Fournier’s gangrene was first identified in 1883, when the French dermatologist and venereologist Jean Alfred Fournier diagnosed a rapidly progressive gangrene of the genitalia with no discernible etiology in five young men . Now defined as a necrotizing fasciitis of the perineal or genital areas [1, 2], Fournier’s gangrene remains unusually rare, with an incidence ranging from 0.002% to 0.005% of annual hospital admissions . The infection can rapidly spread throughout the perineum, thighs, and torso, subsequently leading to gangrene, septic shock, and death if untreated. Although Group A streptococci were thought to be the sole cause of Fournier’s gangrene , subsequent clinical series have emphasized the polymicrobial nature of the disease [1, 16], which is hypothesized to synergize enzyme production and promote rapid multiplication and spread of infection . The most common causative microorganisms include facultative organisms (E. coli, Klebsiella, enterococci), along with anaerobes (Bacteroides, Fusobacterium, Clostridium, or anaerobic or microaerophilic Streptococci). This case is unique because the patient lacked the typical risk factors associated with Fournier’s gangrene, such as diabetes, immune compromise, obesity, drug use, or genital trauma [1–3], and his infection was caused by Streptococcus dysgalactiae subsp. equisimilis (SDSE).
SDSE, a pyogenic β-hemolytic streptococcus , usually colonizes the upper respiratory, gastrointestinal, and female genital tracts . However, it is increasingly being recognized as an important human pathogen , with a wide spectrum of disease similar to that caused by S. pyogenes, including endocarditis, rheumatic fever, and streptococcal toxic shock-like syndrome . In a recent population-based study, the burden of invasive SDSE infections approximated that of invasive S. pyogenes infections . SDSE primarily presents as skin and soft-tissue infections, including pyoderma, cellulitis, wound infections, abscesses, erysipelas, and necrotizing fasciitis . SDSE contains either Lancefield group antigens C or G, but needs to be distinguished from S. anginosus group strains, which frequently contain the same antigens. The use of MALDI-TOF MS to differentiate between streptococcal species has been established [19–21], although misidentification may occur because of striking similarities in proteomic profiles [22, 23]. The organism in our case was misidentified as S. anginosus group by MALDI-TOF MS, because sequencing the 16S rRNA segment confirmed the isolate as SDSE. While few laboratories report identification of β-hemolytic Group C and G streptococci to the species level , differentiation should not be ignored because SDSE is more invasive than the S. anginosus group , and may have virulence factors similar to S. pyogenes[26, 27]. Although the presence of streptococcal superantigens such as SpeG homologues have been described in SDSE [6, 28], our clinical isolate lacked Group A streptococcal superantigen genes and activity. Nevertheless, our case demonstrates the potential benefit of molecular assays in differentiating closely-related streptococcal species, although further studies are needed to assess their clinical impact. To our knowledge, there are no other reports of Fournier’s gangrene caused by Streptococcus dysgalactiae subspecies equisimils (SDSE). One study isolated Group C Streptococcus from the perineum of a diabetic male with Fournier’s gangrene , but the species was not reported, and a potential role for superantigens was not investigated.
At our institution, the incidences of invasive S. anginosus group and SDSE infections were 3.9 and 3.2 cases per 100,000 respectively (Table 2). The rate of invasive S. anginosus group infection is slightly higher than previous studies , while the rate of invasive SDSE infection is slightly lower. Although rare penicillin-resistant SDSE strains have been reported , isolates from our centre were sensitive to penicillin. Six percent of S. anginosus group isolates, however, were resistant to penicillin, which is higher than other studies . While the mechanisms of resistance have yet to be fully elucidated, the potential transfer of penicillin resistance determinants from related Streptococcal species , together with selective antibiotic pressure, may play a role in the emergence of penicillin resistance in the S. anginosus group [4, 33]. Therefore, the addition of an aminoglycoside to a cell wall-active agent may be appropriate for severe S. anginosus group infections to avoid delayed response of infection . Similar to other studies  showing widespread resistance to macrolides (16-24%) we also observed erythromycin resistance (12% and 7% for S. anginosus group and SDSE isolates, respectively), albeit at a lower rate. Additionally, 12% of S. anginosus group isolates and 14% of SDSE isolates were resistant to clindamycin, suggesting that despite the popularity of macrolide and clindamycin use in infected patients, they may not be appropriate for all cases.
In conclusion, we present a case of Fournier’s gangrene of the penis caused by SDSE, highlighting a unique disease presentation of the organism, and underscoring the limitations of MALDI-TOF MS in differentiating between closely-related streptococcal species which may hixave differing pathogenic profiles.