Action of antibiotics on the growth and metabolic processes of streptomycetes and Nocardia

New experimental data on the effect of novobiocin, ristomycin and nystatin on growth and metabolism of Streptomycetes and Nocardia are presented. The study of the organisms producing other antibiotics showed that they were tens, hundreds and even thousands times more sensitive to the tested biologically active compounds than the organisms producing these compounds. The protein synthesis and antibiotic biosynthesis proved to be most sensitive out of the processes studied. The findings showed that during their evolution the antibiotic-producing organisms have developed definite protective mechanisms which enable them to resist relatively high concentrations of their own metabolites (antibiotics). This ensures them in their struggle for existence.     

Direct screening for producers of antibiotics among the Micromonospora

A test system was developed for screening organisms producing antibiotics of definite chemical groups or mechanisms of action. The system includes efficient selection of cultures belonging to a definite microbiological taxon (genus Micromonospora), investigation of their biological and taxonomic features, the use of specific selective media with high concentrations of definite antibiotics for isolating antibiotic-producing cultures from natural substrates, the use of specific methods for antibiotic chemical isolation at the initial stages of the screening and chromatographic study of the screened compounds. The system provided efficient screening of valuable antibiotics in a short period.     

Search for new antitumor antibiotics in the bleomycin group]

The culture of Penicillium avellaneum 444 and its bleomycin resistant variant may serve a rather valuable specific test for detecting organisms producing new antitumor antibiotics of the bleomycin group. The organisms producing antitumor antibiotics of the group of anthracyclines (rubomycin and carminomycin), actinomycins and other chemical groups do not inhibit the growth of these test-organisms. Such tests are also resistant to the effect of antibacterial antibiotics.     

Electron absorption and fluorescence spectra of carbonyl--conjugated pentaenes in various media]

It was found that fluorescence intensity of carbonyl-conjugated pentaens of flavofungin flavopentin and brunefungin in solutions depended on the solvent polarity and specific interactions of the antibiotics with the solvents. Addition of cholesterol into the aqueous solutions of these antibiotics resulted in a hypsochrome shift in their absorption spectra and increased fluorescence intensity. The antibiotics were found by their fluorescence in the yeast cells sensitive to them when their content was close to the concentrations resulting in the cell lysis. Low concentrations of the antibiotics resulted in changed localization of the yeast self fluorescence.     

Preferential inhibition of protein synthesis by ketolide antibiotics in Haemophilus influenzae cells

The ketolide antibiotics are semi-synthetic derivatives of erythromycin A with enhanced inhibitory activity in a wide variety of microorganisms. They have significantly lower MICs than the macrolide antibiotics for many Gram-positive organisms. Two ketolides, telithromycin and ABT-773, were tested for growth-inhibitory effects in Haemophilus influenzae. Both antibiotics increased the growth rate and reduced the viable cell number with IC(50) values of 1.5 microgram/ml. Protein synthesis was inhibited in cells with a similar IC(50) concentration (1.25 microgram/ml). Macrolide and ketolide antibiotics have been shown to have a second equivalent target for inhibition in cells, which is blocking the assembly of the 50S ribosomal subunit. Pulse and chase labeling assays were conducted to examine the effect of the ketolides on subunit formation in H. influenzae. Surprisingly, both antibiotics inhibited 50S and 30S subunit assembly to the same extent, with no specific effect of the compounds on 50S assembly. Over a range of antibiotic concentrations, 30S particle synthesis was diminished to the same extent as 50S formation. H. influenzae cells seem to have only one significant target for these antibiotics, and this may help to explain why these drugs are not more effective than the macrolides in preventing the growth of this microorganism.     

