The condition of acne is known as acne vulgaris. When pores in the skin become blocked by sebum: a type of oil that is supposed to drain to the skin's surface (Acne). When this oil becomes trapped, bacteria are able to and begin to grow (Acne). It is then called a microcomedome when the bacteria blocks a pore (Acne). Adolescents generally have acne because of the increase in the hormone testosterone, which enlarges the sebaceous glands in the skin, increases oil production and clogs pores (Acne). the bacteria can then stay under the skin while the oil slowly drains (Propionibacterium). The contents are released to the surface of the skin to heal (Acne). Different types of acne are distinguished by the types of lesions on the skin (Totora 622). The three types are: comedonal, inflammatory and nodular cystic acne (Tortora 622).
Comedonal acne
The mixture of sebum, cells and bacteria accumulate and form what are known as comedos (Tortora 622). Comedos are also known as whiteheads. This type of acne contains both whiteheads and blackheads. Blackheads form when there is lipid oxidization (Tortora 622).
Inflammatory acne
This is the acne that occurs from bacterial activity. The bacteria Propionibacterium acnes is the common contributor to inflammatory acne. P. acnes acquires its needed glycerol from sebum, which then allows the bacteria to produce free fatty acids (Tortora 655). It is these fatty acids that stimulate an inflammatory response (Tortora 622). Neutrophils accumulate to the site of the inflammatory response and secrete enzymes that damage the hair follicle wall (Tortora 623).
Nodular Cystic acne
This type of acne is defined as nodules are cysts that are pus-filled, deep within the skin (Tortora 623). These lesions can be extremely inflamed and can leave scarring (Tortora 623).
Comedonal acne

Inflammatory acne
Nodular Cystic acne

Propionibacterium acnes

Taxonomy: Kingdom: Bacteria; Phylum: Actinobacteria; Class: Actinomycetales; Order: propionibacteriaceae; Family: propionibacterium; Propionibacterium acnes
Propionibacterium acnes are members of the normal microbiota that inhabit the skin (Tortora 617). Because they are of normal microbiota, this bacteria is generally nonpathogenic, but can cause the condition acne vulagaris. These bacteria are Gram-positve, anaerobic and non-spore forming (Propionibacterium). Even though Propionibacterium are usually obligate anaerobes, there are a few strains that are aerotolerant (Propionibacterium causes the skin disorder, "acne"). Propionibacterium can be rod-shaped or branched; and, can be morphologically single, in pairs, or in groups (Propionibacterium). P. acnes is indole-positive, meaning it has the ability to convert the amino acid known as tryptophan into indole (Propionibacterium). This bacterium is also able to produce catalase and nitrate. Propionibacterium are pleomorphic which means the bacteria can take on a variety of different shapes (Propionibacterium). Another feature of this bacterium is that it is diptheroid-like (Propionibacterium). This means that Propionibacterium resemble actual diptheria bacteria in some functions such as grouping together on the skin causing local infection, but does not produce the diptheria toxin, like the actual diptheroid bacteria Corynebacterium diptheria (eMedexpert).
Propionibacterium acnes causes acne vulgaris by releasing lipase enzymes to digest sebum (Acne). The free fatty acids that are formed from digestion combine with bacterial antigens and stimulate an inflammatory response at the hair follicle (Acne).

Propionibacterium acnes produce propionic acid (Tortora 615). This enables the bacteria to keep a low pH between three to five on the skin (Tortora 615). The bacteria is also able to produce acetic and lactic acid from glucose (Tortora 615).
History of Propionibacterium acnes
P. acnes was originally Corynebacterium acnes until two researchers named Douglas and Gunter proved that it was more closely related with the Propionibacterium (Moore and Cato). Originally, the Propionibacterium were classified as being able to ferment lactose into propionic acid; however they proposed that Propionibacterium be modified to include bacteria that do not ferment lactose into propionic acid; and that C. acnes should then be changed to P. acnes (Moore and Cato). In 1946, Douglas and Gunter had insufficient research to prove that the bacteria were capable of producing lactic acid (Moore and Cato). This modification was added into Berygey's manual in 1957 (Moore and Cato). It was later discovered that P. acnes does actually ferment lactose into propionic acid under anaerobic conditions (Moore and Cato).

Treatments for acne

There are many types of antibiotics used for acne that each work in their own way to kill or remove the bacterium Propionibacterium acnes (P.acnes) from the skin. These treatments also work by reducing redness and swelling seen in the inflammatory forms of acne, which are characterized by papules and pustules. However, they have little significant effect on unplugging blocked pores, such as blackheads and whiteheads. Antibiotics can be taken orally or be applied to the skin as a topical treatment (, 2008). The most commonly used antibiotics are as listed: orally taken tetracyclines, topical antibiotics such as clindamycin and erythromycin, topical retinoids, oral retinoids, oral contraceptives, and other topical medications.

