T E Besser

Washington State University, Pullman, Washington, United States

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Publications (201)657.56 Total impact

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    ABSTRACT: Introduction: Shiga toxin-producing Escherichia coli (STEC) O157:H7 is a zoonotic pathogen of significant public health concern in many countries. Ruminants are asymptomatic carriers of STEC, shedding the pathogen via faeces, and are recognised as an important source of infection in humans. Purpose: To compare the genotype distribution of bovine and human E. coli O157:H7 isolates from New Zealand (NZ), Australia (AU) and the United States (US) using Shiga toxin-encoding bacteriophage insertion (SBI) genotyping data, and assess evidence of E. coli O157:H7 transmission from cattle to humans for each country. Method: SBI typing is a multiplex PCR method for screening specific Shiga toxin (stx)-associated bacteriophage insertion sites and stx genes (stx1, and genetic subtypes stx2a and stx2c of stx2). The characters A, W, Y, S and 1, 2a, 2c represent bacteriophage insertion sites argW, wrbA, yehV, sbcB, and stx genes stx1, stx2a, stx2c, respectively. SBI types of 40, 205, and 143 bovine, and 363, 79, and 179 human E. coli O157:H7 isolates from NZ, AU and the US, respectively, were evaluated. Proportional similarity indices (PSI) were computed based on the frequency distributions of SBI types to illustrate the epidemiological linkage between bovine and human isolates for each country. Results: A distinct prevalence distribution of SBI types was observed between the countries. AY2a was predominant among NZ bovine and human isolates (55.0% and 57.9% respectively), ASY12c was predominant among AU bovine and human isolates (51.7% and 43.0% respectively), and WY12a was predominant among US bovine and human isolates (43.4% and 63.7% respectively). NZ bovine and human genotypes shared the highest similarity (PSI value of 0.92) followed by AU (0.69) and the US (0.61). Significance: Highly evident divergence of genotypes was demonstrated between NZ, AU and the US but the reason for this is unknown. Possibilities include genetic drift and/or selection driven by different environmental factors, such as climate, types of feed, husbandry systems, or animal genetics. There was strong evidence for a close association between cattle and human populations of E. coli O157:H7 isolates in NZ, consistent with transmission of STEC from cattle to humans (or transmission to both hosts from another environmental reservoir).
    International Association for Food Protection (IAFP), Indianapolis, Indiana, USA; 08/2014
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    ABSTRACT: Introduction Shiga toxin-producing Escherichia coli (STEC) O157:H7 is a zoonotic pathogen of significant public health concern worldwide. Ruminants, particularly cattle are considered a primary host of this pathogen and have been identified as a source of infection in both environmental and foodborne outbreaks in humans overseas. Since 1993, when New Zealand’s (NZ) first case of STEC was reported, the annual incidence of notified cases of STEC infections has increased steadily (Institute of Environmental Science and Research Ltd. 2013). In 2013, there were 217 confirmed STEC cases which is equivalent to an incidence of 5.1 STEC cases per 100,000 population. The majority of cases (89.4%, 194/217) were caused by serotype O157:H7 (Institute of Environmental Science and Research Ltd. 2014). STEC infections in New Zealand appear as sporadic cases or small clusters, with outbreaks of STEC infections being rare, suggesting that food is not a significant exposure pathway. This observation is consistent with findings of a national case-control study conducted in 2011/2012 which identified risk factors associated with beef and dairy cattle, indicating that ruminants are the most likely sources of STEC infection in NZ (Jaros et al. 2013). Methods To assess evidence of localised transmission of STEC from cattle to humans in NZ, a molecular epidemiological study was conducted. The geographical distribution and population structure of genotypes of STEC O157:H7 isolated from bovine and human sources in NZ was studied, using multivariate methods applied to pulsed-field gel electrophoresis (PFGE, XbaI) and Shiga toxin-encoding bacteriophage insertion (SBI) genotyping data (Besser et al. 2007; Shringi et al. 2012). A total of 363 STEC O157:H7 isolates from