Journal of Microbiology

Journal Articles

A PadR family transcriptional repressor regulates the transcription of chromate efflux transporter in Enterobacter sp. Z1.: Xueqi Huo, Zijie Zhou, Hongliang Liu, Gejiao Wang, Kaixiang Shi; J. Microbiol. 2024;62(5):355-365. Published online April 8, 2024; DOI: https://doi.org/10.1007/s12275-024-00117-0

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Abstract: Chromium is a prevalent toxic heavy metal, and chromate [Cr(VI)] exhibits high mutagenicity and carcinogenicity. The presence of the Cr(VI) efflux protein ChrA has been identified in strains exhibiting resistance to Cr(VI). Nevertheless, certain strains of bacteria that are resistant to Cr(VI) lack the presence of ChrB, a known regulatory factor. Here, a PadR family transcriptional repressor, ChrN, has been identified as a regulator in the response of Enterobacter sp. Z1(CCTCC NO: M 2019147) to Cr(VI). The chrN gene is cotranscribed with the chrA gene, and the transcriptional expression of this operon is induced by Cr(VI). The binding capacity of the ChrN protein to Cr(VI) was demonstrated by both the tryptophan fluorescence assay and Ni-NTA purification assay. The interaction between ChrN and the chrAN operon promoter was validated by reporter gene assay and electrophoretic mobility shift assay. Mutation of the conserved histidine residues His14 and His50 resulted in loss of ChrN binding with the promoter of the chrAN operon. This observation implies that these residues are crucial for establishing a DNA-binding site. These findings demonstrate that ChrN functions as a transcriptional repressor, modulating the cellular response of strain Z1 to Cr(VI) exposure.

Edaphovirga cremea gen. nov., sp. nov., isolated from the rhizospheric soil of Codonopsis clematidea: Jin-Yan Xue , Meng-Yue Zhang , Yu Zhang , Juan Cheng , Li-Cheng Liu , Ying-Ying Wu , Tian-Yuan Zhang , Yi-Xuan Zhang; J. Microbiol. 2019;57(5):337-342. Published online February 26, 2019; DOI: https://doi.org/10.1007/s12275-019-8408-0

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Abstract: A Gram-negative, facultatively anaerobic, non-motile, nonspore- forming, coccoid or rod-shaped and creamy-pigmented bacterium, designated SYP-B2100T, was isolated from the rhizospheric soil of Codonopsis clematidea in the Xinjiang Uygur Autonomous Region, China. The optimal growth occurred at 28°C, pH 5.0, in the absence of NaCl. The cells tested positive in catalase and methyl red tests but negative in oxidase, urease, gelatinase, milk coagulation, and peptonisation, H2S production, nitrate reduction, and Voges-Proskauer tests. The major isoprenoid quinone was ubiquinone-8 (Q-8). The major cellular fatty acids were C16:0 and summed feature 8. The polar lipids consisted of diphosphatidylglycerol, phosphatidylethanolamine, and phosphatidylglycerol. The 16S rRNA gene sequence of strain SYP-B2100T was the most similar to that of Rahnella inusitata DSM 30078T (96.9%) within the family Enterobacteriaceae. The genomic DNA G+C content of strain SYP-B2100T was 50.3 mol%. The combined data from the phylogenetic, morphological, physiological, biochemical, and chemotaxonomic analyses presented in this study support the conclusion that strain SYP-B2100T represents a novel species of a new genus, for which the name Edaphovirga cremea gen. nov., sp. nov. is proposed; the type strain is SYPB2100T (= CGMCC 1.5857T = DSM 105170T = KCTC 62024T).

Colistin resistance in Enterobacter spp. isolates in Korea: Yoon-Kyoung Hong , Ji-Young Lee , Kwan Soo Ko; J. Microbiol. 2018;56(6):435-440. Published online June 1, 2018; DOI: https://doi.org/10.1007/s12275-018-7449-0

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16 Citations

Abstract: We investigated the colistin resistance rate among 356 Enterobacter spp. clinical isolates from eight hospitals in Korea. Antibiotic susceptibility testing was performed by broth microdilution. While 51 of 213 (23.9%) Enterobacter cloacae isolates were colistin-resistant, only six of 143 (4.2%) E. aerogenes isolates showed resistance. We also identified the skip well phenotype in eight E. cloacae and three E. aerogenes isolates. Multilocus sequence typing for E. cloacae and randomly amplified polymorphic DNA analysis and enterobacterial repetitive intergenic consensus PCR for E. aerogenes revealed that clonal spreading of colistin-resistant and skip well Enterobacter spp. isolates had not occurred. In vitro time-kill assays were performed with three colistin-resistant, three skip well, and two colistin-susceptible isolates of E. cloacae and E. aerogenes. Inconsistent results were observed among isolates with skip well phenotypes; while some were eradicated by 2 mg/L colistin, others were not. This suggests that skip well isolates have differentiated into different categories. As the high rates of colistin resistance in E. cloacae detected are of clinical concern, continuous monitoring is warranted. In addition, the clinical implications and mechanisms of the skip well phenotype should be investigated to ensure the appropriate use of colistin against Enterobacter infections.

