Colony Hybridization Research Articles

Cell population growth regulates dorsalization and caudalization during chick morphogenesis and programmed cell death in lens fibres.

The chick embryo ectoblast was examined for a possible relationship between the state of neural competence and cell population growth. It was found that although ectoblast cells with doubling times ranging between 5 to 20 h exhibit neural competence, the extent of neutralization induced by the Hensen's node depends on the duration of the cell cycle; the longer the doubling time of the competent ectoblast, the stronger the induction and the greater the induced neural tissue. Neural induction in the competent ectoblast occurs in at least two steps: the first lasts for 1-2 h of direct contact with the inducing Hensen's node graft; a contact for another 2 h with even a non-inducing post-nodal fragment is essential to consolidate neutralization. Hensen's node graft induces mitotic activity in the competent ectoblast in contact. Teratogens which inhibit cell population growth, development and blastoderm expansion in chick embryo gastrula cause concomitant caudalization of the embryonic axis. We confirm Yamada's hypothesis that dorsalization is under positive mitogenic control, whereas caudalization is controlled by a negative cell cycle regulation. Reverse transcripts of chick gastrula mRNA were cloned in pBR322. Colony hybridization with cDNA made against chicken yolk RNA showed positive clones. Thus chicken yolk contains maternal mRNAs. cDNA made against mRNA extracted from stage 10 foreheads was hybridized with RNA from stage 1 to 13 embryos, 19 day lens and egg yolk. The hybridization signal, which was low between stages 1 to 7, increased between stages 10-13 and decreased thereafter. Forehead cDNA also hybridized to yolk RNA. Thus, maternal RNA sequences are present in the early chick embryo. During lens development, epithelial cells retain proliferative activity and their progeny reaching a stationary phase join the fibre area and contribute to the growth of fibre cells. The rate of transfer from epithelium to fibre regulates the rate of programmed cell death of the non-dividing differentiated lens fibre cells.

Colonial borders and hybrid identities: Lessons from the case of Eritrea

Abstract Colonialism left numerous borders in its wake that subsequently became contested. These colonial borders have often been discussed as artificial, dividing communities, people or ethnicities that otherwise would belong together. Such an interpretation of colonial borders, I argue in this article, overlooks another important aspect of colonial boundaries: their role in creating nations as ‘imagined communities’ who in making reference to such borders can lay claim to a distinct national identity. While such an identity can be exclusionary and trigger conflict, it can also have a much more positive and ultimately hybrid function. I use the case of Italian colonialism in the Horn of Africa to demonstrate these multiple roles colonial boundaries can occupy and focus specifically on the creation and contestations of the borders of Eritrea. I argue that the acceptance of borders as markers of identity can be a prerequisite for finding innovative ways to overcome exclusions in the everyday lives of borderland groups. Thus, the example of Eritrea could hold wider lessons for addressing postcolonial disputes about borders and boundaries, if institutional arrangements are put in place that allow fluidity in everyday encounters.