clinical STEC cases occurring between 2008 and 2011 were compared to 40 bovine faecal isolates collected from cattle at NZ slaughter plants between 2008 and 2011. Results The molecular analysis of isolates’ PFGE profiles revealed three distinct clusters, each represented by a dominant SBI type (AY2a, WY12a, and ASY2c combined with SY2c). The distribution of SBI types observed differed between North and South Islands in bovine faecal (p<0.001) and human isolates (p<0.001), with SBI types AY2a and WY12a more prevalent in the North Island, and ASY2c/SY2c more common in the South Island. A statistically significant association was observed between SBI types and region of origin among PFGE profiles of human isolates (p<0.001), with clusters containing SBI type AY2a and ASY2c/SY2c being the predominant genotypes in the Taranaki and Gisborne regions in the North Island, respectively. Results of population differentiation also showed a within island clustering of human genotypes, providing evidence for highly localised geographical structuring. Conclusions The observed geographical distinction between bovine and human STEC O157:H7 isolates from the North and South Islands of NZ provides supporting evidence for localised transmission of STEC between cattle and humans. References Besser TE, Shaikh N, Holt NJ, Tarr PI, Konkel ME, Malik-Kale P, Walsh CW, Whittam TS, Bono JL. Greater diversity of Shiga toxin-encoding bacteriophage insertion sites among Escherichia coli O157:H7 isolates from cattle than in those from humans. Applied and Environmental Microbiology 73, 671-9, doi:10.1128/aem.01035-06, 2007 Institute of Environmental Science and Research Ltd. Surveillance report - notifiable and other diseases in New Zealand: annual report 2012. Client Report FW13014. Porirua, New Zealand, 2013 Institute of Environmental Science and Research Ltd. Verocytotoxin-producing E.coli (VTEC/STEC) confirmed by ERL in 2013 (accessed online from https://surv.esr.cri.nz/PDF_surveillance/ERL/VTEC/VTEC_2013.pdf on 20/02/2014), 2014 Jaros P, Cookson A, Campbell D, Besser T, Shringi S, Mackereth G, Lim E, Lopez L, Dufour M, Marshall J, Baker M, Hathaway S, Prattley D, French N. A prospective case-control and molecular epidemiological study of human cases of Shiga toxin-producing Escherichia coli in New Zealand. BMC Infectious Diseases 13, 450, 2013 Shringi S, Schmidt C, Katherine K, Brayton KA, Hancock DD, Besser TE. Carriage of stx2a differentiates clinical and bovine-biased strains of Escherichia coli O157. PLoS ONE 7, e51572, doi:10.1371/journal.pone.0051572, 2012
    New Zealand Veterinary Association (NZVA), Hamilton, New Zealand; 06/2014
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    ABSTRACT: Animal-associated bacterial communities are infected by bacteriophages, although the dynamics of these infections are poorly understood. Transduction by bacteriophage may contribute to transfer of antimicrobial resistance genes, but the relative importance of transduction among other gene transfer mechanisms is unknown. We therefore developed a candidate deterministic mathematical model of infection dynamics of enteric coliphages in commensal Escherichia coli in the large intestine of cattle. We assumed the phages were associated with the intestine and were predominantly temperate. Model simulations demonstrated how, given the bacterial ecology and infection dynamics, most (>90%) commensal enteric E. coli may become lysogens of enteric coliphages during intestinal transit. Using the model and most liberal assumptions of transduction efficiency and resistance gene frequency, we approximated the upper numerical limits ('worst case scenario') of gene transfer through specialized and generalized transduction in E. coli by enteric coliphages when the transduced genetic segment is picked at random. The estimates were consistent with a relatively small contribution of transduction to the lateral gene spread; for example, generalized transduction delivered chromosomal resistance gene to up to 8 E. coli/hour within the 1.47×10(8) E. coli/L luminal content population. In comparison, the plasmidic blaCMY-2 gene carried by ∼2% of enteric E. coli was transferred by conjugation at a rate at least 1.4×10(3) times greater than our generalized transduction estimate. The estimated numbers of transductants varied non-linearly depending on the ecology of bacteria available for phages to infect, that is - on the assumed rates of turn-over and replication of enteric E. coli.