Imipenem-resistant Gram-negative bacterial isolates carried by persons upon medical examination in Korea: So Yeon Kim , Sang Yop Shin , Ji-Young Rhee , Kwan Soo Ko; J. Microbiol. 2017;55(8):612-618. Published online July 18, 2017; DOI: https://doi.org/10.1007/s12275-017-6555-8

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5 Citations

Abstract: Carbapenem-resistant Gram-negative bacteria (CR-GNB) have emerged and disseminated worldwide, become a great concern worldwide including Korea. The prevalence of fecal carriage of imipenem-resistant Gram-negative bacteria (IRGNB) in persons in Korea was investigated. Stool samples were collected from 300 persons upon medical examination. Samples were screened for IR-GNB by using MacConkey agar with 2 μl/ml imipenem. Species were identified by 16S rRNA gene sequence analysis, and antimicrobial susceptibility was determined by the broth microdilution method. In total, 82 IR-GNB bacterial isolates were obtained from 79 (26.3%) out of 300 healthy persons. Multilocus sequence typing analysis showed very high diversity among IR P. aeruginosa, S. maltophilia, and E. cloacae isolates, and pulsedfield gel electrophoresis revealed five main pulsotypes of IR P. mirabilis. As for the presence of metallo-β-lactamases (MBLs), only one IMP-25-producing S. marcescens isolate was identified. Although only one carbapenemase-producing isolate was identified, the high colonization rates with IRGNB isolates in this study is notable because carriers may be a reservoir for the dissemination of resistant pathogens within the community as well as in health care institutions.

Kinetic characterization of a novel acid ectophosphatase from Enterobacter asburiae: Vanessa Sayuri Sato , Renato F. Galdiano Júnior , Gisele Regina Rodrigues , Eliana G. M. Lemos , João Martins Pizauro Junior; J. Microbiol. 2016;54(2):106-113. Published online February 2, 2016; DOI: https://doi.org/10.1007/s12275-015-5354-3

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Abstract: Expression of acid ectophosphatase by Enterobacter asburiae, isolated from Cattleya walkeriana (Orchidaceae) roots and identified by the 16S rRNA gene sequencing analysis, was strictly regulated by phosphorus ions, with its optimal activity being observed at an inorganic phosphate concentration of 7 mM. At the optimum pH 3.5, intact cells released p-nitrophenol at a rate of 350.76 ± 13.53 nmol of p-nitrophenolate (pNP)/min/108 cells. The membrane-bound enzyme was obtained by centrifugation at 100,000 × g for 1 h at 4°C. p-Nitrophenylphosphate (pNPP) hydrolysis by the enzyme follows “Michaelis-Menten” kinetics with V = 61.2 U/mg and K0.5 = 60 μM, while ATP hydrolysis showed V = 19.7 U/mg, K0.5 = 110 μM, and nH = 1.6 and pyrophosphate hydrolysis showed V = 29.7 U/mg, K0.5 = 84 μM, and nH = 2.3. Arsenate and phosphate were competitive inhibitors with Ki = 0.6 mM and Ki = 1.8 mM, respectively. p-Nitrophenyl phosphatase (pNPPase) activity was inhibited by vanadate, while p-hydroxymercuribenzoate, EDTA, calcium, copper, and cobalt had no inhibitory effects. Magnesium ions were stimulatory (K0.5 = 2.2 mM and nH = 0.5). Production of an acid ectophosphatase can be a mechanism for the solubilization of mineral phosphates by microorganisms such as Enterobacter asburiae that are versatile in the solubilization of insoluble minerals, which, in turn, increases the availability of nutrients for plants, particularly in soils that are poor in phosphorus.

