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Created page with "==Introduction== [[File:actinomyces.jpg|right|thumb|250px|<small><center> Agar plate culture of Actinomyces sp. bacteria, a Gram positive opportunistic pathogen of the oral cavit..."
==Introduction==
[[File:actinomyces.jpg|right|thumb|250px|<small><center> Agar plate culture of Actinomyces sp. bacteria, a Gram positive opportunistic pathogen of the oral cavity. (Marco Tollo 2006, Wikimedia commons)</center></small>]]
The actinomycetes comprise a group of '''procaryotes''' that have the ability to form '''Gram-positive, branching filaments''' of less than 1μm in diameter. The main animal pathogens in the actinomycetes are the genera ''Actinomyces'', ''Nocardia'' and ''Dermatophilus''.
''Streptomyces'' species are also included in this group, and they are prolific producers of antimicrobial substances.
==''Actinomyces'' species==
===Morphology and staining===
These are '''gram-positive diphtheroid or filamentous rods''', about 0.5μm in width. Branching filaments are usually found in pathological specimens. In culture, diphtheroid forms predominate.
===Structure and composition===
''Actinomyces'' species have distinctive cell wall constituents. Surface fibrils in ''A. viscosus'' may be adhesins for host cells or other bacteria. Surface antigens are related to chemotactic and mitogenic activities.
===Growth characteristics===
Animal ''Actinomyces'' species are '''capnophilic or facultative anaerobes'''. All require rich media, preferable containing serum or blood. No growth occurs on Sabouraud's agar. Development of macroscopic colonies may require several days at 37°c. Colonical morphology varies between and within species.
===Biochemical activities===
''Actinomyces'' are '''catalase-negative''', with the exceptions of ''A. viscosus'' and ''A. canis''.
===Reservoir===
''Actinomyces'' species live in the '''nasopharyngeal and oral mucosa''', and secondarily in the gastrointestinal tract.
===Disease===
''Actinomyces'' species evoke '''pyogranulomatous reactions''' by unknown mechanisms. Bacterial colonies trigger the suppurative response, and there is also granulation, mononuclear infiltration and fibrosis.
Sinus tracts carry the exudate to the outside. This often contains ''''sulfur granules'''' which are bacterial colonies surrounded by clubs.
Diseases caused by ''Actinomyces'' species include:
'''Ruminants''': ''A. bovis'' causes [[Actinomyces bovis|lumpy jaw]]
'''Horses''': ''Actinomyces'' species have been isolated from cases of [[Poll Evil and Fistulous Withers]] as well as in cases of cervical lymphadenitis.
'''Dogs and cats''': ''Actinomyces'' are common causes of pyonecrotic processes, usually associated with a foreign body such as a migrating grass awn. Commonly isolated species include: ''[[Actinomyces viscosus]]'', ''[[Actinomyces hordeovulneris]]'', ''A. canis'', A. catuli.
'''Pigs''': mastitis, pneumonia and abortion have all be associated with ''Actinomyces'' infections.
==''Nocardia'' species==
===Morphology and staining===
Gram-stained ''Nocardia'' species are '''indistinguishable''' from ''Actinomyces'' species. They alternate between the coccobacillary resting face and the actively-growing filamentous forms.
===Structure and composition===
The cell wall is typical of gram-positive bacteria. It contains a '''high concentration of lipids'''. A superoxide dismutase acts as a virulence factor.
===Growth characteristics===
''Nocardia'' species are '''obligate aerobes''' growing on simple media (Sabouraud's) over a wide temperature range. Colonies are opaque and variously pigmented. The colony surface, which is waxy to powdery to velvety depending on the abundance of growth, wrinkles with age. The diameter of colonies may reach several centimetres.
Biochemical activities include '''catalase production''' and acidification of various carbohydrates.
===Reservoir===
Pathogenic ''Nocardia'' species are '''saprophytic''' and found in many climates in '''soil and water''', either as indigenous flora or as contaminants.
===Disease===
''Nocardia'' species survive within phagocytic vacuoles and lead to a predominantly '''suppurative process'''. '''Lymph nodes are consistently involved'''. Exudates are serosanguinous and sometimes contain 'sulfur-granule-like' debris, which lack the microstructure of ''Actinomyces'' sulfur granules.
