Mycobacterium smegmatis

Mycobacterium smegmatis was first described in November 1884 by Lustgarten, who found a bacillus with the staining pattern of tubercle bacilli in syphilitic chancre. Subsequently, Alvarez and Tavel found organisms similar to those described by Lustgarten and also in normal genital secretions (smegma). This organism was later named M. smegmatis (Trevisan).

Mycobacterium smegmatis belongs to the fast-growing (RGM) acid-fast nontuberculous mycobacteria (NTM). The name "smegmatis" refers to its detection in smegma. Until 1986, this germ was considered nonpathogenic to humans. To date, infections caused by M. segmatis are rare. < than 100 cases have been described in the literature to date. In most cases, there was a connection with various surgical procedures.

Case presentations (see literature):

1) A 56-year-old Asian female patient who had undergone several facial cosmetic procedures in the past 2 years was admitted to our institution with swelling, localized pain, and erythema on the right cheek. Mycobacteirum fortuitum complex isolated from a pus culture was identified as M. wolinskyi by rpoB sequencing. Radiography revealed metallic foreign bodies and an abscess. The pus was incised and drained. Treatment consisted of clarithromycin (500 mg every 12 hours), amikacin (200 mg every 8 hours), and ciprofloxacin (400 mg every 6 hours).

2) 32-year-old healthy woman who developed swelling and erythema with a painful sensation at the injection site 2 weeks after injection of "filler material." The treating physician prescribed intravenous cephalosporin for 3 days to treat the infection without improvement. However, the patient's symptoms worsened as nodules and abscesses formed. Surgical debridement was then performed, and amoxicillin was added to the treatment regimen. The tissue sample from the debridement was sent for testing for common bacteria and fungi, but the results were negative. After two months of unsuccessful treatment with broad-spectrum antibiotics and surgical debridement, the following clinical findings were found; scattered erythematous plaques with subcutaneous nodules and abscesses on both sides of the cheeks, some of which were confluent. No systemic symptoms or lymphadenopathies were noted. Routine laboratory values were within the normal range. Biopsies taken showed granulomatous inflammation in the dermis with epithelioid histiocytes and multinucleated giant cells mixed with abundant lymphocytes, plasma cells, and neutrophilic granulocytes. Microscopically, no evidence of microorganisms. Multiplex real-time PCR assays targeting the HSP65 gene and the 16S rRNA gene of NTM and panfungal multiplex real-time PCR targeting the 28S rRNA gene identified M. smegmatis as the causative pathogen.

Treatment was 300 mg rifampin per day, 150 mg isoniazid per day, and 100 mg minocycline per day for six months. Among them, healing of the infection.

The discovery of plasmids, phages, and mobile genetic elements has enabled the construction of specialized gene inactivation and gene reporter systems. The strain M. smegmatis mc2155 is hypertransformable and is now considered the workhorse of mycobacterial genetics. In addition, it is easily cultured in most synthetic or complex laboratory media, where it can form visible colonies within 3-5 days. These characteristics make it a very attractive model organism for M. tuberculosis and other mycobacterial pathogens. M. smegmatis mc2155 is also used for the cultivation of mycobacteriophages. The complete genome of M. smegmatis has been sequenced.

Transformation is a process in which a bacterial cell takes up DNA that has been released from another cell into the surrounding medium and then incorporates that DNA into its own genome by homologous recombination. Strains of M. smegmatis that possess a particularly efficient DNA repair machinery, as indicated by their greater resistance to the DNA-damaging effects of agents such as UV and mitomycin C, were found to be the most likely to undergo transformation. This suggests that transformation in M. smegmatis is a DNA repair process, presumably a recombinant repair process, as in other bacterial species.

1. Fida M et al (2021) Misidentification of Mycobacterium smegmatis as Mycobacterium fortuitum by DNA line probe assay. J Clin Tuberc Other Mycobact Dis 25:100268.
2. Kumar KJ et al (1995) Fatal pulmonary infection caused by Mycobacterium smegmetis in an infant. Indian J Pediatr 62:619-621.
3. Wang CJ et al (2022) Mycobacterium smegmatis skin infection following cosmetic procedures: report of two cases. Clin Cosmet Investig Dermatol 15:535-540.
4. Yoo SJ et al (2013) Facial skin and soft tissue infection caused by Mycobacterium wolinskyi associated with cosmetic procedures. BMC Infect Dis 13:479. doi: 10.1186/1471-2334-13-479.