Propionibacterium acnes

Propionibacterium acnes is a relatively slow growing, (typically) aerotolerant anaerobic gram positive bacterium that is linked to the skin condition acne; it can also cause chronic blepharitis and endophthalmitis, the latter particularly following intraocular surgery. The genome of the bacterium has been sequenced and a study of the bacterial genome has shown several genes that can generate enzymes for degrading skin and proteins that may be immunogenic (activate the immune system).

This bacteria is largely commensal and thus present on most people's skin; and lives on fatty acids in the sebaceous glands on sebum secreted by pores. It may also be found throughout the gastrointestinal tract in humans and many other animals. It is named after its ability to generate propionic acid.

Role in disease
When a pore is blocked this anaerobic bacteria overgrows and secretes chemicals that break down the wall of the pore, spilling bacteria such as Staphylococcus aureus into the skin, and forming an acne lesion (folliculitis).

It has also been found in corneal ulcers, and on very few occasions damaging heart valves leading to endocarditis, and infections of joints (septic arthritis) have been reported.

Antibiotic sensitivity
P. acnes can be killed by benzoyl peroxide, tetracycline group and other antibiotics, and many antibacterial preparations. However, tetracycline-resistant P. acnes is now quite common. Clindamycin is also frequently used. New facts show,that P.acnes are sensitive to some macrolides such as Azithromycin, which has a wide spectrum of action. It is normally prescribed 500 mg by mouth, three times weekly for 4 to 6 weeks. Azithromycin exhibits post-antibiotic effect by concentrating in the lung tissue for approximately 5 days.Indeed some antibacterial cream or ointment should be used during the therapy, giving a good local effect. Another antibiotic is Nadifloxacin from the group of so called 4-fluoroquinolones (such as Ciprofloxacin, Ofloxacin, Levofloxacin). It has action against P. acnes and some other microorganisms that also take part of the poly-infection.

Photosensitivity
P. acnes glows when exposed to Wood's light&mdash;believed to be due to the presence of endogenous porphyrins.

The bacteria is killed by ultraviolet light. P. acnes is also especially sensitive to light in the 405–420 nm (near the ultraviolet) range due to an endogenic porphyrin–coporphyrin III. A total irradiance of 320 J/cm^2 is found to inactivate this bacteria in vitro. This fact is used in phototherapy.

The photosensitivity can be enhanced by pretreatment with aminolevulinic acid which boosts production of this chemical, although this causes significant side-effects in humans.