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Protein folding in Escherichia coli: role of 23S ribosomal RNA.

Post-translational control of Escherichia coli ribosome on newly synthesised polypeptide leading to its active conformation (protein folding) has been shown in the case of the enzyme beta-galactosidase. As expected, antibiotics chloramphenicol and lincomycin, which bind to 23S rRNA/50S subunit and kasugamycin and streptomycin which interact with the 30S subunit instantaneously inhibited protein synthesis when they were added to the growing cells. The increase in beta-galactosidase activity, though stopped immediately after the addition of chloramphenicol and lincomycin, went on considerably in the presence of streptomycin and kasugamycin even after the stoppage of protein synthesis.

Aminoglycosides↗

The effect of antimicrobial feed additives on the colonization of the alimentary tract of chickens by Salmonella typhimurium.

Groups of 33 chickens were fed continuously on diets containing feed additives that are employed commercially for a variety of purposes, and were infected orally when 4 days old with a nalidixic acid-resistant mutant of Salmonella typhimurium. The amount of S. typhimurium organisms excreted in their faeces was estimated by culturing them at intervals and in a standard manner on brilliant green agar containing sodium nalidixate; when the chickens were killed their caecal contents were examined by the same technique.Avoparcin and lincomycin, like nitrovin and tylosin (Smith & Tucker, 1975b), favoured colonization of the alimentary tract by the S. typhimurium organisms as shown by the fact that the chickens to which they were fed excreted these organisms in their faeces in higher concentration and for longer periods of time than did chickens fed on non-medicated diets. Amprolium, monensin, dimetridazole, arsenilic acid and nitro-hydroxyphenylarsonate had no obvious effect on the salmonella excretion pattern.When only five chickens in each group were experimentally infected so that the effect of the feed additives on infections acquired by contact could be monitored, avoparcin, lincomycin, nitrovin and tylosin again favoured colonization of the alimentary tract with the S. typhimurium organisms and so did dimetridazole. Arsenilic acid, in contrast, hindered the development of infection. Amprolium, monensin and nitro-hydroxyphenylarsonate were without obvious effect.Many of the chickens that were fed on diets that favoured S. typhimurium colonization, but not those fed on non-medicated diets, were still excreting S. typhimurium organisms in their faeces when they were killed at 56 days of age, the age at which broiler chickens kept under commercial conditions are usually slaughtered.

Amprolium↗

Interaction between the antibiotic spiramycin and a ribosomal complex active in peptide bond formation.

The inhibition of peptide bond formation by spiramycin was studied in an in vitro system derived from Escherichia coli. Peptide bonds are formed between puromycin (S) and Ac-Phe-tRNA, which is a component of complex C, i.e., of the [Ac-Phe-tRNA-70S ribosome-poly(U)] complex, according to the puromycin reaction: C+S (Ks)<==>CS (k3)==>C'+P [Synetos, D., & Coutsogeorgopoulos, C. (1987) Biochim. Biophys. Acta 923, 275-285]. It is shown that spiramycin (A) reacts with complex C and forms the spiramycin complex C*A, which is inactive toward puromycin. C*A is the tightest complex formed between complex C and any of a number of antibiotics, such as chloramphenicol, blasticidin S, lincomycin, or sparsomycin. C*A remains stable following gel chromatography on Sephadex G-200 and sucrose gradient ultracentrifugation. Detailed kinetic study suggests that C*A is formed in a variation of a two-step mechanism in which the initial encounter complex CA is kinetically insignificant and C*A is the product of a conformational change of complex CA according to the equation, C+A (kassoc)<==>(kdissoc) C*A. The rate constants of this reaction (spiramycin reaction) are kassoc = 3.0 x 10(4) M-1 s-1 and kdissoc = 5.0 x 10(-5) s-1. Such values allow the classification of spiramycin as a slow-binding, slowly reversible inhibitor; they also lead to the calculation of an apparent overall dissociation constant equal to 1.8 nM for the C*A complex. Furthermore, they render spiramycin a useful tool in the study of antibiotic action on protein synthesis in vitro. Thus, the spiramycin reaction, in conjunction with the puromycin reaction, is applied (i) to detect a strong preincubation effect exerted by chloramphenicol and lincomycin (this effect constitutes further evidence that these two antibiotics combine with complex C as slow-binding inhibitors) and (ii) to determine the rate constant for the regeneration (k7 = 2.0 x 10(-3) s-1) of complex C from the sparsomycin complex C*I [Theocharis, D. A., & Coutsogeorgopoulos, C. (1992) Biochemistry 31, 5861-5868] according to the equation, C+I (Ki)<==>CI (k6)<==>(k7) C*I. The determination of k7 enables us to calculate the apparent association rate constant of sparsomycin, (k7/Ki') = 1.0 x 10(5) M-1 s-1, where Ki' = Ki(k7/k6 + k7). It is also shown that Ac-Phe-tRNA bound to the sparsomycin complex C*I is protected against attack by hydroxylamine.(ABSTRACT TRUNCATED AT 400 WORDS)

