Effect of media and blood on the antimicrobial activity of cephalosporins on serogroup D streptococci: a review.

The influence of culture medium on in vitro of selected cephalosporins on on group D streptococci was investigated by agar diffusion and broth dilution methods. The activity of cephalothin, cefamandole, and cefoperazone were not substantially influenced by the type of culture medium used, but cefuroxime, ceftizoxime, cefotaxime (CTX), cefmenoxime, and ceftriaxone varied markedly with both the commercial brand and the blood content of the broth used. The differences were more likely to occur in some Mueller-Hinton media, particularly when supplemented with 5% lysed sheep blood, and resulted in susceptible results instead of the resistant results that were obtained with these same media without blood. Some strains of Streptococcus faecalis showed these discrepancies, but S. bovis did not. The influence of the media on in vitro activity suggests a complex interaction between some cephalosporins, media components, and organisms. The cephalosporins that were affected by media share an identical moiety at the 7-acyl position (cefuroxime is slightly different); this structure is not shared by those cephalosporins that were not affected, however. It is possible that this structure may play a part in the phenomenon.