Comparative Study of the marR Genes within the Family Enterobacteriaceae: Dan Wang , Changjiang Guo , Longjiang Gu , Xiaohui Zhang; J. Microbiol. 2014;52(6):452-459. Published online April 11, 2014; DOI: https://doi.org/10.1007/s12275-014-3586-2

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8 Citations

Abstract: marR genes are members of an ancient family originally identified in Escherichia coli. This family is widely distributed in archaea and bacteria. Homologues of this family have a conserved winged helix fold. MarR proteins are involved in non-specific resistance systems conferring resistance to multiple antibiotics. Extensive studies have shown the importance of MarR proteins in physiology and pathogenicity in Enterobacteria, but little is known about their origin or evolution. In this study, all the marR genes in 43 enterobacterial genomes representing 14 genera were identified, and the phylogenetic relationships and genetic parameters were analyzed. Several major findings were made. Three conserved marR genes originated earlier than Enterobacteriaceae and a geneloss event was found to have taken place in Yersinia pestis Antiqua. Three functional genes, rovA, hor, and slyA, were found to be clear orthologs among Enterobacteriaceae. The copy number of marR genes in Enterobacteriaceae was found to vary from 2 to 11. These marR genes exhibited a faster rate of nucleotide substitution than housekeeping genes did. Specifically, the regions of marR domain were found to be subject to strong purifying selection. The phylogenetic relationship and genetic parameter analyses were consistent with conservation and specificity of marR genes. These dual characters helped MarR to maintain a conserved binding motif and variable C-terminus, which are important to adaptive responses to a number of external stimuli in Enterobacteriaceae.

Research Support, Non-U.S. Gov'ts

Copper as an Antimicrobial Agent against Opportunistic Pathogenic and Multidrug Resistant Enterobacter Bacteria: Wen-Xiao Tian , Shi Yu , Muhammad Ibrahim , Abdul Wareth Almonaofy , Liu He , Qiu Hui , Zhu Bo , Bin Li , Guan-lin Xie; J. Microbiol. 2012;50(4):586-593. Published online July 21, 2012; DOI: https://doi.org/10.1007/s12275-012-2067-8

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44 Citations

Abstract: Infections by Enterobacter species are common and are multidrug resistant. The use of bactericidal surface materials such as copper has lately gained attention as an effective antimicrobial agent due to its deadly effects on bacteria, yeast, and viruses. The aim of the current study was to assess the antibacterial activity of copper surfaces against Enterobacter species. The antibacterial activity of copper surfaces was tested by overlying 5×106 CFU/ml suspensions of representative Enterobacter strains and comparing bacterial survival counts on copper surfaces at room temperature. Iron, stainless steel, and polyvinylchloride (PVC) were used as controls. The mechanisms responsible for bacterial killing on copper surfaces were investigated by a mutagenicity assay of the D-cycloserin (cyclA gene), single cell gel electrophoresis, a staining technique, and inductively coupled plasma mass spectroscopy. Copper yielded a significant decrease in the viable bacterial counts at 2 h exposure and a highly significant decrease at 4 h. Loss of cell integrity and a significantly higher influx of copper into bacterial cells exposed to copper surfaces, as compared to those exposed to the controls, were documented. There was no increase in mutation rate and DNA damage indicating that copper contributes to bacterial killing by adversely affecting cellular structure without directly targeting the genomic DNA. These findings suggest that copper’s antibacterial activity against Enterobacter species could be utilized in health care facilities and in food processing plants to reduce the bioburden, which would increase protection for susceptible members of the community.

NOTE] Involvement of Curli Fimbriae in the Biofilm Formation of Enterobacter cloacae: Sung-Min Kim , Hee-Woo Lee , Yeh-Wan Choi , Shuk-Ho Kim , Je-Chul Lee , Yoo-Chul Lee , Sung-Yong Seol , Dong-Taek Cho , Jungmin Kim; J. Microbiol. 2012;50(1):175-178. Published online February 27, 2012; DOI: https://doi.org/10.1007/s12275-012-2044-2

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40 Citations

Abstract: In this study, we examined the biofilm forming ability, the mRNA expression of curli genes and the morphologies of curli fimbriae and biofilms in clinical isolates of Enterobacter cloacae. The csgBA operon was found in 11 (78.6%) of the 14 isolates. The ability of E. cloacae isolates to form biofilms was significantly correlated with the mRNA expression level of the csgA and csgD genes. The curli protein fimbriae appeared as tangled fibers and the curli-proficient strain formed mature biofilms. Our data suggest that the expression of the curli fimbriae play an important role in biofilm formation in E. cloacae.