Anti-Bacterial Agents↗

UVB-induced GM-CSF production is suppressed by dexamethasone in HaCaT cells.

BACKGROUND: Epidermal keratinocytes are important sources of a wide variety of cytokines that include the Granulocyte-macrophage Colony Stimulating Factor (GM-CSF). Glucocorticoids have been shown to inhibit the production of several cytokines. However, their effect on GM-CSF synthesis by keratinocytes is still unknown. METHODS: The effects of glucocorticoid on GM-CSF production by keratinocytes were evaluated using ELISA and RT-PCR analysis. RESULTS: GM-CSF secretion by HaCaT cells increased with increasing UVB exposure. Dexamethasone suppressed basal release of GM-CSE In addition, it strongly inhibited both the UVB-mediated augmentation of GM-CSF protein production and mRNA expression. Lincomycin enhanced slightly the inhibitory effect of dexamethasone on GM-CSF synthesis, while lincomycin itself had no effect on GM-CSF secretion. CONCLUSION: Results showed that dexamethasone suppressed basal release and UVB-induced production of GM-CSF by keratinocytes.

Anti-Bacterial Agents↗

"Conjugal" transfer of plasmid DNA among oral streptococci.

The beta plasmid from Streptococcus faecalis strain DS5, which codes for resistance to erythromycin and lincomycin, was introduced into a Lancefield group F streptococcus, strain DR1501, by transformation. This strain, DR1501 (beta), was found to be an excellent donor of the beta plasmid and readily transferred the resistance markers to various lactic acid bacteria, including certain strains of S. mutans, S. sanguis, and S. salivarius. Evidence is presented indicating that the transfer of the beta plasmid is mediated by a mechanism that requires cell-to-cell contact. The transfer of plasmid DNA during conjugation has been confirmed by the isolation of beta plasmid from transconjugant clones and by their ability to then serve as donors of the erythromycin and lincomycin resistance markers.

Conjugation, Genetic↗

A critical role for the Var2 FtsH homologue of Arabidopsis thaliana in the photosystem II repair cycle in vivo.

Using a var2-2 mutant of Arabidopsis thaliana, which lacks a homologue of the zinc-metalloprotease, FtsH, we demonstrate that this protease is required for the efficient turnover of the D1 polypeptide of photosystem II and protection against photoinhibition in vivo. We show that var2-2 leaves are much more susceptible to light-induced photosystem II photoinhibition than wild-type leaves. Furthermore, the rate of photosystem II photoinhibition in untreated var2-2 leaves is equivalent to that of var2-2 and wild-type leaves, which have been treated with lincomycin, an inhibitor of the photosystem II repair cycle at the level of D1 synthesis. This is in contrast to untreated wild-type leaves, which show a much slower rate of photosystem II photoinhibition due to an efficient photosystem II repair cycle. The recovery of var2-2 leaves from photosystem II photoinhibition is also impaired relative to wild-type. Using Western blot analysis in the presence of lincomycin we show that the D1 polypeptide remains stable in leaves of the var2-2 mutant under photoinhibitory conditions that lead to D1 degradation in wild-type leaves and that the abundance of DegP2 is not affected by the var2-2 mutation. We conclude, therefore, that the Var2 FtsH homologue is required for the cleavage of the D1 polypeptide in vivo. In addition, we identify a conserved lumenal domain in Var2 that is unique to FtsH homologues from oxygenic phototrophs.

