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The growth of the polypeptide chain occurs due to the fast and coordinated work of the ribosome and protein elongation factors, EF-Tu and EF-G. However, the exact contribution of each of these components in the overall balance of translation kinetics remains not fully understood. We created an in vitro translation system Escherichia coli replacing either elongation factor with heterologous thermophilic protein from Thermus thermophilus. The rates of the A-site binding and decoding reactions decreased an order of magnitude in the presence of thermophilic EF-Tu, indicating that the kinetics of aminoacyl-tRNA delivery depends on the properties of the elongation factor. On the contrary, thermophilic EF-G demonstrated the same translocation kinetics as a mesophilic protein. Effects of translocation inhibitors (spectinomycin, hygromycin B, viomycin and streptomycin) were also similar for both proteins. Thus, the process of translocation largely relies on the interaction of tRNAs and the ribosome and can be efficiently catalysed by thermophilic EF-G even at suboptimal temperatures.

The ribosome is one of the major targets in the cell for clinically used antibiotics. However, the increase in multidrug resistant bacteria is rapidly reducing the effectiveness of our current arsenal of ribosome-targeting antibiotics, highlighting the need for the discovery of compounds with new scaffolds that bind to novel sites on the ribosome. One possible avenue for the development of new antimicrobial agents is by characterization and optimization of ribosome-targeting peptide antibiotics. Biochemical and structural data on ribosome-targeting peptide antibiotics illustrates the large diversity of scaffolds, binding interactions with the ribosome as well as mechanism of action to inhibit translation. The availability of high-resolution structures of ribosomes in complex with peptide antibiotics opens the way to structure-based design of these compounds as novel antimicrobial agents.

Antibiotics that target the bacterial ribosome make up about half of all clinically used antibiotics. We have studied two ribosome targeting drugs: Fusidic acid and Viomycin. Fusidic acid inhibits bacterial protein synthesis by binding to elongation factor G (EF-G) on the ribosome, thereby inhibiting translocation of the bacterial ribosome. Viomycin binds directly to the ribosome and inhibits both the fidelity of mRNA decoding and translocation. We found that the mechanisms of inhibition of these two antibiotics were unexpectedly complex. Fusidic acid can bind to EF-G on the ribosome during three separate stages of translocation. Binding of the drug to the first and most sensitive state does not lead to stalling of the ribosome. Rather the ribosome continues unhindered to a downstream state where it stalls for around 8 seconds. Dissociation of fusidic acid from this state allows the ribosome to continue translocating but it soon reaches yet another fusidic acid sensitive state where it can be stalled again, this time for 6 seconds. Viomycin inhibits translocation by binding to the pre-translocation ribosome in competition with EF-G. If viomycin binds before EF-G it stalls the ribosome for 44 seconds, much longer than a normal elongation cycle. Both viomycin and fusidic acid probably cause long queues of ribosomes to build up on the mRNA when they bind. Viomycin inhibits translational fidelity by binding to the ribosome during initial selection. We found that the concentration of viomycin required to bind to the ribosome with a given probability during decoding is proportional to the accuracy of the codon∙anticodon pair being decoded. This demonstrated that long standing models about ribosomal accuracy cannot be correct. Finally, we demonstrated that a common viomycin resistance mutation increases the drug binding rate and decreases its dissociation rate. Our results demonstrate that ribosome targeting drugs have unexpectedly complex mechanisms of action. Both fusidic acid and viomycin preferentially bind to conformations of the ribosome other than those that they stabilize. This suggests that determining the structures of stable drug-bound states may not give sufficient information for drug design.

