Journal of Microbiology

Volume 55(11); November 2017

Review

[Minireview] Antibiotic resistance of pathogenic Acinetobacter species and emerging combination therapy: Bora Shin , Woojun Park; J. Microbiol. 2017;55(11):837-849. Published online October 27, 2017; DOI: https://doi.org/10.1007/s12275-017-7288-4

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40 Citations

Abstract: The increasing antibiotic resistance of Acinetobacter species in both natural and hospital environments has become a serious problem worldwide in recent decades. Because of both intrinsic and acquired antimicrobial resistance (AMR) against last-resort antibiotics such as carbapenems, novel therapeutics are urgently required to treat Acinetobacter-associated infectious diseases. Among the many pathogenic Acinetobacter species, A. baumannii has been reported to be resistant to all classes of antibiotics and contains many AMR genes, such as blaADC (Acinetobacter-derived cephalosporinase). The AMR of pathogenic Acinetobacter species is the result of several different mechanisms, including active efflux pumps, mutations in antibiotic targets, antibiotic modification, and low antibiotic membrane permeability. To overcome the limitations of existing drugs, combination theraphy that can increase the activity of antibiotics should be considered in the treatment of Acinetobacter infections. Understanding the molecular mechanisms behind Acinetobacter AMR resistance will provide vital information for drug development and therapeutic strategies using combination treatment. Here, we summarize the classic mechanisms of Acinetobacter AMR, along with newly-discovered genetic AMR factors and currently available antimicrobial adjuvants that can enhance drug efficacy in the treatment of A. baumannii infections.

Journal Articles

Spirosoma flavus sp. nov., a novel bacterium from soil of Jeju Island: Nabil Elderiny , Seung-Yeol Lee , Sangkyu Park , In-Kyu Kang , Myung Kyum Kim , Dae Sung Lee , Leonid N. Ten , Hee-Young Jung; J. Microbiol. 2017;55(11):850-855. Published online October 27, 2017; DOI: https://doi.org/10.1007/s12275-017-7360-0

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Abstract: A novel, Gram-staining negative, yellow pigmented bacterial strain, designated 15J11-2T, was isolated from soil sample on Jeju Island, Republic of Korea. The strain was subjected to a taxonomic study using a polyphasic approach. The strain was able to grow at temperature range from 10°C to 30°C, pH 7–8, and in presence of 0–1% (w/v) NaCl. Comparative 16S rRNA gene sequence analysis showed that strain 15J11-2T belongs to the genus Spirosoma and levels of 16S rRNA gene sequence similarity ranged from 91.5% to 89.8%. The genomic DNA G + C content of strain 15J11-2T was 46.0 mol%. The isolate contained phosphatidylethanolamine and an unidentified aminophospholipid as the main polar lipids, menaquinone MK-7 as the predominant respiratory quinone, and summed feature 3 (C16:1 ω6c/C16:1 ω7c; 39.4%), C16:1 ω5c (27.1%), and C16:0 (13.0%) as the major fatty acids, which supported the affiliation of strain 15J11-2T to the genus Spirosoma. The results of physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain 15J11-2T from recognized Spirosoma species. On the basis of its phenotypic properties, genotypic distinctiveness, chemotaxonomic features, strain 15J11-2T represents a novel species of the genus Spirosoma, for which the name Spirosoma flavus sp. nov. is proposed. The type strain is 15J11-2T (= KCTC 52026T = JCM 31998T).

Spirosoma lituiforme sp. nov., isolated from soil: Weilan Li , Seung-Yeol Lee , Sangkyu Park , Byung-Oh Kim , Leonid N. Ten , Hee-Young Jung; J. Microbiol. 2017;55(11):856-861. Published online October 27, 2017; DOI: https://doi.org/10.1007/s12275-017-7255-0