    Applied and Environmental Microbiology 05/2014; · 3.95 Impact Factor
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    ABSTRACT: AimsMicrocin MccPDI-producing Escherichia coli have a fitness advantage in dairy calves. For this project we determined if MccPDI is responsible for the in vivo fitness advantage, which is a necessary condition before MccPDI strains can be considered viable candidates for inhibiting pathogenic serovars of E. coli.Methods and ResultsNeonatal calves were co-inoculated with either MccPDI-producing E. coli or MccPDI-knockout mutants in conjunction with a susceptible strain. After six days the MccPDI producing E. coli-25 strain clearly dominated the E. coli-186 susceptible strain in the inoculated calves (P=0.003). MccPDI-producing E. coli composed a higher log percentage of the total population of lactose-fermenting bacteria in the feces [~68%, (5.51 log CFU/8.03 log CFU)] compared to the knockout strain [~31%, (2.6 log CFU/8.23 log CFU)] (P=0.01), and it was more consistently recovered from the lower GI tract at the time of necropsy (P=0.01).Conclusion Our findings support the hypothesis that MccPDI is functional in vivo and it is most likely responsible for a fitness advantage in vivo.Significance and Impact of the StudyMccPDI-producing E. coli strongly inhibit pathogenic E. coli strains in vitro. We show herein that MccPDI functions in vivo and thus these strains may be candidate probiotics against pathogenic strains of E. coli.This article is protected by copyright. All rights reserved.
    Journal of Applied Microbiology 05/2014; · 2.20 Impact Factor
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    ABSTRACT: Bronchopneumonia is a population limiting disease of bighorn sheep (Ovis canadensis). The cause of this disease has been a subject of debate. Leukotoxin expressing Mannheimia haemolytica and Bibersteinia trehalosi produce acute pneumonia after experimental challenge but are infrequently isolated from animals in natural outbreaks. Mycoplasma ovipneumoniae, epidemiologically implicated in naturally occurring outbreaks, has received little experimental evaluation as a primary agent of bighorn sheep pneumonia.
    PLoS ONE 01/2014; 9(10):e110039. · 3.53 Impact Factor
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    ABSTRACT: Mortality from epizootic pneumonia is hindering re-establishment of bighorn sheep populations in western North America. Mycoplasma ovipneumoniae, a primary agent of this disease, is frequently carried asymptomatically by the domestic sheep and goats that constitute the reservoir of this agent for transmission to bighorn sheep. Our long-term objective is to reduce the risk of M. ovipneumoniae infection of bighorn sheep; one approach to this objective is to control the pathogen in its reservoir hosts. The safety and immunogenicity of M. ovipneumoniae for domestic sheep was evaluated in three experimental immunization protocols: 1) live M. ovipneumoniae (50 ug protein); 2) killed M. ovipneumoniae (50 ug whole cell protein) in oil adjuvant; and 3) killed M. ovipneumoniae (250 ug whole cell protein) in oil adjuvant. Immunogenicity was assessed by two serum antibody measures: competitive enzyme-linked immunosorbent assay (cELISA) (experiments 1-3) and serum growth inhibition (Experiment 3). Passive immunogenicity was also assessed in the third experiment using the same assays applied to blood samples obtained from the lambs of immunized ewes. Adverse reactions to immunization were generally minor, but local reactions were regularly observed at immunization sites with bacterins in oil adjuvants. No evidence of M. ovipneumoniae specific antibody responses were observed in the first or second experiments and no resistance to colonization was observed in the first experiment. However, the ewes in the third experiment developed strong cELISA serum antibody responses and significant serum M. ovipneumoniae inhibition activity, and these responses were passively transferred to their lambs. The results of these trials indicate that immunization with relatively large antigenic mass combined with an adjuvant is capable of inducing strong active antibody responses in ewes and passively immunizing lambs.
