Lung lesions in SCID-bo and SCID-bg mice after intratracheal inoculation with wild-type or leucotoxin-deficient mutant strains of Mannheimia haemolytica serotype 1.

The purpose of this study was to investigate SCID-bg mice engrafted with bovine haematolymphoid tissues (SCID-bo) as a model for studying bovine Mannheimia haemolytica serotype 1- induced pneumonia, in which leucotoxin (LKT) plays a major role. In experiment A, SCID-bo and SCID-bg mice were inoculated intratracheally with either (1) phosphate-buffered saline (PBS), (2) M. haemolytica wild-type strain 89010807N ("LKT(+)WT"), (3) a M. haemolytica leucotoxin-deficient mutant of strain 89010807N ("LKT(-)mutant"), or (4) the M. haemolytica wild-type Oklahoma strain. Mice were killed for examination at intervals between 20 and 44h after inoculation. Lung lesions consisted of thickened alveolar septa and neutrophil and macrophage infiltrates in the bronchioles and alveoli. Lung lesion scores in the SCID-bo mice inoculated with LKT(+)WT or LKT(-) mutant were significantly (P<0.05) greater than those of the PBS control group, but the two bacterial strains produced results that did not differ significantly. M. haemolytica was isolated from lung, liver and spleen after inoculation but less frequently as time progressed. In experiment B, SCID-bg mice were inoculated intratracheally with live LKT(+)WT or formalin-killed LKT(+)WT and killed 24, 48 or 96 h later. Lung lesions were histologically similar to those observed in experiment A; however, there were no significant differences in the lung lesion scores between groups. It was concluded that the lesions seen in this study were probably not due to LKT, and that the SCID-bo mouse does not provide a good rodent model for bovine pneumonia.

A genotypically unique Babesia gibsoni-like parasite recovered from a dog in Oklahoma.

A small Babesia gibsoni-like parasite was identified and isolated as the cause of clinical babesiosis in a dog from Oklahoma. Because this was potentially the first documented case of B. gibsoni infection in Oklahoma, further characterization was warranted, and the 18S nuclear small subunit ribosomal RNA gene was sequenced. Sequence comparison with other piroplasms from dogs showed significant nucleotide sequence differences between this isolate and both B. canis and B. gibsoni. These findings demonstrate that in domestic dogs in North America there are at least 2 "small" B. gibsoni-like organisms with distinct nucleotide sequences and that the geographic distribution of the "small" canine Babesia species may be wider than previously recognized.

Thematic relations in adults' concepts.

Concepts can be organized by their members' similarities, forming a kind (e.g., animal), or by their external relations within scenes or events (e.g., cake and candles). This latter type of relation, known as the thematic relation, is frequently found to be the basis of children's but not adults' classification. However, 10 experiments found that when thematic relations are meaningful and salient, they have significant influence on adults' category construction (sorting), inductive reasoning, and verification of category membership. The authors conclude that concepts function closely with knowledge of scenes and events and that this knowledge has a role in adults' conceptual representations.

Causes of taxonomic sorting by adults: a test of the thematic-to-taxonomic shift.

The tendency among adults to sort items into taxonomic and thematic categories was examined in two experiments. Past demonstrations of adults' preference for taxonomic categories have usually not used stimuli with a salient thematic organization. The stimuli in Experiment 1 could be divided into three equal-size categories either thematically or taxonomically. Under two sets of instructions, the majority of the college-student subjects sorted thematically. In Experiment 2, a subset of the stimuli was changed so that those within it were strongly taxonomically organized. Subjects then preferred to sort the remaining items taxonomically as well. The two experiments explain why many past sorting studies have yielded a taxonomic preference in adults and provide further evidence against a global change from thematic to taxonomic preference with development.

Feature distribution and background knowledge in category learning.

Three experiments examined the interactions of category structure and prior knowledge in category learning. Experiment 1 examined the distribution of atypical or "crossover" features in category learning. In real categories, crossover features may be unevenly distributed--found primarily in very unusual examples of a category (like whales or ostriches). In contrast, in many psychology experiments, each item has exactly one crossover feature. Even versus uneven distribution of crossover features did not affect category learning when the features were neutral. However, when the features were connected by prior knowledge, it was much harder for subjects to learn the structure with the uneven distribution of crossover features. Experiments 2 and 3 found similar results with a slightly less uneven condition. We conclude that learning is a function of the interaction of category structure and prior knowledge rather than either one alone. Furthermore, knowledge benefits learning even when the category contains contradictions of the knowledge, so long as the contradictions are not very salient.

Naturally occurring Ehrlichia chaffeensis infection in coyotes from Oklahoma.