The aminoglycosides and cyclic polypeptides are essential drugs in the treatment of multidrug-resistant tuberculosis, underscoring the need for accurate and reproducible drug susceptibility testing (DST). The epidemiological cutoff value (ECOFF) separating wild-type susceptible strains from non-wild-type strains is an important but rarely used tool for indicating susceptibility breakpoints against Mycobacterium tuberculosis . In this study, we established wild-type MIC distributions on Middlebrook 7H10 medium for amikacin, kanamycin, streptomycin, capreomycin, and viomycin using 90 consecutive clinical isolates and 21 resistant strains. Overall, the MIC variation between and within runs did not exceed ±1 MIC dilution step, and validation of MIC values in Bactec 960 MGIT demonstrated good agreement. Tentative ECOFFs defining the wild type were established for all investigated drugs, including amikacin and viomycin, which currently lack susceptibility breakpoints for 7H10. Five out of seven amikacin- and kanamycin-resistant isolates were classified as susceptible to capreomycin according to the current critical concentration (10 mg/liter) but were non-wild type according to the ECOFF (4 mg/liter), suggesting that the critical concentration may be too high. All amikacin- and kanamycin-resistant isolates were clearly below the ECOFF for viomycin, and two of them were below the ECOFF for streptomycin, indicating that these two drugs may be considered for treatment of amikacin-resistant strains. Pharmacodynamic indices (peak serum concentration [ C max ]/MIC) were more favorable for amikacin and viomycin compared to kanamycin and capreomycin. In conclusion, our data emphasize the importance of establishing wild-type MIC distributions for improving the quality of drug susceptibility testing against Mycobacterium tuberculosis .

Environmental samples are excellent sources of natural products that possess numerous kinds of therapeutic activities. One important family of natural products is the nonribosomal peptides, which includes penicillin, cyclosporin, viomycin and daptomycin (Cubicin). These peptides are made in bacteria or fungi by large enzymes called nonribosomal peptide synthetases (NRPS). NRPSs are true macromolecular machines or nanofactories, with modular assembly-line logic, a complex catalytic cycle, moving parts and many active sites. Visualization of large fragments of NRPSs at various functional states is required to understand the manner in which NRPSs synthesize their important products. Many excellent structural experiments have been performed to date. Recently, we added to the structural knowledge by visualizing the first module of the NRPS, which makes linear gramicidin, a clinical topical antibiotic, in all its major functional states. These experiments show how the individual domains, including an unusual tailoring domain, function together in assembly-line synthesis. Along with the ever-expanding body of biophysical, biochemical and genetic work, this work brings us closer to a fundamental understanding of these natural antibiotic nanofactories, and perhaps the ability to exploit them to produce novel therapeutics.

Background : The peptide antibiotic viomycin inhibits ribosomal protein synthesis, group I intron self-splicing and self-cleavage of the human hepatitis delta virus ribozyme. To understand the molecular basis of RNA binding and recognition by viomycin, we isolated a variety of novel viomycin-binding RNA molecules using in vitro selection. Results : More than 90% of the selected RNA molecules shared one continuous highly conserved region of 14 nucleotides. Mutational analyses, structural probing, together with footprinting experiments by chemical modification, and Pb 2+ -induced cleavage showed that this conserved sequence harbours the antibiotic-binding site and forms a stem-loop structure. Moreover, the loop is engaged in a long-range interaction forming a pseudoknot. Conclusions : A comparison between the novel viomycin-binding motif and the natural RNA target sites for viomycin showed that all these segments form a pseudoknot at the antibiotic-binding site. We therefore conclude that this peptide antibiotic has a strong selectivity for particular RNA pseudoknots.

The tuberactinomycin antibiotics are essential components in the drug arsenal against Mycobacterium tuberculosis infections and are specifically used for the treatment of multidrug-resistant tuberculosis. These antibiotics are also being investigated for their targeting of the catalytic RNAs involved in viral replication and for the treatment of bacterial infections caused by methicillin-resistant Staphylococcus aureus strains and vancomycin-resistant enterococci. We report on the isolation, sequencing, and annotation of the biosynthetic gene cluster for one member of this antibiotic family, viomycin, from Streptomyces sp. strain ATCC 11861. This is the first gene cluster for a member of the tuberactinomycin family of antibiotics sequenced, and the information gained can be extrapolated to all members of this family. The gene cluster covers 36.3 kb of DNA and encodes 20 open reading frames that we propose are involved in the biosynthesis, regulation, export, and activation of viomycin, in addition to self-resistance to the antibiotic. These results enable us to predict the metabolic logic of tuberactinomycin production and begin steps toward the combinatorial biosynthesis of these antibiotics to complement existing chemical modification techniques to produce novel tuberactinomycin derivatives.

During the last few years, antibiotic multiresistance has been increasing, not only in hospitals, but also, more worryingly, in general medicine. Different ways are being explored to bypass this problem. RNA-acting antibiotics such as aminosides (aminoglycosides) bind to bacterial RNA causing premature termination of proteins and mistranslation in bacteria. It is now possible to study the interactions of such antibiotics with their target by in-vitro selection of RNA molecules that recognize these antibiotics (RNA aptamers, SELEX method). The knowledge of the antibiotic-RNA interactions represents a promising way for the rational design of new bioactive compounds less susceptible to bacterial resistance.

