Cephaloridine and cephalexin had no effect on ribonucleic acid (RNA), deoxyribonucleic acid (DNA), or protein synthesis in Escherichia coli . However, cephalosporin 7/30 [7-( S -benzylthioacetamido)-cephem-3-ylmethyl- N -dimethyldithiocarbamate-4-carboxylic acid] and dimethyldithiocarbamate (DMDT), which occupies the side chain at position 3 in the 7/30 molecule, inhibited protein synthesis (and, to a lesser extent, RNA and DNA syntheses) in E. coli and had an inhibitory effect on the growth of Saccharomyces carlsbergensis . A bioautograph technique showed that two inhibitory spots were obtained with 7/30 but only one such spot with cephaloridine. Release of DMDT onto or in the bacterial cell may be responsible for “unusual” mode of action of cephalosporin 7/30.

7.(s-benzylthioacetamido)-cephem-3-ylmethyl~~~dimeth~ldithiocarbamate~4carboxylic acid (cephalosporin 7/30) prevented benzylpenicillin from inducing spheroplasts in Escherichia coli, and inhibited growth of preformed spheroplasts. These effecrs were also noted with dimethyldithiocarbamate (DMDT), the side-chain at position 3 in 7/30. Cephalosporin 7/30 inhibited growth of protoplasts of Bacillus megaterium and &.repto-COGCUB faeculis. At high concentrations, 7-[(2-thienyl)acetamido]-cephem-3-ylmethyl-Ndimethyldithiocarbamate-4-carboxylic acid (cephalosporin 87/30), with the same sidechain at 7 as cephaloridine but with DMDT at position 3, prevented spheroplast formation in E. coli, and inhibited the growth of preformed spheroplasts. However, a t lower concentrations, 87/30 induced spherical forms in E . coli. The other cephalosporins tested induced spheroplasts in E. coli and had no effect on protoplasts.THE CEPHALOSPORINS are derivatives of 7-aminocephalosporanic acid, individual members differing in substituents R, and R, a t positions 7 and 3, respectively ( Table 1). Cephalosporins are generally considered to kill bacteria by a mechanism similar to, or identical with, that of the penicillins (Bond, Brimblecombe 6 Codner, 1962; Chang & Weinstein, 1964 a, b ; Gonnella, Olexy & Jackson, 1967;Russell, 1969), i.e. by inhibiting a transpeptidation reaction in cell wall synthesis (Park, 1968).However, a cephalosporin known as 7/30 (Table 1) has been found (P. W. Muggleton and C . H. O'Callaghan, pers. comm.) to inhibit, at as low a concentration as 2 pg/ml, the growth of Mycoplasmu pneumoniae and 41. gallisepticum, which suggests that this antibiotic has an effect additional to, or other than, an inhibition of cell wall synthesis. Thus, a comparison of the effects of 7/30 with other cephalosporins and with benzylpenicillin on Escherichia coli and on protoplasts of Bacillus megaterium and Streptococcusfuecalis has been made in an attempt to elucidate (a) its exact mechanism of action and (b) the reasons for the apparent difference in the mechanism of activity between 7/30 and the other cephalosporins. Materials and MethodsOrganisms and mpthods of culture The organisms used were E. coli NCTC 9001, Strep. faecalis ATCC 9790 and B. rnegaterium NCTC 6005. Escherichia coli was grown for 18 h at 37" in 50 ml of Nutrient Broth No. 2 (Oxoid), the culture centrifuged and the pellet washed twice with sterile water and finally resuspended in sterile water to give c. 2 x lo8 viable cells/ml. Streptococcus faecalis was grown for 18 h at 37" on the surface of double strength Brain Heart Infusion Agar (Difco) (BHI), the growth washed off with sterile water, [314