Castro, Angela C. D. de, et al. “ Effect of Subinhibitory Concentrations of Penicillin on Antigens of Group G Streptococci ”. Revista Do Instituto De Medicina Tropical De São Paulo, vol. 28, no. 4, Aug. 1986, pp. 234-8, https://revistas.usp.br/rimtsp/article/view/87494.