    PLoS ONE 01/2014; 9(4):e95698. · 3.53 Impact Factor
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    ABSTRACT: Veterinary nosocomial infections caused by antibiotic resistant bacteria cause increased morbidity, higher cost and length of treatment and increased zoonotic risk because of the difficulty in treating them. In this study, an individual-based model was developed to investigate the effects of movements of canine patients among ten areas (transmission points) within a veterinary teaching hospital, and the effects of these movements on transmission of antibiotic susceptible and resistant pathogens. The model simulates contamination of transmission points, healthcare workers, and patients as well as the effects of decontamination of transmission points, disinfection of healthcare workers, and antibiotic treatments of canine patients. The model was parameterized using data obtained from hospital records, information obtained by interviews with hospital staff, and the published literature. The model suggested that transmission resulting from contact with healthcare workers was common, and that certain transmission points (housing wards, diagnostics room, and the intensive care unit) presented higher risk for transmission than others (lobby and surgery). Sensitivity analyses using a range of parameter values demonstrated that the risk of acquisition of colonization by resistant pathogens decreased with shorter patient hospital stays (P<0.0001), more frequent decontamination of transmission points and disinfection of healthcare workers (P<0.0001) and better compliance of healthcare workers with hygiene practices (P<0.0001). More frequent decontamination of heavily trafficked transmission points was especially effective at reducing transmission of the model pathogen.
    PLoS ONE 01/2014; 9(6):e98589. · 3.53 Impact Factor
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    ABSTRACT: Shiga toxin-producing Escherichia coli (STEC) O157:H7 and related non-O157 STEC strains are enteric pathogens of public health concern worldwide, causing life-threatening diseases. Cattle are considered the principal hosts and have been shown to be a source of infection for both foodborne and environmental outbreaks in humans. The aims of this study were to investigate risk factors associated with sporadic STEC infections in humans in New Zealand and to provide epidemiological information about the source and exposure pathways. During a national prospective case--control study from July 2011 to July 2012, any confirmed case of STEC infection notified to regional public health units, together with a random selection of controls intended to be representative of the national demography, were interviewed for risk factor evaluation. Isolates from each case were genotyped using pulsed-field gel electrophoresis (PFGE) and Shiga toxin-encoding bacteriophage insertion (SBI) typing. Questionnaire data from 113 eligible cases and 506 controls were analysed using multivariate logistic regression. Statistically significant animal and environmental risk factors for human STEC infections were identified, notably 'Cattle livestock present in meshblock' (the smallest geographical unit) (odds ratio 1.89, 95% CI 1.04--3.42), 'Contact with animal manure' (OR 2.09, 95% CI 1.12--3.90), and 'Contact with recreational waters' (OR 2.95, 95% CI 1.30--6.70). No food-associated risk factors were identified as sources of STEC infection. E. coli O157:H7 caused 100/113 (88.5%) of clinical STEC infections in this study, and 97/100 isolates were available for molecular analysis. PFGE profiles of isolates revealed three distinctive clusters of genotypes, and these were strongly correlated with SBI type. The variable 'Island of residence' (North or South Island of New Zealand) was significantly associated with PFGE genotype (p = 0.012). Our findings implicate environmental and animal contact, but not food, as significant exposure pathways for sporadic STEC infections in humans in New Zealand. Risk factors associated with beef and dairy cattle suggest that ruminants are the most important sources of STEC infection. Notably, outbreaks of STEC infections are rare in New Zealand and this further suggests that food is not a significant exposure pathway.
    BMC Infectious Diseases 09/2013; 13(1):450. · 3.03 Impact Factor
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    ABSTRACT: Campylobacteriosis is a frequently-reported bacterial foodborne human disease which can be associated with ruminant reservoirs, although public health messages primarily focus on poultry. In Washington State, the two counties with the highest concentrations of dairy cattle also report the highest incidences of campylobacteriosis. Conditional logistic regression analysis of case-control data from both counties found living or working on a dairy farm (6.7, 1.7 - 26.4) and Hispanic ethnicity (5.9, 2.9 - 12.0) to have the strongest positive associations with campylobacteriosis. When the analysis was restricted to residents of one county, Hispanic ethnicity, (OR 9.3, 95% CI 3.9 - 22.2), contact with cattle (OR 5.0, 95% CI 1.3 - 19.5) and pet ownership (OR 2.6, 95% CI 1.1 - 6.3) were found to be independent risk factors for disease. Campylobacter jejuni isolates from human (n=65), bovine (n=28), and retail poultry (n=27) sources from the same counties were compared using multi-locus sequence typing. These results indicated that sequence types found commonly in human isolates were also commonly found in bovine isolates. These findings suggest that in areas with high concentrations of dairy cattle, exposure to dairy cattle may be more important than foodborne exposure to poultry products as a risk for campylobacteriosis.
