3rd Cause of Acne (out of 4 main causes)

Acne is not infectious. But three major organisms have been identified and isolated from the surface of skin and from pilocebaceous duct of patients with acne. They are propionibacterium acnes (P.acne), staphylococcus epidermidis and malasazzia furfur (causative agent for acne rosasae ). Propionibacterium has three subgroups and they are P. acnes, P. granulosum and P. avidum. P. acnes is most important in pathogenesis & to lesser extent P. granulosurm are also involved.

During adolescence and seborrhea the number of P. acnes increases much more than normal time. But interestingly there is no relationship between increase in numbers of P. acnes and severity of acne. But there is strong relationship of severity of acne with P. acnes recovered from 4 mm punch biopsy. In one of the study cutaneous micro flora from patients with late onset acne, adolescence acne and normal subject without acne were compared. The micro organism found were P. acnes, staphylococci and malassazia and in the first two groups the propionibacterium species were in large numbers compare to other two types of micro organisms.

It was also seen in biopsies that number of micro organisms were higher in inflamed follicles than normal follicles. But if can not be said that these micro organisms are responsible for inflammation. But they are certainly involved in inflammatory process at one point or other. Some authors also say that number of micro organisms increases at every stage as a follicle progresses from normal to comedone and to inflamed lesion. Because there is ten fold increase of organisms in inflamed lesions. But some authors say that inflamed lesion simply provide and environment for growth of organisms. It has been seen in vitro (in laboratory outside living animal) that pH, oxygen tension and nutrition can significantly affect growth of P. acnes and also substances produced by P. acnes like enzymes protease, lipase (metabolize lipids), hyalurame acid lipase, phosphates etc. In vivo (in living subject) the pH of blackheads vary from 3.6 to 6.7. P. acnes grow well in low oxygen tension. But P. acnes also grow well in high oxygen tension if there is light. All the above factors might determine whether or not a follicle will develop into an comedone without inflammation or into inflamed lesion.

P. acne is non motile, but can easily colonize the pilosebaceous duct. Though it is not clear how it colonizes the duct. P. acnes must clump (aggregation of bacteria into irregular masses) to colonizes the polosebaceous duct and clumping is aided by free fatty acids. So bacterial lipase which break triglycerides to free fatty acids may be required for clumping and ductal colonization.

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