ATP-Dependent Proteases↗

Biodegradability and toxicity of pharmaceuticals in biological wastewater treatment plants.

In this experimental study both biological treatability of pharmaceuticals and their potential toxic effect in biological processes were evaluated. The pharmaceuticals were selected among those that are present at higher concentration in the Italian wastewater treatment plant effluents and widely used as antiulcer (ranitidine), beta-blocker (atenolol) and antibiotic (lincomycin). The present paper is the continuation of a work already presented,[1] which used a synthetic wastewater fed to laboratory scale SBR (Sequencing Batch Reactor) operated with different sludge ages (8 and 14 days), different biochemical conditions (aerobic or anoxic-aerobic mode) and several influent drug concentrations (2, 3 and 5 mg/L). In this case a real municipal wastewater was used as influent to the SBR. In parallel, batch tests were conducted to determine the removal kinetics of drugs and nitrogen. Toxicity tests using a titrimetric biosensor to verify possible inhibition on microorganisms were also performed. Finally, the possible adsorption of the pharmaceuticals on activated sludge was evaluated. The drugs under investigation showed different behaviours in terms of both biodegradability and toxicity effect on nitrifiers. Ranitidine showed generally low removal efficiencies (17-26%) and a chronic inhibition on nitrification. Atenolol showed generally higher removal efficiencies than ranitidine, even if the fairly good efficiency obtained in the previous experimentation with synthetic wastewater (up to 90%) was not attained with real wastewater (36%). No inhibition on nitrification was observed on both acclimated and non acclimated microorganisms with a high nitrification activity, whilst it was present with activated sludge characterised by a lower nitrification activity. Consistently with his pharmaceutical properties, lincomycin showed significant inhibition on nitrification activity.

Atenolol↗

Pre- and postjunctional blocking effects of aminoglycoside, polymyxin, tetracycline and lincosamide antibiotics.

The effects of seven antibiotics (streptomycin, amikacin, polymyxin B, lincomycin, clindamycin, tetracycline and oxytetracycline) were compared with those of magnesium, tubocurarine and lignocaine in the frog sciatic nerve--sartorius muscle preparation, using intracellular recording techniques. All compounds except tubocurarine decreased end-plate potential quantal content. The prejunctional effects of magnesium, streptomycin, amikacin, polymyxin B and oxytetracycline (but not the other drugs) were well reversed by increasing the calcium concentration. At concentrations which depressed quantal content, only magnesium, tetracycline and oxytetracycline did not reduce postjunctional sensitivity. Further postjunctional effects of the drugs were revealed by alterations in the time-courses of end-plate potentials. All the drugs tested except magnesium, tubocurarine and lincomycin produced changes in muscle action potentials. None of the compounds had anticholinesterase activity. The results confirm that aminoglycoside, polymyxin, tetracycline and lincosamide antibiotics produce neuromuscular block by a combination of both pre- and postjunctional actions.

Action Potentials↗

Larval Apis mellifera L. (Hymenoptera: Apidae) mortality after topical application of antibiotics and dusts.