Progress of research on the toxicology of antibiotic pollution in aquatic organisms

Antibiotics are widely used to improve human and animal health and treat infections. Antibiotics are often used in livestock farms and fisheries to prevent diseases and promote growth. Recently, there has been increasing interest in the presence of antibiotics in aquatic environments. Low levels of antibiotic components are frequently detected in surface water, seawater, groundwater, and even drinking water. Antibiotics are consistently and continually discharged into the natural environment as parent molecules or metabolites, which are usually soluble and bioactive, and this results in a pseudo and persistent pollution. The effects of environmental antibiotic toxicity on non-target organisms, especially aquatic organisms, have become an increasing concern. Although antibiotics have been detected worldwide, their ecological and developmental effects have been poorly investigated, particularly in non-target organisms. This review describes the toxicity and underlying mechanism of antibiotic contamination in aquatic organisms, including the effects on vertebrate development. A considerable number of antibiotic effects on aquatic organisms have been investigated using acute toxicity assays, but only very little is known about the long-term effects. Aquatic photosynthetic autotrophs, such as Pseudokirchneriella subcapitata, Anabaena flos-aquae, and Lemna minor, were previously used for antibiotic toxicity tests because of low cost, simple operation, and high sensitivity. Certain antibiotics show a different degree of potency in algal toxicity tests on the basis of different test algae. Antibiotics inhibit protein synthesis, chloroplast development, and photosynthesis, ultimately leading to growth inhibition; some organisms exhibit growth stimulation at certain antibiotic concentrations. Daphnia magna and other aquatic invertebrates have also been used for checking the toxicity priority of antibiotics. When investigating the acute effect of antibiotics (e.g., growth inhibition), concentrations in standard laboratory organisms are usually about two or three orders of magnitude higher than the maximal concentrations in the aquatic environment, resulting in the underestimation of antibiotic hazards. Vertebrate organisms show a promising potential for chronic toxicity and potentially subtle effects of antibiotics, particularly on biochemical processes and molecular targets. The adverse developmental effects of macrolides, tetracyclines, sulfonamides, quinolones, and other antibiotic groups have been evaluated in aquatic vertebrates such as Danio rerio and Xenopus tropicalis. In acute toxicity tests, low levels of antibiotics have systematic teratogenic effects on fish. The effects of antibiotics on oxidative stress enzymes and cytochrome P450 have been investigated. Cytotoxicity, neurotoxicity, and genotoxicity have been observed for certain antibiotic amounts. However, there are no firm conclusions regarding the chronic toxicity of antibiotics at environmentally relevant levels because of the lack of long-term exposure studies. Herein, future perspectives and challenges of antibiotic toxicology were discussed. Researchers should pay more attention to the following points: chronic toxicity and potentially subtle effects of environmentally relevant antibiotics on vertebrates; effects of toxicity on biochemical processes and mode of action; combined toxicity of antibiotics and other antibiotics, metabolites, and heavy metals; and environmental factors such as temperature and pH.     

Selective medium with nalidixic acid for isolating antibiotic-producing Actinomyces

The majority of actinomycetes belonging to various genera proved to be resistant to nalidixic acid concentrations having an inhibitory effect on bacteria with trailing growth i.e. B. subtilis and B. mycoides. The bacteria prevented isolation of actinomycetes as pure cultures. The use of a selective medium with nalidixic acid for isolation of soil actinomycetes resulted in 20 per cent increase in the number of the actinomycetes isolated as pure cultures. Preliminary treatment of the soil samples with calcium carbonate under moist conditions followed by the inoculation to the medium with nalidixic acid made it possible to increase isolation of actinomycetes at most 100-fold. With this complex method 495 actinomycete cultures were isolated, their antibiotic properties were studied and their taxonomic position at the genus level was determined. The complex method including the preliminary treatment of soil samples with calcium carbonate followed by inoculation to the selective medium with nalidixic acid is efficient and may be recommended for screening organisms producing new antibiotics.     

Taxonomic characteristics of soil Mycobacteria and their antibiotic properties]

Morphological, cultural and chemotaxonomic properties of 12 gram-positive soil cultures isolated were studied by using a test system developed for screening the organisms producing broad-spectrum antibiotics among Nocardiaforms (Coryneforms). The cultures were found to belong to Actinomycetales, Nocardioforms, Mycobacteriaceae and Mycobacterium. The saprophytic rapidly growing soil mycobacteria showed antibiotic activity against a large number of gram-positive and gram-negative test microbes including those belonging to Pseudomonas and Proteus resistant to the majority of the antibiotics currently used in medicine.     

