Antibiotic adjuvants – A strategy to unlock bacterial resistance to antibiotics

Resistance to available antibiotics in pathogenic bacteria is currently a global challenge since the number of strains that are resistant to multiple types of antibiotics has increased dramatically each year and has spread worldwide. To unlock this problem, the use of an ‘antibiotic adjuvant’ in combination with an antibiotic is now being exploited. This approach enables us to prolong the lifespan of these life-saving drugs. This digests review provides an overview of the main types of antibiotic adjuvants, the basis of their operation and the remaining issues to be tackled in this field. Particular emphasis is placed on those compounds that are already in clinical development, namely β-lactamase inhibitors.     

Antibiotic and insecticide resistance modeling--is it time to start talking?

Mathematical models have played an important part in understanding both antibiotic and insecticide resistance. However, there has been little, if any, interdisciplinary work between these two areas of active research. One primary reason for this is that bacterial population genetics differ substantially from the population genetics of diploid organisms. This article examines these differences and their effect on resistance. It explores what efforts have gone into modeling resistance mathematically in both arenas, and offers suggestions on how the two groups could work together to gain a more comprehensive understanding of the resistance phenomenon     

Using Interactive Family Science Shows to Improve Public Knowledge on Antibiotic Resistance: Does It Work?

The public plays an important role in controlling the emergence and spread of antibiotic resistance. A large British survey showed that there is still public misunderstanding about microbes and antibiotics. e-Bug, a European DG Sanco sponsored project, aims to disseminate a school antibiotic and hygiene educational pack and website across Europe. Interactive science shows based on the e-Bug educational packs were developed to take the key health and hygiene messages from the e-Bug school resources to families. The science show was evaluated to assess public knowledge and understanding of antibiotics and antibiotic resistance pre and post intervention. An interactive stall comprised of a 3×2 m backing stand with background information, an interactive activity and discussions with a trained demonstrator was on display at a family holiday resort. Pre-piloted knowledge questionnaires were completed by parents and children pre and post intervention. Adult (≥19 years) baseline knowledge regarding antibiotics and antibiotic resistance was high although significant knowledge improvement was observed where baseline knowledge was low. Children''s (5–11 years) knowledge around antibiotics and antibiotic resistance was significantly improved for all questions. The science show can be viewed as a success in improving parents'' and children''s knowledge of antibiotic use thereby highlighting the importance of educating the public through interaction.     

Synthesis of Certain 4-Substituted-1-β-D-Ribofuranosyl-3-Hydroxypyrazoles Structurally Related to the Antibiotic Pyrazofurin

Abstract

Several 4-substituted-1-β-D-ribofuranosyl-3-hydroxypyrazoles were prepared as structural analogs of pyrazofurin. Glycosylation of the TMS derivative of ethyl 3(5)-hydroxypyrazole-4-carboxylate (3) with 1-0-acetyl-2,3,5-tri-0-benzoyl-D-ribofuranose in the presence of TMS-triflate gave predominantly ethyl 3-hydroxy-1-(2,3,5-tri-0-benzoyl-β-D-ribofuranosyl)pyrazole-4-carboxylate (4a), which on subsequent ammonolysis furnished 3-hydroxy-1-β-D-ribofuranosylpyrazole-4-carboxamide (5). Benzylation of 4a with benzyl bromide and further ammonolysis gave 3-benzyloxy-1-β-D-ribofuranosylpyrazole-4-carboxamide (8a). Catalytic (Pd/C) hydrogenation of 8a afforded yet another high yield route to 5. Saponification of the ester function of ethyl 3-benzyloxy-1-β-D-ribofuranosylpyrazole-4-carboxylate (7b) gave the corresponding 4-carboxylic acid (6a). Phosphorylation of 8a and subsequent debenzylation of the intermediate 11a gave 3-hydroxy-1-β-D-ribofuranosylpyrazole-4-carboxamide 5′-phosphate (11b). Dehydration of 3-benzyloxy-1-(2,3,5-tri-0-acetyl-β-D-ribofuranosyl)pyrazole-4-carboxamide (8b) with POCl₃ provided the corresponding 4-carbonitrile derivative (10a), which on debenzylation with Cl₃SiI gave 3-hydroxy-1-(2,3,5-tri-0-acetyl-β-D-ribofuranosyl)pyrazole-4-carbonitrile (13). Reaction of 13 with H₂S/pyridine and subsequent deacetylation gave 3-hydroxy-1-β-D-ribofuranosylpyrazole-4-thiocarboxamide (12b). Similarly, treatment of 13 with NH₂OH afforded 3-hydroxy-1-β-D-ribofuranosylpyrazole-4-carboxamidoxime (14a), which on catalytic (Pd/C) hydrogenation gave the corresponding 4-carboxamidine derivative (14b). The structural assignment of these pyrazole ribonucleosides was made by single-crystal X-ray analysis of 6a. None of these compounds exhibited any significant antitumor or antiviral activity in cell culture.     

