No abstract

Summary The human gut microbiota is an important reservoir of antibiotic resistance genes (ARGs). A metagenomic approach and network analysis were used to establish a comprehensive antibiotic resistome catalog and to obtain co‐occurrence patterns between ARGs and microbial taxa in fecal samples from 180 healthy individuals from 11 different countries. In total, 507 ARG subtypes belonging to 20 ARG types were detected with abundances ranging from 7.12 × 10−7 to 2.72 × 10−1 copy of ARG/copy of 16S‐rRNA gene. Tetracycline, multidrug, macrolide‐lincosamide‐streptogramin, bacitracin, vancomycin, beta‐lactam and aminoglycoside resistance genes were the top seven most abundant ARG types. The multidrug ABC transporter, aadE, bacA, acrB, tetM, tetW, vanR and vanS were shared by all 180 individuals, suggesting their common occurrence in the human gut. Compared to populations from the other 10 countries, the Chinese population harboured the most abundant ARGs. Moreover, LEfSe analysis suggested that the MLS resistance type and its subtype ‘ermF’ were representative ARGs of the Chinese population. Antibiotic inactivation, antibiotic target alteration and antibiotic efflux were the dominant resistance mechanism categories in all populations. Procrustes analysis revealed that microbial phylogeny structured the antibiotic resistome. Co‐occurrence patterns obtained via network analysis implied that 12 species might be potential hosts of 58 ARG subtypes.

Linezolid is a member of a novel class of antibiotics, with resistance already being reported. We used whole-genome sequencing on three independent Streptococcus pneumoniae strains made resistant to linezolid in vitro in a step-by-step fashion. Analysis of the genome assemblies revealed mutations in the 23S rRNA gene in all mutants including, notably, G2576T, a previously recognized resistance mutation. Mutations in an additional 31 genes were also found in at least one of the three sequenced genomes. We concentrated on three new mutations that were found in at least two independent mutants. All three mutations were experimentally confirmed to be involved in antibiotic resistance. Mutations upstream of the ABC transporter genes spr1021 and spr1887 were correlated with increased expression of these genes and neighboring genes of the same operon. Gene inactivation supported a role for these ABC transporters in resistance to linezolid and other antibiotics. The hypothetical protein spr0333 contains an RNA methyltransferase domain, and mutations within that domain were found in all S. pneumoniae linezolid-resistant strains. Primer extension experiments indicated that spr0333 methylates G2445 of the 23S rRNA and mutations in spr0333 abolished this methylation. Reintroduction of a nonmutated version of spr0333 in resistant bacteria reestablished G2445 methylation and led to cells being more sensitive to linezolid and other antibiotics. Interestingly, the spr0333 ortholog was also mutated in a linezolid-resistant clinical Staphylococcus aureus isolate. Whole-genome sequencing and comparative analyses of S. pneumoniae resistant isolates was useful for discovering novel resistance mutations.

Mice are widely used as experimental models for gut microbiome (GM) studies, yet the majority of mouse GM members remain uncharacterized. Here, we report the construction of a mouse gut microbial biobank (mGMB) that contains 126 species, represented by 244 strains that have been deposited in the China General Microorganism Culture Collection. We sequence and phenotypically characterize 77 potential new species and propose their nomenclatures. The mGMB includes 22 and 17 species that are significantly enriched in ob/ob and wild-type C57BL/6J mouse cecal samples, respectively. The genomes of the 126 species in the mGMB cover 52% of the metagenomic nonredundant gene catalog (sequence identity ≥ 60%) and represent 93-95% of the KEGG-Orthology-annotated functions of the sampled mouse GMs. The microbial and genome data assembled in the mGMB enlarges the taxonomic characterization of mouse GMs and represents a useful resource for studies of host-microbe interactions and of GM functions associated with host health and diseases.