A nested polymerase chain reaction assay was used to determine the presence of Ehrlichia chaffeensis, E. canis, and E. ewingii DNA in blood samples of free-ranging coyotes from central and northcentral Oklahoma. Of the 21 coyotes examined, 15 (71%) were positive for E. chaffeensis DNA; none was positive for E. canis or E. ewingii. Results suggest that E. chaffeensis infections are common in free-ranging coyotes in Oklahoma and that these wild canids could play a role in the epidemiology of human monocytotropic ehrlichiosis.

Category learning with minimal prior knowledge.

In 6 experiments, the authors examined the use of prior knowledge in category learning. Previous studies of the effects of knowledge on category learning have used categories in which knowledge was related to all of the category's features. However, people's knowledge of real-world categories often consists of many "rote" features that are not related to their prior knowledge. Five experiments found that even minimal prior knowledge (1 knowledge-relevant feature and 5 rote features per exemplar) can facilitate category learning. Posttests revealed that although the knowledge aided learning, subjects also acquired the rote features that were not related to knowledge, contradicting predictions of an attentional explanation of the knowledge effect. The results of Experiment 6 suggested that subjects attempt to link even rote features to their knowledge.

Attempted transmission of Ehrlichia chaffeensis among white-tailed deer by Amblyomma maculatum.

A deer was needle-exposed intravenously to Ehrlichia chaffeensis (Rickettsiales: Ehrlichieae) in canine macrophage (DH82) cells and 7 days later was infested with laboratory-reared Amblyomma maculatum (Koch) (Acari:Ixodidae) nymphs for acquisition feeding. After molting, the adult ticks were allowed to feed on a naive deer. The organism was reisolated from the needle-exposed deer by cell culture and E. chaffeensis DNA was detected in the deer's blood by PCR. Similar isolation/recovery techniques were used for the tick-exposed deer and no evidence of infection was found. Although these findings must be considered as preliminary owing to inadequate controls, the data suggest that A. maculatum is probably not a suitable vector for E. chaffeensis.

Synchronizing visual and language processing: an effect of object name length on eye movements.

Are visual and verbal processing systems functionally independent? Two experiments (one using line drawings of common objects, the other using faces) explored the relationship between the number of syllables in an object's name (one or three) and the visual inspection of that object. The tasks were short-term recognition and visual search. Results indicated more fixations and longer gaze durations on objects having three-syllable names when the task encouraged a verbal encoding of the objects (i.e., recognition). No effects of syllable length on eye movements were found when implicit naming demands were minimal (i.e., visual search). These findings suggest that implicitly naming a pictorial object constrains the oculomotor inspection of that object, and that the visual and verbal encoding of an object are synchronized so that the faster process must wait for the slower to be completed before gaze shifts to another object. Both findings imply a tight coupling between visual and linguistic processing, and highlight the utility of an oculomotor methodology to understand this coupling.

Induction with cross-classified categories.

One of the main functions of categories is to allow inferences about new objects. However, most objects are cross-classified, and it is not known whether and how people combine information from these different categories in making inferences. In six experiments, food categories, which are strongly cross-classified (e.g., a bagel is both a bread and a breakfast food), were studied. For each food, the subjects were told fictitious facts (e.g., 75% of breads are subject to spoilage from Aspergillus molds) about two of the categories to which it belonged and then were asked to make an inference about the food (e.g., how likely is a bagel to be subject to spoilage from Aspergillus molds?). We found no more use of multiple categories in these cases of cross-classification than in ambiguous classification, in which it is uncertain to which category an item belongs. However, some procedural manipulations did markedly increase the use of both categories in inferences, primarily those that focused the subjects' attention on the critical feature in both categories.

What is learned in knowledge-related categories? Evidence from typicality and feature frequency judgments.

When a category's features are tied together by integrative knowledge, subjects learn the category faster than when the features are not directly related. What do subjects learn about the category in such circumstances? Some research has suggested that the subjects can use the knowledge itself in performing the category learning task and, thus, do not learn the details of the category's features. Two experiments investigated this hypothesis by collecting feature frequency estimates after category learning. The results showed that integrative knowledge about a category did not decrease subjects' sensitivity to feature frequency--if anything, knowledge improved it. A third experiment found that integrative knowledge did reduce sensitivity to feature frequency in typicality ratings. The results suggest that knowledge does not inhibit the learning of detailed category information, though it may replace its use in some tasks.

The acquisition of category structure in unsupervised learning.

Four experiments examined the extent to which prior knowledge influences the acquisition of category structure in unsupervised learning conditions. Prior knowledge is general knowledge about a broad domain that explains why an object has the features it does. Category structure refers to the statistical regularities of features within and across categories. Subjects viewed items and then divided them up into the categories that seemed most natural. Each item had one feature that was related to prior knowledge and five features that were not. The results showed that even this small amount of prior knowledge helped subjects to discover the category structure. In addition, prior knowledge enhanced the learning of many of the category's features, and not just the features that were directly relevant to the knowledge. The results suggest that prior knowledge may help to integrate the features of a category, thereby improving the acquisition of category structure.

