Etude taxonomique de souches appartenant ou apparentées au genre Erwinia, groupe Herbicola, et à l’espece Enterobacter agglomerans

Complete Genomic Data of Enterobacter asburiae Strain SD4L Associated with Bacterial Palea Browning of Rice in China

Enterobacter asburiae is the causal agent of rice bacterial palea browning disease. Here, we report the complete genome of E. asburiae strain SD4L, which represents the first whole genome sequence of an isolate from rice seedlings in China. The assembled genome consisted of two contigs, with a circular chromosome of 4,574,166 bp, and a plasmid of 85,271 bp, respectively. This complete genome will provide a valuable resource for further studies on bacterial palea browning worldwide.

Characterization, Phylogenetic Analyses, and Pathogenicity of Enterobacter cloacae on Rice Seedlings in Heilongjiang Province, China

Rice is used as a staple food in different areas of world, especially in China. In recent years, rice seedlings have been affected seriously by symptoms resembling bacterial palea browning (BPB) in Heilongjiang Province. To isolate and identify the pathogenic bacteria responsible for the disease, 40 bacterial strains were isolated from diseased rice seedlings collected from the four major accumulative-temperature zones of rice fields cultivated in Heilongjiang Province, and these were identified as 13 species based on morphological characteristics and 16S ribosomal RNA (rRNA) gene sequences. Inoculation of all the isolates on healthy rice seedlings showed that the nine Enterobacter cloacae isolates were the pathogens causing typical symptoms of BPB, including yellowing to pale browning, stunting, withering, drying, and death. Moreover, the nine E. cloacae isolates could also cause symptoms of bacterial disease on the seedlings of soybean (Glycine max), maize (Zea mays L.), and tomato (Solanum lycopersicum). Phylogenetic analysis based on the 16S rRNA gene sequences and phenotypic and biochemical characteristics indicated that these nine pathogenic isolates were E. cloacae. In addition, analysis of the sequences of four housekeeping genes (rpoB, gyrB, infB, and atpD) from the selected strain SD4L also assigned the strain to E. cloacae. Therefore, E. cloacae is the pathogen causing disease of rice seedlings in Heilongjiang Province, which we propose to classify as a form of BPB. To the best of our knowledge, this is the first study to identify E. cloacae as a causal agent of BPB in rice.

A selective differential medium for Enterobacter sakazakii, a preliminary study

Enterobacter sakazakii can cause fatal invasive infection of neonates associated with the presence of this organism in powdered infant milk formula. A new chromogenic medium (Druggan-Forsythe-Iversen agar, DFI) is described for the selective detection of this emergent pathogen. The medium is based on the alpha-glucosidase reaction which is detected using 5-bromo-4-chloro-3-indolyl-alpha,D-glucopyranoside (XalphaGlc). Ent. sakazakii hydrolyses this substrate to an indigo pigment, producing blue-green colonies on this medium. DFI was compared with the current method of detection on violet red bile glucose agar (VRBGA) followed by pigment production on tryptone soy agar (TSA) after 48-72 h at 25 degrees C and subsequent biochemical profile determination using Biomerieux API20E. Ninety-five clinical and food strains of Ent. sakazakii were detected on the DFI chromogenic medium 2 days sooner than the alternative method. The characteristics of 148 strains representing 17 genera of non-Ent. sakazakii Enterobacteriaceae were compared using the two methods. Only 16/18 Escherichia vulneris strains, 2/3 strains of Pantoea spp. and 1/8 Citrobacter koseri strains gave false positive results on DFI agar. Eight alpha-glucosidase positive strains were identified as Pantoea using their API20E biochemical profile, but had higher percentage identification as Ent. sakazakii using ID32E. Therefore the DFI medium enables the detection of Ent. sakazakii within mixed cultures of Enterobacteriaceae, whereas the organism could be missed when using VRBGA since the latter is a general Enterobacteriaceae selective medium. In addition, the common use of API20E to check yellow pigmented colonies on TSA may lead to false negative results and consequently the acceptance of a batch of infant formula milk (IFM) that contains Ent. sakazakii.

