Dysgalactiae

Dysgalactiae refers to Streptococcus dysgalactiae, a species of Gram-positive, catalase-negative cocci that grow in pairs or chains. It is a member of the genus Streptococcus and belongs to Lancefield groups C and G. The species comprises at least two clinically important subspecies: Streptococcus dysgalactiae subsp. dysgalactiae, commonly associated with bovine mastitis, and Streptococcus dysgalactiae subsp. equisimilis (SDSE), which is primarily a human pathogen. SDSE is typically beta-hemolytic and can be isolated from the human oropharynx and skin, where it exists as part of the normal flora in some individuals.

In humans, SDSE can cause a range of infections from mild to severe, including pharyngitis, cellulitis, erysipelas, necrotizing fasciitis, bacteremia, endocarditis, septic arthritis, and osteomyelitis. In animals, S. dysgalactiae subsp. dysgalactiae is a common cause of bovine mastitis and can contribute to other livestock infections. Zoonotic transmission is possible but uncommon.

Diagnosis relies on standard microbiological techniques: Gram-positive cocci in chains, beta-hemolysis on blood agar, and Lancefield grouping (C or G). Identification can be confirmed by MALDI-TOF mass spectrometry or molecular methods. Antimicrobial susceptibility testing guides treatment, as susceptibility patterns vary. Penicillin and other beta-lactams are typically effective first-line therapies, but resistance to macrolides and tetracyclines has been reported in some SDSE isolates, so therapy should be guided by local susceptibility data and clinical context.

Prognosis is generally favorable with appropriate antibiotic therapy, though invasive infections can occur, particularly among older adults or individuals with underlying health conditions.