The mechanism of action of many antimycobacterial agents is poorly understood. To obtain preliminary information on whether the targets for some of these drugs might also occur in other bacteria, the in vitro activities of selected agents against Escherichia coli, Bacillus subtilis and Staphylococcus aureus were determined. Dapsone, p-aminosalicylic acid and thiacetazone failed to inhibit the above organisms (MIC values > 100 micrograms/ml) that may therefore lack targets for these drugs. Capreomycin, viomycin and clofazimine demonstrated activity against some of the organisms (MIC values < 100 micrograms/ml) suggesting that the targets of these drugs may not be restricted to mycobacterial species. The agents were all potent inhibitors of Mycobacterium bovis bacille Calmette-Guerin (MIC values 0.08-0.5 microgram/ml).

Phenotypes of isolates of Mycobacterium tuberculosis H37RV showing resistance to the aminoglucoside antibiotics streptomycin, viomycin, kanamycin, capreomycin, tuberactinomycin N, lividomycin and paromomycin could be grouped into the following types: (I) resistant only to different levels of streptomycins; (2) resistant only to a low level of kanamycin; (3) triply resistant, to low levels of viomycin, tuberactinomycin N and capreomycin; (4) triply resistant, to a low level of kanamycin and high levels of lividomycin and paromomycin; (5) quadruply resistant, to a low level of capreomycin and high levels of kanamycin, lividomycin and paromomycin; (6) hextuply resistant, to high levels of viomycin, tuberactinomycin N, capreomycin, kanamycin, lividomycin, and paromomycin. Three modificatied types of the latter were also observed. Appearance rates of the six types were estimated as 10(-6) to 10(-9), 10(-6), 10(-6) to 10(-7), 10(-8), 10(-8), and 10(-8) to 10(-9), respectively, in a total viable population of the parent strain. Mutations to all phenotypes were considered to be produced by single mutations. According to cross-resistance relationships, aminoglucoside antibiotics were classified into three groups: (I) streptomycin; (II) viomycin, tuberactinomycin N and capreomycin; (III) kanamycin, lividomycin and paromomycin. No cross-resistance relationship between streptomycin and other antibiotics was observed. Resistances to viomycin, tuberactinomycin N and capreomycin occurred by single mutation to type 3. Resistances to kanamycin, lividomycin and paromomycin occurred by single mutations to types 4 and 5. Low resistance to capreomycin was produced by mutation to type 5. Therefore capreomycin was considered to be an intermediate between the second and third groups. These two groups had a close relationship, as resistance to all six agents in these groups could be produced by a single mutation to type 6 (and its modified types).

Viomycin and capreomycin, antibiotics produced by Streptomyces vinaceus and S. capreolus respectively, are potent inhibitors of bacterial protein synthesis. Although these organisms are highly tolerant of their own products in vivo, their ribosomes are fully sensitive to the action of the drugs in vitro. However, they possess novel, antibiotic-inactivating enzymes (viomycin phosphotransferase, capreomycin phosphotransferase, capreomycin acetyl-transferase) which, in addition to possible biosynthetic roles, may contribute to the resistances observed in vivo.

The response of selected strains ofRhizobium japonicum to fifty-five antibiotics was determined. The most effective antibiotics for these strains include Kanaymcin, Streptomycin, Dihydrostreptomycin, Triburon, and Viomycin. Mutants were recovered which were resistant to these drugs individually and in various combinations of two. Single and double mutants, which grew as well as the sensitive parent strain on nonselective media, were tested for infectivity and effectiveness of nitrogen-fixation in soybeans. Six weeks after germination, plants were harvested and compared with respect to size, number of nodules, color, number of trifoliate leaves, dry weight, and total nitrogen.

An unidentified Streptomyces, designated as Strain H 1051-MY 10, was proved to produce viomycin and two new antibiotics. The new antibiotics were extracted from the cultured mycelia with acetone and transferred to ethyl acetate after acetone was removed in vacuo. The extracted antibiotics were separated into two components by alumina column chromatography and named carbazomycins A and B, because both antibiotics were proved to contain a carbazole nucleus. The molecular formulae of carbazomycins A and B were determined to be C16H17NO2 and C15H15NO2, respectively. Further, carbazomycin B was methylated with diazomethane to give carbazomycin A. Carbazomycins inhibited the growth of phytophathogenic fungi and further showed weak antibacterial and antiyeast activities.

