Microbiologic testing: Recommendations

What is the role of microbiological and endocrine testing in evaluating patients with adult acne and acne vulgaris in adolescents to adults?

  • Routine microbiologic testing is not recommended in the evaluation and management of patients with acne.
  • Those who exhibit acne-like lesions suggestive of gram-negative folliculitis may benefit from microbiologic testing.

Strength of Recommendation: B  Level of Evidence: II, III

Propionibacterium acnes (P. acnes), a gram-positive anaerobic rod, is the primary bacterium implicated in acne.40-42 It has specific, non-standard culture requirements that prohibit routine culture. Currently, microbiologic testing of acne lesions is largely unnecessary as it does not affect management, and successful antibiotic treatment may not result from a reduction of bacterial numbers.40 The antibiotics typically used in the management of acne, the tetracyclines, have additional anti-inflammatory actions independent of microbial killing. As additional information is learned about P. acnes from a molecular and genetic perspective, and its role in inciting inflammation in acne,43-48 more targeted therapeutic interventions in the future may result.

The prime situation where microbiologic testing is useful in acne patients is in evaluating for gram-negative folliculitis. This uncommon disorder presents as uniform and eruptive pustules, with rare nodules, in the perioral and perinasal regions, typically in the setting of prolonged tetracycline use. It is caused by various bacteria such as Klebsiella and Serratia, and is unresponsive to many conventional acne treatments. Gram-negative folliculitis is typically diagnosed via culture of the lesions, and is generally treated with isotretinoin or an antibiotic to which the bacteria are sensitive. In cases of acne unresponsive to typical treatments, particularly with prominent truncal involvement and/or monomorphic appearance, pityrosporum folliculitis should be considered. Staphylococcus aureus cutaneous infections may appear similar to acne, and should be considered in the differential, particularly in cases of acute eruptions; swab culture may be helpful in these cases.

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