Gauguin's Challenge: New Perspectives after Postmodernism ed. by Norma Broude

Reviewed by: Gauguin's Challenge: New Perspectives after Postmodernism ed. by Norma Broude Catherine Gaughan Broude, Norma, ed. Gauguin's Challenge: New Perspectives after Postmodernism. Bloomsbury, 2018. ISBN 978-1-5013-4250-9. Pp. 306. This collection of essays not only sheds light on Gauguin as an artist but delves into crucial questions concerning the significance of his paintings today. These questions range from ambivalence and androgyny to colonial hybridity and primitivism, which in turn highlight various complexities and contradictions that continue to make Gauguin's art relevant, yet oftentimes troubling for his audiences. The ten essays take into account the world of Gauguin through the lens of sociopolitical, cultural, and aesthetic issues. They look beyond traditional interpretations of his famous renderings of Polynesia to deeper meanings of his works and their place in the twenty-first century. After a well-thought-out introduction, "Gauguin after Postmodernism," the book offers a cross-section of essays ranging from gender, religion, and power in order to come to terms with thorny questions of colonialism and sexism as well as ways in which his artwork impacts our experience today. Famous for his paintings of Tahiti involving large forms, bold shapes, and bright panes of color as well as self-portraits, the book explores Gauguin's contributions to symbolism, science, and spirituality up until his last burst of creativity at the turn of the century. Considering the more contentious aspects of his paintings involving tensions between male/female, civilized/savage, [End Page 260] writer/artist, the topics addressed provide many original intercultural references that are frequently dismissed. The essays toward the end of the volume are particularly worthy of attention in terms of a contemporary reading of Gauguin, such as those of Elizabeth C. Childs and Heather Waldroup, who look at the influence that Gauguin's work had on his and future generations of female artists through contemporary multimedia installations, digital prints, and montages. Many of the essays allow the reader to come face-to-face with the troubling subjects and representations of sexuality in Gauguin's works emphasizing how European clichés and fantasies of the Polynesian body continue to complicate the reception of his paintings over one hundred years later. The stunning series of prints, both black-and-white and color, make this book a significant cultural memento and a point of reflection in terms of both Gauguin's paintings and personality. Well researched and engaging both in its form and content, Gauguin's Challenge offers many critical points of view that challenge the orthodoxies of the artist's time and our own. For those art historians who have an unadulterated passion for Gauguin and for others who may not have quite as much knowledge, this collection of essays will reveal the importance of his influence and the inherent struggle with the place of his work in the twenty-first century. Catherine Gaughan University of Toronto Copyright © 2020 American Association of Teachers of French

Decreasing Traffic Congestion in VANETs Using an Improved Hybrid Ant Colony Optimization Algorithm

Vehicular Ad-hoc Network (VANET) is a definitive form of mobile ad-hoc network (MANET), which delivers data communication in a vehicular environment, using wireless transmission. Its fundamental goal is to increase the service quality of Intelligent Transportation Systems (ITS), such as road safety, logistics, and environmental kindliness, as well as information interchange. Smart cities are encountering problematic traffic congestion, particularly in developing countries. This paper presents an Improved Hybrid Ant Colony Optimization (IHACO) algorithm for decreasing congestion in smart cities. The objective of the proposed scheme is to choose a best routing path during rush hours by providing an optimal path. The scheme also introduces the IHACO algorithm to improve QoS for ITS. This algorithm (IHACO) differs from other algorithms, such as particle swarm optimization (PSO), in terms of pheromone update processes, which makes it more efficient. Also, the ant colony hybrid routing protocol (ACOHRP) protocol is introduced to improve the service quality of intelligent traffic systems (ITS). It delivers superlative efficiency through a better origination of packet delivery ratio, throughput, and end-to-end delay. Simulation-based testing is performed using Matlab simulation. It was found that traffic congestion time decreased gradually when using IHACO, unlike with other algorithms. The computed results demonstrated that the IHACO algorithm offers improved performance in terms of reliability, period, distance, and throughput, compared with different algorithms presented in this paper.

A New Hybrid Algorithm for Cold Chain Logistics Distribution Center Location Problem

According to the perishable characteristics of refrigerated food and the objective of minimizing the total cost, the mathematical optimization model of cold chain logistics distribution center location problem is established by introducing such constraints as the freshness and time window. In order to solve the problems of slow convergence and easy to fall into local optimal solution in the process of the traditional wolf colony optimization, an immune wolf colony hybrid algorithm is proposed to solve the location problem of distribution center. In this hybrid algorithm, the idea of vaccination of immune algorithm is introduced into the wolf colony algorithm. By adjusting the antibody concentration and selecting immune operator, the diversity of the wolf colony algorithm is improved, and then the search space of the solution is expanded; the convergence speed and solution accuracy of the wolf colony algorithm are improved by using immune memory cells and immune vaccine. The simulation results show that the immune wolf colony algorithm can quickly converge to the global optimal solution and optimize the location model of logistics distribution center. The algorithm has good feasibility and robustness.