Characterization of Conjugative Plasmids Carrying Antibiotic Resistance Genes Encoding 16S rRNA Methylase, Extended-Spectrum Beta-Lactamase, and/or Plasmid-Mediated AmpC Beta-Lactamase: Hee Young Kang , Jungmin Kim , Sung Yong Seol , Yoo Chul Lee , Je Chul Lee , Dong Taek Cho; J. Microbiol. 2009;47(1):68-75. Published online February 20, 2009; DOI: https://doi.org/10.1007/s12275-008-0158-3

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21 Citations

Abstract: In this study, we identified extended-spectrum ß-lactamase (ESBL) and plasmid-mediated AmpC ß-lactamase which were associated with 16S rRNA methylase gene on the conjugative plasmid. Among 82 clinical isolates of Enterobacteriaceae that carry 16S rRNA methylase gene (64 strains, armA, and 18 strains, rmtB), blaSHV-12 was detected either alone or combined with blaDHA-1, blaCTX-M-3, and blaCTX-M-14 in 30 strains carrying armA and 6 strains carrying rmtB. The blaCTX-M-3 was detected in 13 of 64 strains carrying armA but no strains carrying rmtB. Whereas blaCTX-M-14 was detected in 15 of 18 strains carrying rmtB but only 2 of 64 strains carrying armA. Overall, blaSHV-12 and blaCTX-M-14 was the most common ESBL gene which was associated with armA and rmtB, respectively. In addition, we found that blaCTX-M-3 localized with armA on the same IncL/M plasmid and blaCTX-M-14 localized with rmtB on the same IncA/C plasmid. Restriction fragment length polymorphism of conjugative plasmids and pulsed-field gel electrophoresis of genomic DNAs revealed that intercellular horizontal transfer of conjugative plasmid and clonal transmission have been occurred at the same time.

Enteric Bacteria Isolated from Acute Diarrheal Patients in the Republic of Korea between the Year 2004 and 2006: Seung-Hak Cho , Hyun-Ho Shin , Yeon-Hwa Choi , Mi-Sun Park , Bok-Kwon Lee; J. Microbiol. 2008;46(3):325-330. Published online July 5, 2008; DOI: https://doi.org/10.1007/s12275-008-0015-4

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41 Citations

Abstract: In an epidemiological survey of human enterobacterial infections in the Republic of Korea during three years from 2004 to 2006, we isolated 1,784 (6.2%, isolation rate of enteropathogens from stool samples) in 2004, 2,547 (9.5%) in 2005 and 3,506 bacteria (12.3%) from people who visited clinics. Among the isolated bacteria, pathogenic Escherichia coli, especially, EAEC was the most frequently identified pathogen in both urban and rural regions followed by Staphylococcus aureus, Salmonella species, Bacillus cereus, Vibrio parahaemolyticus, Campylobacter jejuni, Clostridium perfringens, and Shigella species. Distinct seasonality was found in V. parahaemolyticus species, while this pathogen showed no age-specific patterns. However, other bacteria, i.e., pathogenic E. coli, S. aureus, Salmonella spp., and B. cereus showed similar seasonality throughout the year, showing a slight increase in the infection rate during the summer months and high prevalence among children under 10 years of age and elder-age people. The antibiotic susceptibility patterns of pathogenic E. coli, Salmonella spp., and S. aureus showed high resistance to penicillins. However, both pathogenic E. coli and Salmonella spp. were susceptible to several cephems, imipenem, and amikacin. Moreover, S. aureus strains resistant to vancomycin were not found. In conclusion, these surveillances can play an important role for the control and prevention to the diseases originated by enteritis bacteria.

Impact of Genetically Modified Enterobacter cloacae on Indigenous Endophytic Community of Citrus sinensis Seedlings: Fernando Dini Andreote , Marcelo Jose Mortatti Gullo , Andre Oliveira de Souza Lima , Walter Maccheroni Junior , Joao Lucio Azevedo , Welington Luiz Araujo; J. Microbiol. 2004;42(3):169-173.

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Abstract: Enterobacter cloacae (strain PR2/7), a genetically modified endophyte (GME) in citrus plants, carrying different plasmids (pEC3.0/18, pCelE, pEglA and pGFP), was inoculated into Citrus sinensis seedlings under greenhouse conditions. The impact of this on the indigenous bacterial endophytic community was studied by analyses of 2 different morphologic groups. The germination rates of inoculated seeds were evaluated in greenhouse, and plasmid stability under in vitro conditions. Results demonstrated a great and diverse endophytic community inside plants, and specialization in tissue colonization by some bacterial groups, in different treatments. Shifts in seed germination rate were observed among treatments: in general, the PR2/7 harboring pEglA bacterial clone significantly reduced seed germination, compared to the PR2/7 harboring pEC3.0/18 clone. This suggests that the presence of the pEglA plasmid changes bacteria-seed interactions. The endophytic community of citrus seedlings changed according to treatment. In seedlings treated with the PR2/7 with pEglA clone, the population of group II decreased significantly, within the context of the total endophytic community. These results indicate that the application of GMEs induces shifts in the endophytic bacterial community of citrus seedlings.

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