Antigenic substances from livers of mice infected with Tyzzer's disease were purified by means of sucrose density gradient zonal centrifugation and affinity column chromatography using antiserum and checking antigenicity with the complement fixation test. Fractions obtained from zonal centrifugation fell into three main groups with different molecular weights, two of which (Fr. I and Fr. 11) positively reacted with antiserum in the complement fixation test. Both fractions were further purified by affinity column chromatography. The molecular weights of the main antigenic substances derived from Fr. I and Fr. I1 were determined to be about 52000 and 66000, respectively, by means of SDS-PAGE.
The mechanism by which Chlamydia trachomatis is endocytosed by host cells is unclear. Studies of the kinetics of chlamydial attachment and uptake in the susceptible HeLa229 cell line showed that chlamydial endocytosis was rapid and saturable but limited by the slow rate of chlamydial attachment. To overcome this limitation and to investigate the mechanism of endocytosis, chlamydiae were centrifuged onto the host cell surface in the cold to promote attachment. Endocytosis of the adherent chlamydiae was initiated synchronously by rapid warming to 36 °C. Electron micrographs of chlamydial uptake 5 min after onset showed that chlamydial ingestion involves movement of the host cell membrane, leading to interiorization in tight, endocytic vacuoles which were not clathrin coated. Chlamydial ingestion was not inhibited by monodansylcadaverine or amantadine, inhibitors of receptor-mediated endocytosis and chlamydiae failed to displace [3H]sucrose from micropinocytic vesicles. Chlamydial endocytosis was markedly inhibited by cytochalasin D, an inhibitor of host cell microfilament function, and by vincristine or vinblastine, inhibitors of host cell microtubules. Hyperimmune rabbit antibody prevented the ingestion of adherent chlamydiae, suggesting that endocytosis requires the circumferential binding of chlamydial and host cell surface ligands. These findings were incompatible with the suggestion that chlamydiae enter cells by taking advantage of the classic mechanism of receptor-mediated endocytosis into clathrin-coated vesicles, used by the host cell for the internalization of δ-lipoprotein and other macromolecules, but were consistent with the hypothesis that chlamydiae enter cells by a microfilament-dependent zipper mechanism.
Induction of δ-lactamase was monitored in a strain of Enterobacter cloacae exhibiting high resistance to most p-lactam antibiotics. Large amounts of the enzyme were induced not only in the presence of /I-lactams, but also in the presence of other bicyclic molecules such as folic acid, thiamin, tryptophan or haemin. Moreover, complex media (such as Trypticase soy broth and Schaedler's broth) and various body fluids (serum, pleural fluid and cerebrospinal fluid) also possessed considerable induction potency. Neither ‘specific’ induction (by P-lactams) nor ‘nonspecific’ induction (by other bicyclic compounds) could be augmented by addition of exogenous CAMP. These findings indicate that inducible β-lactamases deserve more attention, above all with respect to the development of resistance against third-generation cephalosporins.
The acids produced in broth culture by various species of oral haemophili and by stock strains of capsulated and other haemophili were identified and measured by gas-liquid chromatography. Succinic acid was the major acid end-product of all strains, with acetic acid also being regularly produced but in smaller amounts. A stock strain, Haemophilus paraintftuenzae NCTC 4101, produced less succinic acid than other strains of this species and produced much more oxalacetic and pyruvic acid than all the other strains of haemophili. Strain NCTC 4101 possessed all the enzymes of the tricarboxylic acid cycle, as previously reported, but in the other haemophili examined only succinic dehydrogenase, fumarase and malate dehydrogenase could be detected. No other enzymes of the tricarboxylic acid cycle were detected and isocitrate lyase, malate synthase and pyruvate carboxylase were also absent. Phosphoenolpyruvate-carboxylase was present in all strains. A partial tricarboxylic acid cycle and marked malate dehydrogenase activity appear to be characteristic of haemophili. The pathway to succinate in haemophili appears to be via carboxylation of phosphoenolpyruvate to oxalacetate and thence via malate and fumarate. The results of tracer studies on a single oral strain of H. parain8uenzae using various labelled substrates were in keeping with this proposed metabolic pathway.
The biosynthesis of DNA, proteins, RNA and phospholipids in Mycobacterium smegmatis ATCC 607 was investigated by studying the incorporation of radiolabelled components in the presence of antiserum to mannophosphoinositides. The antiserum had an inhibitory effect on the rate of synthesis of these macromolecules. However, the inhibition was greater when antibody was present together with complement.