Genotypification, in vitro toxigenic evaluation, and antibiotic sensitivity of Escherichia coli strains isolated from diarrheic and fatal cases in neonatal alpacas

Se analizaron 27 hisopos diarreicos rectales y 24 contenidos patológicos del intestino de 51 alpacas de 1 a 7 semanas de edad para aislar y genotificar Escherichia coli, y caracterizar su sensibilidad antimicrobiana. Los aislamientos de E. coli fueron genotipificados por PCR múltiple para detectar genes de virulencia: stx1 y stx2 (shigatoxina 1 y 2), eae (intimina) y bfp (Bundle-Forming Pili), lt (toxina termolábil), sta y stb (toxina termoestable A y B), presentes en E. coli enterohemorrágica (EHEC), enteropatógena (EPEC) y enterotoxigénica (ETEC). Paralelamente, cepas positivas a stx1 o stx2 fueron analizadas en células Vero para detectar efectos verocitotóxicos. Posteriormente, todas las cepas aisladas fueron evaluadas para determinar su sensibilidad antimicrobiana a ocho antibióticos frecuentemente utilizados en ganaderías alpaqueras altoandinas. Los análisis microbiológicos y moleculares determinaron aislamientos de E. coli potencialmente patógenas en 19/27 (70.4%) de los hisopados clínicos y en 11/24 (45.8%) de los contenidos analizados. En crías padeciendo diarreas clínicas, se identificaron 18/19 (94.7%) cepas EPEC y la restante EHEC positiva al gen stx2 de baja actividad verocitotóxica (1:16). Once de las cepas EPEC contenían ambos genes eae y bfp y las siete restantes solamente el gen eae. De las crías muertas con antecedentes diarreicos, en 6/11 (54.5%) se aislaron cepas EPEC positivos al gen eae, mientras que las cinco restantes (45.5%) fueron EHEC. Tres de las 5 EHEC tenían el gen stx1 (dos con alta actividad verocitotóxica), la cuarta presentó el gen stx2 expresando alta actividad verocitotóxica, pero en el quinto aislado, positivo a ambos genes stx1 y stx2, no pudo evaluarse la actividad verocitotóxica. El 80% del total de E. coli (patogénicas y no patogénicas) aisladas en el estudio demostraron resistencia a la neomicina, y el 25% a la oxitetraciclina. Los resultados evidencian que las alpacas albergan cepas de E. coli potencialmente patógenas y probablemente causantes de patologías intestinales en crías de alpacas andinas.Clinical rectal diarrheic swabs (n=27) and pathological intestinal contents (n=24) from 51 alpacas between 1 to 7 weeks of age were used to isolate and genotype Escherichia coli, and to test for antimicrobial sensibility. All the E. coli isolates, confirmed by the API system, were genotyped by Multiplex PCR to determine the presence of virulence genes: stx1 and stx2 (shigatoxin 1 and 2), eae (intimin), bfp (Bundle-Forming Pili), lt (heat-labile toxin), sta and stb (heat-stable toxin A and B), in enterohemorrhagic (EHEC), enteropathogenic (EPEC) or enterotoxigenic (ETEC) E. coli strains. Positive stx1 and stx2 strains were tested on Vero cells for verocytotoxicity, and all isolates were tested for antimicrobial sensibility to the eight most frequent used antibiotics in Andean livestock. Microbiological and molecular analysis revealed the presence of pathogenic E. coli strains in 19/27 (70.4%) of the clinical diarrhea cases and 11/24 (45.8%) of the pathological intestinal content samples. In crias suffering from diarrhea, 94.7% (18/19) of the pathogenic isolates were EPEC strains while the remaining was stx2 EHEC with a low expression of verocytoxic activity (1:16). Eleven of the 18 EPEC were positive for both eae and bfp, while the remaining seven were eae positive only. Six of the 11 (54.5%) isolates from intestinal contents were EPEC eae positive only, while the remaining five (45.5%) were EHEC isolates. Three of the 5 EHEC isolates tested positive to stx1 with two expressing high verocytotoxicity, while the fourth tested positive for stx2 with similar high expression of verocytotoxicity, and the fifth was positive for both stx1 and stx2 genes but could not be evaluated the verocytotoxicity. Eighty percent of the pathogenic and non-pathogenic E. coli strains showed resistance to neomycin, and 25% to oxytetracycline. These results indicate that alpacas harbor potentially pathogenic E. coli strains that might cause clinical and fatal intestinal disorders in young animals

Desarrollo de pruebas e investigación en Plásticos y Materias Primas S.A. de C.V.

