Mutation of serine residue 318 in the class C β-lactamase of Enterobacter cloacae 908R

The involvement of the serine residue 318 in the specificity of a class C beta-lactamase was investigated. Multiple site-directed mutants at this position were generated using a polymerase chain reaction technique. These mutants were then probed for their activity towards various beta-lactam compounds. One mutant, S318G was further purified and its physico-chemical and catalytic properties determined. It was shown that the observed minimal inhibitory concentration values of this mutant could be correlated to its kinetic properties using a 'diffusion-hydrolysis' model. However, the data showed that residue 318 has little influence on the specificity of class C beta-lactamases.     

Isolation and PCR detection of <Emphasis Type="Italic">Enterobacter sakazakii</Emphasis> in South African food products,specifically infant formula milks

Enterobacter sakazakii has recently been identified as an opportunistic pathogen. The current culture-dependent detection methods for these bacteria are time-consuming and in this study a PCR method for the detection of E. sakazakii in South African food products, including an internal amplification control (IAC) was developed. DNA was isolated and amplified from the products and they were plated on selective growth media after pre-enrichment and enrichment in Enterobacteriaceae enrichment broth. Four of the 22 products tested positive for the presence of E. sakazakii, confirmed by PCR detection and growth on selective media. The PCR method proved effective in detecting E. sakazakii in South African products after three days and could serve as an alternative for traditional microbiological techniques.     

164株阴沟肠杆菌的药物敏感性分析

目的了解阴沟肠杆菌的药物敏感性情况以指导临床合理用药。方法对中山大学附属第一医院近3年分离出的阴沟肠杆菌的标本分布及耐药情况进行回顾性分析。结果共分离出164株阴沟肠杆菌,其对亚胺培南、头孢吡肟、阿米卡星和氧氟沙星的敏感性较高。结论阴沟肠杆菌对3代头孢菌素耐药严重,呈多重耐药性,亚胺培南仍为治疗阴沟肠杆菌严重感染的首选用药。     

Plantago lanceolata and Plantago rugelii Extracts are Toxic to Meloidogyne incognita but not to Certain Microbes

Extracts from the plants Plantago lanceolata and P. rugelii were evaluated for toxicity to the root-knot nematode Meloidogyne incognita, the beneficial microbes Enterobacter cloacae, Pseudomonas fluorescens and Trichoderma virens, and the plant-pathogenic fungi Fusarium oxysporum f. sp. gladioli, Phytophthora capsici, Pythium ultimum, and Rhizoctonia solani. Wild plants were collected, roots were excised from shoots, and the plant parts were dried and ground to a powder. One set of extracts (10% w/v) was prepared in water and another in methanol. Treatments included extract concentrations of 25%, 50%, 75% and 100%, and water controls. Meloidogyne incognita egg hatch was recorded after 7-day exposure to the treatments, and second-stage juvenile (J2) activity after 48 hours. All extracts were toxic to eggs and J2, with P. lanceolata shoot extract tending to have the most activity against M. incognita. Numbers of active J2 remained the same or decreased in a 24-hour water rinse following the 48-hour extract treatment, indicating that the extracts were lethal. When data from water- and methanol-extracted roots and shoots of both plant species were combined for analysis, J2 tended to be more sensitive than eggs to the toxic compounds at lower concentrations, while the higher concentrations (75% and 100%) were equally toxic to both life stages. The effective concentrations causing 50% reduction (EC₅₀) in egg hatch and in J2 viability were 44.4% and 43.7%, respectively. No extract was toxic to any of the bacteria or fungi in our assays.     

亚胺培南不敏感的阴沟肠杆菌碳青霉烯酶基因检测

为了解亚胺培南不敏感的阴沟肠杆菌碳青霉烯酶的主要基因型及其流行情况,收集哈尔滨医科大学附属第一医院临床分离出的亚胺培南不敏感的阴沟肠杆菌24株,采用Vitek-2 Compact进行细菌鉴定、药敏试验,聚合酶链反应（PCR）扩增,DNA测序确定菌株产碳青霉烯酶基因型情况。结果显示,24株阴沟肠杆菌均表现为多重耐药,20株菌扩增出KPC-2条带,经测序证实为KPC-2型碳青霉烯酶基因。该院亚胺培南不敏感的阴沟肠杆菌产碳青霉烯酶的主要基因型别为KPC-2型,临床与实验室应加强监测和控制。     

Isolation and Characterization of the Enterobacter cloacae cheR Mutant Defective in Phosphate Taxis

A chemotaxis-defective mutant of Enterobacter cloacae IFO3320, designated EC1, was isolated after N-methyl-N'-nitro-N-nitrosoguanidine (NTG) mutagenesis. Computer-assisted capillary assays showed that EC1 failed to show chemotactic responses to peptone and inorganic phosphate (P_i). Cloning and sequence analysis showed that EC1 is a cheR mutant, suggesting that P_i taxis by E. cloacae is dependent on a methyl-accepting chemotaxis protein(s)(MCP). EC1 was further mutagenized with NTG to construct cheR pstS and cheR pstA double mutants. A recombinant plasmid pECT01.2, which contained the E. cloacae cheR gene, restored the ability of these double mutants to show chemotaxis toward peptone but not P_i. These results suggest that the phosphate-specific transport (Pst) system, together with a MCP(s), is required for detecting P_i in E. cloacae.     

