Genome Sequence-Guided Finding of Lucensomycin Production by Streptomyces achromogenes Subsp. streptozoticus NBRC14001

Information on microbial genome sequences is a powerful resource for accessing natural products with significant activities. We herein report the unveiling of lucensomycin production by Streptomyces achromogenes subsp. streptozoticus NBRC14001 based on the genome sequence of the strain. The genome sequence of strain NBRC14001 revealed the presence of a type I polyketide synthase gene cluster with similarities to a biosynthetic gene cluster for natamycin, which is a polyene macrolide antibiotic that exhibits antifungal activity. Therefore, we investigated whether strain NBRC14001 produces antifungal compound(s) and revealed that an extract from the strain inhibited the growth of Candida albicans. A HPLC analysis of a purified compound exhibiting antifungal activity against C. albicans showed that the compound differed from natamycin. Based on HR-ESI-MS spectrometry and a PubChem database search, the compound was predicted to be lucensomycin, which is a tetraene macrolide antibiotic, and this prediction was supported by the results of a MS/MS analysis. Furthermore, the type I polyketide synthase gene cluster in strain NBRC14001 corresponded well to lucesomycin biosynthetic gene cluster (lcm) in S. cyanogenus, which was very recently reported. Therefore, we concluded that the antifungal compound produced by strain NBRC14001 is lucensomycin.

Conformational Changes in a Macrolide Antibiotic Binding Protein From Mycobacterium smegmatis Upon ADP Binding

Rv3197 (MABP-1), a non-canonical ABC protein in Mycobacterium tuberculosis, has ATPase activity and confers inducible resistance to the macrolide family of antibiotics. Here we have shown that MSMEG_1954, the homolog of Rv3197 in M. smegmatis, has a similar function of conferring macrolide resistance. Crystal structures of apo-MSMEG_1954 (form1 and form 2) and MSMEG_1954 in complex with ADP have been determined. These three structures show that MSMEG_1954 has at least two different conformations we identify as closed state (MSMEG_1954-form 1) and open state (MSMEG_1954-form 2 and MSMEG_1954-ADP). Structural superimposition shows that the MSMEG_1954-form 2 and MSMEG_1954-ADP complex have similar conformation to that observed for MABP-1 and MABP-1-erythromicin complex structure. However, the antibiotic binding pocket in MSMEG_1954-form 1 is completely blocked by the N-terminal accessory domain. When bound by ADP, the N-terminal accessory domain undergoes conformational change, which results in the open of the antibiotic binding pocket. Because of the degradation of N terminal accessory domain in MSMSG_1954-form 2, it is likely to represent a transitional state between MSMEG_1954-form 1 and MSMEG_1954-ADP complex structure.

Midecamycin Is Inactivated by Several Different Sugar Moieties at Its Inactivation Site

Glycosylation inactivation is one of the important macrolide resistance mechanisms. The accumulated evidences attributed glycosylation inactivation to a glucosylation modification at the inactivation sites of macrolides. Whether other glycosylation modifications lead to macrolides inactivation is unclear. Herein, we demonstrated that varied glycosylation modifications could cause inactivation of midecamycin, a 16-membered macrolide antibiotic used clinically and agriculturally. Specifically, an actinomycetic glycosyltransferase (GT) OleD was selected for its glycodiversification capacity towards midecamycin. OleD was demonstrated to recognize UDP-D-glucose, UDP-D-xylose, UDP-galactose, UDP-rhamnose and UDP-N-acetylglucosamine to yield corresponding midecamycin 2′-O-glycosides, most of which displayed low yields. Protein engineering of OleD was thus performed to improve its conversions towards sugar donors. Q327F was the most favorable variant with seven times the conversion enhancement towards UDP-N-acetylglucosamine. Likewise, Q327A exhibited 30% conversion enhancement towards UDP-D-xylose. Potent biocatalysts for midecamycin glycosylation were thus obtained through protein engineering. Wild OleD, Q327F and Q327A were used as biocatalysts for scale-up preparation of midecamycin 2′-O-glucopyranoside, midecamycin 2′-O-GlcNAc and midecamycin 2′-O-xylopyranoside. In contrast to midecamycin, these midecamycin 2′-O-glycosides displayed no antimicrobial activities. These evidences suggested that besides glucosylation, other glycosylation patterns also could inactivate midecamycin, providing a new inactivation mechanism for midecamycin resistance. Cumulatively, glycosylation inactivation of midecamycin was independent of the type of attached sugar moieties at its inactivation site.

Assessment for the passage of tylosin into the milk of Anatolian buffaloes

Tylosin is a broad-spectrum macrolide antibiotic commonly employed in veterinary medicine to treat bacterial infections. The present study assessed the milk-passage patterns of tylosin up to the 16th milking after a single intramuscular injection at the dose of 10 mg/kg/b.w. to Anatolian buffaloes. The residue levels of tylosin in milk samples of each animal were analysed by LC-MS/MS. The detection and determination limits of the employed method were 0.19 μg/kg and 0.64 μg/kg, respectively. The highest level of tylosin was found to be at the second milking. At the ninth milking, tylosin residue level decreased under the maximum residue limit of 50 μg/kg. Additionally, the employed LC-MS/MS method is used to assess tylosin residue in 40 milk samples and all of the samples were found to be tylosin free. In conclusion, this study determined the milk passaged levels of tylosin into milk of Anatolian buffaloes using an LC-MS/MS method.

Iso-Partricin, an Aromatic Analogue of Amphotericin B: How Shining Light on Old Drugs Might Help Create New Ones

Partricin is a heptaene macrolide antibiotic complex that exhibits exceptional antifungal activity, yet poor selective toxicity, in the pathogen/host system. It consists of two compounds, namely partricin A and B, and both of these molecules incorporate two cis-type bonds within their heptaenic chromophores: 28Z and 30Z. In this contribution, we have proven that partricins are susceptible to a chromophore-straightening photoisomerization process. The occurring 28Z→28E and 30Z→30E switches are irreversible in given conditions, and they are the only structural changes observed during the experiment. The obtained all-trans partricin’s derivatives, namely iso-partricins A and B, exhibit very promising features, potentially resulting in the improvement of their selective toxicity.

Long-term, low-dose macrolide antibiotic treatment in pediatric chronic airway diseases

Macrolide antibiotics are one of the most commonly used broad-spectrum antibiotics. They have an inhibitory effect on a variety of respiratory pathogens; besides, they have non-anti-infective effects, including anti-inflammatory, regulating airway secretion, immune regulation, and other effects. A growing number of studies have shown that the non-anti-infective effects of macrolides have important and potential value in the treatment of pediatric chronic airway diseases; the therapy was described as “long-term, low-dose usage”; unfortunately, there is no guideline or consensus that applies to children. To better carry out the mechanism and clinical research of non-anti-infective effect and promote its rational use in children, the authors summarize the evidence of the usage of long-term, low-dose macrolide antibiotic therapy (LLMAT) in the treatment of chronic airway diseases in children and the progress in recent years. Impact This review summarizes the evidence (mostly in recent 5 years) of the usage of long-term, low-dose macrolide antibiotic therapy in the treatment of chronic airway diseases. The recent studies and guidelines support and enrich the point that long-term, low-dose macrolide antibiotic therapy has potential benefit for children with severe asthma, CF, non-CF bronchiectasis, and BO, which provides clinical references and is of clinical interest. Long-term, low-dose macrolide antibiotic therapy has good safety, and no serious events have been reported; however, potential cardiac side effects and macrolide resistance should be clinically noted.