Motility of pathogenic T. pallidum was maintained in aerobic in vitro cultures for several weeks using a special medium. The latter consisted of McCoy's 5a medium supplemented with glutathione, sodium pyruvate, HEPES buffer, gentamycin (garamycin), and fetal calf serum. The virulence of the organisms was lost in 5 to 6 days. No multiplication of the organisms was observed. Four antibiotics (viomycin, kanamycin, gentamycin (garamycin), and neomycin) were tested for their bactericidal action and possible toxicity to T. pallidum. Gentamycin proved to be superior to the other three antibiotics in being non-toxic to the treponemes and showing a possible stimulatory effect on their motility and longevity. Cultivation of T. pallidum in cultured cells in the presence of the enzymes, superoxide dismutase and catalase, in a special medium showed possibilities for future experimentation under monitored, reduced oxygen pressure with a continuous system to dismutate superoxide radicals.

The peptide antibiotic viomycin at a concentration of 10 muM inhibits E. coli ribosomes to the extent of about 70% as measured in the poly (U) system, and to about 85% in a natural mRNA (R17) system. Ribosomes from M. smegmatis show no activity at all at this concentration of the antibiotic. Experiments on the Mg+2 dependent dissociation and association of the ribosomal subunits revealed that viomycin stabilizes the 70S couples and promotes association of ribosomal subunits. This response is related to the drug action as indicated by the observation that viomycin resistant strains are not affected by viomycin with respect to dissociation and 70S couple information. A model for the inhibitory action of the drug is proposed.

Summary The minimal inhibitory concentration of rifamide in Dubos liquid medium without tween 80 for human type tubercle bacilli is 0·5 μg. or less. The bovine type is slightly more sensitive than the human type. Avian strains, photochromogens and nonchromogens are resistant. There is no evidence of cross-resistance between rifamide and other antituberculosis drugs. The intravenous rifamide and the oral rifampicin are similar in their inhibitory activity. Individual doses of 450 mg. or 600 mg. rifampicin before a meal are generally followed at two hours by serum levels of 16 or 32 μg./ml. At 12 hours they are 1 or 2 μg. and at 24 hours only a trace or nil.

An evaluation of 80 patients with pulmonary tuberculosis who received intermittent viomycin, two grams every third day, singly or combined with intermittent streptomycin or daily para-aminosalicylic acid for 120 days suggests that this agent is capable of exerting a favorable effect on the clinical course of the disease. The therapeutic effectiveness of this drug was considerably less than streptomycin, but approximated that of PAS. Viomycin combined with either streptomycin or para-aminosalicylic acid was superior to any of the drugs employed alone. The high incidence of clinical and laboratory toxicity which accompanied intermittent viomycin was predominantly minor, transient, and reversible after termination of therapy. This is in striking contrast to toxicity reported when viomycin is administered daily. It is believed that viomycin is a relatively safe drug when administered intermittently, provided its potential toxicity is appreciated and appropriate clinical and laboratory surveillance is maintained.

The author discusses little investigated antagonistic effects of certain antibiotics, manifested by the inhibition of chlorophyll synthesis inEuglena gracilis. Two main types of depigmentation were found—temporary and permanent. The oldest substrains ofEuglena gracilis var.bacillaris, strain Mainx, permanently bleached by erthromycin, streptomycin, carbomycin, spiramycin, kanamycin and viomycin, were kept in the light for at least two years without showing any signs of turning green. These antibiotics caused permanent apochlorosis, but reversible apoplastidy. The euglena cultures remained permanently heterotrophic, Picromycin, methymycin and neomycin. however, only temporarily inhibited chlorophyll synthesis. When transferred to medium not containing these antibiotics and incubated in the light, these cultures again produced chlorophyll.