ITESO, A.C

Search for Electroweak Production of Single Top Quarks in ppbar Collisions

We present a search for electroweak production of single top quarks in the electron+jets and muon+jets decay channels. The measurements use ~90 pb^-1 of data from Run 1 of the Fermilab Tevatron collider, collected at 1.8 TeV with the DZero detector between 1992 and 1995. We use events that include a tagging muon, implying the presence of a b jet, to set an upper limit at the 95% confidence level on the cross section for the s-channel process ppbar->tb+X of 39 pb. The upper limit for the t-channel process ppbar->tqb+X is 58 pb.Comment: 11 pages, 2 figures. This is the published versio

Probing BFKL Dynamics in the Dijet Cross Section at Large Rapidity Intervals in ppbar Collisions at sqrt{s}=1800 and 630 GeV

Inclusive dijet production at large pseudorapidity intervals (delta_eta) between the two jets has been suggested as a regime for observing BFKL dynamics. We have measured the dijet cross section for large delta_eta in ppbar collisions at sqrt{s}=1800 and 630 GeV using the DO detector. The partonic cross section increases strongly with the size of delta_eta. The observed growth is even stronger than expected on the basis of BFKL resummation in the leading logarithmic approximation. The growth of the partonic cross section can be accommodated with an effective BFKL intercept of a_{BFKL}(20GeV)=1.65+/-0.07.Comment: Published in Physical Review Letter

Direct Search for Charged Higgs Bosons in Decays of Top Quarks

We present a search for charged Higgs bosons in decays of pair-produced top quarks in pbar p collisions at sqrt(s) = 1.8 TeV using 62.2 pb^-1 of data recorded by the D0 detector at the Fermilab Tevatron collider. No evidence is found for signal, and we exclude at 95% confidence most regions of the (M higgs, tan beta) parameter space where the decay t->H b has a branching fraction greater than 0.36 and B(H -> tau nu) is large.Comment: 11 pages, 4 figures, submitted to Phys. Rev. Let

A Quasi-Model-Independent Search for New Physics at Large Transverse Momentum

We apply a quasi-model-independent strategy ("Sleuth") to search for new high p_T physics in approximately 100 pb^-1 of ppbar collisions at sqrt(s) = 1.8 TeV collected by the DZero experiment during 1992-1996 at the Fermilab Tevatron. Over thirty-two e mu X, W+jets-like, Z+jets-like, and 3(lepton/photon)X exclusive final states are systematically analyzed for hints of physics beyond the standard model. Simultaneous sensitivity to a variety of models predicting new phenomena at the electroweak scale is demonstrated by testing the method on a particular signature in each set of final states. No evidence of new high p_T physics is observed in the course of this search, and we find that 89% of an ensemble of hypothetical similar experimental runs would have produced a final state with a candidate signal more interesting than the most interesting observed in these data.Comment: 28 pages, 17 figures. Submitted to Physical Review

Search for R-parity Violating Supersymmetry in Dimuon and Four-Jets Channel

We present results of a search for R-parity-violating decay of the neutralino chi_1^0, taken to be the Lightest Supersymmetric Particle. It is assumed that this decay proceeds through one of the lepton-number violating couplings lambda-prime_2jk (j=1,2; k=1,2,3). This search is based on 77.5 pb-1 of data, collected by the D0 experiment at the Fermilab Tevatron in ppbar collisions at a center of mass energy of 1.8 TeV in 1992-1995.Comment: 10 pages, 3 figure

Search for Large Extra Dimensions in Dielectron and Diphoton Production

We report a search for effects of large extra spatial dimensions in ppbar collisions at a center-of-mass energy of 1.8 TeV with the DZero detector, using events containing a pair of electrons or photons. The data are in good agreement with the expected background and do not exhibit evidence for large extra dimensions. We set the most restrictive lower limits to date, at the 95% confidence level, on the effective Planck scale between 1.0 TeV and 1.4 TeV for several formalisms and numbers of extra dimensions.Comment: 6 pages, 2 figures, submitted to Phys. Rev. Let

Search for Second Generation Leptoquark Pairs in pbar-p Collisions at sqrt(s) = 1.8 TeV

We have searched for second generation leptoquark (LQ) pairs in the \mu\mu+jets channel using 94+-5 pb^{-1} of pbar-p collider data collected by the D0 experiment at the Fermilab Tevatron during 1993-1996. No evidence for a signal is observed. These results are combined with those from the \mu\nu+jets and \nu\nu+jets channels to obtain 95% confidence level (C.L.) upper limits on the LQ pair production cross section as a function of mass and $beta, the branching fraction of a LQ decay into a charged lepton and a quark. Lower limits of 200(180) GeV/c^2 for \beta=1(1/2) are set at the 95% C.L. on the mass of scalar LQ. Mass limits are also set on vector leptoquarks as a function of \beta.Comment: 6 pages, 4 figures. Submitted to Phys. Rev. Let