Preferential Inhibition of Protein Synthesis by Ketolide Antibiotics in <Emphasis Type="Italic">Haemophilus influenzae</Emphasis> Cells

The ketolide antibiotics are semi-synthetic derivatives of erythromycin A with enhanced inhibitory activity in a wide variety of microorganisms. They have significantly lower MICs than the macrolide antibiotics for many Gram-positive organisms. Two ketolides, telithromycin and ABT-773, were tested for growth-inhibitory effects in Haemophilus influenzae. Both antibiotics increased the growth rate and reduced the viable cell number with IC₅₀ values of 1.5 μg/ml. Protein synthesis was inhibited in cells with a similar IC₅₀ concentration (1.25 μg/ml). Macrolide and ketolide antibiotics have been shown to have a second equivalent target for inhibition in cells, which is blocking the assembly of the 50S ribosomal subunit. Pulse and chase labeling assays were conducted to examine the effect of the ketolides on subunit formation in H. influenzae. Surprisingly, both antibiotics inhibited 50S and 30S subunit assembly to the same extent, with no specific effect of the compounds on 50S assembly. Over a range of antibiotic concentrations, 30S particle synthesis was diminished to the same extent as 50S formation. H. influenzae cells seem to have only one significant target for these antibiotics, and this may help to explain why these drugs are not more effective than the macrolides in preventing the growth of this microorganism. Received: 21 February 2002 / Accepted: 30 April 2002     

Dual inhibitory effects of the peptide antibiotics leucinostatins on oxidative phosphorylation in mitochondria

The effects of the hydrophobic peptide antibiotics leucinostatins A and B, originally isolated by Arai, T., Y. Mikami, K. Fukushima, T. Utsumi, and K. Yazawa. (J. Antibiotics (1973) 26: 157-161), on the functions of rat liver mitochondria were examined. At a concentration of 240 nM, these compounds completely inhibited state 3 respiration and ATPase activity that was stimulated by weakly acidic uncouplers. However, at higher concentrations, they induced uncoupling, probably by their protonophoric action. The uncoupling action was potentiated by known phosphoryl transfer inhibitors such as venturicidin, DCCD and oligomycin. The binding site of leucinostatins at lower concentrations was suggested to be located at, or very close to that of venturicidin. The potencies of the two analogues of leucinostatin were almost the same for all their actions. Their effects were very similar to those of the peptide antibiotics A20668's, which have been used as leucinostatins without any chemical and biological confirmation that they are in fact leucinostatins. Thus, the chemical structures of leucinostatins are thought to be analogues to those of the A20668's.     

Various approaches to the search for the producers of bacteriocin-like substances among bacteria of the genus Pseudomonas

Some methods providing rapid and methodically simple study of large microbial collections and detection of cultures producing bacteriocin-like substances perspective for further investigation are described. The use of cellophane disks and study of the proteolytic enzyme effects allowed the authors to detect organisms producing high molecular antibiotics of protein nature.     

Diversifications in the Tube Dilution Test for Antibiotic Sensitivity of Microorganisms

The tube dilution method of performing antibiotic sensitivity tests is commonly employed as an accurate method for defining the minimal inhibitory concentration in relation to pathogenic organisms. It is also used as a reference for comparing minimal inhibitory concentrations with the size of the zone of inhibition in the agar diffusion test. Although surveys have shown that there is no standardized method and technique of performing the tube dilution test, it is generally assumed that all of the diversified methods will yield the same results and interpretations. With the assistance of five experts, seven different tube dilution methods were compared; 16 antibiotics, and three organisms for each antibiotic, were used. The conclusions drawn are that, although the accuracy of a single method within its own confines is acknowledged, the minimal inhibitory concentrations and interpretations cannot be interpolated from one laboratory to another where a different technique is employed. The results are frequently discrepant. It is suggested that a uniform method be developed and promulgated for general use.     

Antibiotic Sensitivities of Organisms Isolated from Mastitic and Nonmastitic Mammary Secretions

Antibiotic sensitivity tests to determine the minimal inhibitory concentrations (MIC) and the minimal lethal concentrations (MLC) for six antibiotics were conducted against mastitic isolates of staphylococci in skim milk and broth. The MIC and the MLC for all the antibiotics except benzylpenicillin were considerably higher in skim milk than in broth. Benzylpenicillin was the most effective antibiotic tested in either medium, and dihydrostreptomycin was the least effective against the organisms tested.     