Dietary supplementation of recombinant tilapia piscidin 4-expressing yeast enhances growth and immune response in Lates calcarifer

Marine antimicrobial peptide tilapia piscidin (TP) 4 possesses antibacterial and immune regulatory activities, making it a potentially valuable feed supplement in aquaculture. In this study, we expressed the TP4 peptide, originally identified from Oreochromis niloticus, in yeast (Pichia pastoris) under the control of an alcohol oxidase (Aox) 1 promoter. Recombinant (r)TP4 expression was induced by methanol. Transformation was confirmed by PCR, and expression was confirmed by colony hybridization. For scalable production, transformed yeast was cultured and induced in a bench-top fermenter bioreactor system under controlled conditions. The rTP4-expressing yeast cells were then pelleted and fed to 28-day-old Lates calcarifer as a 0, 1, 3 or 5 % supplement to the normal diet. Growth performance and immune response were monitored in the fish for four weeks. The 3 and 5 % rTP4-yeast groups showed significant improvements in weight gain, feed efficiency, survival, protein efficiency ratio, and hepatosomatic index. In addition, rTP4-yeast increased the levels of IgM, which plays a critical role in innate immunity. Furthermore, rTP4-yeast-containing diet elevated SOD, GPx and catalase activities. Since feeding L. calcarifer with bioreactor-produced rTP4-expressing yeast significantly enhanced growth and immunity, rTP4 should be considered for use as a functional feed supplement to replace excessively administered antibiotics in farmed fish.

Organic and Inorganic Chinas: Desire and Fatigue in Global Hong Kong

ABSTRACTCold War discourses reconceived of Chinese cultures as two Chinas, one of the People’s Republic of China (PRC), and the other of the “other China” (Taiwan), or “Greater China” (Hong Kong, Singapore). Today, this discourse has extended to reimagine Chineseness as either “inorganic” (signifying one-party rule and social engineering) or as “organic” (signifying colonial hybridity and laissez-faire capitalism). We explore three texts about Hong Kong—the film Chinese Box (1997) and the video games Sleeping Dogs (2012) and Shenmue II (2001)—to ask how the inorganic/organic binary reveals the desires for globality that construct both Chinas as competing global entities.

The copy as original: the presence of the absent Spanish Habsburg king and colonial hybridity

AbstractThe political culture that defined the Spanish empire was made up of elements that, borrowing from their different points of contact, travelled the world‐around being transformed in the process into a mixed style that defied a clear origin (or original). This political culture was based on sixteenth‐ and seventeenth‐century understandings of the copy as an original that not only made possible the dissemination in the empire of the figure and powers of the absent king by making him ‘present’, but also produced common understandings of his figure, powers, and genesis of the empire. By examining ceremonial deployments of royal simulacra in various cities of the vast Spanish monarchy, and coeval understandings of the copy, this article, argues that the cultural production of this empire cannot be best understood within ahistorical centre‐periphery frameworks of cultural production and/or as derivative colonial phenomena, as do notions of cultural hybridity and of ‘colonial’ art.

An alternative approach to neural network training based on hybrid bio meta-heuristic algorithm

Metaheuristic algorithms are popular techniques used to solve several optimization problems. Among the key algorithms, cuckoo search (CS) is a comparatively novel and promising metaheuristic algorithm. Various researchers have shown that it performs better when compared to other metaheuristic algorithms while searching for optimal value and is being used to solve various real-world problems. However, the basic CS algorithm can be improved by enhancing the probabilities of survival of the eggs. It will decrease the possibility of the eggs getting ruined by the host bird. The cuckoo birds move to a new position looking for more search space to get better solutions. Furthermore, better search space can be obtained by executing levy flight with accelerated particle swarm optimization (APSO). This research proposes a new method known as hybrid accelerated cuckoo particle swarm optimization (HACPSO) algorithm, based on two metaheuristic algorithms. In the proposed HACPSO algorithm, APSO provides communication for looking better place having the best nest with greater survivability for cuckoo birds. Different simulation has been carried using standard dataset and efficiency of the proposed algorithm is compared with CS, artificial bee colony and other similar hybrid variants. The simulation results demonstrate that the HACPSO algorithm performs better as compared to other algorithms in term of accuracy, MSE, SD, and with fast convergence rate to the target space.

