The ~-lactam antibiotics can be classified into 3 groups on the basis of their inducer activity for r3-lactamase in Proteus rettgeri and Proteus vulgaris.In our previous paper1), we reported that the S-lactam antibiotics could be classified into several groups on the basis of their inducer activity for (3-lactamase in Enterobacter cloacae. There are a few reports concerned with the inducible formation of (3-lactamase2-6). Proteus rettgeri and Proteus vulgaris also produce inducible cephalosporinases (CSase) which are species-specific in their substrate profiles7-9). This paper deals with the inducer activity of a number of (3-lactam antibiotics for the production of ,3-lactamases by P. rettgeri and by P. vulgaris. P. rertgeri GN4430 and P. vulgaris GN76 are clinical isolates maintained as stock cultures in this laboratory. For determination of inducer activity, various concentrations of each drug were added to a mid log phase culture and shaking of the culture continued. After a further 2 hours of incubation, the cells were harvested and washed once with 0.1 M phosphate buffer (pH 7.0). The drug concentrations added to the culture ranged from 10 x MIC to 0.01 x MIC. MIC (Minimal inhibitory concentration) was determined by the agar dilution method. A loopful (5 /l) of 106/ml cells was inoculated on a heart infusion (HI) agar (Difco) plate containing a series of serial twofold dilutions of a drug. The MIC was scored after 18 hours of incubation at 37°C. Under these conditions most of the drugs showed little or no effect on the growth of P. rettgeri GN4430 when their concentrations were less than 100 jig/ml. Antibacterial activity and inducer activity of various 13-lactam antibiotics against P. rettgeri GN4430 are shown in Table 1. P. rettgeri GN4430 was resistant to many 13-lactam antibiotics except for the newly-introduced drugs. Both the cefuroxime type cephalosporins such as cefotaxime and ceftizoxime, and cephamycin derivatives such as latamoxef and cefotetan were highly active against P. rettgeri GN4430. Based on inducer activity, the j3-lactam antibiotics can be classified into three groups, i.e., with high (A), intermediate (B), and low (C) inducibility.Cephaloridine, cephalothin, cephalexin and cefazolin which are easily hydrolyzed by the cephalosporinase, and the cephamycin derivatives such as cefoxitin, cefinetazole and cefotetan which are not hydrolyzed by the cephalosporinase, showed very high inducer activities for enzyme induction. Cefamandole, cefotiam, cefsulodin, cefuroxime, benzylpenicillin and ampicillin are also in the same group (A). Methicillin and cloxacillin10) and clavulanic acid'l~ also showed high inducer activity. However, latamoxef, carbenicillin and apalcillin showed intermediate inducer activity (group (B)). Cefoperazone, cefotaxime and piperacillin showed low inducer activity (group (C)).
There is an optimal salt concentration of mating in the conjugal transfer of an R plasmid, and incompatibility (Inc) group C R-plasmids are characteristic in that they demand high salt concentration such as 0.34M or more in the efficient R-transfer.Both sodium and potassium salt are effective but divalent cation (Mg) are not.Many pili-like structure of Escherichia coli carrying an Inc C plasmid Rms 417 were observed on an L agar plate which contained 0.34M salt, but few in the absence of salt. Therefore, the pili could be considered sex pili that E. coli R+ produced in the presence of a moderate amount of monovalent salt.
We isolated 56 Haemophilus (Actinobacillus) pleuropneumoniae strains from the pneumonic porcine lung tissues and tested them for antimicrobial susceptibility. Two drug-resistant strains were obtained. One, named KH-265, was resistant to streptomycin (SM) and sulfonamide (SA), and the other, named KH-195, was resistant to tetracycline (TC). The minimum inhibitory concentrations (MICs) of drugs for resistant strains were 100 micrograms/mliters for SM, 3200 micrograms/mliters for SA, and 12.5 micrograms/mliters for TC. KH-265 possessed a 8.3Kb nonconjugative plasmid, pMS260, encoding SM and SA resistance, which was transformable to E. coli strains. pMS260 belonged to none of 14 incompatibility groups including Inc. P and Inc. Q, so far tested. It was mobilizable to various causative strains for respiratory infections, Pseudomonas aeruginosa, Bordetella bronchiseptica, Pasteurella multocida and Haemophilus pleuropneumoniae, by RP4 (Inc. P) plasmid.
SummaryWe examined the inhibitory effects of "group A saponin" and "group B saponin" fractions, which were extracted and separated from soybean seed hypocotyls, on water-soluble 2,2'-azobis(2-amidinopropane) (AAPH)-and lipid-soluble 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN)-initiated lipid peroxidation reactions that were conducted with mouse liver microsomes. The simultaneous addition of the group A saponin fraction dose-dependently inhibited AAPH-or AMVN-initiated lipid peroxidation in microsomes more strongly than that of the group B saponin fraction. The group A saponin fraction inhibited the AAPHinitiated lipid peroxidation with a lag phase, while it immediately blocked the AMVN-initiated lipid peroxidation. The group A saponin fraction inhibited microsomal AAPH-initiated lipid peroxidation even when added to the reaction mixture after the lag phase period. Microsomes pretreated with the group A saponin fraction showed inhibition of AAPH-initiated lipid peroxidation with a prolonged lag phase, and the saponin fraction-pretreated microsomes showed inhibition of the AMVN-initiated lipid peroxidation in which a lag phase was found. These results indicate that in mouse liver microsomes, the group A saponin fraction from soybean seed hypocotyls, which is present outside and/or near the microsomal membranes, inhibits AAPH-initiated lipid peroxidation by inhibiting the initiation and propagation of this reaction, while it prevents microsomal AMVN-initiated lipid peroxidation mainly by inhibiting the propagation of this reaction. In addition, the
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