Surface Microstructure and Component Changes of Chromium-resistant Enterobacter Cloacae CYS-25 Strain

Enterobacter cloacae CYS-25 strain was isolated from a chromate plant. This bacterium was capable of resisting high hexavalent chromium concentration and reducing Cr（VI） under aerobic condition. CrO4^2- stimulated the increase of bacterial size and production of compact convex paths containing chromium on the bacterial surface. The increase of bacterial size was caused by integrative growth but not extracellular polymeric substance hyperplasia. IR and SDS-PAGE analyses showed the extracellular polymeric substance （EPS） components were mainly proteins and had no obvious changes whether the strains were induced by Cr（VI） or not. The EPS was amorphous and contained trivalent chromium. Under CrO4^2- growth condition, the extracellular substance of Enterobacter cloacae CYS-25 strains and Cr（VI） had redox reaction. The products were Cr^3＊-protein complexes which formed a piece of compact convex paths on the surface of bacteria and prevented Cr（VI） from entering into cells.

The status of drug resistance and ampC gene expression in Enterobacter cloacae

Objective To investigate the status of the drug resistance and the ampC gene expression of Enterobacter cloacae . Methods Disk diffusion tests were made for detecting the susceptibility of antimicrobial agents against Enterobacter cloacae . AmpC gene was amplified by polymerase chain reaction (PCR) and verified by DNA sequencing. AmpC gene expression was analyzed according to antimicrobial agent sensitive phenotype. Results The sensitivity rates of 144 strains to imipenam,cefepime and cefoperazone/sulbactam were 98.61%,65.97% and 63.89%,respectively. The sensitivity rates of 144 strains to other antimicrobial agents were lower. Among the 144 strains 120 were found to be positive by PCR for ampC. The PCR product showed high homology to the GenBank ampC sequence. Stably derepressed strains,hyperinducible strains and unexpressing or lower level expressing strains accounted for 30.0% (36/120),37.5% (45/120),and 32.5% (39/120),respectively. Fifty-six out of 120 strains (46.67%) also produced extended spectrum β-lactamases (ESBLs). The hyperinducible strains were highly sensitive to all the antimicrobial agents except amoxicillin/clavulanic acid and cefuroxime,while the stably derepressed strains were only sensitive to imipenam and cefepime. However,sensitivity to cefepime decreased if the strains also produced ESBLs. Conclusions The durg resistant status of Enterobacter cloacae is severe. Clearing out the expressive status of ampC gene will be helpful in selection of antimicrobial agents in the treatment of clinical infection.

Detection of AmpC β-lactamase and drug resistance of Enterobacter cloacae

In order to provide useful information for effective control and clinical therapy of infection,the resistance status and the rate of carrying AmpC β-lactamase of Enterobacter cloacae(E.cloacae)were investigated.By VITEK(Bacterial automatic biochemical analyzer),the isolates of E.cloacae were identified and the drug resistance was measured.The AmpC enzyme was detected by thefive-disk diffusion test.Antibiotic sensitivity test showed that the resistance effects of E.cloacae to cefazolin,cefoxitin and ampicillin were more serious,with resistant rates of 80.5%,75.3%and 70.1%,respectively.However,it was more sensitive to Sulperazone(cefoperazone/sulbactam,13.0%),amikacin(16.9%)and ciprofloxacin(19.5%).Meanwhile,the phenotype detection showed that 35.06%(27/77)isolates of E.cloacae produced AmpCβ-lactamase.Most of E.cloacae are multi-drug resistant strains.Sulperazone(cefoperazone/sulbactam),a kind of componentβ-lactamase,is a more effective antibiotic for treating infection caused by E.cloacae.Unreasonable application of the third generation cephalosporins plays an important role in leading to emergence of high-yield AmpCβ-lactamase strains,so antibiotics should be used wisely.

土壤源孔雀石绿脱色菌的筛选及脱色条件分析

从土壤来源的细菌中,筛选可使孔雀石绿(MG)脱色的菌株,结果得到1株阴沟肠杆菌(Enterobacter cloacae)(S1-2)对MG有较强的脱色能力。通过MG被脱色前后溶液吸光度的变化衡量脱色率,用单一变量法分析影响菌株S1-2发挥MG脱色作用的不同条件。结果表明,菌株S1-2在36 h内可使1100 mg/L的MG完全脱色,处理后的MG对解淀粉芽孢杆菌、壁芽孢杆菌抑制率降低了43.98%~48.21%。用300 mg/L的MG进行脱色条件分析发现,按0.5%~7.0%接菌,脱色率达91.67%~93.91%;不同pH培养环境中,该菌在pH 6、7时对MG脱色率为90.02%~94.54%;在20~40℃条件下培养,该菌对MG脱色率达84.61%~94.56%;在6~18 g/L的NaCl浓度下,该菌对MG的脱色率达91.85%~93.77%。

Detection,isolation,and identification of cadmium-resistant bacteria based on PCR-DGGE

This study focused on the screening of cadmium-resistant bacterial strains from Pb-Zn tailing. We investigated the diversity of microbial community inhabiting Dong-san-cha Pb-Zn tailing in Beijing, China, by polymerase chain reaction-denaturing gradient gel electrophoresis （DGGE） of 16S rRNA gene of bacterial strain, and found two dominant strains in the DGGE profile. Using special culture media, we isolated two strong cadmium-resistant bacterial strains. On the basis of morphological, physiological, and biochemical characteristics, BIOLOG, and 16S rDNA sequencing, the two strains were identified as Bacillus cereus and Enterobacter cloacae. Minimal inhibitory concentrations （MICs） of heavy metals for the bacteria were determined. E. cloacae showed higher MIC values for heavy metals and a larger range of antibiotic resistance than B. cereus.

Atrazine biodegradation efficiency, metabolite detection, and trzD gene expression by enrichment bacterial cultures from agricultural soil

Atrazine is a selective herbicide used in agricultural fields to control the emergence of broadleaf and grassy weeds. The persistence of this herbicide is influenced by the metabolic action of habituated native microorganisms. This study provides information on the occurrence of atrazine mineralizing bacterial strains with faster metabolizing ability. The enrichment cultures were tested for the biodegradation of atrazine by high-performance liquid chromatography(HPLC) and mass spectrometry. Nine cultures JS01.Deg01 to JS09.Deg01 were identified as the degrader of atrazine in the enrichment culture. The three isolates JS04.Deg01, JS07.Deg01, and JS08.Deg01 were identified as efficient atrazine metabolizers. Isolates JS04.Deg01 and JS07.Deg01 produced hydroxyatrazine(HA) N-isopropylammelide and cyanuric acid by dealkylation reaction. The isolate JS08.Deg01 generated deethylatrazine(DEA), deisopropylatrazine(DIA), and cyanuric acid by N-dealkylation in the upper degradation pathway and later it incorporated cyanuric acid in their biomass by the lower degradation pathway. The optimum pH for degrading atrazine by JS08.Deg01 was 7.0 and 16S rDNA phylogenetic typing identified it as Enterobacter cloacae strain JS08.Deg01. The highest atrazine mineralization was observed in case of isolate JS08.Deg01, where an ample amount of trzD mRNA was quantified at 72 h of incubation with atrazine. Atrazine bioremediating isolate E. cloacae strain JS08.Deg01 could be the better environmental remediator of agricultural soils and the crop fields contaminated with atrazine could be the source of the efficient biodegrading microbial strains for the environmental cleanup process.