Dermatophilus congolensis is a gram positive bacterium and is the etiologic agent of a disease called Dermatophilosis (sometimes called Mud fever

Mud fever

Mud fever is a group of diseases of horses causing irritation and dermatitis in the lower limbs of horses. Often caused by a mixture of bacteria, typically Dermatophilus congolensis, and Staphylococcus spp, mud fever can also be caused by fungal organisms...

) in animals and humans, a dermatologic condition that manifests itself with the formation of crusty scabs that contain the microorganism. Some people erroneously call it mycotic dermatitis. Rainscald

Rainscald

Rainscald is a common skin disease in horses that is caused by Dermatophilus congolensis. This is the same organism that causes Mud fever in horses. This disease is very common in cows, sheep and goats and is also found occasionally in cats, dogs, and humans. D...

 is another condition often seen in animals, which is also caused by Dermatophilus congolensis bacteria.

Morphology

D. congolensis is facultative anaerobic actinomycete bacteria. It has two morphologic forms: filamentous hyphae and motile zoospores. The hyphae are characterized by branching filaments (1-5 µm in diameter) that ultimately fragment by both transverse and longitudinal separation into packets of coccoid cells. The coccoid cells mature into flagellated ovoid zoospores (0.6-1 µm in diameter). With the microscope one can observe the characteristic "tramcar line"-like D. congolensis colonies together with gram positive thin filaments and coccoid forms.

Cultivation

D. congolensis is a carboxiphylic germ, so they need carbon dioxide to properly grow on laboratory media. The germ grows well on sheep-blood enriched agarose media; the media must then be incubated at a 37 degrees Celsius temperature and a 5-10% atmosphere. The bacteria colonies become visible in 24–48 hours. Initially they are small, with a ~1 mm diameter and with a grey-yellow colour. After 3–4 days the isolated bacterial colonies can reach a 3 mm diameter, they have a rough surface and a yellow-golden pigmentation. Around the colonies circular hemolysis

Hemolysis

Hemolysis —from the Greek meaning "blood" and meaning a "loosing", "setting free" or "releasing"—is the rupturing of erythrocytes and the release of their contents into surrounding fluid...

zones can be seen.

Pathogenesis

D. congolensis causes severe skin infections in animals and humans. More frequently cattle, horses, sheep and goats are affected. Humans can also get this skin disease if elementary hygiene measures are not respected after dealing with infected animals. This dermatologic condition is known by many names: cutaneous streptothrichosis (on cattle, goats, and horses), "rain-scald" (on horses), "lumpy wool" (on sheep), "strawberry foot rot".

The pathogenic factors are very diverse, but the most important ones are the ones of enzymatic nature (adenase and lecitinase).