Beekeepers apply various dusts to honey bee, Apis mellifera L., colonies to dislodge parasitic mites and control bacterial brood diseases. Anecdotal reports by beekeepers indicate that the antibiotic oxytetracycline (OTC) can be toxic when applied in powdered sugar to cells containing immature bee brood, but it was not known whether the purported toxicity is caused by the antibiotic or the sugar carrier. Additionally, the toxicity of various dusts, proposed for parasitic mite control, is poorly known. In the current studies, we tested OTC and two other antibiotics (tylosin and lincomycin, candidate compounds for use in honey bee colonies) in a powdered sugar carrier for larval toxicity. We also tested for larval toxicity, several dusts that have been proposed for mite control. OTC caused significant brood mortality of approximately 80% at the concentrations used in the hive (200 mg in 20 g sugar). In contrast, tylosin and lincomycin at the 200 mg dose were both similar to untreated controls, and only five times that concentration (1000 mg) caused significant brood mortality of approximately 65%. The addition of dusts, wheat flour, talc, and a commercially available protein supplement, BeePro, resulted in mortality levels between 65 and 80%, similar to that seen with OTC. The common antibiotic carrier, powered confectioners sugar, was nontoxic. The use of 100 unsealed brood cells was demonstrated to be a reliable means of assessing potential adverse affects of dry compounds on larval honey bees. Two new candidate antibiotics for use in honey bee colonies were less toxic to larval bees than the currently labeled antibiotic, OTC.

Animals↗

Variation in the properties of a strain of Staphylococcus aureus isolated over three months from a single hospital.

A strain of Staphylococcus aureus has been isolated from a hospital environment over 3 months. Every isolate was lysed by phage 77, had high-level resistance to streptomycin, and was resistant to about 250 pg per ml of both tetracycline and sulphonamide; a combination of sulphamethoxazole and trimethoprim produced little bacteristatic synergy towards each isolate. All These organisms were thus considered to be "the same"; the variation in other properties was probably due to rapid evolutionary change in vivo. the variation in senxitivity to methicillin and neomycin, and the absence of penicillinase production in some isolates, probably indicated loss of the relevant genes. Several isolates had probably acquired resistance to lincomycin by a one-step mutatuon in vivo. The usefulness of lincomycin and analogues in treating staphylococcal infections seems limited.

Bacteriophage Typing↗

Cooperative and antagonistic interactions of peptidyl-tRNA and antibiotics with bacterial ribosomes.

There is a single-site interaction of [methylene-14C]thiamphenicol and [methylene-14C]chloramphenicol with run-off ribosomes with dissociation constants Kd = 6.8 micronM and Kd = 4.6 micronM respectively. Similar affinities for the antibiotics are observed in polysomes totally deprived of nascent peptides, or bearing nascent peptides on the A-site. However, two types of interaction are observed in endogenous polysomes with some ribosomes bearing nascent peptides on the P-site and other in the A-site. The lower-affinity bindings (dissociation constants Kd = 6.4 micronM and Kd = 1.5 micronM for thiamphenicol and chloramphenicol respectively) are due to the ribosomes bearing nascent peptides on the A-site. The higher-affinity bindings (dissociation constants Kd = 2.3 micronM and Kd = 1.5 micronM for thiamphenicol and chloramphenicol, respectively) are due to the ribosomes bearing nascent peptides on the P-site. Therefore binding of nascent peptides to the A-site does not affect the affinities of thiamphenicol and chloramphenicol for the ribosome. On the other hand interaction of the nascent peptides with the P-site of the ribosomes increases the affinities of both antibiotics for the ribosome. Thiamphenicol and chloramphenicol are thus good inhibitors of peptide bond formation in ribosomes and polysomes. Their affinities are increased precisely when the peptidyl-tRNA is placed in the P-site preceeding the peptide bond formation step, which is specifically blocked by the antibiotics. There is a single-site interaction per ribosome for [35S]thiostrepton, which does not appear to be affected by the attachment to the ribosomes of mRNA, tRNA and nascent peptides either to the A or the P-site. [N-methyl-14C]Lincomycin, [N-methyl-14C]erythromycin, [G-3H]streptogramin B and [G-3H]-streptogramin A bind to run-off ribosomes and polysomes totally free from nascent peptides. However, these antibiotics do not interact with ribosomes bearing nascent peptides either in the A or the P-site and therefore are not active on preformed polysomes. Thus lincomycin and streptogramin A only interact with free ribosomes and 50-S subunits and block the early rounds of peptide bond formation prior to polysome formation. Erythromycin and streptogramin B do not inhibit either initiation or the first round of peptide bond formation. However, erythromycin and streptogramin B, prebound to the ribosome, block peptide elongation probably by steric hindrance with the growing oligopeptide chain when this reaches a certain critical length.