Deciphering the Bacterial Microbiome of Citrus Plants in Response to ‘Candidatus Liberibacter asiaticus’-Infection and Antibiotic Treatments

The bacterial microbiomes of citrus plants were characterized in response to ‘Candidatus Liberibacter asiaticus’ (Las)-infection and treatments with ampicillin (Amp) and gentamicin (Gm) by Phylochip-based metagenomics. The results revealed that 7,407 of over 50,000 known Operational Taxonomic Units (OTUs) in 53 phyla were detected in citrus leaf midribs using the PhyloChip™ G3 array, of which five phyla were dominant, Proteobacteria (38.7%), Firmicutes (29.0%), Actinobacteria (16.1%), Bacteroidetes (6.2%) and Cyanobacteria (2.3%). The {"type":"entrez-protein","attrs":{"text":"OTU62806","term_id":"1193547623","term_text":"OTU62806"}}OTU62806, representing ‘Candidatus Liberibacter’, was present with a high titer in the plants graft-inoculated with Las-infected scions treated with Gm at 100 mg/L and in the water-treated control (CK₁). However, the Las bacterium was not detected in the plants graft-inoculated with Las-infected scions treated with Amp at 1.0 g/L or in plants graft-inoculated with Las-free scions (CK₂). The PhyloChip array demonstrated that more OTUs, at a higher abundance, were detected in the Gm-treated plants than in the other treatment and the controls. Pairwise comparisons indicated that 23 OTUs from the Achromobacter spp. and 12 OTUs from the Methylobacterium spp. were more abundant in CK₂ and CK₁, respectively. Ten abundant OTUs from the Stenotrophomonas spp. were detected only in the Amp-treatment. These results provide new insights into microbial communities that may be associated with the progression of citrus huanglongbing (HLB) and the potential effects of antibiotics on the disease and microbial ecology.     

The Primary Resistance of Helicobacter pylori in Taiwan after the National Policy to Restrict Antibiotic Consumption and Its Relation to Virulence Factors—A Nationwide Study

Objective

The Taiwan Government issued a policy to restrict antimicrobial usage since 2001. We aimed to assess the changes in the antibiotic consumption and the primary resistance of H. pylori after this policy and the impact of virulence factors on resistance.

Methods

The defined daily dose (DDD) of antibiotics was analyzed using the Taiwan National Health Insurance (NHI) research database. H. pylori strains isolated from treatment naïve (N=1395) and failure from prior eradication therapies (N=360) from 9 hospitals between 2000 and 2012 were used for analysis. The minimum inhibitory concentration was determined by agar dilution test. Genotyping for CagA and VacA was determined by PCR method.

