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Morganella morganii is a facultative anaerobic, gram-negative bacillus belonging to the Enterobacteriaceae family. Though traditionally considered an opportunistic pathogen, it has emerged as a significant cause of skin and skin structure infections (SSSIs), particularly in immunocompromised individuals, surgical patients, and those with chronic wounds. Its increasing resistance profile adds complexity to clinical management. Microbiological Characteristics

Klebsiella species, primarily Klebsiella pneumoniae, are gram-negative bacilli associated with healthcare-associated infections and opportunistic community-acquired cases. While most commonly implicated in urinary tract and respiratory infections, Klebsiella can also cause severe skin and skin structure infections (SSSIs), especially in immunocompromised or hospitalized individuals. Pathogenesis of Klebsiella in Skin and Soft Tissue Klebsiella species possess virulence

Skin and skin structure infections (SSSIs) encompass a wide spectrum of bacterial infections involving the epidermis, dermis, subcutaneous tissue, fascia, and muscle. These infections vary in severity from mild superficial conditions to life-threatening necrotizing fasciitis. Accurate classification and prompt intervention are vital to minimizing complications and ensuring effective treatment. Classification of SSSIs Based on Severity

Fusobacterium species are obligate anaerobic, gram-negative bacilli commonly found in the oropharynx, gastrointestinal tract, and genitourinary system. Though often commensal, these bacteria can cause severe infections under the right conditions, particularly when the skin barrier is compromised. Among soft tissue pathogens, Fusobacterium necrophorum and Fusobacterium nucleatum are notable for their involvement in necrotic skin and

Enterococcus species, primarily Enterococcus faecalis and Enterococcus faecium, are gram-positive, facultative anaerobic cocci that commonly inhabit the gastrointestinal tract. Although often considered low-virulence organisms, they have emerged as significant nosocomial pathogens, particularly in skin and skin structure infections (SSSIs), where their intrinsic resistance and capacity to acquire new resistance genes complicate treatment. Pathogenesis of Enterococcus

Enterobacter species, primarily Enterobacter cloacae and Enterobacter aerogenes (now Klebsiella aerogenes), are gram-negative, facultative anaerobic bacilli within the Enterobacteriaceae family. While commonly colonizing the gastrointestinal tract, these organisms are opportunistic pathogens in hospitalized and immunocompromised patients. Their role in skin and skin structure infections (SSSIs) has grown due to increasing antimicrobial resistance and prevalence in

Escherichia coli (E. coli) is a facultative anaerobic, gram-negative bacillus that predominantly inhabits the gastrointestinal tract. While widely recognized as a cause of urinary tract and gastrointestinal infections, E. coli has also emerged as a significant pathogen in skin and skin structure infections (SSSIs), especially among immunocompromised patients, surgical wound cases, and polymicrobial infections. Its

Clostridium species are anaerobic, spore-forming, gram-positive bacilli found ubiquitously in soil, the gastrointestinal tract, and human skin. Certain species, particularly Clostridium perfringens, Clostridium septicum, and Clostridium sordellii, are highly pathogenic and associated with severe skin and skin structure infections (SSSIs), including cellulitis, fasciitis, and life-threatening gas gangrene (Clostridial myonecrosis). These infections typically arise from contaminated

Citrobacter species, members of the Enterobacteriaceae family, are gram-negative, facultatively anaerobic bacilli. While commonly associated with urinary tract and gastrointestinal infections, they are increasingly implicated in nosocomial skin and skin structure infections (SSSIs), especially in immunocompromised or hospitalized individuals. Among the most clinically relevant are Citrobacter freundii and Citrobacter koseri. Pathogenesis and Virulence Factors in

Bacteroides fragilis is an obligate anaerobic, gram-negative bacillus commonly found in the gastrointestinal flora. While typically commensal, it becomes pathogenic when introduced into sterile areas such as skin and subcutaneous tissues, particularly following trauma, surgery, or mucosal barrier disruption. Among anaerobes, B. fragilis is notable for its virulence, antibiotic resistance, and role in mixed polymicrobial