Summary The late results, five years after the start of treatment, are given in 122 patients with far-advanced tuberculosis and cultures resistant to streptomycin, isoniazid and PAS. Thirty-nine had chemotherapy and early surgical treatment and 83 had chemotherapy alone (surgical treatment was used in four after a relapse). The following drugs were used: ethionamide (0·5 g, twice daily), pyrazinamide (0·5 g. three times daily), cycloserine (0·25 g. three times daily), viomycin (1 g. daily or 2 g, twice a week). Fifty-five of the 83 patients were treated initially with three of the secondary drugs for a minimum of three months and an average period of 12 months; treatment was then continued with two drugs. Fifty-three (96%) became negative on culture. In two patients the treatment failed initially; both had one of the drugs (viomycin) intermittently and, as discovered later, one had no appreciable concentration of ethionamide in the serum after either oral or rectal administration of the drug. Eight (14%) had a late bacteriological relapse. They did not take drugs regularly. In four of them the cultures became resistant to secondary drugs. Five became negative again with further treatment (two of them after surgery). Ten patients died, six of them after the sputum had become persistently negative. Twenty-eight patients had only one or two drugs initially: only 11 (40%) became negative, three of them after retreatment with three-drug combinations. Nineteen died and in 16 of these sputum was still positive. There was no significant difference between the three-drug and two-drug group in the severity of disease and other relevant factors. The difficulties of treatment with secondary drugs are emphasized. However, satisfactory long-term results can be obtained if some basic rules and principles of good chemotherapy are observed, and if the patients are willing to co-operate.

Interference thresholds have been determined for a number of antibiotics in the microbial assays of specific antibiotics. Two aspects were considered in order to facilitate the quantitative analysis of mixtures of antibiotics: the “interference threshold,” which is the concentration of an antibiotic causing a significant interference in the presence of another antibiotic in a given assay, and the “sensitivity threshold,” which is the concentration of an antibiotic causing a response in the assay for a different antibiotic.

Summary: The bactericidal activities of mixtures of various chemotherapeutic drugs were tested against the H37Rv strain of Mycobacterium tuberculosis when growing in Tween albumin medium. Oxytetracycline (terramycin) antagonized the bactericidal activities of streptomycin, isoniazid and viomycin, whereas p-aminosalicylic acid (PAS) was slightly synergistic or did not influence their activities. Mixtures of viomycin and streptomycin were slightly less bactericidal than streptomycin alone, but more bactericidal than viomycin alone. Viomycin acted synergistically with isoniazid, and with isoniazid + streptomycin. The emergence of strains resistant to streptomycin, isoniazid or viomycin was not prevented in the cultures by the presence of oxytetracycline, probably because of its rapid inactivation. Drug resistance emerged in dual mixtures which included PAS, where the concentrations of streptomycin, isoniazid or PAS were low, but not when these concentrations were high. Resistant strains did not emerge in cultures containing viomycin + streptomycin or viomycin + isoniazid.

1) Viomycin in doses of 2 grams twice weekly combined with 12 grams of PAS daily is of slight toxicity. 2) Tinnitus may be expected to occur. Allergic symptoms have not been a major problem. Auditory nerve damage of a serious degree is not frequent. 3) Streptomycin resistant organisms are affected by viomycin and patients having such organisms improve under intermittent viomycin treatment. 4) Bacterial resistance to viomycin did not develop to a significant degree among patients treated for six months. 5) Clinical and x-ray improvement is more striking in streptomycin-PAS treated patients, however, the effectiveness of viomycin-PAS is definite and demonstrable. 6) The clinical use of viomycin is feasible in the presence of streptomycin resistant organisms, and allergic sensitivity to streptomycin. Its use with newer antimicrobials should be explored.

Summary Twenty patients with chronic far-advanced pulmonary tuberculosis have been treated with viomycin and oxytetracycline, most for six months or more. Previous treatment for a mean of twenty-three months with streptomycin, PAS and isoniazid had failed and in all high bacillary resistance had emerged. Results were good, considering the apparently hopeless state of most of the patients. In 4, there was cavity closure. In 5, there was moderate to very considerable resolution, but ‘insurance operations’ were performed afterwards. In 5, there was little or no improvement, but operations were subsequently carried out without major incident. In 4, there was no radiological change; in 1 there was deterioration and 1 died from amyloidosis. Among the 10 patients who subsequently underwent operation, there was no major complication. Changes in sensitivity to these drugs appeared only with oxytetracycline, in 3 cases.

The test of sensitivity to chemotherapeutic ag e n ts wqs performed on becteria isolated from the urine of 105 patients suffering from urinary tract infection, and7the results were compared with the clinical effect of chemotherapeutic agents for these patients. 1) In the acute simple urinary tract infection, the clinical experimen t proved a succeeded effect of chemotherapy regardless the result of the sensitivity test. 2) For the urinary tract infection with complication, the clinical experiment failed to produce a good effect, unless the complication was eliminated. 3) In both the chronic simple urinary tract infec tion and the urinary tract infection after urological operation, better clinical effect was produced by agents with positive sensitivity test than those with negative sensitivity test. 4) Kanamycin proved to be most effe ctive agent regardless the result of the sensitivity test.

