Dermatophilus congolensis

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

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 septation 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 mediums. The germ grows well on sheep-blood enriched agarose mediums; the mediums must then be incubated at a 37 degrees Celsius temperature and a 5-10% atmosphere. The bacteriae colonies become visible in 24-48 hours. Initially they are small, with a ~1mm diameter and with a grey-yellow colour. After 3-4 days the isolated bacterial colonies can reach a 3mm diameter, they have a rough surface and a yellow-golden pigmentation. Around the colonies circular hemolysis 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 hygene measures are not respected after dealing with infected animals. This dermatologic condition is known by many names: streptotrichosis, "rain-scald", "lampy wool", "strawberry foot rot".

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