Enterobacteriaceae, Klebsiella, Escherichia or Serratia genera, i.e. those collectively designated as  lactose-fermenting  Gram-negative rods (LFGNR),  are recovered on culture of the pustules and  anterior nares. Deep nodular and cystic lesions are seen in the remaining 20 per cent of patients, and culture  of the lesions and anterior nares yields Proteus organisms.

Overgrowth of Gram-negative  enterobacteria occurs only when the coagulase-negative Gram-positive cocci and  aerobic diphtheroids are either greatly reduced in number or  eradicated.  A case has been described in which a patient  treated only with topical clindamycin, followed by benzoyl peroxide and topical erythromycin, developed Gram-negative folliculitis caused by Escherichia coli. Gram-negative folliculitis Gram-negative folliculitis is  an infection with Gramnegative organisms that may occur as a complication, usually during longterm treatment of patients for acne vulgaris.29,30 Patients with acne controlled on longterm oral antibiotic  treatment who have  a  sudden flare  of pustular or cystic lesions or who are considered to be resistant to treatment  should be examined  for Gramnegative folliculitis. This condition is one of the commonest reasons for 'clinically resistant' acne.

  Two clinical varieties of Gram-negative folliculitis are recognized. Approximately 80 per cent  of patients with Gram-negative folliculitis have  superficial pustules without comedones, extending from the infranasal area to the chin and cheeks, though the  lesions can Treatment Clinical improvement may occur  within  2-4  weeks when antibiotic  therapy  (such as ampicillin or cotrimoxazole) is directed  against  the  Gram-negative organisms. Relapse of the infection often occurs when antibiotic  therapy is discontinued. Leyden et al noted improvement with  systemic antibiotics, but were unable to 'cure' any of their patients.

  Another report  by Leyden et al described three patients with otitis externa and Gram-negative folliculitis, both  caused by Pseudomonas organisms,  which cleared and remained clear with local antibiotic therapy and  treatment  of the otitis. In  this  report Leyden again indicated that Gram-negative folliculitis caused by LFGNR or Proteus organisms, was rarely cured because eradication of the offending organisms seemed to be almost impossible; some patients had been observed for years without cure.

  Aly and Maibach have also stated that elimination of the organisms in such infections is difficult and  that antibiotic  therapy is not routinely curative.

  In this  author's department, of the last  fifteen patients seen  with Gram-negative folliculitis,  four responded  to a  conventional  antibiotic  approach  but eleven  needed,  and  responded well to, isotretinoin. During a follow-up  period of 6-40 months, three of the eleven have required a repeat  course of isotretinoin.