    Journal of clinical microbiology 09/2013; · 4.16 Impact Factor
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    ABSTRACT: Escherichia coli O157:H7 is a zoonotic human pathogen for which cattle are an important reservoir host. Using both previously published and new sequencing data, a 48-locus single nucleotide polymorphism (SNP) based typing panel was developed that redundantly identified eleven genogroups that span six of the eight lineages recently described for E. coli O157:H7 (Bono JL, Smith TP, Keen JE, Harhay GP, McDaneld TG, Mandrell RE, Jung WK, Besser TE, Gerner-Smidt P, Bielaszewska M, Karch H, Clawson ML. 2012. Mol Biol Evol 29:2047-2062), and additionally define subgroups within four of those lineages. This assay was applied to 530 isolates from human and bovine sources. The SNP-based lineage groups were concordant with previously identified E. coli O157:H7 genotypes identified by other methods, and were strongly associated with carriage of specific Stx genes. Two SNP lineages (Ia and Vb) were disproportionately represented among cattle isolates and three others (IIa, Ib and IIb) were disproportionately represented among human clinical isolates. This 48-plex SNP assay efficiently and economically identifies biologically relevant lineages within E. coli O157:H7.
    Applied and Environmental Microbiology 09/2013; · 3.95 Impact Factor
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    ABSTRACT: E. coli O157 is a food borne pathogen whose major reservoir has been identified as cattle. Recent genetic information has indicated that populations of E. coli O157 from cattle and humans can vary genetically and that this variation may impact on their ability to cause severe human disease. In addition, there is emerging evidence that E. coli O157 from different geographical regions may also be genetically divergent. To investigate the extent of this variation, we analyzed 606 isolates representing both Australian and U.S.A. cattle and human populations for Shiga toxin bacteriophage insertion sites (SBI), lineage specific polymorphisms (LSPA-6), multi-locus tandem repeats (MLVA) and a tir 255T>A polymorphism. Both uni- and multi-variate analyses of these data show a strong association between country of origin and multi-locus genotypes (P<0.0001). In addition, our results identify factors that may play a role in virulence also varied in isolates from each country, including the carriage of stx1 in the argW locus uniquely observed in Australian isolates and the much higher frequency of stx2 positive strains in the U.S.A. isolates (4% of Australian isolates vs. 69% of U.S.A. isolates). LSPA-6 lineages varied between the two continents with the majority of Australian isolates belonging to LI/II (LI, 2%; LI/II 85%; LII, 13%) and U.S.A. isolates to LI (LI, 60%; LI/II, 16%; LII, 25%). This study provides strong evidence of phylogeographic structuring of E. coli O157 populations, suggesting divergent evolution of enterohemorrhagic E. coli O157 in Australia and the U.S.A..
    Applied and Environmental Microbiology 06/2013; · 3.95 Impact Factor
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    Preventive Veterinary Medicine 05/2013; 109(s 3–4):185. · 2.39 Impact Factor
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    ABSTRACT: Individual host immune responses to infectious agents drive epidemic behavior and are therefore central to understanding and controlling infectious diseases. However, important features of individual immune responses, such as the strength and longevity of immunity, can be challenging to characterize, particularly if they cannot be replicated or controlled in captive environments. Our research on bighorn sheep pneumonia elucidates how individual bighorn sheep respond to infection with pneumonia pathogens by examining the relationship between exposure history and survival in situ. Pneumonia is a poorly understood disease that has impeded the recovery of bighorn sheep (Ovis canadensis) following their widespread extirpation in the 1900s. We analyzed the effects of pneumonia-exposure history on survival of 388 radio-collared adults and 753 ewe-lamb pairs. Results from Cox proportional hazards models suggested that surviving ewes develop protective immunity after exposure, but previous exposure in ewes does not protect their lambs during pneumonia outbreaks. Paradoxically, multiple exposures of ewes to pneumonia were associated with diminished survival of their offspring during pneumonia outbreaks. Although there was support for waning and boosting immunity in ewes, models with consistent immunizing exposure were similarly supported. Translocated animals that had not previously been exposed were more likely to die of pneumonia than residents. These results suggest that pneumonia in bighorn sheep can lead to aging populations of immune adults with limited recruitment. Recovery is unlikely to be enhanced by translocating naïve healthy animals into or near populations infected with pneumonia pathogens.