The Foundations of the Modern Philippine State: Imperial Rule and the American Constitutional Tradition in the Philippine Islands, 1898–1935

Leia Castañeda Anastacio has produced a volume that will likely become a go-to text for those interested in the constitutional history of the Philippines and for those who study the legal history of the United States. The central argument that guides readers through the interaction of these two intersecting legal histories is that the colonial governmental and legal structures created by the American imperial experiment in the early-twentieth century provided a blueprint for the Philippine constitution. From the start, Anastacio links the authoritarian ruler of her youth, Ferdinand Marcos (the Philippine president from 1965 to 1986), directly to the strong executive leadership model established during U.S. imperial rule in the islands, which saw Filipinos “enjoy the trappings of popular sovereignty while depriving them of political control” (p. 10). The author sees the roots of this uneven distribution of power in the prevailing racialized and “civilizing” notions of the era. For many U.S. imperialists, the full-scale transferral of American institutions and legal systems was simply not practicable, and, thus, a strange and distorted colonial hybrid emerged; its impact is still felt today.

Research on a Task Planning Method for Multi-Ship Cooperative Driving

A new method for a cooperative multi-task allocation problem (CMTAP) is proposed in this paper, taking into account the multi-ship, multi-target, multi-task and multi-constraint characteristics in a multi-ship cooperative driving (MCD) system. On the basis of the general CMTAP model, an MCD task assignment model is established. Furthermore, a genetic ant colony hybrid algorithm (GACHA) is proposed for this model using constraints, including timing constraints, multi-ship collaboration constraints and ship capacity constraints. This algorithm uses a genetic algorithm (GA) based on a task sequence, while the crossover and mutation operators are based on similar tasks. In order to reduce the dependence of the GA on the initial population, an ant colony algorithm (ACA) is used to produce the initial population. In order to meet the environmental constraints of ship navigation, the results of the task allocation and path planning are combined to generate an MCD task planning scheme. The results of a simulated experiment using simulated data show that the proposed method can make the assignment more optimized on the basis of satisfying the task assignment constraints and the ship navigation environment constraints. Moreover, the experimental results using real data also indicate that the proposed method can find the optimal solution rapidly, and thus improve the task allocation efficiency.

Load balancing optimization based on hybrid Heuristic-Metaheuristic techniques in cloud environment

Load balancing among virtual machines (VMs) is significant for delivering the cloud services in optimized way with minimum cost paid and total time acquired to deliver the services. In this paper, the various research gaps for load balancing optimization in the past literature have been presented, which need to be addressed for solving the load balancing problem in cloud environment. In present work, Hybrid approach based resource provisioning and load balancing framework for workflows execution has been proposed to optimize the utilization of VMs with uniform load distribution. The proposed framework is based on the hybridization of heuristic techniques with metaheuristic algorithm to achieve its optimal performance in terms of makespan and cost. Two hybrid approaches have been proposed for HDD-PLB framework-Hybrid Predict Earliest Finish Time (PEFT) Heuristic with Ant Colony Optimization (ACO) metaheuristic (HPA) and Hybrid Heterogeneous Earliest Finish Time (HEFT) heuristic with ACO (HHA). The two proposed approaches for load balancing have been analyzed and compared to determine which is superior for proposed HDD-PLB framework.