Results

The DDD per 1000 persons per day of macrolides reduced from 1.12 in 1997 to 0.19 in 2008, whereas that of fluoroquinolones increased from 0.12 in 1997 to 0.35 in 2008. The primary resistance of amoxicillin, clarithromycin, metronidazole, and tetracycline remained as low as 2.2%, 7.9%, 23.7%, and 1.9% respectively. However, the primary levofloxacin resistance rose from 4.9% in 2000–2007 to 8.3% in 2008–2010 and 13.4% in 2011–2012 (p=0.001). The primary resistance of metronidazole was higher in females than males (33.1% vs. 18.8%, p<0.001), which was probably attributed to the higher consumption of nitroimidazole. Neither CagA nor VacA was associated with antibiotic resistance.

Conclusions

The low primary clarithromycin and metronidazole resistance of H. pylori in Taiwan might be attributed to the reduced consumption of macrolides and nitroimidazole after the national policy to restrict antimicrobial usage. Yet, further strategies are needed to restrict the consumption of fluoroquinolones in the face of rising levofloxacin resistance.     

The Synthesis of an Aminocyclitol Antibiotic SF–733

Lipophilicity and the tendency for decomposition of imidacloprid and related compounds by oxygen, hydrolytic mediums, and simulated sunlight were studied to see whether these physicochemical factors have any relation to the biological activity of the compounds in vitro, in a greenhouse, or under field conditions. Lipophilicity indices based on HPLC bore no definite relationship with the binding affinity to the acetylcholine receptor. However, the compounds having high insecticidal potential in greenhouse tests were generally less hydrophilic. In neutral water or in an oxygen-saturated solution, the compounds tested were completely stahle. An evident difference was observed in their behavior toward the sunlight wavelength, the nitromethylene compounds decomposing far more rapidly than nitroimines like imidacloprid. The photolability of the nitromethylenes is ascribed to their longer maximum absorption wavelength of over 320 nm.     

Constitutional Amino Acids of the Antibiotic YA–56

Acid hydrolysis of the antibiotic YA-56 X (Zorbamycin) and Y belonging to the phleomycin-bleomycin group was carried out and the following constitutional amino acids were isolated from the hydrolyzate of YA–56 X: β-Amino-β-(4-amino-6-carboxy-5-methylpyrimidine-2-yl)- propionic acid, β-aminoalanine, L-erythro-β-hydroxyhistidine and 3 unidentified amino acids. Though the former 3 amino acids were known to be constituents of phleomycins and bleomycins, the latter three were not found in phleomycins and bleomycins. YA–56 Y gave one more unidentified amino acid.

Furthermore, isolation of β-alanine and 2-acetylthiazole-4-carboxylic acid from the hydrolyzate indicated the presence of 2-(2-(2-aminoethyl)-Δ²-thiazoline-4-yl)-thiazole-4-carboxylic acid in YA–56 X and Y as in phleomycins.     

Antibiotic Resistance Among Anaerobes: What Does it Mean?

Antibiotic resistance among anaerobes is increasing, with significant resistance to clindamycin, cephalosporins, cephamycins, and penicillins noted at community hospitals and major medical centers. A total of 615 anaerobes isolated from various Chicago area hospitals in 1996 were tested against 13 antibiotics, and the resistance patterns compared with similar data from 1991. For the Bacteroides fragilis group anaerobes, the most effective antibiotics were the β-lactam/β-lactamase inhibitor combination agents, carbapenems, trovafloxacin and metronidazole. High levels of resistance to clindamycin, piperacillin, cefoxitin and ceftizoxime were seen 1996. For non- B. fragilis group anaerobes, resistance was mush lower, and was notable only in Clostridium spp. (clindamycin and cephamycins) and Prevotella spp. (clindamycin and piperacillin). Despite the prevalence of antibiotic resistance among anaerobes, the frequency of antimicrobial susceptibility testing of anaerobes is declining. There are a number of factors that account for this decline, including a general reduction in funding of hospital clinical laboratories, a concomitant loss of expertise at these institutions, a lack of automated testing for anaerobes, and a failure to consider resistance as important to clinicians. The case for increased susceptibility testing is built upon the changing patterns of resistance such as those reported in this paper, the identification and transfer of genetic determinants corresponding to antibiotic resistance, as well as the correlation of resistance and clinical outcome.     

