Antibiotic substance produced by a Cephalosporium sp. cultivated from the sea near Sardinia. Crude cephalosporin P contains at least 5 components: P1, P2, P3, P4, P5, the major active substance being cephalosporin P1. Isoln: Burton, Abraham, Biochem. J. 50, 168 (1951). Structure: Baird et al., Proc. Chem. Soc. London 1961, 257; Halsall et al., ibid. 1963, 16; Melera, Experientia 19, 565 (1963); Halsall et al., Chem. Commun. 1966, 685.