    PLoS ONE 01/2013; 8(4):e61919. · 3.53 Impact Factor
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    ABSTRACT: Pneumonia of bighorn sheep (Ovis canadensis) is a dramatic disease of high morbidity and mortality first described more than 80 years ago. The etiology of the disease has been debated since its initial discovery, and at various times lungworms, Mannheimia haemolytica and other Pasteurellaceae, and Mycoplasma ovipneumoniae have been proposed as primary causal agents. A multi-factorial "respiratory disease complex" has also been proposed as confirmation of causation has eluded investigators. In this paper we review the evidence for each of the candidate primary agents with regard to causal criteria including strength of association, temporality, plausibility, experimental evidence, and analogy. While we find some degree of biological plausibility for all agents and strong experimental evidence for M. haemolytica, we demonstrate that of the alternatives considered, M. ovipneumoniae is the best supported by all criteria and is therefore the most parsimonious explanation for the disease. The strong but somewhat controversial experimental evidence implicating disease transmission from domestic sheep is consistent with this finding. Based on epidemiologic and microbiologic data, we propose that healthy bighorn sheep populations are naïve to M. ovipneumoniae, and that its introduction to susceptible bighorn sheep populations results in epizootic polymicrobial bacterial pneumonia often followed by chronic infection in recovered adults. If this hypothesized model is correct, efforts to control this disease by development or application of vectored vaccines to Pasteurellaceae are unlikely to provide significant benefits, whereas efforts to ensure segregation of healthy bighorn sheep populations from M. ovipneumoniae-infected reservoir hosts are crucial to prevention of new disease epizootics. It may also be possible to develop M. ovipneumoniae vaccines or other management strategies that could reduce the impact of this devastating disease in bighorn sheep.
    Preventive Veterinary Medicine 12/2012; · 2.39 Impact Factor
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    ABSTRACT: Salmonellosis is usually associated with foodborne transmission. To identify risk from animal contact, we compared animal exposures of case-patients infected with bovine-associated Salmonella subtypes with those of control-patients infected with non-bovine-associated subtypes. We used data collected in New York and Washington, USA, from March 1, 2008, through March 1, 2010. Contact with farm animals during the 5 days before illness onset was significantly associated with being a case-patient (odds ratio 3.2, p = 0.0008), after consumption of undercooked ground beef and unpasteurized milk were controlled for. Contact with cattle specifically was also significantly associated with being a case-patient (odds ratio 7.4, p = 0.0002), after food exposures were controlled for. More cases of bovine-associated salmonellosis in humans might result from direct contact with cattle, as opposed to ingestion of foods of bovine origin, than previously recognized. Efforts to control salmonellosis should include a focus on transmission routes other than foodborne.
    Emerging Infectious Diseases 12/2012; 18(12):1929-36. · 6.79 Impact Factor
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    ABSTRACT: Since the first case of Escherichia coli O157:H7 was detected in New Zealand (NZ) in 1993, the number of Shiga toxin-producing E. coli (STEC) notifications per year has increased steadily. Cattle are considered as a source of infection for both environmental and foodborne outbreaks of STEC in humans. As part of a source attribution investigation, E. coli O157:H7 isolates were obtained from the national Enteric Reference Laboratory and compared to bovine E. coli O157:H7 isolates from faecal samples collected from very young calves and adult cattle at four slaughter plants. A total of 28 bovine and 209 human isolates, originating from the North and South Islands of NZ, were screened for the presence of virulence genes characteristic of STEC, and genotyped using pulsed-field gel electrophoresis (PFGE), stx-encoding bacteriophage insertion (SBI) and single nucleotide polymorphisms (SNP) typing. The genotypic analysis of bovine isolates revealed three distinct PFGE profiles, each represented by a specific SBI type (1, 3, and 5). A distinct between-Island prevalence distribution of SBI types was observed among bovine and human isolates (p=0.001). SBI type 5 (SNP IVa) accounted for 21% of the studied human isolates. Internationally, this genotype has been reported only rarely in association with STEC infections in humans and is therefore of particular interest. Findings of this molecular study provide evidence for historical introduction of O157 strains into NZ and localised transmission between cattle and humans. A prospective case-control study is underway currently to investigate source attribution risks and possible exposure pathways for human cases of STEC in NZ.