Anti-Bacterial Agents↗

Antibiotics in exudate from periapical lesions in dogs.

Forty-eight periapical lesions were induced in the mandible of dogs. Subsequently, the dogs were given a single intramuscular injection of either benzylpenicillin, erythromycin, lincomycin or clindamycin. The antibiotic concentration in serum and exudate from the periapical lesions was measured. The highest concentration of benzylpenicillin in serum (4.3 micrograms/ml) was obtained 30 min after the injection and in exudate (1.8 micrograms/ml) 60 min after injection. The highest concentration of erythromycin in serum (0.8 microgram/ml) was reached after 120 min and in exudate (0.6 microgram/ml) 240 min after the injection. The highest concentration of clindamycin in serum (2.3 micrograms/ml) was obtained 120 min after the injection and in the exudate (2.2 micrograms/ml) after 240 min. The highest concentration of lincomycin in serum (4.2 micrograms/ml) was noted 120 min after the injection and in exudate (4.5 micrograms/ml) 240 min after the injection. The results of this study indicated that the sampling method used might be suitable for analyzing the concentration of antibiotics in a clinical situation.

Animals↗

A method for reproducing fatal idiopathic colitis (colitis X) in ponies and isolation of a clostridium as a possible agent.

Severe colitis was induced in two ponies after oral pretreatment with clindamycin and lincomycin, followed by intestinal content from two horses which had died from naturally-occurring idiopathic colitis. Two ponies treated with antibiotic alone, and two ponies treated with intestinal content alone, were unaffected. In a further study, three ponies treated on separate occasions with lincomycin, administered orally, died or were destroyed 67 to 72 h after initial treatment. No established salmonella, yersinia or campylobacter pathogens were isolated from these ponies, but a clostridium closely resembling Clostridium cadaveris was isolated as the predominant clostridium from them all and from the colonic content of one of six horses which died from naturally-occurring idiopathic colitis. It was not isolated from six horses with non-fatal diarrhoea. This clostridium is a candidate as an agent of some cases of fatal colitis in horses.

Animals↗

Novel mechanisms of resistance to lincosamides in Staphylococcus and Arthrobacter spp.

Clinical isolates of Staphylococcus and Arthrobacter spp. were screened for lincosamide resistance. Six different patterns of resistance were found. Strains designated SF27 and SF28 showed low-level resistance to lincosamides: one was susceptible to erythromycin (SF27) and the other was resistant (SF28). Analysis of ribosomes from the resistant strains in an in vitro poly(U)-dependent protein-synthesizing system showed that ribosomes of both strains were sensitive to lincomycin and clindamycin. Four patterns of high-level resistance to lincosamides were observed (strains SF4, SF19, SF30, and SF31). All of these except SF30 had ribosomes which were highly resistant in vitro to the antibiotics and showed a close correlation with results of the in vivo experiments. In vivo protein synthesis by strain SF30 was resistant to lincomycin and sensitive to clindamycin, whereas the ribosomes were sensitive when assayed in vitro. Lincosamide-inactivating enzymes were not detected in cell extracts of the six resistant strains. Strains SF19 and SF31 demonstrated two ribosome-mediated lincosamides resistance mechanisms that were not previously reported. Both strains were highly resistant to lincosamides and susceptible to erythromycin, but SF19 was also highly resistant to oleandomycin and partially resistant to various macrolides.

Aminoglycosides↗

Parasiticidal effect of clindamycin on Toxoplasma gondii grown in cultured cells and selection of a drug-resistant mutant.