Advances in the bacteriology of the coliform group: their suitability as markers of microbial water safety

Advances in the elaboration of novel genomic types of beta-galactosidase-positive Enterobacteriaceae and comprehensive studies of their habitats have resulted in an innovative approach to the assessment of the merits and shortcomings of the thermotrophic and fecal species Escherichia coli and all other coliforms as markers of the microbiological safety of water. As one of the consequences, it is recommended to abolish the "technical" designation fecal coliforms because their current method of detection will result in the isolation of thermotrophic organisms that have been demonstrated, beyond a doubt, to be of environmental, rather than uniquely enteric origin. Additional population studies have demonstrated that none of the coliforms can function as reliable markers for all enteric pathogens (index organisms sensu Ingram), nor be of use in validating adequate processing for safety of raw water, which represents the indicator function of markers, as defined by Ingram. Future studies along these lines will have to provide the data required to assess the suitability of additional markers for the reliable monitoring of drinking water for microbiological safety.

Biochemical characteristics of Enterobacter agglomerans and related strains found in buckwheat seeds

Thirty strains of bacteria were randomly isolated and identified from buckwheat seeds. The phenotypic characteristics of these strains agree well with those of the Enterobacter agglomerans-Erwinia herbicola complex. On the basis of the difference in indole production and gas production from D-glucose, the isolates were divided into 3 phenotypic groups, viz. I, II and III. Twenty two strains were in phenotypic group 1, which is negative for indole production and gas production from D-glucose, and resembles Pantoea agglomerans. All six strains in phenotypic group II, which is positive for indole production and negative for gas production from D-glucose, were identified as Erwinia ananas. Two strains in phenotypic group III, which is negative for indole production and positive for gas production from D-glucose, were identified as Rahnella aquatilis.

Serological difference between Erwinia herbicola strains of plant and human origin

Fifty Erwinia herbicola isolates obtained from host plants were examined in an agglutination reaction with antiserum prepared against E. ananas (E. herbicola) strain CCM 2407 antigen of plant origin and with antiserum prepared against Enterobacter agglomerans strain CNCTC M 269 antigen of human origin. In tests with strain CCM 2407 antiserum, 56% isolates showed a positive reaction, while in tests with strain CNCTC M 269 antiserum only 14% isolates showed a positive reaction. Among E. herbicola isolates which showed a positive reaction with CCM 2407 antiserum 18% showed a positive reaction with the CNCTC M 269 antiserum too. Our results confirmed the serological heterogeneity of E. herbicola population. In spite of the difference in the origin of the two antigens used for the preparation of antisera (plant, human; Japan, Czech Republic) our results indicate that some of our E. herbicola strains and E. agglomerans strain CNCTC M 269 are serologically identical.

Rahnella aquatilis, a potential contaminant in lager beer breweries

The species Rahnella aquatilis has been isolated mostly from water, soil, and, in a few cases, from human clinical specimens; little is known about its ecological role. The application of polyacrylamide gel electrophoresis of soluble proteins, DNA-DNA hybridizations and API 20 E systems has shown that Rahnella aquatilis might also be encountered as a contaminant in lager beer breweries.

Phenotypical properties of Enterobacter agglomerans (Pantoea agglomerans) from human, animal and plant sources

Clinical, animal and plant isolates, representing different geographical areas, were identified as Enterobacter agglomerans (Pantoea agglomerans) using a quantitative bacterial dot method for DNA-DNA hybridization. The phenotypical properties of the 65 strains were investigated by conventional test methods. No strain decarboxylated ornithine. Twenty-two strains, mainly plant isolates, showed delayed acid production from alpha-methyl-glycoside, a trait which may have ecological significance. With regard to these two properties, our results differed from the description of Pantoea agglomerans given by Gavini et al. (6); further investigations will clarify these differences. Three non-pigmented, maltose-negative and salicin-negative variants were derived from yellow pigmented, maltose-positive, salicin-positive strains.