Biofilms and Biocides: Are there Implications for Antibiotic Resistance?

Considerable controversy surrounds the use of biocides in an ever increasing range of consumer products and the possibility that their indiscriminate use might reduce biocide effectiveness and alter susceptibilities towards antibiotics. These concerns have been based largely on the isolation of resistant mutants from in vitro monoculture experiments. To date, however the emergence of biocide-resistant strains in-vivo has not been reported and a number of environmental survey studies have failed to associate biocide use with antibiotic resistance. This article gives an overview of the issues as they currently stand and reviews data generated in our laboratory over the last five years where we have used laboratory microcosms of the environment and oral cavity to better understand the possible effects of real-life biocide exposure of these high risk ecosystems. In general, whilst biocide susceptibility changes can be demonstrated in pure culture, especially for E. coli towards triclosan, it has not been possible to reproduce these effects during chronic, sublethal dosing of complex communities. We conclude from this review that whilst the incorporation of antibacterial agents into a widening sphere of personal products may not overtly impact on the patterns of microbial susceptibility observed in the environment, the precautionary principle suggests that the use of biocides should be limited to applications where clear hygienic benefits can be demonstrated.     

New Anthracycline Antibiotic CG12 Obtained by Microbial Glycosidation of α-Citromycinone

We studied the effects of peptidylarginine deiminase, a Ca²⁺-dependent protein-modulating enzyme that catalyzes the deimination of arginyl residues in protein on two major trypsin inhibitors in mouse plasma. One of these inhibitors was α-1-antitrypsin and the other was a recently characterized trypsin inhibitor termed contrapsin (H. Takahara and H. Sinohara, J. Biol. Chem., 257, 2438 (1982)). The enzyme abolished the trypsin-inhibiting activity of contrapsin in a process that was pseudo-first order with the rate dependent on enzyme concentration (second order rate constant = 3.4 × 10³ m^-1 · s^-1), but no detectable changes in the activity was noted for α-1-antitrypsin. Millimolar Ca²⁺ and dithiothreitol were absolutely required for the inactivation of contrapsin by peptidylarginine deiminase. Although no significant alterations of the charge and the size in modified contrapsin were observed, the modified inhibitor indicated that 1 arginyl residue was converted to a citrullyl residue. Modified contrapsin whose anti-tryptic activity was lost inhibited chymotrypsin much more strongly than the native inhibitor. These data suggest that a vital amino acid residue for the anti-tryptic activity of mouse contrapsin is an arginyl residue and the conversion of this arginyl residue to a citrullyl residue causes the functional changes of the inhibitor.     

Antibiotic N", N""-Dibenzyleremomycin with a Reduced 1,2-Peptide Bond

Eremomycin derivatives with benzylated amino groups of both residues of eremosamine and with (R) or (S)-2-amino-4-methylpentyl substituted for N-methyl-D-Leu, the first amino acid residue of its heptapeptide, were synthesized in order to study the role of the peptide bond between the first and second amino acid residues of the heptapeptide moiety of the antibiotic in its interaction with the precursors of the bacterial cell wall peptidoglycan and the exhibition of its antibacterial activity. Comparison of the antibacterial activities of N",N"-dibenzyleremomycin, de-(N-methyl-D-Leu)-N",N"-dibenzyleremomycin, and its N-(2-amino-4-methylpentyl)-derivative (1,2-deoxo-N",N"-dibenzyleremomycin) demonstrated that cleavage or replacement of the first amino acid residue by the corresponding aminoalkyl residue results in a decrease in its antibacterial activity towards both vancomycin-sensitive and vancomycin-resistant strains of microorganisms.