Clindamycin, which has been reported to have no significant in vitro activity against Toxoplasma gondii, actually markedly inhibits the growth of this parasite in infected human fibroblasts. When measured 3 days after treatment, the concentration required to reduce parasite growth by 50% is about 1 ng/ml. Some observers failed to note this inhibition because of its markedly delayed onset. At 6 ng/ml, clindamycin is parasiticidal, and the rate and extent of parasite killing increase with higher drug concentrations. With the aid of chemical mutagenesis, we isolated a parasite mutant that is approximately 100-fold more resistant to clindamycin than is the wild type. Lincomycin inhibits T. gondii at a higher 50% inhibitory concentration, about 100 ng/ml. The clindamycin-resistant mutant is partially cross-resistant to lincomycin.

Animals↗

A new resistance gene, linB, conferring resistance to lincosamides by nucleotidylation in Enterococcus faecium HM1025.

Resistance to lincomycin and clindamycin in the clinical isolate Enterococcus faecium HM1025 is due to a ribosomal methylase encoded by an ermAM-like gene and the plasmid-mediated inactivation of these antibiotics. We have cloned and determined the nucleotide sequence of the gene responsible for the inactivation of lincosamides, linB. This gene encodes a 267-amino-acid lincosamide nucleotidyltransferase. The enzyme catalyzes 3(5'-adenylation) (the adenylation of the hydroxyl group in position 3 of the molecules) of lincomycin and clindamycin. Expression of linB was observed in both Escherichia coli and Staphylococcus aureus. The deduced amino acid sequence of the enzyme did not display any significant homology with staphylococcal nucleotidyltransferases encoded by linA and linA' genes. Sequences homologous to linB were found in 14 other clinical isolates of E. faecium, indicating the spread of the resistance trait in this species.

Anti-Bacterial Agents↗

Monophenol monooxygenase and lincomysin biosynthesis in Streptomyces lincolnensis.

Monophenol monooxygenase (monophenol, dihydroxyphenylalanine:oxygen oxidoreductase EC 1.14.18.1) was studied in melanin-positive and melanin-negative mutants of Streptomyces lincolnensis NCIB 9413, varying in the lincomycin synthesizing ability. The activities of laccase and tyrosine phenol lyase (EC 4.1.99.2) are absent in this organism. The monophenol monooxygenase catalyzes hydroxylation of monophenols (K(m) and V(max) for l-tyrosine, 2 x 10(-4) M and 8.0 nmol of O(2)/min per ml, respectively) at a slower rate than it dehydrogenates diphenols to o-quinones (K(m) and V(max) for l-3,4-dihydroxyphenylalanine, 7 x 10(-5) M and 51.7 nmol of O(2)/min per ml, respectively. It is inhibited by KCN, beta-mercaptoethanol, ethylenediaminetetraacetate, dipyridyl, thiourea, p-aminobenzoic acids and by some tryptophan metabolites. Changes in the activity of monophenol monooxygenase caused by mutation or by inhibitors are reflected in the synthesis of the antibiotic. Its participation in the biogenesis of the propylhygric moiety of lincomycin is discussed.

Amino Acids↗

Mutation to erythromycin dependence in Escherichia coli K-12.

A nitrosoguanidine-induced mutant of Escherichia coli K-12 strain JC12 was absolutely dependent on erythromycin or related macrolide antibiotics for growth. The only other drugs which permitted growth (lincomycin and chloramphenicol) are, like the macrolides, inhibitors of the 50S ribosome. The order of relative effectiveness of these drugs was macrolides > lincomycin > chloramphenicol. Rates of growth with all drugs were concentration dependent. Erythromycin starvation was followed by normal rates of increase in cell mass and macromolecular synthesis for approximately one mass-doubling time, after which macromolecular synthesis abruptly ceased and cell lysis and death occurred. The dependent mutant gave rise spontaneously to revertants to independence with very high frequency (10(-4)). The gene (mac) for macrolide dependence is located near minute 25 on the E. coli chromosome; it does not result in increased resistance to these drugs. A separate gene for erythromycin resistance (eryA) is located in the cluster of ribosomal structural genes near spc, close to minute 63. Dependence on macrolides was most clearly evident in strains carrying mutations at both eryA and mac.

Anti-Bacterial Agents↗