gammahemolytic

Gamma-hemolysis, or gamma-hemolytic, is a term used in microbiology to describe bacteria that do not lyse red blood cells when grown on blood agar. In contrast to alpha-hemolysis (partial, greenish discoloration) and beta-hemolysis (complete clearing of the surrounding red cells), gamma-hemolysis results in no visible change in the surrounding medium.

Detection is performed by streaking colonies on 5% sheep blood agar and incubating for 18-24 hours at 35-37°C in air or CO2 depending on the organism. After incubation, colonies with no zone of red blood cell lysis or discoloration are described as gamma-hemolytic. The pattern can be combined with other biochemical tests for species identification.

Gamma-hemolysis is observed in a variety of Gram-positive cocci, including many non-hemolytic streptococci and some Enterococcus species. These organisms may be part of normal flora but can also be opportunistic or pathogenic, causing infections such as urinary tract infections, endocarditis, or wound infections, particularly in hospital settings.

Limitations: Hemolysis patterns can vary with incubation time, temperature, and medium composition; some strains may appear non-hemolytic under standard conditions but show weak or delayed hemolysis later, leading to misclassification. Therefore, gamma-hemolysis is one part of a broader phenotypic profile used for identification.