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Abstract: A Gram-staining-negative, non-motile, curved rod-shaped, aerobic bacterium, designated S1-2-4T, was isolated from soil in Jeollabuk-do province, Republic of Korea, and was characterized taxonomically using a polyphasic approach. Comparative 16S rRNA gene sequence analysis showed that strain S1-2-4T was a member of the family Cytophagaceae and most closely related to ‘Spirosoma radiotolerans’ DG5A (97.2%), Spirosoma fluviale MSd3T (96.4%), and Spirosoma linguale DSM 74T (96.3%). The genomic DNA G + C content of strain S1-2-4T was 49.7 mol%. The major fatty acids were summed feature 3 (C16:1 ω7c/C16:1 ω6c), C16:1 ω5c, and C16:0, and the major polar lipid was phosphatidylethanolamine. MK-7 was the predominant respiratory quinone. Phenotypic and chemotaxonomic data supported the affiliation of strain S1-2-4T with the genus Spirosoma. DNA-DNA hybridization between strain S1-2-4T and ‘Spirosoma radiotolerans’ showed relatively low DNA-DNA relatedness (31%). Strain S1-2-4T could be distinguished from its closest phylogenetic neighbors based on its phenotypic, genotypic, and chemotaxonomic features. Therefore, strain S1-2-4T represents a novel member of the genus Spirosoma, for which the name Spirosoma lituiforme sp. nov. is proposed. The type strain is S1- 2-4T (= KCTC 52724T = JCM 32128T).

Magnetite production and transformation in the methanogenic consortia from coastal riverine sediments: Shiling Zheng , Bingchen Wang , Fanghua Liu , Oumei Wang; J. Microbiol. 2017;55(11):862-870. Published online October 27, 2017; DOI: https://doi.org/10.1007/s12275-017-7104-1

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13 Citations

Abstract: Minerals that contain ferric iron, such as amorphous Fe(III) oxides (A), can inhibit methanogenesis by competitively accepting electrons. In contrast, ferric iron reduced products, such as magnetite (M), can function as electrical conductors to stimulate methanogenesis, however, the processes and effects of magnetite production and transformation in the methanogenic consortia are not yet known. Here we compare the effects on methanogenesis of amorphous Fe (III) oxides (A) and magnetite (M) with ethanol as the electron donor. RNAbased terminal restriction fragment length polymorphism with a clone library was used to analyse both bacterial and archaeal communities. Iron (III)-reducing bacteria including Geobacteraceae and methanogens such as Methanosarcina were enriched in iron oxide-supplemented enrichment cultures for two generations with ethanol as the electron donor. The enrichment cultures with A and non-Fe (N) dominated by the active bacteria belong to Veillonellaceae, and archaea belong to Methanoregulaceae and Methanobacteriaceae, Methanosarcinaceae (Methanosarcina mazei), respectively. While the enrichment cultures with M, dominated by the archaea belong to Methanosarcinaceae (Methanosarcina barkeri). The
results
also showed that methanogenesis was accelerated in the transferred cultures with ethanol as the electron donor during magnetite production from A reduction. Powder X-ray diffraction analysis indicated that magnetite was generated from microbial reduction of A and M was transformed into siderite and vivianite with ethanol as the electron donor. Our data showed the processes and effects of magnetite production and transformation in the methanogenic consortia, suggesting that significantly different effects of iron minerals on microbial methanogenesis in the iron-rich coastal riverine environment were present.

De novo transcriptome assembly and characterization of the 10-hydroxycamptothecin-producing Xylaria sp. M71 following salicylic acid treatment: Xiaowei Ding , Kaihui Liu , Yonggui Zhang , Feihu Liu; J. Microbiol. 2017;55(11):871-876. Published online October 27, 2017; DOI: https://doi.org/10.1007/s12275-017-7173-1

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8 Citations

Abstract: In the present study, we identified genes that are putatively involved in the production of fungal 10-hydroxycamptothecin via transcriptome sequencing and characterization of the Xylaria sp. M71 treated with salicylic acid (SA). A total of 60,664,200 raw reads were assembled into 26,044 unigenes. BLAST assigned 8,767 (33.7%) and 10,840 (41.6%) unigenes to 40 Gene Ontology (GO) annotations and 108 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, respectively. A total of 3,713 unigenes comprising 1,504 upregulated and 2,209 downregulated unigenes were found to be differentially expressed between SA-induced and control fungi. Based on the camptothecin biosynthesis pathway in plants, 13 functional genes of Xylaria sp. M71 were mapped to the mevalonate (MVA) pathway, suggesting that the fungal 10-hydroxycamptothecin is produced via the MVA pathway. In summary, analysis of the Xylaria sp. M71 transcriptome allowed the identification of unigenes that are putatively involved in 10-hydroxycamptothecin biosynthesis in fungi.

