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==Introduction==
==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>]]
[[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''.
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 [[:Category:Actinomyces|''Actinomyces'']], [[:Category:Nocardia species|''Nocardia'']] and [[Dermatophilus congolensis|''Dermatophilus'']].
''Streptomyces'' species are also included in this group, and they are prolific producers of antimicrobial substances.
''Streptomyces'' species are also included in this group, and they are prolific producers of antimicrobial substances.
==''Actinomyces'' species==
==''Actinomyces'' species==
===Morphology and staining===
===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.
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===
===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.
''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===
===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.
Animal ''Actinomyces'' species are '''capnophilic or facultative anaerobes'''. All require rich media, preferably 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===
===Biochemical Activities===
''Actinomyces'' are '''catalase-negative''', with the exceptions of ''A. viscosus'' and ''A. canis''.
''Actinomyces'' are '''catalase-negative''', with the exceptions of ''A. viscosus'' and ''A. canis''.
Diseases caused by ''Actinomyces'' species include:
Diseases caused by ''Actinomyces'' species include:
:'''Ruminants''': ''A. bovis'' causes [[Actinomyces bovis|lumpy jaw]].
'''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.
'''Horses''': ''Actinomyces'' species have been isolated from cases of [[Poll Evil and Fistulous Withers]] as well as in cases of cervical lymphadenitis.
:'''Pigs''': mastitis, pneumonia and abortion have all be associated with ''Actinomyces'' infections.
'''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==
==''Nocardia'' species==
===Morphology and staining===
===Morphology and Staining===
Gram-stained ''Nocardia'' species are '''indistinguishable''' from ''Actinomyces'' species. They are '''partially acid-fast''' so a Ziehl-Neelsen stain would differentiate them from ''Actinomyces''. They alternate between the coccobacillary resting face and the actively-growing filamentous forms.
Gram-stained ''Nocardia'' species are '''indistinguishable''' from ''Actinomyces'' species. They are '''partially acid-fast''' so a Ziehl-Neelsen stain would differentiate them from ''Actinomyces''. They alternate between the coccobacillary resting phase and the actively-growing filamentous forms.
===Structure and composition===
===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.
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===
===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.
''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.
Diseases in different species include:
Diseases in different species include:
:'''Ruminants''': mastitis, bovine farcy, pneumonia, abortion and lymphadenitis
'''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
'''Horses''': local or general infections due to underlying immunosuppression (EPPID), placentitis which causes abortion.
:'''Pigs''': pneumonia, abortion, lymphadenitis
'''Dogs and cats''': pneumonia, suppurative pleuritis with empyema, dissemination to kidneys, CNS, bones, joints.
'''Pigs''': pneumonia, abortion, lymphadenitis
==''Dermatophilus'' species==
==''Dermatophilus'' species==
''[[Dermatophilus congolensis]]'' is the only species, and is a '''gram-positive filamentous bacterium'''.
''[[Dermatophilus congolensis]]'' is the only species, and is a '''gram-positive filamentous bacterium'''.
===Morphology and composition===
===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.
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===
===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.
''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.
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 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).
It causes lesions on the back ([[Dermatophilosis - Horse|rain scald in horses]], [[Dermatophilosis - Sheep|lumpy wool in sheep]]), feet and legs ([[Dermatophilosis - Sheep|strawberry footrot]] in sheep and [[Greasy Heel|grease heel]] in horses).
==''Streptomyces'' species==
==''Streptomyces'' species==
These are not pathogenic but are similar to ''Nocardia'' species in cultures. Some species '''produce antibiotics''', and they are common '''laboratory contaminants'''.
These are not pathogenic but are similar to ''Nocardia'' species in cultures. Some species '''produce antibiotics''', and they are common '''laboratory contaminants'''.
{{Learning
|flashcards = [[Cytology Q&A 02]]
}}
==References==
==References==
Hirsh, D. (2004) '''Veterinary microbiology''' ''Wiley-Blackwell''
Hirsh, D. (2004) '''Veterinary microbiology''' ''Wiley-Blackwell''
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