Comparative performance of TCBS and TSA for the enumeration of trh+ Vibrio parahaemolyticus by direct colony hybridization

Vibrio parahaemolyticus is one of the important foodborne pathogens is of public health concern due to the emergence of pandemic strains causing disease outbreaks worldwide. We evaluated the DNA based colony hybridization technique for the detection and enumeration of total and pathogenic V. parahaemolyticus from the bivalve shellfish, clam using non-radioactive, enzyme-labeled probe targeting the tlh and trh genes, respectively. The digoxigenin (DIG) labeled probes designed in this study showed 100% specificity by dot blot assay. Colony hybridization using DIG probes was performed using both non-selective, trypticase soy agar (TSA) and the selective medium, thiosulfate citrate bile salts sucrose (TCBS) agar. Of 32 clam samples analyzed, 71.88% had>10,000 V. parahaemolyticus cells/g in TSA whereas it was 18.75% in case of TCBS. All the samples showed the presence of total V. parahaemolyticus in TSA and 97% in the case of TCBS. Interestingly, results of the trh+V. parahaemolyticus samples were quite high while using TCBS plates (62.5%) as compared to TSA (43.75%). However, the cell numbers obtained from TSA were higher than from TCBS. Several yellow colonies on TCBS turned out to be V. parahaemolyticus using colony hybridization, which was further confirmed by PCR and sucrose utilization test. Colony hybridization using DIG-labeled probe was found to be highly sensitive and could differentiate and enumerate pathogenic and non-pathogenic strains of V. parahaemolyticus. Since traditional methods are not only labor-intensive and time-consuming but also less sensitive, colony hybridization using DIG-labeled probes would be a useful alternative for the enumeration of V. parahaemolyticus in naturally contaminated seafood.

A capacitor based fast I-V characteristics tester for photovoltaic arrays

In order to efficiently evaluate the operating status of photovoltaic (PV) arrays, a design of fast current-voltage (I-V) characteristic tester is proposed in this paper. The tester uses the dynamic capacitor charging method to quickly sweep I-V characteristic curves. Then, a new artificial bee colony and Nelder-Mead simplex (ABC-NMS) hybrid algorithm is used to extract parameters of the single diode model of PV arrays. The experimental results show that the tester can quickly measure high-quality I-V curves of PV array and achieve accurate model parameters extraction. In addition, the root mean square error (RMSE) of curve fitting can be used to effectively indicate the partial shading condition.

Music Theory, Cultural Transfer, and Colonial Hybridity

In this introductory essay, a number of cautionary reminders are suggested for any historian seeking to trace the reception of European music theory outside of its traditional borders. Using a range of examples from Medieval Arabic music theory, Jean-Philippe Rameau’s theory of harmony, and Schenkerian theory, it is shown that a global dissemination and absorption of music-theoretical ideas is rarely a straightforward process of import and export. Perspectives drawn from contemporary theories of cultural transfer and postcolonialism offer some suggestive ways to think about the migration of a music theory across cultures as a more dialogical process in which notions of hybridity and agency play important roles. In dieser Einleitung wird eine Reihe von Zusammenhangen aufgezeigt, die dort zur Zuruckhaltung mahnen sollen, wo Historiker*innen versuchen die Rezeption europaischer Musiktheorie auserhalb ihrer traditionellen Grenzen nachzuvollziehen. Es wird gezeigt, dass die globale Verbreitung und Rezeption musiktheoretischer Ideen selten als schlichte Import- oder Exportvorgange verstanden werden konnen, wie anhand von Beispielen aus der mittelalterlichen arabischen Musiktheorie, der Harmonielehre Jean-Philippe Rameaus und Heinrich Schenkers Theorie veranschaulicht wird. Perspektiven aus den Bereichen der Kulturtransferforschung und postkolonialer Forschung erlauben es, die transkulturelle Migration einer musikalischen Theorie als einen starker dialogischen Prozess zu verstehen, in dem die Phanomene der Hybriditat und der Handlungsmacht (agency) eine wichtige Rolle einnehmen.

