According to the invention there is provided a antibacterial cephalosporin derivative of the formula:
in which X is sulphur, oxygen, methylene or sulphinyl; R3 is hydrogen or methoxy; R1 und R2 are known in the cephalosporin art and R4 is an aminomethyl group in which the amino group carries one of various positively charged nitrogen-containing species set out in the specification and optionally a further substituent selected from hydrogen, lower alkyl, benzyl or heteroailyloweralkyl groups.