Molecular cloning of the Pasteurella haemolytica pomA gene and identification of bovine antibodies against PomA surface domains.

The gene (pomA) encoding PomA, an OmpA-like major outer membrane protein of the bovine respiratory pathogen Pasteurella haemolytica, was cloned, and its nucleotide sequence was determined. The deduced amino acid sequence of PomA has significant identity with the sequences of other OmpA family proteins. Absorption of three different bovine immune sera with whole P. haemolytica cells resulted in a reduction of bovine immunoglobulin G reactivity with recombinant PomA in Western immunoblots, suggesting the presence of antibodies against PomA surface domains.

Food for thought: cross-classification and category organization in a complex real-world domain.

Seven studies examined how people represent, access, and make inferences about a rich real-world category domain, foods. The representation of the category was assessed by category generation, category ratings, and item sortings. The first results indicated that the high-level category of foods was organized simultaneously by taxonomic categories for the kind of food (e.g., vegetables, meats) and script categories for the situations in which foods are eaten (e.g., breakfast foods, snacks). Sortings were dominated by the taxonomic categories, but the script categories also had an influence. The access of the categories was examined both by a similarity rating task, with and without the category labels, and by a speeded priming experiment. In both studies, the script categories showed less access than the taxonomic categories, but more than novel ad hoc categories, suggesting some intermediate level of access. Two studies on induction found that both types of categories could be used to make a wide range of inferences about food properties, but that they were differentially useful for different kinds of inferences. The results give a detailed picture of the use of cross-classification in a complex domain, demonstrating that multiple categories and ways of categorizing can be used in a single domain at one time.

Identification of immunogenic, surface-exposed outer membrane proteins of Pasteurella haemolytica serotype 1.

Pasteurella haemolytica serotype 1 (S1) is the bacterium most frequently recovered from the lungs of cattle that have succumbed to shipping fever pneumonia. P. haemolytica outer membrane proteins (OMPs) are important immunogens in the development of resistance to pneumonic pasteurellosis. The purpose of this study was to identify the repertoire of immunogenic, surface-exposed P. haemolytica (S1) OMPs, that could be important in the development of protective immunity. We determined surface exposure of OMPs by (1) their susceptibility to protease treatment and (2) their ability to adsorb out antibodies from bovine immune sera. For a comprehensive identification of immunogenic, surface-exposed OMPs, we used bovine antisera from calves that were resistant to experimental P. haemolytica challenge after (1) natural exposure to P. haemolytica, (2) vaccination with live P. haemolytica, or (3) vaccination with P. haemolytica OMPs. We identified 21 immunogenic, surface-exposed P. haemolytica OMPs. Most were recognized by all three immune sera. However, some were recognized by one or two of the three antisera. Our analyses identified surface-exposed, immunogenic proteins that were not identified in previous studies.

A molecular and serologic survey of Ehrlichia canis, E. chaffeensis, and E. ewingii in dogs and ticks from Oklahoma.

Polymerase chain reaction and Southern hybridization were used to survey for the presence of Ehrlichia canis, Ehrlichia chaffeensis, and Ehrlichia ewingii in blood samples of 65 dogs that harbored ticks from northcentral and northeastern Oklahoma. Dog blood samples were also examined for antibodies against E. canis and E. chaffeensis, using an immunofluorescent antibody test. Ten of 65 dogs (15.4%) examined were positive for Ehrlichia spp. by PCR. Four (6.2%) were positive for E. ewingii, 2 (3.1%) for E. canis, and 4 (6.2%) for E. chaffeensis. Seven dogs (10.8%) were seropositive for E. canis or E. chaffeensis. Ticks collected from PCR-positive dogs were examined by PCR for the presence of Ehrlichia DNA. Several groups of ticks were PCR-positive for E. ewingii or E. canis. E. canis was detected in Rhipicephalus sanguineus, which is considered the major vector for that organism. E. ewingii was detected in a larger variety of ticks, including the only known vector Amblyomma americanum, as well as in Dermacentor variabilis and R. sanguineus. Results suggest that Ehrlichia spp. which are canine and human pathogens circulate in dogs in Oklahoma and in several tick species that feed on dogs.

Genetic and immunologic analyses of PlpE, a lipoprotein important in complement-mediated killing of Pasteurella haemolytica serotype 1.