Hibriditas Kolonial Dan Nilai Pendidikan Karakter Pada Novelet Dorodasih Karya Imam Budhi Santosa

This study aims to (1) describe and explain the colonial hybridity Dorodasih novella by Imam Budhi Santosa, and (2) to describe the value of character education at Dorodasih novella by Imam Budhi Santosa. This study used a qualitative descriptive method to describe the hybridity and the educational value of the character in the novella Dorodasih of Imam Budhi Santosa. The data in this study of words, phrases, sentences contained in Dorodasih novella by Imam Budhi Santosa, published by Reader Literature LKIS Yogyakarta. Data collection techniques used in this study is a non-interactive technique. Mechanical noninteractive done by intensive reading of the novella and make record actively with content analysis. The validity of the data used to use data triangulation to collect the same data. In a sense the same or similar data will be valid truth when used several different data sources. The conclusions from the results of this study as follows: (1) the existence of the colonial hybridity Dorodasih novella by Imam Budhi Santosa, and (2) the value of character education that existed at novelet Dorodasih is hard work . --- Abstract This study aims to (1) describe and explain the colonial hybridity Dorodasih novella by Imam Budhi Santosa, and (2) to describe the value of character education at Dorodasih novella by Imam Budhi Santosa. This study used a qualitative descriptive method to describe the hybridity and the educational value of the character in the novella Dorodasih of Imam Budhi Santosa. The data in this study of words, phrases, sentences contained in Dorodasih novella by Imam Budhi Santosa, published by Reader Literature LKIS Yogyakarta. Data collection techniques used in this study is a non-interactive technique. Mechanical noninteractive done by intensive reading of the novella and make record actively with content analysis. The validity of the data used to use data triangulation to collect the same data. In a sense the same or similar data will be valid truth when used several different data sources. The conclusions from the results of this study as follows: (1) the existence of the colonial hybridity Dorodasih novella by Imam Budhi Santosa, and (2) the value of character education that existed at novelet Dorodasih is hard work. DOI: 10.15408/al-turas.v23i1.4802

Hibriditas Kolonial Dan Nilai Pendidikan Karakter Pada Novelet Dorodasih Karya Imam Budhi Santosa

Abstract This study aims to (1) describe and explain the colonial hybridity Dorodasih novella by Imam Budhi Santosa, and (2) to describe the value of character education at Dorodasih novella by Imam Budhi Santosa. This study used a qualitative descriptive method to describe the hybridity and the educational value of the character in the novella Dorodasih of Imam Budhi Santosa. The data in this study of words, phrases, sentences contained in Dorodasih novella by Imam Budhi Santosa, published by Reader Literature LKIS Yogyakarta. Data collection techniques used in this study is a non-interactive technique. Mechanical noninteractive done by intensive reading of the novella and make record actively with content analysis. The validity of the data used to use data triangulation to collect the same data. In a sense the same or similar data will be valid truth when used several different data sources. The conclusions from the results of this study as follows: (1) the existence of the colonial hybridity Dorodasih novella by Imam Budhi Santosa, and (2) the value of character education that existed at novelet Dorodasih is hard work.---Abstract This study aims to (1) describe and explain the colonial hybridity Dorodasih novella by Imam Budhi Santosa, and (2) to describe the value of character education at Dorodasih novella by Imam Budhi Santosa. This study used a qualitative descriptive method to describe the hybridity and the educational value of the character in the novella Dorodasih of Imam Budhi Santosa. The data in this study of words, phrases, sentences contained in Dorodasih novella by Imam Budhi Santosa, published by Reader Literature LKIS Yogyakarta. Data collection techniques used in this study is a non-interactive technique. Mechanical noninteractive done by intensive reading of the novella and make record actively with content analysis. The validity of the data used to use data triangulation to collect the same data. In a sense the same or similar data will be valid truth when used several different data sources. The conclusions from the results of this study as follows: (1) the existence of the colonial hybridity Dorodasih novella by Imam Budhi Santosa, and (2) the value of character education that existed at novelet Dorodasih is hard work. DOI: 10.15408/al-turas.v23i1.4802

An Improved Particle Swarm Optimization Algorithm Using Eagle Strategy for Power Loss Minimization

