Beta-hemolytic streptococci colonise mucosal surfaces of both animals and humans, where they are capable of initiating a diverse number of diseases. Two human-associated species, group A streptococcus (GAS) and group B streptococcus (GBS) are major human pathogens that contribute to morbidity and mortality. The group G streptococcus (GGS) is the neglected cousin of these two pathogens. Long considered a commensal, or only able to cause opportunistic disease in susceptible individuals, evidence is accumulating that GGS is capable of causing a similar spectrum of disease as GAS in humans. In this review we draw attention to the epidemiological and clinical features pertinent to this organism as a human pathogen. We also highlight the virulence factors that enable this bacterium to cause disease. As many of these virulence factors are also found in GAS, horizontal gene transfer events between these two species may account for the apparent increase in pathogenicity of human GGS.
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