Kundrymycin, a new antibiotic, was isolated from fermentations of Streptomyces metachromogenes, sp. n., ATCC 21, 440, by methylene chloride extraction. It is an acid-base indicator with a molecular weight of 878.9. Biologically it is inhibitory to gram-positive bacteria, moderately cytotoxic to HeLa cells and inhibitory in vivo to WALKER 256 tumors in rats.

Summary The experiments described demonstrated statistically significant activity against mouse toxoplasmosis for aureomycin, terramycin, fumagillin, and chloramphenicol; however, with the possible exception of aureomycin, none is believed to be sufficiently active to be of practical importance. Aureomycin produced apparent cures in some mice, but only at extremely high dosages, higher than those attainable in man. Comparison of the results of these experiments with those of others indicates the existence of strains of Toxoplasma differing in their response to this drug. Viomycin, Neomycin, Fracidin, Prodigiosin and R-2007 produced no effect on mouse toxoplasmosis under the conditions of our experiments.

The well characterized translocation inhibitor viomycin (=tuberactinomycin B) promotes translational errors (misreading) in an in vitro system from Escherichia coli. It strongly stimulates both the binding of noncognate Tyr-tRNA to poly(U)-programmed ribosomes and the subsequent synthesis of acPhe(Tyr)n-tRNA ( n ⋍20 ). The closely related antibiotics capreomycin and tuberactinomycins A,N and O also inhibit translocation and induce misreading.

The rate of sputum conversion (continuously negative cultures for six months or more) was compared among four regimens given to 83 patients with moderately advanced, cavitary lung disease caused by Mycobacterium avium complex untreated previously. The regimens of rifampin + isoniazid + enviomycin and rifampin + isoniazid + streptomycin appeared to be superior to the regimen of rifampin + isoniazid + ethambutol. No statistically significant difference was observed between the regimens rifampin + isoniazid + enviomycin and rifampin + isoniazid + streptomycin.

The mechanism of resistance of Mycobacterium intracellulare strain 103 and other clinical isolates to a variety of drugs including aminoglycoside and peptide antibiotics was investigated. Enzymatic inactivation of aminoglycoside and peptide antibiotics could not be demonstrated. Ribosomes of the strain were found to be sensitive to the antibiotics. The levels of resistance of strain 103 and other clinical isolates decreased dramatically when the culture medium was changed from Dubos agar to Tween 80-containing agar. These results suggest that a permeability barrier is the reason for naturally occurring resistance in M. intracellulare.

As an extension of the investigations on structure-activity relationships of viomycin (VM), a tuberculostatic antibiotic, chemical modifications of its chromophore group by oxidative reactions were studied. Oxidations with KMnO4 gave normal oxidation products named oxoviomycin and its derivative while, with bromine, gave abnormal products V, VI and VIII, those of which were characterized by chemical and physical analyses. Antimicrobial potencies of both oxidation products of VM showed the nullified activities, the results of which were agreeable from the predictions that D-form or dehydro derivative of amino acid residue is important factor for their potencies of original antibiotics.

1. Neomycin plus polymyxin in 1 to 10 ratio potentiates the inhibitory effect of neomycin and polymyxin onShigella paradysenteriac (Flexner, Boyd and Sonne) 5 to 30-fold and 25 to 70-fold respectively. 2. Neomycin plus streptomycin in 1 to 10 ratio potentiates the inhibitory effect of neomycin and streptomycin on Shigella 1.5 to 2.5-fold and 2.5 to 3-fold respectively. 3. Neomycin plus tetracycline or oxytetracycline in 1 to 10 ratio potentiates the inhibitory effect of neomycin onShigella 1.5 to 2.5-fold and 2.5 to 3-fold 3-fold. 4. Neomycin plus Magnamycin in 1 to 1250 ratio enhances the inhibitory effect of neomycin 1.5 to 2.5-fold, and of Magnamycin 0.5 to 8-fold, and in the same ratio, neomycin phis bacitracin enhances the effect of neomycin 2.5 to 3-fold and of bacitracin effect 1 to 2-fold. 5. Neomycin plus viomycin in 1 to 10 ratio results in mutual depression.

