facultative anaerobes but they often fail to grow aerobically on primary culture
grow best under anaerobic or micro-aerophilic conditions with the addition of 5-10% carbon dioxide
narrow temperature range of growth around 35-37 degrees
responsible for the disease known as actinomycosis which in humans is usually caused by Actinomyces israeli and A.gerencseriae. A further four species A.meyeri,A.naeslundii,A.odontolyticus,A.viscosus are very rare causes of human actinomycosis
b) Pathogenesis
actinomycosis is a very chronic disease characterized by multiple abscesses and granulomata,tissue destruction,extensive fibrosis and the formation of sinuses
within diseased tissues,the actinomycetes form large masses of mycelia embedded in an amorphous protein-polysaccharide matrix and surrounded by a zone of Gram-negative,weakly acid-fast,club-like structures formed entirely by the bacteria
the mycelial masses may be large enough to be visible to the naked eye and they are often light yellow in colour,thus also are called as sulphur granules
in man,the great majority of cases of actinomycosis occur in the cervicofacial region and the jaw is often involved
the disease is endogenous in origin : dental caries is a predisposing factor and infection may follow tooth extractions or other dental procedures
thoracic actinomycosis commences in the lung,probably as a result of aspiration of actinomyces from the mouth
sinuses often appear on the chest wall and the ribs and spine may be eroded
abdominal cases commence in the appendix or less frequently in colonic diverticula
the lymphatics are not usually involved in actinomycosis but haematogenous spread to the liver,brain and other internal organs occasionally occurs
c) Laboratory diagnosis
obtained specimen directly from lesions by open biopsy,needle aspiration or in the case of pulmonary lesions
examination of sputum is of no value as it frequently contains oral actinomycetes
material from suspected cases is shaken with sterile water in a tube. Sulphur granules settle to the bottom and may be removed with a pasteur pipette. Granules crushed between two glass slides are used to prepare Gram and Ziehl-Neelsen-stained films which reveal the Gram-positive mycelia and the zone of radiating acid-fast clubs
granules for culture are washed throughly in saline in a tube or petri dish,crushed in a drop of saline with a glass rod and used to inoculate brain-heart infusion agar,blood agar and either glucose broth,enriched thioglycollate broth or commercially available actinomyces broth
cultures are incubated,both aerobically and anaerobically,with the addition of 5% carbon dioxide for up to 10 days
d) Treatment
actinomyces are sensitive to many antibiotics,but the penetration of drugs into the densely fibrotic diseased tissue is poor
surgical debridement reduces scarring and deformity,hastens healing and lowers the incidence of recurrences
penicillins such as aminopenicillins are frequently used. Tetracyclines are used if the patient is allergic to penicillin
Nocardia
a) Description
strictly aerobic
branched Gram positive bacteria
environmental saprophytes with a broad temperature range of growth
most species are acid-fast when decolorized with 1% sulphuric acid,but a few are not acid fast
b) Pathogenesis
nocardiae,principally N.asteroides are uncommon causes of opportunist pulmonary disease that usually,but not always,occurs in immunocompromised individuals including those receiving corticosteriod therapy and post-transplant immunosuppressive therapy and those with the acquired immune deficiency syndrome (AIDS)
pre-existing lung disease,notably nocardial proteinosis,also pre-disposes to nocardial disease
the infection is exogenous,resulting from inhalation of the bacilli
N.asteroides also cause other primary post-traumatic or post-inoculation cutaneous infections with involvement of the lymphatics
c) Laboratory diagnosis
by microscopical examination of sputum
nocardiae are not easily seen in tissue biopsies stained by the Gram and modified Ziehl-Neelsen methods but they may be seen in preparations stained by the Gomori methenamine silver method
technique such as paraffin baiting may be used. A paraffin wax-coated glass rod is placed in inoculated carbon-free broth. Nocardiae grow on the rod at the air/liquid interface and may be subcultured onto agar media
d) Treatment
sulphonamide with or without trimethoprim is the therapy of choice,/LI>
alternative useful agents are minocycline,amikacin and imipenem,particularly for the treatment of AIDS patient who are unable to tolerate the standard drugs
