Structural basis for differential inhibition of eukaryotic ribosomes by tigecycline.

Tigecycline is widely used for treating complicated bacterial infections for which there are no effective drugs. It inhibits bacterial protein translation by blocking the ribosomal A-site. However, even though it is also cytotoxic for human cells, the molecular mechanism of its inhibition remains unclear. Here, we present cryo-EM structures of tigecycline-bound human mitochondrial 55S, 39S, cytoplasmic 80S and yeast cytoplasmic 80S ribosomes. We find that at clinically relevant concentrations, tigecycline effectively targets human 55S mitoribosomes, potentially, by hindering A-site tRNA accommodation and by blocking the peptidyl transfer center. In contrast, tigecycline does not bind to human 80S ribosomes under physiological concentrations. However, at high tigecycline concentrations, in addition to blocking the A-site, both human and yeast 80S ribosomes bind tigecycline at another conserved binding site restricting the movement of the L1 stalk. In conclusion, the observed distinct binding properties of tigecycline may guide new pathways for drug design and therapy.

Evaluation of ceftazidime/avibactam alone and in combination with amikacin, colistin and tigecycline against Klebsiella pneumoniae carbapenemase-producing K. pneumoniae by in vitro time-kill experiment.

Klebsiella pneumoniae carbapenemase-producing K. pneumoniae (KPC-Kp) poses a major threat to human health worldwide. Combination therapies of antibiotics with different mechanisms have been recommended in literatures. This study assessed in vitro antibacterial activities and synergistic activities of ceftazidime/avibactam alone and in combinations against KPC-Kp. In total, 70 isolates from 2 hospitals in Beijing were examined in our study. By using the agar dilution method and broth dilution method, we determined the minimum inhibitory concentration (MIC) of candidate antibiotics. Ceftazidime/avibactam demonstrated promising susceptibility against KPC-Kp (97.14%). Synergistic activities testing was achieved by checkerboard method and found ceftazidime/avibactam-amikacin displayed synergism in 90% isolates. Ceftazidime/avibactam-colistin displayed partial synergistic in 43% isolates, and ceftazidime/avibactam-tigecycline displayed indifference in 67% isolates. In time-kill assays, antibiotics at 1-fold MIC were mixed with bacteria at 1 × 105 CFU/ml and Mueller-Hinton broth (MHB). Combinations of ceftazidime/avibactam with amikacin and tigecycline displayed better antibacterial effects than single drug. Ceftazidime/avibactam-colistin combination did not exhibit better effect than single drug. In KPC-Kp infections, susceptibility testing suggested that ceftazidime/avibactam may be considered as first-line choice. However, monotherapy is often inadequate in infection management. Thus, our study revealed that combination therapy including ceftazidime/avibactam colistin and ceftazidime/avibactam tigecycline may benefit than monotherapy in KPC-Kp treatment. Further pharmacokinetic/pharmacodynamic and mutant prevention concentration studies should be performed to optimize multidrug-regimens.

Long-term antibacterial composite via alginate aerogel sustained release of antibiotics and Cu used for bone tissue bacteria infection.

Bone related-bacterial diseases including wound infections and osteomyelitis (OM) remain a serious problem accompanied with amputation in most severe cases. In this work, we report an exceptional effective antibacterial alginate aerogel, which consists of tigecycline (TGC) and octahedral Cu crystal as an organo-inorganic synergy platform for antibacterial and local infection therapy applications. The alginate aerogel could greatly prolong the release of copper ions and maintain effective antibacterial concentration over 18 days. The result of in-vitro experiments demonstrated that the alginate aerogel has an exceptional effective function on antibacterial activity. Cytotoxicity tests indicated that the alginate aerogel has low biological toxicity (average cell viability >75%). These remarkable results suggested that the alginate aerogel exhibits great potential for the treatment of OM, and has a prosperous future of application in bone tissue engineering.

Structure of the 70S Ribosome from the Human Pathogen Acinetobacter baumannii in Complex with Clinically Relevant Antibiotics.

Acinetobacter baumannii is a Gram-negative bacterium primarily associated with hospital-acquired, often multidrug-resistant (MDR) infections. The ribosome-targeting antibiotics amikacin and tigecycline are among the limited arsenal of drugs available for treatment of such infections. We present high-resolution structures of the 70S ribosome from A. baumannii in complex with these antibiotics, as determined by cryoelectron microscopy. Comparison with the ribosomes of other bacteria reveals several unique structural features at functionally important sites, including around the exit of the polypeptide tunnel and the periphery of the subunit interface. The structures also reveal the mode and site of interaction of these drugs with the ribosome. This work paves the way for the design of new inhibitors of translation to address infections caused by MDR A. baumannii.

Synthesis, characterization, and evaluation of antimicrobial activity of novel Chitosan/Tigecycline composite.

