E_{8} Spectra of Quasi-One-Dimensional Antiferromagnet BaCo_{2}V_{2}O_{8} under Transverse Field

We report ^{51}V NMR and inelastic neutron scattering (INS) measurements on a quasi-1D antiferromagnet BaCo_{2}V_{2}O_{8} under transverse field along the [010] direction. The scaling behavior of the spin-lattice relaxation rate above the Néel temperatures unveils a 1D quantum critical point (QCP) at H_{c}^{1D}≈4.7  T, which is masked by the 3D magnetic order. With the aid of accurate analytical analysis and numerical calculations, we show that the zone center INS spectrum at H_{c}^{1D} is precisely described by the pattern of the 1D quantum Ising model in a magnetic field, a class of universality described in terms of the exceptional E_{8} Lie algebra. These excitations are nondiffusive over a certain field range when the system is away from the 1D QCP. Our results provide an unambiguous experimental realization of the massive E_{8} phase in the compound, and open a new experimental route for exploring the dynamics of quantum integrable systems as well as physics beyond integrability.

Nationwide survey of human Listeria monocytogenes infection in Japan

Listeriosis, caused by Listeria monocytogenes, is a significant public-health concern as a result of its clinical severity and high mortality. Large foodborne outbreaks of listeriosis have occurred during the last two decades in Europe and the United States, but to date there have been no food-mediated epidemics of the disease and very little information is available on the number of cases of listeriosis in Japan. We performed a nationwide surveillance study of listeriosis. The data were collected between 1980 and 2002, and 95 case reports were identified from 1996 to 2002. We divided 13.6 (cases per year between 1996 and 2002) by the ratio of the number of beds in hospitals that replied to the questionnaire, to that of all the hospitals in Japan and estimated that there is an average of 83 cases of listeriosis per year and an incidence of 0.65 cases per million of the population in Japan.

Comparison of bacteriological, genetic and pathological characters between Escherichia coli O115a,c:K(B) and Citrobacter rodentium

Murine pathogenic Escherichia coli O115a,c:K(B) (MPEC) is the causative agent of mouse megaenteron, the pathology of which resembles that of transmissible murine colonic hyperplasia caused by Citrobacter rodentium. We compared their genetic and pathological features to reveal the relationship between these two bacteria. To evaluate the genetic distances, 16S rDNA genes were sequenced and biochemical reactions were tested. Mouse strain susceptibility tests, using CF1 MPEC-susceptible germfree mice and BALB/cA(Jic) resistant mice were performed. MPEC strains and C. rodentium showed more than 99.6% identity by comparison of 16S rDNA gene sequences. All results from biochemical reactions and the mouse strain susceptibility tests were identical. It is proposed that MPEC should be reclassified as C. rodentium.

Isolation and characterization of mini-Tn5Km2 insertion mutants of enterohemorrhagic Escherichia coli O157:H7 deficient in adherence to Caco-2 cells

Adherence of enterohemorrhagic Escherichia coli (EHEC) to intestinal epithelium is essential for initiation of the infection. To identify genes involved in adherence, an EHEC O157:H7 strain (O157Sakai) was mutagenized by mini-Tn5Km2, where Km refers to kanamycin resistance, and 4,677 insertion mutants were screened for their ability to form microcolonies (MC) on Caco-2 cells. The less adherent mutants were divided into three groups: those with no adherent ability (designated as class 1 mutants, n = 10), those less adherent than the wild type (class 2 mutants, n = 16), and those unable to form MC but which adhered in a diffuse manner (class 3 mutants, n = 1). The sites of insertion in class 1 mutants were all found within genes of the locus for enterocyte effacement (LEE) thought to be required for type III protein secretion. Indeed, the class 1 mutants failed to secrete type III secreted proteins such as EspA and Tir into the culture medium. The insertions in class 2 mutants were outside the LEE, and all the mutants except one were able to secrete type III proteins into the culture medium. The class 3 mutant had the insertion in the tir gene in the LEE and was deficient in Tir and intimin expression, suggesting that in the absence of intimin-Tir, O157Sakai can still adhere to Caco-2 cells but in a diffused manner. This was confirmed by construction of a nonpolar eae (encoding intimin) mutant. Examination of the eae mutant together with O157Sakai and one of the class 1 mutants for the ability to form MC revealed that EHEC initially adhered diffusely at 1.5 h after infection. Following washing out of the nonadherent bacteria, while wild-type EHEC bacteria developed MC for another 2 to 3 h on Caco-2 cells, the eae mutant diffusely adhered throughout the infection without forming MC. MC with O157Sakai but not the diffusely adherent eae mutant could evoke F-actin condensation beneath the bacterium. Our results suggest that EHEC encodes additional adherence-associated loci and that the type III secreted proteins are involved in the initial diffuse adherence, while the intimin-Tir interaction is required for the subsequent development of MC.