Trichothecin (1.6 mcg/ml) completely inhibited multiplication of Newcastle disease virus in cultures of chick embryo fibroblasts infected with 50 plaque forming units/cell ; while at lower concentrations, where complete inhibition was not observed, a dose-response effect was shown by a lengthening of the lag time before the beginning of hemagglutinin synthesis. Trichothecin had no effect on free virus particles or on viral adsorption to host cells. The antibiotic exerted its activity whenever it was added during a viral growth cycle, and the inhibitory action was reversed upon removal of trichothecin by washing. Protein synthesis was promptly suppressed after addition of trichothecin (3.0 mcg/ml), but actinomycin D-insensitive RNA synthesis proceeded in the presence of the antibiotic. The RNA was analysed on a methylated albumin-kiselguhr column.
Some semi-synthetic penicillins and cephalosporins are resistant to hydrolysis by beta-latamases. Hence, penicillin-resistant staphylococci exhibiting beta-lactamase activity become susceptible to these beta-lactam antibiotics. Methicillin (2, 6-dimethoxyphenyl penicillin) in combination with ampicillin (D(-)-alpha-aminobenzyl penicillin) showed either a synergistic (14 strains) or an additive (3 strains) effect (never antagonistic), against 17 methicillin-resistant staphylococcal strains. One of these strains did not produce beta-lactamase. This strain No. 667 grew well in broth containing either 50 mcg/ml of methicillin or half the minimum inhibitory concentration of ampicillin which indicated that inhibition of cell wall synthesis was not apparent. However, ampicillin in combination with methicillin, using half of the above concentrations, exhibited synergism* against the strain 667. In the presence of sub-lethal doses of either ampicillin or methicillin, Escherichia coli became thread-like, while spheroplasts of E. coli were formed under similar conditions when these 2 beta-lactam antibiotics were combined. Since methicillin has no inhibitory action on strain 667, it can be concluded that the inhibition of growth by the combined penicillin might be due to a change in mechanism or site of action (or change of pathways). This is more suggestive as (a) the staphylococcal strain 667 did not produce any beta-lactamase and (b) spheroplasts of E. coli were formed only when the 2 penicillins were combined.
A new macrolide antibiotic complex has been isolated from fermentation broths of two strains of a news pecies of Micromonospora, M. megalomicea sp. n. The antibiotic complex has been differentiated from other known macrolides and methods for its production, isolation and separation of components have been devised. Like other macrolides, it is primarily active against gram-positive bacteria and is more active at an alkaline pH. Of the four known components, megalomicin A has been studied most extensively. It has activity equal to or slightly less than that of erythromycin both in vitro and in vivo. In dogs dosed orally, it is better tolerated and gives higher peak serum levels with a much greater duration than erythromycin.
A new antibiotic complex named megalomicin, which is a member of the macrolide group of antibiotics, has been isolated from the fermentation broth of Micromonospora megalomicea. Details of the isolation of the megalomicin complex and separation and purification of its components are given. Evidence is also presented indicating the presence of desosamine in the individual antibiotic components.
In vitro studies with megalomicin A base demonstrated enhanced activity with increased pH, decreased activity with increasing serum content in the medium and serum binding in the range of 20-30%. There is an inoculum effect with megalomicin A. In vivo studies in mice demonstrate that megalomicins A, B, C1, and C2 as well as the complex are active in conventional protection tests and have low acute LD50's. Absorption of megalomicin A and C1 in mice like erythromycin is better after parenteral than oral administration. In rats, and dogs, megalomicin A gives higher serum levels than erythromycin after oral dosing. Megalomicin A base is not emetic in dogs. Both megalomicins A and C1 give more prolonged serum levels in dogs than does erythromycin. Megalomicin A is absorbed along the entire intestinal tract in dogs and gives a depot effect after intramuscular dosing.
Kanamycin-phosphorylating enzyme was extracted from Pseudomonas aeruginosa and purified by ammonium sulfate fractionation, Sephadex G-100 column and DEAE Sephadex A-50 column chromatography. This enzyme has no ATPase activity and catalyzes the reaction in which ATP reacts with kanamycin on an equimolar basis yielding kanamycin-3'-phosphate and ADP. Mg++ is required for the reaction and can be substituted with Mn++, Zn++ or Co++. The enzyme is protected from heat denaturation by the addition of kanamycin. Substrates having the specific structures of 6-amino-6-deoxy-α-D-glucopyranosyl, 2, 6-diamino-2, 6-dideoxy-α-D-glucopyranosyl or 2-amino-z-deoxy-a-D-glucopyranosyl 2-deoxystreptamines are required for the reaction. Methyl 3-amino-3-deoxy-α-D-glucopyranoside and formycin are competitive inhibitors of kanamycin and ATP respectively. Adenosine shows stronger inhibition than ADP, AMP and adenine.