Characterization of siderophore produced by Pseudomonas syringae BAF.1 and its inhibitory effects on spore germination and mycelium morphology of Fusarium oxysporum: Sumei Yu , Chunying Teng , Jinsong Liang , Tao Song , Liying Dong , Xin Bai , Yu Jin , Juanjuan Qu; J. Microbiol. 2017;55(11):877-884. Published online October 27, 2017; DOI: https://doi.org/10.1007/s12275-017-7191-z

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26 Citations

Abstract: In this study, an antagonistic bacterium against Fusarium oxysporum was identified and designated as Pseudomonas syringae strain BAF.1 on the basis of 16S rDNA sequence analysis and physiological-biochemical characteristics. It produced catechol-species siderophore at a molecular weight of 488.59 Da and a maximum amount of 55.27 μg/ml with glucose as a carbon source and asparagine as a nitrogen source at a C/N ratio of 10:1, 30°C and pH 7. The siderophore exhibited prominent antagonistic activity against Fusarium oxysporum with a maximum inhibition rate of 95.24% and had also suppressive effects on other kinds of 11 phytopathogenic fungi in the absence of FeCl3·6H2O. Spore germination was completely inhibited by 50 μl of the siderophorecontaining solution, and the ultrastructures of mycelia and spores were also considerably suppressed by siderophore treatment as established by electron microscopy observation. These results indicate that the siderophore produced by Pseudomonas syringae BAF.1 could be potentially used for biocontrol of pathogenic Fusarium oxysporum.

The NADPH oxidase AoNoxA in Arthrobotrys oligospora functions as an initial factor in the infection of Caenorhabditis elegans: Xin Li , Ying-Qian Kang , Yan-Lu Luo , Ke-Qin Zhang , Cheng-Gang Zou , Lian-Ming Liang; J. Microbiol. 2017;55(11):885-891. Published online October 27, 2017; DOI: https://doi.org/10.1007/s12275-017-7169-x

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18 Citations

Abstract: Reactive oxygen species (ROS) produced by NADPH oxidases can serve as signaling molecules to regulate a variety of physiological processes in multi-cellular organisms. In the nematophagous fungus Arthrobotrys oligospora, we found that ROS were produced during conidial germination, hyphal extension, and trap formation in the presence of nematodes. Generation of an AoNoxA knockout strain demonstrated the crucial role of NADPH oxidase in the production of ROS in A. oligospora, with trap formation impaired in the AoNoxA mutant, even in the presence of the nematode host. In addition, the expression of virulence factor serine protease P186 was up-regulated in the wild-type strain, but not in the mutant strain, in the presence of Caenorhabditis elegans. These results indicate that ROS derived from AoNoxA are essential for full virulence of A. oligospora in nematodes.

Bile salt hydrolase-mediated inhibitory effect of Bacteroides ovatus on growth of Clostridium difficile: Soobin Yoon , Junsun Yu , Andrea McDowell , Sung Ho Kim , Hyun Ju You , GwangPyo Ko; J. Microbiol. 2017;55(11):892-899. Published online October 27, 2017; DOI: https://doi.org/10.1007/s12275-017-7340-4

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34 Citations

Abstract: Clostridium difficile infection (CDI) is one of the most common nosocomial infections. Dysbiosis of the gut microbiota due to consumption of antibiotics is a major contributor to CDI. Recently, fecal microbiota transplantation (FMT) has been applied to treat CDI. However, FMT has important limitations including uncontrolled exposure to pathogens and standardization issues. Therefore, it is necessary to evaluate alternative treatment methods, such as bacteriotherapy, as well as the mechanism through which beneficial bacteria inhibit the growth of C. difficile. Here, we report bile acid-mediated inhibition of C. difficile by Bacteroides strains which can produce bile salt hydrolase (BSH). Bacteroides strains are not commonly used to treat CDI; however, as they comprise a large proportion of the intestinal microbiota, they can contribute to bile acid-mediated inhibition of C. difficile. The inhibitory effect on C. difficile growth increased with increasing bile acid concentration in the presence of Bacteroides ovatus SNUG 40239. Furthermore, this inhibitory effect on C. difficile growth was significantly attenuated when bile acid availability was reduced by cholestyramine, a bile acid sequestrant. The findings of this study are important due to the discovery of a new bacterial strain that in the presence of available bile acids inhibits growth of C. difficile. These
results
will facilitate development of novel bacteriotherapy strategies to control CDI.

