actinomycetes and nocardia
DESCRIPTION
ACTINOMYCETES ( Includes Nocardia)TRANSCRIPT
Dr.T.V.Rao MD 1
ACTINOMYCETES( Includes Nocardia)
Dr.T.V.Rao MD
Dr.T.V.Rao MD 2
ACTINOMYCETES MORPHOLOGY
• Have filamentous growth, like fungi
• On substrate, grow on and in it
• Thallus -- tissuelike mass, grown in culture
• Mycelium -- tangled mass of hyphae, found in nature
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Actinomyctes.
• Actinomyctes are branching Gram-positive bacilli. They are facultative anaerobes, but often fail to grow aerobically on primary culture. They grow best under anaerobic or micro-aerophilic conditions with the addition of 5-10% carbon dioxide
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Morphology of Actinomycetes
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ACTINOMYCETES MORPHOLOGY
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ACTINOMYCETES ECOLOGY
• Predominantly soil bacteria
• Good at degrading recalcitrant
compounds such as chitin & cellulose
• Often active at higher pH (contrast to
fungi who may dominate at lower pH)
• Give soil the “earthy” smell
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Commensals in the Mouth
• Almost all species are commensals of the mouth and have a narrow temperature range of growth of around 35-37°C. They are responsible for the disease known as actinomycosis.
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Species of Actinomyctes• Three-quarters of human cases are
caused by Actinomyces israelii. Less common causes include A. gerencseriae, A. naeslundii, A. odontolyticus, A. viscosus, A. meyeri, Arachnia propionica and members of the genus Bifidobacterium.
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Actinomycetes• Classification – Order – Actinomycetales • Show fungus-like characteristics such as branching in
tissues or in culture (look like mycelia). – The filaments frequently segment during growth to produce
pleomorphic, diphtheroidal, or club shaped cells.
• The cell wall and the internal structures are typical of bacteria rather than fungi. • Some are aerobic and others are anaerobic. • All are slow growing
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Clinical Presentation
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Clinical presentation• Cervicofacial infection, which
accounts for more than half of reported cases; 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.
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Who Get Infected• Men are affected more
frequently than women, and in some regions the disease is more common in rural agricultural workers than in town dwellers, probably owing to lower standards of dental care in the former.
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Thoracic actinomycosis • 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. Primary endobronchial actinomycosis is an uncommon complication of an inhaled foreign body.
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Abdominal Actinomyctes
• Abdominal cases commence in the appendix or, less frequently, in colonic diverticulae.
• Pelvic actinomycosis occurs occasionally in women fitted with plastic intra-uterine contraceptive devices.
• Actinomyces have been isolated from cases of chronic granulomatous disease and should be vigorously sought in this rare condition.
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Actinomycetes• Clinical significance– Are part of the NF found in the cavities of humans and
other animals.– All may cause actinomycosis or “lumpy jaw” which is a
cervicofacial infection that used to occur following tooth extractions or dental surgery which provided traumatized tissue for growth of the microorganism which may also invade the bone. » This is rare today because of prophylactic antibiotic
therapy.–May cause thoracic or abdominal infections–May cause meningitis, endocarditis, or genital infections
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Actinomycetes–Every kind of infection is
characterized by draining sinuses, usually containing characteristic granules which are colonies of bacteria that look like dense rosettes of club-shaped filaments in radial arrangement
•Treatment–Penicillin
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Diagnosis • Specimens should be obtained directly from
lesions by open biopsy, needle aspiration or, in the case of pulmonary lesions, by fibreoptic bronchoscopy. 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.
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Diagnosis • Granules crushed between two glass
slides are stained by the Gram and Ziehl-Neelsen (modified by using 1% sulphuric acid for decolorization) methods, which reveal the Gram-positive mycelia and the zone of radiating acid-fast clubs.
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Identification• Sulphur granules and
mycelia in tissue sections are identifiable by use of fluorescein-conjugated specific antisera. In-situ PCR has been used to detect A. israelii in tissue biopsies.
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Actinomyctes spp Obtained from the CDC Public Health Image Library
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Culturing • For culture, suitable
media, such as blood or brain-heart infusion agar, glucose broth and enriched thioglycollate broth, are inoculated with washed and crushed granules.
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Culturing• Cultures are incubated aerobically and
anaerobically for up to 14 days. After several days on agar medium, A. israelii may form so-called spider colonies that resemble molar teeth. The identity may be confirmed by biochemical tests, by staining with specific fluorescent antisera or by gas chromatography of metabolic products of carbohydrate fermentation.
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Antibiotics in Actinomyctes
• Actinomyces are sensitive to many antibiotics, but the penetration of drugs into the densely fibrotic diseased tissue is poor. Thus, large doses are required for prolonged periods, and recurrence of disease is not uncommon. Surgical debridement reduces scarring and deformity, hastens healing and lowers the incidence of recurrences..