    International Symposia on Veterinary Epidemiology and Economics (ISVEE), Maastricht, the Netherlands; 08/2012
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    ABSTRACT: A novel phenotype was recently identified in which specific strains of Escherichia coli inhibit competing E. coli strains via a mechanism that was designated "proximity-dependent inhibition" (PDI). PDI-expressing (PDI(+)) E. coli is known to inhibit susceptible (PDI(-)) E. coli strains, including several enterohemorrhagic (EHEC) and enterotoxigenic (ETEC) E. coli strains. In this study, every strain from a genetically diverse panel of E. coli O157:H7 (n = 25) and additional strains of E. coli serovar O26 were susceptible to the PDI phenotype. LIVE/DEAD staining was consistent with inhibition by killing of susceptible cells. Comparative genome analysis identified the genetic component of PDI, which is composed of a plasmid-borne (Incl1) operon encoding a putative microcin and associated genes for transport, immunity, and microcin activation. Transfer of the plasmid to a PDI(-) strain resulted in transfer of the phenotype, and deletion of the genes within the operon resulted in loss of the inhibition phenotype. Deletion of chromosomally encoded tolC also resulted in loss of the inhibitory phenotype, and this confirmed that the putative microcin is most likely secreted via a type I secretion pathway. Deletion of an unrelated plasmid gene did not affect the PDI phenotype. Quantitative reverse transcription (RT)-PCR demonstrated that microcin expression is correlated with logarithmic-phase growth. The ability to inhibit a diversity of E. coli strains indicates that this microcin may influence gut community composition and could be useful for control of important enteric pathogens.
    Applied and Environmental Microbiology 07/2012; 78(18):6592-9. · 3.95 Impact Factor
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    ABSTRACT: Epizootic pneumonia of bighorn sheep is a devastating disease of uncertain etiology. To help clarify the etiology, we used culture and culture-independent methods to compare the prevalence of the bacterial respiratory pathogens Mannheimia haemolytica, Bibersteinia trehalosi, Pasteurella multocida, and Mycoplasma ovipneumoniae in lung tissue from 44 bighorn sheep from herds affected by 8 outbreaks in the western United States. M. ovipneumoniae, the only agent detected at significantly higher prevalence in animals from outbreaks (95%) than in animals from unaffected healthy populations (0%), was the most consistently detected agent and the only agent that exhibited single strain types within each outbreak. The other respiratory pathogens were frequently but inconsistently detected, as were several obligate anaerobic bacterial species, all of which might represent secondary or opportunistic infections that could contribute to disease severity. These data provide evidence that M. ovipneumoniae plays a primary role in the etiology of epizootic pneumonia of bighorn sheep.
    Emerging Infectious Diseases 03/2012; 18(3):406-14. · 6.79 Impact Factor
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    ABSTRACT: Cattle are a major reservoir for Shiga toxin-producing Escherichia coli O157 (STEC O157) and harbor multiple genetic subtypes that do not all associate with human disease. STEC O157 evolved from an E. coli O55:H7 progenitor; however, a lack of genome sequence has hindered investigations on the divergence of human- and/or cattle-associated subtypes. Our goals were to 1) identify nucleotide polymorphisms for STEC O157 genetic subtype detection, 2) determine the phylogeny of STEC O157 genetic subtypes using polymorphism-derived genotypes and a phage insertion typing system, and 3) compare polymorphism-derived genotypes identified in this study with pulsed field gel electrophoresis (PFGE), the current gold standard for evaluating STEC O157 diversity. Using 762 nucleotide polymorphisms that were originally identified through whole-genome sequencing of 189 STEC O157 human- and cattle-isolated strains, we genotyped a collection of 426 STEC O157 strains. Concatenated polymorphism alleles defined 175 genotypes that were tagged by a minimal set of 138 polymorphisms. Eight major lineages of STEC O157 were identified, of which cattle are a reservoir for seven. Two lineages regularly harbored by cattle accounted for the majority of human disease in this study, whereas another was rarely represented in humans and may have evolved toward reduced human virulence. Notably, cattle are not a known reservoir for E. coli O55:H7 or STEC O157:H(-) (the first lineage to diverge within the STEC O157 serogroup), which both cause human disease. This result calls into question how cattle may have originally acquired STEC O157. The polymorphism-derived genotypes identified in this study did not surpass PFGE diversity assessed by BlnI and XbaI digestions in a subset of 93 strains. However, our results show that they are highly effective in assessing the evolutionary relatedness of epidemiologically unrelated STEC O157 genetic subtypes, including those associated with the cattle reservoir and human disease.