Three strains of mycobacteria were made resistant to viomycin. As compared with the normally sensitive parent strain, the increase in resistance obtained was ca. 100 times inMyc. phlei, whereas inMyc. avium andMyc. tuberculosis H37Rv resistance levels of only 10 or 20 times the normal value could be reached. A high degree of viomycin resistance induced at the same time cross resistance to neomycin, aureomycin and terramycin, and, to a lesser extent, also to streptomycin and choloromycetin. No cross resistance could be established in strains of lower resistance levels. The species investigated followed the multi-step penicillin pattern in their developing resistance.

SummaryA study has been made of the absorption and excretion of viomycin following intramuscular administration in humans. Maximum serum concentrations of 82 to 125 μg per ml were attained within 2 hours after a single dose of 25 to 50 mg per kilo. Reasonably high concentrations were achieved in the serum of patients receiving daily maintenance doses of the drug. Small concentrations of viomycin, 10 to 12.5 μg per ml, were detected in the cerebrospinal fluid in the presence of high serum concentrations of the drug, 100 to 125 |mUg per ml. Viomycin was excreted in the urine in high concentrations, and from 65 to 100% of the administered dose was recovered in the urine within 24 hours.

Identity tests for antibiotic sensitivity disks have been developed. Suitable tests previously reported in the literature have been modified and adapted to the micro-quantities involved in these disks. Once a system of testing had been established, it was screened for interference from all other disk antibiotics. Penicillins are identified generally by an iodometric method and specifically by thin-layer chromatography (TLC). The polypeptide antibiotics are differentiated by TLC in combination with nitration, reduction, and diazotization to further distinguish colistin from polymyxin. Lincomycin, oleandomycin, and kanamycin are identified by TLC systems, the tetracyclines by paper chromatography. Under varying conditions of solvents and wavelengths, streptomycin, erythromycin, nystatin, vancomycin, novobiocin, cephalothin, and viomycin are identified spectrophotometrically. Color tests have been devised for chloramphenicol, dihydrostreptomycin, and neomycin.

Publisher Summary This chapter discusses the chemistry and pharmacy of bacitracin, polymyxin, and viomycin. Bacitracin is a complex mixture of at least ten closely related polypeptides which can be separated by counter-current distribution. The major component is bacitracin A, which accounts for most of the antibacterial activity of crude bacitracin. Bacitracins B and C also show significant antibacterial activity, though less than that of A, but the activities of the remaining components are comparatively low. The commercial product known as bacitracin appears to be a mixture mainly of A with smaller amounts of B, D, E and F. Bacitracin has an antimicrobial spectrum similar to that of penicillin being active against a wide variety of Gram-positive bacteria, a few Gram-negative organisms, including Neisseria gonorrhoeae, and several spirochaetes. The chemistry of polymyxin B has been more exhaustively studied than that of any other member of the complex. The main use of polymyxin B sulphate is in topical applications for the treatment of local infections and to prevent contamination in burns and skin grafting. For these purposes, it is frequently combined with other antibiotics, including bacitracin and neomycin. Polymyxin B is not absorbed from the gastro-intestinal tract, and is thus used orally for the treatment of intestinal infections because of Shigella and Pseudomonas species. It is used parenterally for the treatment of urinary tract infections and for bacteriaemia because of Pseudomonas species but being somewhat toxic, only in cases which have proved refractory to other drugs.

Non-infective pigmented variants of Rhizobium have been isolated from several cultures after treatment with antibiotics, heat and U.V. irradiation. These variants tolerated much higher doses of heat, U.V. and certain antibiotics than the wild type strains from which they originated. Some of the pigmented variants produced reverse mutants on subculture which had lost their pigment but recovered their infectivity. These reverse mutants also lost their extreme U.V.-resistance. However, many pigmented mutants were very stable and reverted only after U.V. irradiation.

SUMMARY: A procedure for testing the sensitivity of streptomycetes to antibiotics is described. Eight antibiotics, at various concentrations, were incorporated into filter-paper discs and by selection of suitable concentrations results of diagnostic value were obtained. Streptomycetes previously grouped together by using other criteria had identical or very similar antibiotic sensitivity patterns. It is considered that the reactions of streptomycetes to a range of antibiotics would be of value for description of species and studies of overall similarity.