Background. Streptococcus pneumoniae is a very rare cause of skin and soft tissue infections (SSTI). The aim of this study was to determine the clinical and microbiological characteristics of these infections. Material and methods. The medical records of patients with SSTIs due to S. pneumoniae diagnosed at the University Hospital of Guadalajara between January 2012 and December 2020 were retrospectively reviewed. Microbiological identification was performed using conventional procedures. Antimicrobial sensitivity was performed using the MicroScan WalkAway-96 plus automatic system and E-test strips following the recommendations of the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Results. Fifteen cases of SSTIs were diagnosed. 73,3% of the cases presented underlying diseases, neoplasias being the most frequent. 60% of the cases presented predisposing factors, immunosuppression being the most common. The clinical presentations were: abscesses in different locations, ulcers, surgical wounds, lactational mastitis and necrotizing fasciitis. Polymicrobial infections were detected in 73.3% and the etiology was nosocomial in 6.6%. The clinical course was favorable in 90.9% of the cases. The antibiotics with the highest percentages of sensitivity against S. pneumoniae were cefotaxime, levofloxacin, vancomycin, linezolid and rifampicin. Conclusions. S. pneumoniae should be kept in mind as a possible causative agent of SSTIs, especially in patients with neoplasias and immunosuppression. Its involvement in infections such as lactational mastitis and necrotizing fasciitis should be highlighted. The clinical evolution is favorable in most patients, but it is important to pay special attention to cases of necrotizing fasciitis due to the severity of these infections.

Mycobacterium smegmatis is an environmental microorganism that has been rarely implicated in skin and soft tissue infections (SSTIs). In the present report, we present a cutaneous abscess associated with cellulitis that occurred after an infiltration with corticosteroids for a trochanteric bursitis. Clinical outcome was good after treatment with oral doxycycline for 6 months. The review of the literature showed that M. smegmatis has been implicated in SSTIs after trauma or surgery. The treatment was carried out with a wide variety of therapeutic regimens associated with surgery in many of them. In conclusion, M. smegmatis should be considered as a cause of SSTI, especially after trauma or surgery. M. smegmatis infections can be underdiagnosed if microbiological cultures are not incubated for a long time. The optimal therapeutic regimen for treating SSTIs remains unclear, but prolonged treatment with doxycycline can be a good option.