Immunological relationship among glyceraldehyde-3-phosphate dehydrogenases in the genera Enterobacter and Escherichia

The comparative immunological study of glyceraldehyde-3-phosphate dehydrogenase (G-3-PDH) among Enterobacteriaceae carried out with an anti-Enterobacter cloacae G-3-PDH serum pointed out the large heterogeneity of the genera Enterobacter and Escherichia. The use of two-dimensional maps integrating our new data and previously acquired quantitative data confirmed these results.

Clinical strains of Enterobacter agglomerans (synonyms: Erwinia herbicola, Erwinia milletiae) identified by DNA-DNA-hybridization

Using DNA-DNA-hybridization it could be shown that 52 of 86 clinical isolates of Enterobacter agglomerans were closely related to each other, to the type strain of the species and also to the type strains of Erwinia herbicola and Erwinia milletiae. Most of the strains investigated were of the biogroups 1 and G1 of Ewing & Fife. All strains of the genetically defined group belonged to these two biogroups; none of these isolates fermented dulcitol, and with few exceptions they were also cellobiose, lactose and sorbitol negative.

Separation of Escherichia adecarboxylata from the "Erwinia herbicola-Enterobacter agglomerans" complex and from the other Enterobacteriaceae by nucleic acid and protein electrophoretic techniques

The species Escherichia adecarboxylata was examined for DNA relatedness to the "Erwinia herbicola-Enterobacter agglomerans" complex and to other members of the family Enterobacteriaceae. DNA-DNA hybridizations (nitrocellulose filter method) showed that strains received as E. adecarboxylata were highly related to each other (73-100% homology). Three strains of E. agglomerans and one strain of E. herbicola showed, respectively, 77, 96, 97 and 92% relatedness with the labelled DNA of E. adecarboxylata. Two groups (E2 and E3) of "atypical coliforms" previously described by Gavini et al. (1983) showed high reassociation values (76-79% and 80-89%, respectively) with E. adecarboxylata. Most of these strains produced similar or nearly identical protein electrophoregrams. All these strains were therefore classified in E. adecarboxylata. This taxon yielded hybridization values lower than 53% with the previously described phenetic or genetic groups belonging to or related to the "herbicola-agglomerans" complex and values lower than 64% with 56 other species of the Enterobacteriaceae. It was concluded that E. adecarboxylata is a species different from E. agglomerans and the other species of the family Enterobacteriaceae. A new definition of the species E. adecarboxylata is presented.

Differentiation of Enterobacteriaceae and Vibrionaceae by a micromethod for determination of carbon substrate assimilation

The assimilation techniques described for taxonomic study are unsuitable for routine diagnosis because of the need for purification and standardization of substrates, the great quantity of medium consumed and difficulties in interpreting the results. A standardized micromethod (API strip) for the study of carbon substrate assimilation by bacteria has recently been described (Zbl. Bakt. Hyg., I. Abt. Orig. A 255 (1983) 479-488). The prototype gallery used consisted of two strips of 32 microtubes each containing dehydrated carbon substrate. Each strip contained 30 tests plus positive and negative controls. The suspension medium was a synthetic semi-gel. A total of 914 strains of Gram negative rods representing 44 species of Enterobacteriaceae and Vibrionaceae were tested (Table 1). Automatic reading was performed after incubation at 32 degrees C for one day, or two days for slow growing bacteria using an ATB - 1500 reader (API System) linked to a HP 85 microcomputer (Hewlett-Packard). Most species showed typical carbon substrate assimilation patterns allowing their differentiation from other species within each genus (Table 2). The results obtained with the micromethod agreed in large measure with the nutritional patterns reported by other workers. It should be possible to use these results to construct a coherent framework of tests suitable for identifying species of Enterobacteriaceae and Vibrionaceae of clinical significance.