Microbiology: The bactericidal activity of ceftriaxone results ctericidal from inhibition of cell wall synthesis Ceftriaxone exerts in vitro activity against a wide range of gram-negative andgram-positive microorganisms. It is highly stable to most B-lactamases, both penicillinases and cepha losporinases of gram positive and gram-negative bacteria Ceftriaxone is usually active against the following microor- ganisms in vitro and in clinical infections (see Indications) sensitive), Staphylococci coagulase-negative, Streptococ- cus pyogenes (B-hemolytic group A) Streptococcus agalac- tiae (B-hemolytic group