) ACTINOMYCETES (Some may be facultatively anaerobic)

THE TAXONOMY OF ACTINOMYCETES IS IN FLUX It has become complex with numerous newly described genera and species The genera that medical students should remember are: Corynebacterium Mycobacterium Nocardia Rhodococcus Actinomyces Streptomyces Keep in mind that there are a large number of other Actinomycete genera that may be encountered in human medicine, and that additional genera are being described with increasing frequency.

II. NOCARDIA A STRICTLY AEROBIC ACTINOMYCETE A Partially acid-fast (A), Gram Positive (B), beaded filamentous bacterium that fragments to form rods and cocci during growth A B

Many species of Nocardia being defined 1. N. asteroides Complex (Includes N. farcinica, N. nova and N. transvalensis) MOST COMMONLY RECOGNIZED NOCARDIAE IN THE US. 2. N. brasiliensis 3. N. otiditiscaviarum

B. AT LEAST FOUR BASIC FORMS OF DISEASE ARE RECOGNIZED IN HUMANS (Nocardial diseases in humans are often thought to be opportunistic, but this is not an absolute requirement since healthy humans can also be infected) 1. Pulmonary Nocardiosis 2. Localized extrapulmonary and systemic Nocardiosis (including infections of the brain) 3. Cutaneous Nocardiosis (sporotrichoid) 4. Mycetomas

1. PULMONARY NOCARDIOSIS

2. LOCALIZED EXTRAPULMONARY AND SYSTEMIC NOCARDIOSIS (including infections of the brain) BRAIN ABSCESS EYE (RETINAL LESIONS)

3. CUTANEOUS NOCARDIOSIS (SPOROTRICHOID)

4. MYCETOMAS

IT IS WELL KNOWN THAT NOCARDIAE INFECT (Causing brain abscesses) THE HUMAN BRAIN (Causing brain abscesses) There are numerous publications in the world literature to legitimately raise the following question: Is it possible that some strains of Nocardiae may be etiologically involved in some cases of Parkinson’s disease?

C. NOCARDIAL PHYSIOLOGY 1. Growth on simple medium 2. Grow at either ambient temperatures or 37OC 3. Strictly aerobic 4. Produce dry wrinkled colonies 5. Produce aerial filaments (mycelia) on colonies 6. Species differentiated by growth characteristics 7. Susceptible to antibiotics (Sulfonamides Drugs of choice)

D. ECOLOGY 1. Habitat-SOIL 2. Transmission-either inhalation or by puncture wounds 3. Pathogenic Mechanisms-Complex 4. Pathogenic Course: a. Respiratory, my mimic many other infections such as tuberculosis. b. Mycetoma: must be differentiated from Actinomycosis, Mycetomas caused by fungi and other Actinomycetes. 5. Epidemiology: a. Spread from environmental sources (generally not human to Human) b. Worldwide occurrence c. Immunosuppression increases susceptibility (Opportunistic pathogen?)

E. TREATMENT: Sulfadiazine drug of choice. Other drugs may work such as: Bactrim (TMS), Tetracycline, Amikacin, Imepenem and Cefotaxime Penicillin is not a good choice since most nocardiae produce beta lactamase. Surgical intervention may be required.

III. RHODOCOCCUS There are many species (Taxonomy complex and in flux) These organisms are very similar to Nocardia, (more rapidly growing than nocardiae, fragment earlier, and produce soft, buttery colonies on agar). They are Opportunistic Pathogens. Rhodococcus equi is an important pathogen in AIDS (causing pulmonary and systemic disease)

IV. ACTINOMYCES Gram positive, branched filamentous bacteria (A) they are anaerobic to microaerophilic (B). Some will grow aerobically (facultative anaerobe) Superficially, they look like nocardiae. They are not acid fast, they are part of the normal flora Type species: Actinomyces israelii B A

Actinomyces israelii Causes 4 forms of Actinomycosis in humans A B (Almost always a mixed anaerobic infection; Granules in the pus is characteristic (A) 1. Cervicofacial form (B - Called lumpy jaw) 2. Thoracic form (anaerobic pulmonary abscess) 3. Abdominal form (often secondary to trauma) 4. Intra-uterine form (secondary to use of IUD) Drug of choice is penicillin may require surgical intervention A B