Diseases in different species include:
'''Ruminants''': mastitis, bovine farcy, pneumonia, abortion and lymphadenitis
'''Horses''': local or general infections due to underlying immunosuppression (EPPID), placentitis which causes abortion.
'''Dogs and cats''': pneumonia, suppurative pleuritis with empyema, dissemination to kidneys, CNS, bones, joints.
'''Pigs''': pneumonia, abortion, lymphadenitis
==''Dermatophilus'' species==
''[[Dermatophilus congolensis]]'' is the only species, and is a '''gram-positive filamentous bacterium'''.
===Morphology and composition===
The reproductive unit of the bacterium is the '''motile coccoid zoospore'''. Upon germinating, the zoospores sprout a germ tube which elongates and thickens, dividing transversely and longitudinally, forming a strand several layers thick. '''Multiflagellated zoospores''' are liberated as the strand disintegrates.
===Growth characteristics===
''D. congolensis'' grows on blood media, but not on Sabouraud's agar. It is '''aerobic and capnophilic'''. '''Haemolytic colonies''' develop within 48 hours and vary from mucoid to viscous and waxy and whitish-grey to yellow. '''Catalase, urease and proteases''' are produced. The bacterium survives well in the soil and on fomites.
===Reservoir===
''D. congolensis'' does not multiply saprophytically. Its '''reservoir is infected animals'''. Cattle, sheep, goats and horses are common hosts but it has been diagnosed in many other animals.
===Disease===
It causes an '''exudative dermatitis''', with activity confined to the living epidermis. There is a scab consisting of layers of neutrophilic exudate and keratinising epidermis. Wetting favours expansion of the lesions.
It causes lesions on the back (rain scald in horses, lumpy wool in sheep), feet and legs (strawberry footrot in sheet and grease heel in horses).
==''Streptomyces'' species==
These are not pathogenic but are similar to ''Nocardia'' species in cultures. Some species '''produce antibiotics''', and they are common '''laboratory contaminants'''.
==References==
Quinn, P. (1994) '''Clinical veterinary microbiology''' ''Elsevier Health Sciences''
Hirsh, D. (2004) '''Veterinary microbiology''' ''Wiley-Blackwell''
[[Category:To Do - Helen]]
[[Category:To Do - Review]]
[[File:actinomyces.jpg|right|thumb|250px|<small><center> Agar plate culture of Actinomyces sp. bacteria, a Gram positive opportunistic pathogen of the oral cavity. (Marco Tollo 2006, Wikimedia commons)</center></small>]]
The actinomycetes comprise a group of '''procaryotes''' that have the ability to form '''Gram-positive, branching filaments''' of less than 1μm in diameter. The main animal pathogens in the actinomycetes are the genera ''Actinomyces'', ''Nocardia'' and ''Dermatophilus''.
''Streptomyces'' species are also included in this group, and they are prolific producers of antimicrobial substances.
==''Actinomyces'' species==
===Morphology and staining===
These are '''gram-positive diphtheroid or filamentous rods''', about 0.5μm in width. Branching filaments are usually found in pathological specimens. In culture, diphtheroid forms predominate.
===Structure and composition===
''Actinomyces'' species have distinctive cell wall constituents. Surface fibrils in ''A. viscosus'' may be adhesins for host cells or other bacteria. Surface antigens are related to chemotactic and mitogenic activities.
===Growth characteristics===
Animal ''Actinomyces'' species are '''capnophilic or facultative anaerobes'''. All require rich media, preferable containing serum or blood. No growth occurs on Sabouraud's agar. Development of macroscopic colonies may require several days at 37°c. Colonical morphology varies between and within species.
===Biochemical activities===
''Actinomyces'' are '''catalase-negative''', with the exceptions of ''A. viscosus'' and ''A. canis''.
===Reservoir===
''Actinomyces'' species live in the '''nasopharyngeal and oral mucosa''', and secondarily in the gastrointestinal tract.
===Disease===
''Actinomyces'' species evoke '''pyogranulomatous reactions''' by unknown mechanisms. Bacterial colonies trigger the suppurative response, and there is also granulation, mononuclear infiltration and fibrosis.
Sinus tracts carry the exudate to the outside. This often contains ''''sulfur granules'''' which are bacterial colonies surrounded by clubs.
