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Gram-negative folliculitis

6 June 2019, by AZEVEDO A.


Chapter written with the help of the EADV, the Fondation René Touraine and the Therapeutics in Dermatology


Folliculitis is a very common skin disorder caused by the inflammation of the hair follicle. A hair follicle is a sac under the skin from which hair grows. Folliculitis is usually caused by a bacterial infection. Occasionally, folliculitis is caused by a fungal infection, or by irritants, physical trauma or drugs. Within folliculitis caused by bacteria, Staphylococcus aureus is the most common cause. Staphylococcus aureus are gram-positive bacteria that normally live on the skin without causing problems. Gram-negative folliculitis refers to a bacterial folliculitis caused by a group of bacteria different from Staphylococcus aureus. The term "Gram negative" refers to the staining pattern of the organisms in the laboratory. Certain bacteria do not take up a stain known as "Gram". Gram-negative bacteria causing folliculitis include Pseudomonas aeruginosa, responsible for the commonly known “hot tub folliculitis”, and others such as Enterobacter, Klebsiella, Proteus, or Escherichia, which may infect patients receiving long-term antibiotic therapy for acne.


"Hot tub folliculitis" appears as small red bumps or white-headed pimples that develop around hair follicles. These small bumps are often itchy and appear 8 to 48 hours after exposure to contaminated water with Pseudomonas aeruginosa. The lesions are commonly found on the trunk and buttocks in the distribution of the wet bathing suit or other areas exposed to contaminated water.

Gram-negative folliculitis due to Klebsiella, Enterobacter, or Proteus is usually seen in patients with acne receiving antibiotic pills for long periods of time. Signs and symptoms include small red bumps or large swellings and pus-filled blisters located in the central area of face, around the area of the upper lip under the nose, to the chin and cheeks. It is often mistaken as a worsening of acne and should be suspected in patients with these lesions and with poor response to usual anti-acne antibiotics.


"Hot tub folliculitis" is caused by contact with water contaminated with Pseudomonas aeruginosa, that is found in spa pools, whirlpools, swimming pools and hot tubs where the chlorine levels and pH balance are not adequately monitored.

Long-term antibiotic therapy, usually with a group of antibiotics called tetracyclines, in patients with acne may cause gram-negative folliculitis. The antibiotics affect the bacterial balance in the skin, reducing the number of bacteria that normally live on the skin, particularly on the nose, and increasing gram-negative bacteria. In some patients, the increased number of gram-negative organisms results in a transfer of organisms from the nose to neighboring areas of the face. Theses gram-negative bacteria, including Enterobacter, Klebsiella, Proteus, or Escherichia, populate existing acne lesions and can also cause more small red bumps and pus-filled blisters. In addition, these gram-negative bacteria require a sufficiently moist environment to survive and proliferate. Therefore, the oily skin of patients with acne may contribute to the survival of gram-negative organisms.


“Hot tube folliculitis” due to Pseudomonas aeruginosa can resolve on its own within 7 to 10 days with just good skin hygiene. An antibacterial soap can be use. Antibiotics pills, particularly ciprofloxacin, can be prescribed for severe cases or in patients who have a compromised immune system. To prevent “hot tube folliculitis” is important to avoid contaminated water and only use pools and hot tubs that have its acid and chlorine levels monitored and maintained.

Treatment for gram-negative folliculitis due to long-term systemic antibiotic therapy usually includes antibiotic pills to which the gram-negative organisms are sensitive. Ciprofloxacin, ampicillin or trimethoprim/sulfamethoxazole are common first-line options. Treatment with antibiotic cream or gel with benzoyl peroxide can be associated to the oral antibiotic. In resistant or recurrent cases after antibiotic pills, the treatment of choice is oral isotretinoin. Isotretinoin is a medicine that act by suppressing sebum production and drying out the skin and mucous membranes, especially the nasal mucous membranes, which is where causative bacteria are found. 


— Folliculitis appears when a hair follicle gets infected and most cases of folliculitis get better without treatment.

— It is important to see a doctor if the small bumps get larger or more painful, the small bumps go away but then come back or if the patient get fever.

— Gram-negative folliculitis includes the “hot tube folliculitis” that appears hours to 2 days after exposure to contaminated water from a pool or hot tube. Most cases will get better on their own within 7 to 10 days. To relief the pruritus and discomfort the patient can apply a warm, moist washcloth or compress on the small bumps, and repeated as needed. Severe cases may need antibiotics pills.

— Gram-negative folliculitis should be suspected in patients with acne who, despite receiving long-term systemic antibiotic therapy, experience a worsening of acne-like lesions. These cases usually clear with antibiotics to which the organisms are sensitive. Oral isotretinoin can be used in severe cases.

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