No abstract

Data mining of the Corynebacterium glutamicum genome identified 4 genes analogous to the mshA, mshB, mshC, and mshD genes that are involved in biosynthesis of mycothiol in Mycobacterium tuberculosis and Mycobacterium smegmatis. Individual deletion of these genes was carried out in this study. Mutants mshC ؊ and mshD ؊ lost the ability to produce mycothiol, but mutant mshB ؊ produced mycothiol as the wild type did. The phenotypes of mutants mshC ؊ and mshD ؊ were the same as the wild type when grown in LB or BHIS media, but mutants mshC ؊ and mshD ؊ were not able to grow in mineral medium with gentisate or 3-hydroxybenzoate as carbon sources. C. glutamicum assimilated gentisate and 3-hydroxybenzoate via a glutathione-independent gentisate pathway. In this study it was found that the maleylpyruvate isomerase, which catalyzes the conversion of maleylpyruvate into fumarylpyruvate in the glutathione-independent gentisate pathway, needed mycothiol as a cofactor. This mycothiol-dependent maleylpyruvate isomerase gene (ncgl2918) was cloned, actively expressed,andpurifiedfromEscherichiacoli.Thepurifiedmycothioldependent isomerase is a monomer of 34 kDa. The apparent K m and V max values for maleylpyruvate were determined to be 148.4 ؎ 11.9 M and 1520 ؎ 57.4 mol/min/mg, respectively (mycothiol concentration, 2.5 M). Previous studies had shown that mycothiol played roles in detoxification of oxidative chemicals and antibiotics in streptomycetes and mycobacteria. To our knowledge, this is the first demonstration that mycothiol is essential for growth of C. glutamicum with gentisate or 3-hydroxybenzoate as carbon sources and the first characterization of a mycothiol-dependent maleylpyruvate isomerase.Mycothiol (1), also known as MSH and chemically 1D-myo-inosityl-2-(N-acetyl-L-cysteinyl)amido-2-deoxy-␣-D-glucopyranoiside, is the major low-molecular mass thiol in mycobacteria and streptomycetes (2). Some investigations showed that mycothiol is associated with protection of Mycobacterium tuberculosis and Mycobacterium smegmatis against antibiotics such as rifampin (3, 4) and also helped these pathogens to detoxify reactive oxygen species produced by host cells (5).Thus, mycothiol is a potential target for medical treatment and has raised interest from both academia and industry. In addition, mycothiol also has the ability to protect cells against a range of toxic compounds. For example, in Amycolatopsis methanolica and Rhodococcus erythropolis, mycothiol detoxifies formaldehyde by acting as a cofactor for a formaldehyde dehydrogenase (6) and detoxifies alkylating agents such as monobromobimane by converting them to S-conjugates of mycothiol (7, 8). To date, the understanding of the physiological function of mycothiol is limited to detoxification and the protection of living cells (9), whereas essential metabolic roles for cell growth have not been reported.A survey on the distribution of low-molecular mass thiols in microorganisms showed that Corynebacterium diphtheriae produced mycothiol (2). However, the occurrence of mycoth...

Gold nanobipyramids (Au NBPs) with two sharp tips present an extremely strong electric field enhancement, which endows them with more advantages in biomedical photonics than other gold nanostructures. The application of Au NBPs for diagnosis and therapy is now under intensive investigation. Here, we report Au NBPs for surface-enhanced Raman scattering (SERS) detection and photothermal therapy (PTT) of MCF-7 cancer cells both in vitro and in vivo via bioconjugation with Raman reporter 2-naphthalenethiol (2-NAP) and folic acid (FA). The results showed that bioconjugated Au NBPs not only could be used for the quantitative detection of the MCF-7 cells in the range of 5−500 cells/mL, but also lead to the enhanced Raman signal in MCF-7 tumor-bearing nude mice with high specificity. Moreover the bioconjugated Au NBPs exhibited excellent photothermal performance in both in vitro and in vivo therapies, in which the cell viability decreased to 6.44% and the relative volume of MCF-7 tumors treated with bioconjugated Au NBPs reduced to 0.037 under the irradiation of an 808 nm laser. Our results indicate that bioconjugated Au NBPs offer an excellent nanoplatform for PTT and SERS detection in the future.

No abstract