    Molecular Biology and Evolution 02/2012; 29(8):2047-62. · 10.35 Impact Factor
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    ABSTRACT: Enterohemorrhagic Escherichia coli O157:H7 (EHEC O157) is an important cause of food and waterborne illness in the developed countries. Cattle are a reservoir host of EHEC O157 and a major source of human exposure through contaminated meat products. Shiga toxins (Stxs) are an important pathogenicity trait of EHEC O157. The insertion sites of the Stx-encoding bacteriophages differentiate EHEC O157 isolates into genogroups commonly isolated from cattle but rarely from sick humans (bovine-biased genotypes [BBG]) and those commonly isolated from both cattle and human patients (clinical genotypes [CG]). Since BBG and CG share the cardinal virulence factors of EHEC O157 and are carried by cattle at similar prevalences, the infrequent occurrence of BBG among human disease isolates suggests that they may be less virulent than CG. We compared the virulence potentials of human and bovine isolates of CG and BBG in newborn conventional pig and weaned Dutch Belted rabbit models. CG-challenged piglets experienced severe disease accompanied by early and high mortality compared to BBG-challenged piglets. Similarly, CG-challenged rabbits were likely to develop lesions in kidney and intestine compared with the BBG-challenged rabbits. The CG strains used in this study carried stx2 and produced significantly higher amounts of Stx, whereas the BBG strains carried the stx2c gene variant only. These results suggest that BBG are less virulent than CG and that this difference in virulence potential is associated with the Stx2 subtype(s) carried and/or the amount of Stx produced.
    Infection and immunity 01/2012; 80(1):369-80. · 4.21 Impact Factor

Publication Stats

5k Citations
657.56 Total Impact Points


  • 1985–2014
    • Washington State University
      • • Department of Veterinary Microbiology & Pathology (VMP)
      • • Department of Veterinary Clinical Sciences (VCS)
      • • College of Veterinary Medicine
      Pullman, Washington, United States
  • 2010–2012
    • Massachusetts Institute of Technology
      • • Division of Comparative Medicine
      • • Department of Biological Engineering
      Cambridge, Massachusetts, United States
    • University of California, Davis
      • Department of Population Health and Reproduction (VM)
      Davis, CA, United States
  • 1994–2010
    • University of Idaho
      • • School of Food Science
      • • Department of Animal and Veterinary Science
      Moscow, Idaho, United States
  • 1994–2008
    • WSU West
      Seattle, Washington, United States
  • 2005–2007
    • Seoul National University
      • Department of Microbiology and Immunology
      Seoul, Seoul, South Korea
  • 2006
    • Washington University in St. Louis
      San Luis, Missouri, United States
    • The Ohio State University
      • Ohio Agricultural Research and Development Center
      Columbus, OH, United States
  • 2003
    • United States Department of Agriculture
      • Agricultural Research Service (ARS)
      Washington, D. C., DC, United States
  • 2002
    • University of Missouri
      • Department of Veterinary Medicine and Surgery
      Columbia, MO, United States
  • 2001
    • University of Vermont
      • Department of Animal Science
      Burlington, VT, United States
  • 1995–2000
    • University of Washington Seattle
      • • Division of Gastroenterology
      • • Department of Pediatrics
      Seattle, WA, United States
  • 1998
    • Animal and Plant Health Inspection Service
      Buzzards Bay, Massachusetts, United States
  • 1996–1998
    • Virginia Polytechnic Institute and State University
      • Department of Large Animal Clinical Sciences
      Blacksburg, VA, United States
  • 1993
    • Corvinus University of Budapest
      Budapeŝto, Budapest, Hungary