Pasteurella haemolytica serotype 1 is the bacterium most commonly associated with bovine shipping fever. The presence of antibodies against P. haemolytica outer membrane proteins (OMPs) correlates statistically with resistance to experimental P. haemolytica challenge in cattle. Until now, specific P. haemolytica OMPs which elicit antibodies that function in host defense mechanisms have not been identified. In this study, we have cloned and sequenced the gene encoding one such protein, PlpE. Analysis of the deduced amino acid sequence revealed that PlpE is a lipoprotein and that it is similar to an Actinobacillus pleuropneumoniae lipoprotein, OmlA. Affinity-purified, anti-PlpE antibodies recognize a protein in all serotypes of P. haemolytica except serotype 11. We found that intact P. haemolytica and recombinant E. coli expressing PlpE are capable of absorbing anti-PlpE antibodies from bovine immune serum, indicating that PlpE is surface exposed in P. haemolytica and assumes a similar surface-exposed conformation in E. coli. In complement-mediated killing assays, we observed a significant reduction in killing of P. haemolytica when bovine immune serum that was depleted of anti-PlpE antibodies was used as the source of antibody. Our data suggest that PlpE is surface exposed and immunogenic in cattle and that antibodies against PlpE contribute to host defense against P. haemolytica.

Characterization of a Pasteurella haemolytica A1 mutant deficient in production of three membrane lipoproteins.

OBJECTIVE: To determine whether a Pasteurella haemolytica A1 mutant that is unable to produce membrane lipoproteins has reduced susceptibility to complement-mediated killing, and to characterize the mutant strain. SAMPLE POPULATION: 12 sera from cattle resistant to P haemolytica challenge exposure after vaccination with P haemolytica or its antigens, or after natural exposure. PROCEDURES: Complement-mediated killing assays were performed, using wild-type and mutant strains and, as antibody source, various immune sera from cattle that were resistant to P haemolytica challenge exposure. Antibody response to whole-cell antigens produced by mutant and wild-type strains, production of outer membrane proteins and iron-regulated outer membrane proteins by the 2 strains, and growth of the 2 strains in various media were analyzed. RESULTS: Compared with wild-type P haemolytica, the lipoprotein mutant strain had increased susceptibility to bovine complement-mediated killing. Aside from the lipoproteins that are not produced by the mutant, immunoblot analysis did not reveal differences between immunoreactive antigens that are produced by the 2 strains. Some iron-regulated, outer membrane proteins, which usually are only produced by P haemolytica under iron-deficient conditions, were produced constitutively by the mutant. The mutant grew to a lower final cell density and at a lower rate under conditions likely to reflect those encountered in vivo. CONCLUSIONS: Lack of 3 membrane lipoproteins resulted in enhanced susceptibility to bovine complement-mediated killing. Site-specific mutagenesis of genes encoding P haemolytica membrane lipoproteins alters production of iron-regulated outer membrane proteins by P haemolytica. Growth characteristics of the mutant suggested that it may have reduced capacity for survival in vivo.

Development of a non-radioactive DNA probe and in situ hybridization for detection of Anaplasma marginale in ticks and cattle.

A non-radioactive DNA probe was developed for detection of Anaplasma marginale in ticks and cattle. The probe was labeled with digoxigenin 11-dUTP by polymerase chain reaction. The probe was tested on bovine blood and was found to be a sensitive and specific detection method for A. marginale in cattle. The DNA probe was then adapted for in situ hybridization (ISH) of A. marginale in Dermacentor andersoni and D. variabilis ticks infected either as nymphs or adults. One-half of each tick was studied with ISH while the other half was examined with light and electron microscopy. In male ticks infected as adults, tick gut cells first became infected with A. marginale while ticks fed on an infected calf, and they remained infected as they transmission fed on a second, susceptible calf. At the onset of transmission feeding, salivary glands became infected with A. marginale. During transmission feeding infection was also observed in interstitial, reproductive, skeletal muscle, fat body and Malpighian tubule tissue, resulting in a generalized A. marginale infection. When adult ticks that acquired infection as nymphs were examined with ISH and microscopy, gut tissues of both D. andersoni and D. variabilis became infected with A. marginale. However, salivary gland infection was seen only in D. variabilis, even though both species of ticks transmitted A. marginale to susceptible calves. A. marginale was not seen with ISH or microscopy in hemocytes collected from both species of ticks and, thus, hemocytes do not appear to play a role in the development of A. marginale in ticks.

Alignment and category learning.

Recent research shows that similarity comparisons involve an alignment process in which features are placed into correspondence. In 6 studies, the authors showed that alignment is involved in category learning as well. Within a category, aligned matches (feature matches occurring on the same dimension) facilitate learning more than nonaligned matches do (matches on different dimensions), although nonaligned matches still facilitate learning relative to nonmatches. Analogously, feature matches that cross category boundaries hurt learning more if they occur on the same versus a different dimension, and cross-category feature matches on different dimensions hurt learning relative to nonmatching features. Representational assumptions of category learning models must be modified to account for the differences between aligned and nonaligned feature matches.