Experimental studies on the ecological role of antibiotic production in bacteria

Summary Genetically well-characterized strains of antibiotic-producing soil bacteria (Streptomyces griseus andStreptomyces coelicolor) were used to examine the ecological role of antibiotic production. Streptomycetes were competed against sensitive and resistantBacillus subtilis, another soil bacterium, on surface (agar) culture. The ecological role of antibiotics was examined in three levels of competition. (1) Capacity of antibiotics to allow invasion of producing organisms (B. subtilis established and streptomycetes added later). (2) Capacity of antibiotics to mediate competition between established populations (B. subtilis and streptomycetes co-inoculated). (3) Capacity of antibiotics to prevent invasion by competitors (streptomycetes established andB. subtilis added later). Antibiotic production was found to play a significant role in preventing the invasion of competitors in these experiments. Antibiotic production did not improve the ability of producers to invade a population of sensitive cells nor did it play a strong role in mediating competition between established populations. Antibiotic production also selected for antibiotic-resistant bacteria among invading competitors.     

Recombinant microorganisms for industrial production of antibiotics

The enhancement of industrial antibiotic yield has been achieved through technological innovations and traditional strain improvement programs based on random mutation and screening. The development of recombinant DNA techniques and their application to antibiotic producing microorganisms has allowed yield increments and the design of biosynthetic pathways giving rise to new antibiotics. Genetic manipulations of the cephalosporin producing fungus Cephalosporium acremonium have included yield improvements, accomplished increasing biosynthetic gene dosage or enhancing oxygen uptake, and new biosynthetic capacities as 7-aminocephalosporanic acid (7-ACA) or penicillin G production. Similarly, in Penicillium chrysogenum, the industrial penicillin producing fungus, heterologous expression of cephalosporin biosynthetic genes has led to the biosynthesis of adipyl-7-aminodeacetoxycephalosporanic acid (adipyl-7-ADCA) and adipyl-7-ACA, compounds that can be transformed into the economically relevant 7-ADCA and 7-ACA intermediates. Escherichia coli expression of the genes encoding D-amino acid oxidase and cephalosporin acylase activities has simplified the bioconversion of cephalosporin C into 7-ACA, eliminating the use of organic solvents. The genetic manipulation of antibiotic producing actinomycetes has allowed productivity increments and the development of new hybrid antibiotics. A legal framework has been developed for the confined manipulation of genetically modified organisms. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 216-226, 1997.     

Study of the L-transforming action on Brucella cells of tetracycline, streptomycin, rifampicin and their combinations with penicillin in in vitro experiments]

The in vitro study of the possible formation of L-forms of Brucella under the effect of tetracycline, streptomycin, rifampicin or their combinations with penicillin showed that passages of various Brucella species on media containing increasing concentrations of the antibiotics resulted in insignificant morphological changes in the cells. Passages of the same cultures on media containing combinations of the above antibiotics with penicillin resulted in more significant changes in the cell morphology, up to formation of spheroplasts. No L-transformation was observed under the experimental conditions.     

东海区底拖网作业三类主要渔获物的时空关系

目前海洋捕捞渔获物主要分为三大类,包括鱼类、甲壳类和头足类。这三类生物共存于一片水域,同处一个生态系统,相互之间存在着诸多联系,如捕食与被捕食、生存空间竞争等。基于生态系统水平的海洋生物资源管理与研究已经成为国际趋势和国内要求,将各种生物、群落和环境作为一个整体进行研究是基于生态系统管理与研究的基本途径,而目前多数研究还是将三类生物分开,缺少三者相互关系的综合研究。根据2000年东海区渔业资源大面积调查数据,就三类生物的主要分布区域水平空间关系、三类生物空间分布的距离及其季节变化特征等方面进行了探讨。研究结果发现,三类生物主要分布区域存在空间分离趋势,且该趋势随着三类生物集中区域的聚集程度越高,空间分离的现象越为明显,这种分离特征可能是三类生物相互竞争、相互适应、长期演化的结果,是一种典型的生态位分化现象。四季三类生物的空间分布距离,呈现出春夏季距离远、秋冬季距离近的特点;可能是由于春夏季是多数鱼类的产卵繁殖期,其分布水域主要聚集在产卵场或育卵场,而其它生物无显著聚集或聚集水域不同,从而导致鱼类与其它生物之间的距离增加;而秋冬季是多数鱼类的索饵和越冬洄游季节,分布水域相对分散,从而导致三类生物之间的距离相对近。三类生物的空间分布距离,呈现出头足类与鱼类距离近、鱼类与甲壳类和甲壳类与头足类距离相对远的特点;可能是由于三类生物的不同活动能力所导致,甲壳类活动能力差,一般处于海洋最底水层,头足类活动能力强于甲壳类,能活跃于多个水层,但其游泳能力具有间歇性特点,而鱼类活动能力最强,能长期持续在多水层之间游动。活动能力导致鱼类与头足类的空间交叉区域较多,因而距离较近;而甲壳类与鱼类和头足类的交叉区域较少,因而距离较远。三类生物空间分布的分离特征对于渔业管理也有一定的指导意义,如适当引导不同作业渔船在不同水域进行生产,从而能减少或避免渔船为争夺渔场而发生的纠纷和摩擦。     

