What is Propionibacterium acnes
Propionibacterium acnes is a Gram-positive anaerobic, non-spore-forming bacterium that normally dwells in human skin, particularly in pilo-sebaceous follicles, where it gets the nutrients it needs from sebum, by-products of skin metabolism and cellular debris present in these areas.
Role in Acne
Propionibacterium acnes prefers the conditions of anaerobiosis (absence of oxygen) associated with the presence of abundant sebaceous secretions; these circumstances take place inside the comedones ("plugs of the skin pores"), miniature black dots that prevent the normal flow of sebum into the ductus of the pilosebaceous follicle, and from there to the skin surface.
The activity of Propionibacterium acnes within the comedones determines an inflammatory response mediated by the release of various substances capable of playing a role in the pathogenesis of acne: hyaluronidase, protease, lipase and chemotactic factors for neutrophils, lymphocytes and macrophages. The ability of Propionibacterium acnes to produce an extracellular lipase that hydrolyzes sebum triglycerides to glycerol and fatty acids is well known in this regard, favoring the growth of other bacterial species, predisposing to comedogenesis and aggravating local inflammation. This phlogosis undermines the integrity of the keratinocytes and the follicular wall, damaging it until it ruptures.
In some subjects, the inflammatory skin reaction to these events is such as to trigger an exponentially growing inflammatory reaction, which culminates in the typical signs of acne: formation of papules, pustules and nodules.
Treatment
Due to the important role of Propionibacterium acnes in the aetiopathogenesis of acne, antibiotics - both topical and systemic - are an important aid in the pharmacological therapy of acne, especially pustular.
Normally, the use of topical antibiotic therapy is reserved only for the most serious cases of acne, more so in the case of oral antibiotic therapy, in order to avoid the onset of resistance to the same antibiotics.
In fact, despite the bacteriostatic, bactericidal and anti-inflammatory action of these drugs is therapeutically advantageous, the growth of Propionibacterium acnes strains resistant to some of the antimicrobials normally used in topical therapy, such as clindamycin, erythromycin, benzoyl peroxide, is already known, meclociclina, nadifloxacin, gentamicin and azelaic acid.
For this reason, the use of antibiotics must take place in full compliance with medical prescriptions. In general, the treatment of acne with topical antibiotics should be limited to a period of 6-8 weeks and, above all, these drugs should not be used as monotherapy.
Topical retinoids (such as the adapalene, tretinoin or isotretinoin) increase the anti-acne efficacy of antimicrobials by facilitating their penetration into obstructed pilosebaceous follicles, where Propionibacterium acnes dwells .
Other pathologies
Propionibacterium acnes is not only and exclusively implicated in the appearance or worsening of acne manifestations.
In fact, this beating can also become an opportunistic pathogen, occasionally identified as responsible for arthritis, osteomyelitis, endocarditis, meningitis and surgical infections (being protected inside the pilosebaceous follicles, it resists very well to the preoperative procedures of skin disinfection).
Moreover, some studies have shown the presence of P. acnes in patients suffering from sarcoidosis and sciatica, thus hypothesizing a relationship between these pathologies and the presence of an eventual infection caused by this beating.
In patients with sarcoidosis, P. acnes was found inside the lymph nodes. In patients with sciatica, however, the beating has been found at the level of the intervertebral discs.
Finally, the inflammation caused at the skin level by Propionibacterium acnes can create favorable conditions for the development of secondary infections from other bacteria that normally are not part of the cutaneous commensal flora, such as, for example, Staphylococcus epidermidis .
