The what, when and how in performing and interpreting microbiological diagnostic tests in skin and soft tissue infections.

Purpose of review To summarize and classify the most recent and relevant microbiological studies for each type of skin and soft tissue infection (SSTI). Recent findings Following Infectious Diseases Society of America and Food and Drug Administration classifications of SSTIs, we differentiate between two large groups, the superficial or uncomplicated infections and the complicated infections with deep involvement. It is not usually necessary to obtain microbiological samples in uncomplicated infections, except in cases of recurrences or for epidemiological control purposes. In the case of complicated infections, the samples are of two different types: those obtained from the affected area (surgical samples, punctures of abscesses or swabs) and systemic samples (i.e. blood cultures). The clinical condition also determines the type of samples to be obtained. In cases of systemic involvement, blood cultures are mandatory. For immunocompromised patients, who may present atypical infections, detection of antigens, serologies or molecular biology techniques may be helpful. The rapid diagnosis is currently the goal to be pursued by implementing techniques such as matrix assisted laser desorption ionization-time of flight, commercial real-time PCR or the promising metagenomics. Summary Microbiological diagnosis is one of the cornerstones of the management of SSTIs. Prompt obtaining and processing of the necessary samples, depending on the clinical situation of the patient, is of relevance in the decision-making process. Rapid and fluid reporting of the results (identification, mechanisms of resistance and antibiogram) will improve the management of these patients.