Recombinant baculovirus-based vaccine expressing M2 protein induces protective CD8+ T-cell immunity against respiratory syncytial virus infection: Jeong-Yoon Lee , Jun Chang; J. Microbiol. 2017;55(11):900-908. Published online October 27, 2017; DOI: https://doi.org/10.1007/s12275-017-7306-6

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10 Citations

Abstract: Respiratory syncytial virus (RSV) is an important cause of acute lower respiratory tract disease in infants, young children, immunocompromised individuals, and the elderly. However, despite ongoing efforts to develop an RSV vaccine, there is still no authorized RSV vaccine for humans. Baculovirus has attracted attention as a vaccine vector because of its ability to induce a high level of humoral and cellular immunity, low cytotoxicity against various antigens, and biological safety for humans. In this study, we constructed a recombinant baculovirus- based vaccine expressing the M2 protein of RSV under the control of cytomegalovirus promoter (Bac_RSVM2) to induce CD8+ T-cell responses which play an important role in viral clearance, and investigated its protective efficacy against RSV infection. Immunization with Bac_RSVM2 via intranasal or intramuscular route effectively elicited the specific CD8+ T-cell responses. Most notably, immunization with Bac_RSVM2 vaccine almost completely protected mice from RSV challenge without vaccine-enhanced immunopathology. In conclusion, these results suggest that Bac_RSVM2 vaccine employing the baculovirus delivery platform has promising potential to be developed as a safe and novel RSV vaccine that provides protection against RSV infection.

Dense Granule Protein-7 (GRA-7) of Toxoplasma gondii inhibits viral replication in vitro and in vivo: Prasanna Weeratunga , Thilina U. B. Herath , Tae-Hwan Kim , Hyun-Cheol Lee , Jae-Hoon Kim , Byeong-Hoon Lee , Eun-Seo Lee , Kiramage Chathuranga , W. A. Gayan Chathuranga , Chul-Su Yang , Jin Yeul Ma , Jong-Soo Lee; J. Microbiol. 2017;55(11):909-917. Published online October 27, 2017; DOI: https://doi.org/10.1007/s12275-017-7392-5

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15 Citations

Abstract: Dense granule protein-7 (GRA-7) is an excretory protein of Toxoplasma gondii. It is a potential serodiagnostic marker and vaccine candidate for toxoplasmosis. Previous reports demonstrated that GRA-7 induces innate immune responses in macrophages by interacting with TRAF6 via the MyD88- dependent pathway. In the present study, we evaluated the antiviral activity and induction of an antiviral state by GRA-7 both in vitro and in vivo. It was observed that GRA-7 markedly reduced the replication of vesicular stomatitis virus (VSVGFP), influenza A virus (PR8-GFP), coxsackievirus (H3- GFP), herpes simplex virus (HSV-GFP), and adenovirus-GFP in epithelial (HEK293T/HeLa) and immune (RAW264.7) cells. These antiviral activities of GRA-7 were attributed to the induction of type I interferon (IFN) signaling, resulting in the secretion of IFNs and pro-inflammatory cytokines. Additionally, in BALB/c mice, intranasal administration of GRA-7 prevented lethal infection by influenza A virus (H1N1) and exhibited prophylactic effects against respiratory syncytial virus (RSV-GFP). Collectively, these results suggested that GRA-7 exhibits immunostimulatory and broad spectrum antiviral activities via type I IFN signaling. Thus, GRA-7 can be potentially used as a vaccine adjuvant or as a candidate drug with prophylactic potential against viruses.

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