Therapeutic effect of some antibiotics on experimental staphylococcal infection and its correlation with in vitro activity of antibiotics in sub-inhibitory concentration against Staphylococcus aureus strains

The aim of the study was to demonstrate of whether the therapeutic effects of antibiotics depend on their in vitro activity in sub-inhibitory concentrations against staphylococci. Cloxacillin, gentamicin and lincomycin were used in the study. Groups of S. aureus strains, containing 6 strains with similar MIC values each but different sensitivity to sub-inhibitory antibiotic concentrations (sub-MIC) were selected (a total of 36 trains): i. strains increasing their sensitivity to phagocytosis and bactericidal activity of rabbit leukocytes after incubation with an antibiotic in 0.1 MIC concentration, ii. strains with sensitivity to the above factors unaffected by incubation with an antibiotic in 0.5 MIC concentration. The doses of staphylococci causing death of 90-100% of Swiss albino mice 10 days after i.p. infection were determined. The injected doses (LD 90-100) and various doses of antibiotics were used to determine ED50 values as well as the survival rate of the mice with experimental staphylococcal infections after treatment with these antibiotics. It was demonstrated that effective doses (ED 50) of the antiboitics were significantly lower when the antibiotics were administered once to mice infected with strains S. aureus sensitive to sub-MIC concentrations of the investigated antibiotics than for mice infected with strains resistant to their sub-MIC concentrations. Similar correlations were observed in mice which were given the antibiotics several times (for 7 days): the percentage of the surviving mice was higher in the group infected with sub-MIC sensitive strains. The therapeutic effect of cloxacillin, gentamicin and lincomycin demonstrated a significant correlation with the S. aureus strains used to induce the infections and their sensitivity, or lack of sensitivity in vitro, to phagocytosis and bactericdal activity of leukocytes in the presence of antibiotics in sub-MIC concentrations.     

Evolution of the clusters of genes for beta-lactam antibiotics: a model for evolutive combinatorial assembly of new beta-lactams.

beta-Lactam antibiotics are produced by prokaryotic and eukaryotic organisms. The genes for beta-lactam biosynthesis are organized in clusters but the location of the different genes is not identical. Biosynthesis genes are clustered with genes for resistance (bla, pbp) and for the efflux of the antibiotic (cmcT) in prokaryotes. Comparison of proteins reveals much larger differences for primary metabolism enzymes than for beta-lactam biosynthesis enzymes in producing organisms. This suggests a horizontal transfer of the beta-lactam antibiotic biosynthesis genes.     

Sensitivity to antibiotics of pneumococci isolated from patients with chronic nonspecific pneumonia and bronchitis

Four hundred and twenty two pneumococcal strains isolated from 300 patients with chronic nonspecific pneumonia and bronchitis were studied with respect to their sensitivity to 18 antibiotics within a period from 1982 to 1985. It was shown with the method of serial dilutions on solid media that 91.7, 87.8, 85 and 81 per cent of the isolates were sensitive to benzylpenicillin, ampicillin, lincomycin and cefuroxime, respectively. A significant percentage of the pneumococcal strains had decreased sensitivity to benzylpenicillin (MIC close to the therapeutic concentration). On this basis it was recommended to use lower concentrations of benzylpenicillin (less than 0.25 units/ml) in assay of sensitivity in clinical strains of Pneumococcus.