Group Of Related Strains Research Articles

Extended and global phylogenetic view of the Bacillus cereus group population by combination of MLST, AFLP, and MLEE genotyping data

The Bacillus cereus group of bacteria includes species that can cause food-poisoning or spoilage, such as B. cereus, as well as Bacillus anthracis, the cause of anthrax. In the present report we have conducted a multi-datatype analysis using tools from the HyperCAT database ( http://mlstoslo.uio.no/) that we recently developed, combining data from multilocus sequence typing ( Tourasse et al., 2010), amplified fragment length polymorphism, and multilocus enzyme electrophoresis typing techniques. We provide a comprehensive snapshot of the B. cereus group population, incorporating 2213 isolates including 450 from food and dairy products, in the form of both phylogenetic supertrees and superclusters of genetically closely related isolates. Our main findings include the detection of phylogenetically separated groups of isolates possibly representing novel evolutionary lineages within the B. cereus group, a putative new branch of B. anthracis, as well as new groups of related strains containing both environmental and clinical isolates. In addition, the multi-datatype analysis revealed to a larger extent than previously recognized that food-borne isolates can share identical genotyping profiles with strains from various other origins. Altogether, the global analysis confirms and extends the results underlining the opportunistic nature of B. cereus group organisms, and the fact that isolates responsible for disease outbreaks and contamination of foodstuffs can originate from various genetic backgrounds.

Phenotypic and genetic diversity of Paenibacillus azotofixans strains isolated from the rhizoplane or rhizosphere soil of different grasses

Fifty-three strains identified as Paenibacillus azotofixans were isolated from the rhizoplane and rhizosphere of different grasses and from soil. To study the diversity within this species, four approaches were used: assessment of homology with a nifKDH probe in hybridization experiments; use of a selected 20-mer primer to produce RAPD profiles and of BOX- PCR to generate genomic fingerprintings; and phenotypic tests using the API50CH system. The API tests performed with the 53 P. azotofixans strains showed that all strains produced acid from 15 carbohydrates; using six other carbohydrates (sorbitol, dulcitol, tagarose, starch, glycogen and D- arabitol), the strains could be divided in five groups of related strains. All strains tested showed homology to Klebsiella pneumoniae nifKDH genes, resulting in 14 different hybridization patterns with this probe. Using RAPD- fingerprinting with one appropriate primer, 23 different amplification patterns were observed. The BOX-PCR approach confirmed the grouping suggested by the RAPD fingerprinting. A comparison of the 53 strains by similarity matrix analysis using the data obtained in all approaches resulted in a phenogram, grouping them into five broad groups at 74% similarity and into 27 subgroups at 94% similarity. At 100% similarity, 31 groups of strains could be formed, indicating a high degree of diversity among the strains tested. Overall, the diversity was independent from the origin of strains, since a variety of different groups was isolated from each plant studied. However, some clusters were dominant in wheat and sugarcane samples. The results indicated that the methods used here are sensitive indicators of diversity among the strains studied and can be applied as efficient and reliable means for further ecological and biogeographical studies.

Variation of Clonal, Mesquite-Associated Rhizobial and Bradyrhizobial Populations from Surface and Deep Soils by Symbiotic Gene Region Restriction Fragment Length Polymorphism and Plasmid Profile Analysis

Genetic characteristics of 14 Rhizobium and 9 Bradyrhizobium mesquite (Prosopis glandulosa)-nodulating strains isolated from surface (0- to 0.5-m) and deep (4- to 6-m) rooting zones were determined in order to examine the hypothesis that surface- and deep-soil symbiont populations were related but had become genetically distinct during adaptation to contrasting soil conditions. To examine genetic diversity, Southern blots of PstI-digested genomic DNA were sequentially hybridized with the nodDABC region of Rhizobium meliloti, the Klebsiella pneumoniae nifHDK region encoding nitrogenase structural genes, and the chromosome-localized ndvB region of R. meliloti. Plasmid profile and host plant nodulation assays were also made. Isolates from mesquite nodulated beans and cowpeas but not alfalfa, clover, or soybeans. Mesquite was nodulated by diverse species of symbionts (R. meliloti, Rhizobium leguminosarum bv. phaseoli, and Parasponia bradyrhizobia). There were no differences within the groups of mesquite-associated rhizobia or bradyrhizobia in cross-inoculation response. The ndvB hybridization results showed the greatest genetic diversity among rhizobial strains. The pattern of ndvB-hybridizing fragments suggested that surface and deep strains were clonally related, but groups of related strains from each soil depth could be distinguished. Less variation was found with nifHDK and nodDABC probes. Large plasmids (>1,500 kb) were observed in all rhizobia and some bradyrhizobia. Profiles of plasmids of less than 1,000 kb were related to the soil depth and the genus of the symbiont. We suggest that interacting selection pressures for symbiotic competence and free-living survival, coupled with soil conditions that restrict genetic exchange between surface and deep-soil populations, led to the observed patterns of genetic diversity.

The Epidemiology of Listeriosis in the United States—1986

To determine the morbidity and mortality due to listeriosis in the United States, the authors undertook an active surveillance project in 1986 to identify all cases in which Listeria monocytogenes was isolated from cultures of ordinarily sterile sites in a population of 34 million persons. The authors estimated that at least 1,700 cases of listeriosis and 450 deaths occurred in the United States in 1986; 27% of these cases occurred in pregnant women, with 22% of perinatal cases resulting in stillbirths or neonatal deaths. The risk of listeriosis in adults (0.5 per 100,000 population) was similar in all regions studied; the incidence of perinatal listeriosis was three times higher in Los Angeles County, California, than in the other areas (24.3/100,000 live births vs. 7.8/100,000 live births). Geographic variation may have resulted from underdiagnosis of perinatal listeriosis in five of the study areas. Multilocus electrophoretic enzyme typing was useful for elucidating the molecular epidemiology of L. monocytogenes; perinatal listeriosis was significantly associated with one group of related strains. Multilocus electrophoretic enzyme typing also identified three clusters representing possible common-source outbreaks. These findings document the substantial morbidity due to listeriosis in the United States; to the extent that sporadic listeriosis is foodborne, this morbidity could be reduced by appropriate preventive measures, particularly in persons known to be at increased risk of infection.

Hantavirus strains isolated from rodentia and insectivora in rural China differentiated by polymerase chain reaction assay

Polymerase chain reaction (PCR) assay and other techniques were applied to differentiate Hantavirus strains isolated from different animal hosts and geographic regions in China. Two groups of related strains, Hantaan and Seoul, have been classified by cross-neutralization, radioimmunoprecipitation (RIP), and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) assays. The molecular weights of glycoprotein 1 (G1) of Hantaan and Seoul viruses were 72k and 80k, whereas those of the nucleocapsid (N) and glycoprotein 2 (G2) remained the same, respectively. The PCR assay was used to differentiate these isolates using synthetic oligonucleotide primers selected from various regions of the M genome of 76118 and R22 strains. 76118-specific primers amplified only the RNAs extracted from Hantaan strains while R22-specific primers, the RNAs from Seoul strains. The PCR results for classification are consistent with those obtained by cross-neutralization, RIP and SDS-PAGE assays.