Oral Antibiotics:
Under the category of orally taken antibiotics are tetracyclines. This includes tetracycline, doxycycline, and minocycline. Tetracyclines are the most commonly used antibiotic to treat acne. They work by reducing two things: the papules, elevations of skin that are tender and pink, red, purple or brown in color containing no visible fluid, and pustules, which are elevations of skin with pus inside (whiteheads). Oral antibiotics are taken by people with more red, extensive, and tender acne. They usually begin with a higher dosage. As the acne gets better, the dosage is reduced. Oral antibiotics can be related with more side effects than topical ones. Antibiotics are generally prescribed for six months or less (Kerr, 2008). Over time, the P. acnes bacteria can become resistant to the antibiotic being used to treat it, therefore another antibiotic or alternative treatment can be administered. The P. acnes becomes resistant to the antibiotic because of natural selection.
Chemical structure of tetracycline

Topical Antibiotics:
Topical antibiotics include clindamycin and erythromycin. These antibiotics are applied directly to the skin and work by killing Propionibacterium acnes (P. acnes) bacteria (Lai, 2009). They also indirectly keep the pores of the skin open.


Topical Retinoids:
Topical retinoids are prescribed to treat acne that range from mild to moderately severe. Retinoids are synthetic vitamin A derivatives. Medicines derived from vitamin A are useful for treating several types of acne lesions. (Differin), tretinoin (Retin-A, Retin-A Micro. Avita, Renova), tazarotene (Avage), and tazarotene (Tazorac) are common topical retinoids (, 2008). These work by increasing skin cell turnover, which pushes out the plugged material in the follicle. They also prevent new acne blemishes, whiteheads and blackheads, as examples, from forming.
This type of acne antibiotic is very effective. It usually takes six to nine weeks to see a difference. To see the most significant results it would be best to take there for at least a year. Topical retinoids also help diminish fine lines and wrinkles (Kerr, 2008). It takes at least six months to notice a difference in the reduction of wrinkles.


Oral Retinoids:
Oral retinoids are used for treating the more extensive nodular type of acne or severe inflammatory acne, which has not responded to other treatments. Isotretinoin (Accutane) is a type of oral retinoid. It works by shrinking the sebaceous glands within the skin, which reduces the amount of oil produced. The decrease in oil production within the follicle means less clogging of the pores, thereby reducing overall breakouts. A study published in the Journal of the American Academy of Dermatology (2001, vol. 45, pgs. 187-195) 69-75% of the people who completed a course of isotretinoin had a decrease in breakouts or their acne went away completely. A course treatment usually lasts sixteen to twenty weeks followed by a time of rest. If there is not a significant amount of clearing of the acne by the end of the treatment then another session is administered. Usually only one course is needed, but about 20% of patients require a second session.
Isotretionoin can have serious side effects, such as miscarriage, birth defects if mothers take this medication while pregnant, elevated blood fats (triglycerides), and damage to the liver. In order for someone to take this medication they need to register with an online risk management program called iPLEDGE. This program is used to help make sure that female patients are not pregnant when starting the use of isotretionoin and that they do not become pregnant while using this treatment. Both female and male patients need to register with this program because the patients need to promise they are aware of the risks isotretinoin poses, such as depression and suicidal thoughts (, 2008).


Oral Contraceptives:
Oral contraceptives are usually prescribed for hormonal acne. They have shown to successfully clear acne in women by restraining the overactive sebaceous glands and can be used as a long-term acne treatment (, 2008). The birth control brands Ortho Tri-Cyclen and Estro-Step are the only ones approved by the FDA, but expert believe that any low-dose contraceptive would improve acne. These should not be taken by women who have a blood-clotting disorder, have a history of migraine headaches, who smoke, or are older than 35 years of age. In some cases, birth control can make acne worse (Kerr, 2008).

Other Types of Topical Medications:

Other topical medications include azelaic acid, benzoyl peroxide, and salicylic acid. Azelaic acid is used to treat mild to moderate inflammatory and non-inflammatory acne. It works by reducing the P. acnes populations, lessening inflammation, and reducing the abnormal shedding of skin cells. It has also been proven to be effective in treating the dark spots that develop with acne patients who have skin of color. It is tolderated well by most people and can be used for many years at a time. Side effects are lightening of the skin where applied and skin dryness. This antibiotic is as effective as tretinoin and can have increased effectiveness if used with tretinoin. Benzoyl peroxide is used to treat mild acne. It works by killing P. acnes bacteria. Although, it does not have anti-inflammatory properties. It is available as an over the counter medication in a wide amount of strengths. It can be found as a gel, cream, wash, lotion, or cleanser. A lot of acne medications contain benzoyl peroxide because research has shown that it increases the effectiveness of some medicines, like the topical antibiotics clindamycin and erythromycin. When used in combination with other antibiotics it can reduce the likelihood of the body becoming immune to the treatment (Lai, 2009). The most common side effects are skin irritation, bleaching of hair and fabrics, and the cause of allergenic reactions. Salicylic acid belongs to a group of medicines called keratolytics. These work by slowing down the shedding of cells inside follicles, preventing them from clogging. They also help in the breakdown of whiteheads and blackheads. All strengths of salicylic acid are available without a prescription.

Azelaic Acid
Benzoyl Peroxide
Salicylic Acid


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