It is widely suspected that the anaerobic bacterial species Propionibacterium acnes ( P. acnes ) contributes to the development of acne, but its exact role is not well understood.  There are specific sub-strains of P. acnes associated with normal skin, and moderate or severe inflammatory acne.  It is unclear whether these undesirable strains evolve on-site or are acquired, or possibly both depending on the person. These strains have the capability of changing, perpetuating, or adapting to the abnormal cycle of inflammation, oil production, and inadequate sloughing of dead skin cells from acne pores. Infection with the parasitic mite Demodex is associated with the development of acne.   It is unclear whether eradication of the mite improves acne. 
Tetracycline antibiotics were first discovered as a natural product found in soil, in 1945, by American plant physiologist Benjamin Duggar. Three years later, the first tetracycline, called Aureomycin, was prescribed. Tetracyclines belong to a class of antibiotics that are bacteriostatic in action and have been used safely since this time, demonstrating a wide spectrum of activity against numerous pathogens and having additional immune-modulating effects. Today, they are commonly prescribed by dermatologists for extended periods of time to treat teenage acne. Tetracyclines are considered to be less subject to the promotion of disease-resistant strains of bacteria in terms of their mode of action and the types of bacteria they target. This has been evidenced by their continued efficacy over the past 70 years.
This condition presents with blackheads appearing around the face, neck, chest, upper arms and buttocks in groups of two or three. The pimples form around the blackheads. They are large and engorged with fluid and may be sensitive to touch. They remain for a while and continue to grow and fill with pus until they finally rupture. After the lesion has drained, it fills up again. After they rupture, several nodules can fuse together to form larger shapes. The lesions remain for a long time. They form a scab in the center but they continue to spread outwards. When the lesions do eventually heal, they leave scars that can be the usual type of acne scar (atrophic) or can be the raised bump normally left behind by a burn or a cut (keloidal).