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Antibiotics in Actinomyctes
• Prolonged penicillin-based regimens are increasingly being replaced by shorter regimens based on amoxicillin with clavulanic acid (the clavulanic acid is required because lesions are often concomitantly infected with β-lactamase-producing bacteria) or cephalosporins, especially ceftriaxone.
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Antibiotics in Actinomyctes
• Alternative agents include tetracyclines, macrolides, fluoroquinolones and imipenem but in-vitro sensitivity testing is unreliable. Additional drugs, including aminoglycosides and metronidazole, may be required when concomitant organisms are present.
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NOCARDIA
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Nocardiosis• Nocardiosis primarily presents as a pulmonary
disease or brain abscess in the U.S. In Latin America, it is more frequently seen as the cause of a subcutaneous infection, with or without draining abscesses. It can even present as a lesion in the chest wall that drains onto the surface of the body similar to actinomycosis. Brain abscesses are frequent secondary lesions.
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Morphology of Nocardia
–The Nocardia are branched, strictly aerobic, Gram-positive bacteria that are closely related to the rapidly growing mycobacteria. Like the latter, but unlike Actinomyctes, they are environmental saprophytes with a broad temperature range of growth. . Most isolates are acid-fast when decolorized with 1% sulphuric acid.
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Epidemiology
• Many species of Nocardia are found in the environment, notably in soil, and a range of species cause human opportunist disease, notably Nocardia asteroids, so named because of its star-shaped colonies, N, abscessus, N. farcinica, N. brasiliensis, N. brevicatena, N. otitidiscaviarum, N. nova and N. transvalensis. A wider range of species is encountered in profoundly immunosuppressed patients.
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Other Species Infective
• Nocardiae, principally N. asteroides, are uncommon causes of opportunist pulmonary disease, which usually, but not always, occurs in immunocompromised individuals, including those receiving post-transplant immunosuppressive therapy or chemotherapy for cancer and those with acquired immune deficiency syndrome (AIDS).
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Nocardia and Corticosteroid Therapy
• Corticosteroid therapy is a strong risk factor. As a result, the frequency and diversity of clinical manifestations of Nocardia disease has increased over the past few decades. Pre-existing lung disease, notably alveolar proteinosis, also predisposes to nocardial disease. The infection is exogenous, resulting from inhalation of the bacilli. The clinical and radiological features are very variable and non-specific, and diagnosis is not easy
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Clinical presentation• Most cases there are multiple confluent
abscesses with little or no surrounding fibrous reaction, and local spread may result in pleural effusions, empyema and invasion of bones. In some cases the disease is chronic, whereas in others it spreads rapidly through the lungs.
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Other Complications
• Secondary abscesses in the brain and, less frequently, in other organs occur in about one-third of patients with pulmonary nocardiosis. Acute dissemination with involvement of many organs occurs in profoundly immunosuppressed persons, notably those with AIDS. Recurrence is common in immunosuppressed patients and mortality is high.
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Other Complications
• Nocardiae also cause primary post-traumatic, postoperative or post-inoculation cutaneous infections (primary cuteneous nocardiasis). The most frequent cause is N. brasiliensis but some cases are caused by N. asteroides or other species. In the USA and the southern hemisphere, but rarely in Europe, cutaneous infections may result in fungating tumour-like masses termed mycetomas.
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Diagnosis of Nocardia Infections
• A presumptive diagnosis of pulmonary nocardiasis may be made by a microscopical examination of sputum. In many cases the sputum contains numerous lymphocytes and macrophages, some of which contain pleomorphic Gram-positive and weakly acid-fast bacilli, and occasional extracellular branching filaments.
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Modified Z N Staining• Nocardia are not so
easily seen in tissue biopsies stained by the Gram or modified Ziehl-Neelsen methods, but may be seen in preparations stained by the Gram-Weigert or Gomori methenamine silver methods.
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Culturing Nocardia• Nocardiae grow on blood agar,
although growth is better on enriched media including Löwenstein-Jensen medium, brain-heart infusion agar and Sabouraud's dextrose agar containing chloramphenicol as a selective agent.
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Culture on Media• Growth is visible after
incubation for between 2 days and 1 month; selective growth is favoured by incubation at 45°C. Colonies are cream, orange or pink coloured; their surfaces may develop a dry, chalky appearance, and they adhere firmly to the medium
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Treating Nocardia• Widely used regimen is
sulfamethoxazole with trimethoprim (co-trimoxazole) for 3-6 months, although this prolonged course often causes adverse drug reactions. In addition, some strains, especially of N. farcinica, are resistant to sulphonamides.
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Other drugs in Use
• An alternative regimen, particularly in severe disease, is high-dose imipenem with amikacin for 4-6 weeks. Minocycline, third generation cephalosporins, amoxicillin-clavulanate combinations and linezolid, an oxazolidinone, are also effective.
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