Biohydrogen production by dark fermentation of glycerol using Enterobacter and Citrobacter Sp

Glycerol is an attractive substrate for biohydrogen production because, in theory, it can produce 3 mol of hydrogen per mol of glycerol. Moreover, glycerol is produced in substantial amounts as a byproduct of producing biodiesel, the demand for which has increased in recent years. Therefore, hydrogen production from glycerol was studied by dark fermentation using three strains of bacteria: namely, Enterobacter spH1, Enterobacter spH2, and Citrobacter freundii H3 and a mixture thereof (1:1:1). It was found that, when an initial concentration of 20 g/L of glycerol was used, all three strains and their mixture produced substantial amounts of hydrogen ranging from 2400 to 3500 mL/L, being highest for C. freundii H3 (3547 mL/L) and Enterobacter spH1 (3506 mL/L). The main nongaseous fermentation products were ethanol and acetate, albeit in different ratios. For Enterobacter spH1, Enterobacter spH2, C. freundii H3, and the mixture (1:1:1), the ethanol yields (in mol EtOH/mol glycerol consumed) were 0.96, 0.67, 0.31, and 0.66, respectively. Compared to the individual strains, the mixture (1:1:1) did not show a significantly higher hydrogen level, indicating that there was no synergistic effect. Enterobacter spH1 was selected for further investigation because of its higher yield of hydrogen and ethanol. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2013     

路德维希肠杆菌噬菌体的分离及生物学特性

【背景】噬菌体能够特异性杀死宿主细菌,特别是耐药性细菌,可以作为新型杀菌剂,而关于路德维希肠杆菌噬菌体的研究尚属空白。【目的】分离路德维希肠杆菌噬菌体,并对其生物学特性进行研究。【方法】通过双层平板法分离、纯化、鉴定噬菌体;通过SDS-PAGE电泳分析结构蛋白;通过透射电子显微镜分析噬菌体的形态;通过结晶紫染色法和刚果红平板法分析生物被膜。【结果】以路德维希肠杆菌X20为指示菌从环境样品中分离获得了噬菌体GM20,噬菌斑透明且有较小晕环,直径大小平均为0.47 mm。透射电镜观察显示,噬菌体GM20具有可伸缩尾部,属于肌尾噬菌体科(Myoviridae)。GM20的滴度为7.65×10~9PFU/mL,为烈性噬菌体。一步生长曲线结果显示,噬菌体的潜伏期约为15 min,释放量约为164.3 PFU/infection center。进一步分析显示,GM20具有较好的抑菌效果,耐噬菌体菌株突变株平均突变率为1.06×10~(-5)。【结论】烈性噬菌体GM20能够杀死路德维希肠杆菌X20,有可能应用于路德维希肠杆菌感染的预防与控制。     

老年患者阴沟肠杆菌感染的临床特点及耐药性分析

目的了解我院老年患者阴沟肠杆菌感染的临床分布及耐药性变迁,为临床合理用药提供参考依据。方法采用回顾性分析方法,统计临床数据并分析我院2011年9月至2016年4月期间老年患者感染标本中分离出的阴沟肠杆菌的感染现状及耐药性。结果共检出149株阴沟肠杆菌,主要分离于痰液、全血和尿液中,分别占31.54%、24.16%和18.12%。在科室分布中,阴沟肠杆菌感染主要来源于普通外科、重症监护病房和呼吸内科,分别占26.84%、14.10%和14.10%。药敏结果显示阴沟肠杆菌对美罗培南、亚胺培南和阿米卡星具有较好的抗菌活性,敏感率分别为100.00%、96.64%和95.97%,而对阿莫西林/克拉维酸、氨苄西林、头孢替坦、头孢西丁和头孢唑啉的耐药率分别为96.36%、96.36%、97.67%、100.00%和100.00%。结论阴沟肠杆菌易引起呼吸道、泌尿道以及伤口的感染,且其耐药现象较为严重,应加强耐药性的监测,根据药敏结果合理选用抗菌药物,以控制医院感染。