Diseases caused by ''Actinomyces'' species include:
'''Ruminants''': ''A. bovis'' causes [[Actinomyces bovis|lumpy jaw]]
'''Horses''': ''Actinomyces'' species have been isolated from cases of [[Poll Evil and Fistulous Withers]] as well as in cases of cervical lymphadenitis.
'''Dogs and cats''': ''Actinomyces'' are common causes of pyonecrotic processes, usually associated with a foreign body such as a migrating grass awn. Commonly isolated species include: ''[[Actinomyces viscosus]]'', ''[[Actinomyces hordeovulneris]]'', ''A. canis'', A. catuli.
'''Pigs''': mastitis, pneumonia and abortion have all be associated with ''Actinomyces'' infections.
==''Nocardia'' species==
===Morphology and staining===
Gram-stained ''Nocardia'' species are '''indistinguishable''' from ''Actinomyces'' species. They alternate between the coccobacillary resting face and the actively-growing filamentous forms.
===Structure and composition===
The cell wall is typical of gram-positive bacteria. It contains a '''high concentration of lipids'''. A superoxide dismutase acts as a virulence factor.
===Growth characteristics===
''Nocardia'' species are '''obligate aerobes''' growing on simple media (Sabouraud's) over a wide temperature range. Colonies are opaque and variously pigmented. The colony surface, which is waxy to powdery to velvety depending on the abundance of growth, wrinkles with age. The diameter of colonies may reach several centimetres.
Biochemical activities include '''catalase production''' and acidification of various carbohydrates.
===Reservoir===
Pathogenic ''Nocardia'' species are '''saprophytic''' and found in many climates in '''soil and water''', either as indigenous flora or as contaminants.
===Disease===
''Nocardia'' species survive within phagocytic vacuoles and lead to a predominantly '''suppurative process'''. '''Lymph nodes are consistently involved'''. Exudates are serosanguinous and sometimes contain 'sulfur-granule-like' debris, which lack the microstructure of ''Actinomyces'' sulfur granules.
Diseases in different species include:
'''Ruminants''': mastitis, bovine farcy, pneumonia, abortion and lymphadenitis
'''Horses''': local or general infections due to underlying immunosuppression (EPPID), placentitis which causes abortion.
'''Dogs and cats''': pneumonia, suppurative pleuritis with empyema, dissemination to kidneys, CNS, bones, joints.
'''Pigs''': pneumonia, abortion, lymphadenitis
==''Dermatophilus'' species==
''[[Dermatophilus congolensis]]'' is the only species, and is a '''gram-positive filamentous bacterium'''.
===Morphology and composition===
The reproductive unit of the bacterium is the '''motile coccoid zoospore'''. Upon germinating, the zoospores sprout a germ tube which elongates and thickens, dividing transversely and longitudinally, forming a strand several layers thick. '''Multiflagellated zoospores''' are liberated as the strand disintegrates.
===Growth characteristics===
''D. congolensis'' grows on blood media, but not on Sabouraud's agar. It is '''aerobic and capnophilic'''. '''Haemolytic colonies''' develop within 48 hours and vary from mucoid to viscous and waxy and whitish-grey to yellow. '''Catalase, urease and proteases''' are produced. The bacterium survives well in the soil and on fomites.
===Reservoir===
''D. congolensis'' does not multiply saprophytically. Its '''reservoir is infected animals'''. Cattle, sheep, goats and horses are common hosts but it has been diagnosed in many other animals.
===Disease===
It causes an '''exudative dermatitis''', with activity confined to the living epidermis. There is a scab consisting of layers of neutrophilic exudate and keratinising epidermis. Wetting favours expansion of the lesions.
It causes lesions on the back (rain scald in horses, lumpy wool in sheep), feet and legs (strawberry footrot in sheet and grease heel in horses).
==''Streptomyces'' species==
These are not pathogenic but are similar to ''Nocardia'' species in cultures. Some species '''produce antibiotics''', and they are common '''laboratory contaminants'''.
==References==
Quinn, P. (1994) '''Clinical veterinary microbiology''' ''Elsevier Health Sciences''
Hirsh, D. (2004) '''Veterinary microbiology''' ''Wiley-Blackwell''
[[Category:To Do - Helen]]
[[Category:To Do - Review]]