Studies on the Mode of Action of Some Cephalosporin Derivatives

Abstract

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

The Effect of Cephaloridine and a Cephalosporin Derivative on Mycoplasmas

“…The finding that 7/30 and DMDT are inhibitory to mycoplasmas supports the observations reported by Fountain & Russell (1969). Compound 7/30 appears to affect processes other than cell wall synthesis as mycoplasmas do not have a cell wall.…”

“…DJIDT has antibacterial action and preliminary experiments show that it has an PVIIC in broth of 1.5 pglml €or a strain ofStaphylococcus aureus and one of Streptococcus pyoqeiies. As found by Fountain & Russell (1969) the MIC for enterobacteriaceae may be high Sensitivity tests on horse blood agar using filter paper discs containing 10 pg of UXDT gave zones of inhibition with Llaemophilus infiuenxae that were slightly narrowcr than with the strain of Strep. pyogenes and zones with Xtrpp.…”

Aspects of the Mechanism of Action of Some Cephalosporins

“…A possible reason for this, namely, the liberation onto or in the bacterial cell of dimethyldithiocarbamate (DMDT), which occupies position 3 in the 7/30 molecule (Fig. 1), was suggested previously (7).…”

SCE-129, Antipseudomonal Cephalosporin: In Vitro and In Vivo Antibacterial Activities

“…Cephalosporin 7/30 [7-(S-benzylthioacetamido)-cephen-3-ylmethyl-N-dimethyldithiocarbamate-4-carboxylic acid)] inhibited the growth of E. coli, but did not reveal the bacteriolytic action (5). It is also reported that cephalosporin 7/30 inhibited the protein synthesis of E. coli (4). The mode of action of SCE-129 against P. aeruginosa needs further investigation.…”

“…It has been reported that cephalosporins, like penicillins, are inhibitors of cell-wall synthesis (1)(2)(3)(4)(5)16). The accumulation of N-acetylaminosugar in the cells of S. aureus treated with SCE-129 was observed at the concentration of 10 ,ug/ml, which did not affect the synthesis of DNA, RNA, and protein.…”