With the increase of antibiotic resistance currently available at an alarming rate, new improved films of Chitosan (CS) have been achieved with different levels of Tigecycline (TIGE) using traditional casting technology. The structural, optical, and morphological characterizations of the prepared (CS/TIGE) composites were investigated using XRD, FT-IR, UV-visible, and FE-SEM. Also, the antibacterial characterization was investigated. XRD pattern shows a semi-crystalline peak at 2θ = 21° begins to appear at Cs/TIGE2 concentration and its intensity increase with increasing TIGE concentration which indicate the interaction between TIGE and Cs. FT-IR reveals conservation of the distinctive bands with change in both intensity and position that attributed to increase the ratios of TIGE in Chitosan. UV-vis spectra confirmed the interaction of the CS and the drug TIGE. FE-SEM photos confirm the increasing of TIGE particles on the surface of CS/TIGE films by increasing the ratios of TIGE. The antimicrobial effect of Chitosan and five different ratios of Chitosan with TIGE have been identified against four different bacterial species, two gram-negative (Escherichia coli, Bacillus subtilis) and two gram-positive bacteria (Staphylococcus aureus, Pseudomonas aeruginosa). The obtained results indicated that the composite Cs/TIGE can be used in many antimicrobial applications because of its greatly antimicrobial activity.

Tocopherol polyethylene glycol succinate-modified hollow silver nanoparticles for combating bacteria-resistance.

Multiple drug resistance and the increase in the appearance of superbugs together with the exceedingly scant development of new potent antibiotic drugs pose an urgent global medical threat and imminent public security crisis. In the present study, we fabricated well-dispersed tocopherol polyethylene glycol succinate (TPGS)-capped silver nanoparticles (AgNPs) of about 10 nm in size. The hollow structure of the TPGS-capped AgNPs (TPGS/AgNPs) was confirmed and applied to load antibiotics. The TPGS/AgNPs proved to be able to cross the bacterial cell wall and penetrate into bacteria, thereby delivering more of the antibiotic to the interior of bacteria and thus enhancing the in vitro antibacterial effect of the antibiotic, even overcoming the drug-resistance in drug-resistant E. coli and Acinetobacter baumannii. It was found that the TPGS modification in the TPGS/AgNPs could decrease the activity of the efflux pumps AdeABC and AdeIJK in drug-resistant Acinetobacter baumannii via inhibiting the efflux pump genes adeB and adeJ, thus increasing the accumulation of the delivered antibiotic and overcoming the drug-resistance. Tigecycline delivered by TPGS/AgNPs could effectively antagonize drug-resistance in an acute peritonitis model mice, thereby increasing the survival rate and alleviating the inflammatory response. TPGS/AgNPs were developed as a novel and effective antibiotic delivery system and TPGS was demonstrated to have great potential as a pharmaceutical excipient for use in drug-resistant infection therapy.

Microwave-assisted solid-phase synthesis of antisense acpP peptide nucleic acid-peptide conjugates active against colistin- and tigecycline-resistant E. coli and K. pneumoniae.

Recent discovery of potent antibacterial antisense PNA-peptide conjugates encouraged development of a fast and efficient synthesis protocol that facilitates structure-activity studies. The use of an Fmoc/Boc protection scheme for both PNA monomers and amino acid building blocks in combination with microwave-assisted solid-phase synthesis proved to be a convenient procedure for continuous assembly of antisense PNA-peptide conjugates. A validated antisense PNA oligomer (CTCATACTCT; targeting mRNA of the acpP gene) was linked to N-terminally modified drosocin (i.e., RXR-PRPYSPRPTSHPRPIRV; X = aminohexanoic acid) or to a truncated Pip1 peptide (i.e., RXRRXR-IKILFQNRRMKWKK; X = aminohexanoic acid), and determination of the antibacterial effects of the resulting conjugates allowed assessment of the influence of different linkers as well as differences between the L- and D-forms of the peptides. The drosocin-derived compound without a linker moiety exhibited highest antibacterial activity against both wild-type Escherichia coli and Klebsiella pneumoniae (MICs in the range 2-4 µg/mL ∼ 0.3-0.7 µM), while analogues displaying an ethylene glycol (eg1) moiety or a polar maleimide linker also possessed activity toward wild-type K. pneumoniae (MICs of 4-8 µg/mL ∼ 0.6-1.3 µM). Against two colistin-resistant E. coli strains the linker-deficient compound proved most potent (with MICs in the range 2-4 µg/mL ∼ 0.3-0.7 µM). The truncated all-L Pip1 peptide had moderate inherent activity against E. coli, and this was unaltered or reduced upon conjugation to the antisense PNA oligomer. By contrast, this peptide was 8-fold less potent against K. pneumoniae, but in this case some PNA-peptide conjugates exhibited potent antisense activity (MICs of 2-8 µg/mL ∼ 0.3-1.2 µM). Most interestingly, the antibacterial activity of the D-form peptide itself was 2- to 16-fold higher than that of the L-form, even for the colistin- and tigecycline-resistant E. coli strains (MIC of 1-2 µg/mL ∼ 0.25-0.5 µM). Low activity was found for conjugates with a two-mismatch PNA sequence corroborating an antisense mode of action. Conjugates containing a D-form peptide were also significantly less active. In conclusion, we have designed and synthesized antisense PNA-drosocin conjugates with potent antibacterial activity against colistin- and tigecycline-resistant E. coli and K. pneumonia without concomitant hemolytic properties. In addition, a truncated D-form of Pip1 was identified as a peptide exhibiting potent activity against both wild-type and multidrug-resistant E. coli, P. aeruginosa, and A. baumannii (MICs within the range 1-4 µg/mL ∼ 0.25-1 µM) as well as toward wild-type Staphylococcus aureus (MIC of 2-4 µg/mL ∼ 0.5-1.0 µM).