The power loss in electrical power systems is an important issue. Many techniques are used to reduce active power losses in a power system where the controlling of reactive power is one of the methods for decreasing the losses in any power system. In this paper, an improved particle swarm optimization algorithm using eagle strategy (ESPSO) is proposed for solving reactive power optimization problem to minimize the power losses. All simulations and numerical analysis have been performed on IEEE 30-bus power system, IEEE 118-bus power system, and a real power distribution subsystem. Moreover, the proposed method is tested on some benchmark functions. Results obtained in this study are compared with commonly used algorithms: particle swarm optimization (PSO) algorithm, genetic algorithm (GA), artificial bee colony (ABC) algorithm, firefly algorithm (FA), differential evolution (DE), and hybrid genetic algorithm with particle swarm optimization (hGAPSO). Results obtained in all simulations and analysis show that the proposed method is superior and more effective compared to the other methods.

An improved particle swarm-ant colony hybrid algorithm for HMM training

The traditional parameter estimation methods of Hidden Markov Models (HMM) are easy to fall into local optimum, have higher requirements for initial parameter values and might result in over-coupling phenomena. In order to improve the robustness and identification performance of the model, a novel HMM parameter training method based on an improved particle swarm-ant colony algorithm (IPSAA) is presented. First, extremum disturbance is added into particle swarm optimisation algorithm (PSO) and parameters of ant colony algorithm (ACA) such as stimulating factor, volatilisation coefficients and pheromone are all improved adaptively. Second, the fitness function values of particles' history optimal solutions after PSO coarse search are used to adjust the initial pheromone distribution in fine search of ACA. Finally, Baum-Welch algorithm (B-W) is adopted to locally modify the approximate global optimal solution. The new algorithm not only solves the BW dependency on initial values and the trapped local optimum problem, but also makes full use of the global search ability of IPSAA and local development ability of B-W. The experimental results show that the system using the new algorithm is more efficient, more stable, and has better classification performance than that of traditional HMM training algorithm.

Serotypes, virulence markers and cell invasion ability of Shiga toxin-producing Escherichia coli strains isolated from healthy dairy cattle.

The occurrence of virulence markers, serotypes and invasive ability were investigated in Shiga toxin-producing Escherichia coli (STEC) isolated from faecal samples of healthy dairy cattle at Rio de Janeiro State, Brazil. From 1562 stx-positive faecal samples, 105 STEC strains were isolated by immuno-magnetic separation (IMS) or plating onto MacConkey agar (MC) followed by colony hybridisation. Fifty (47·6%) strains belonged to nine serotypes (O8:H19, O22:H8, O22:H16, O74:H42, O113:H21, O141:H21, O157:H7, O171:H2 and ONT:H21). The prevalent serotypes were O157:H7 (12·4%), O113:H21 (6·7%) and O8:H19 (5·7%). Virulence genes were identified by polymerase chain reaction (PCR). E-hlyA (77·1%) was the more prevalent virulence marker, followed by espP (64·8%), saa (39%), eae (24·8%) and astA (21·9%). All O157:H7 strains carried the γ (gamma) variant of the locus of enterocyte effacement (LEE) genes and the stx2c gene, while the stx1/stx2 genotype prevailed among the eae-negative strains. None of the eae-positive STEC produced the localized adherence (LA) phenotype in HEp-2 or Caco-2 cells. However, intimate attachment (judged by the fluorescent actin staining test) was detected in some eae-positive strains, both in HEp-2 (23·1%) and in Caco-2 cells (11·5%). Most strains (87·5%) showed 'peripheral association' (PA) adherence phenotype to undifferentiated Caco-2 cells. Twenty-five (92·6%) of 27 strains invaded Caco-2 cells. The highest average value of invasion (9·6%) was observed among the eae-negative bovine strains from serotypes described in human disease. Healthy dairy cattle is a reservoir of STEC carrying virulence genes and properties associated with human disease. Although reports of human disease associated with STEC are scarce in Brazil, the colonization of the animal reservoir by potentially pathogenic strains offers a significant risk to our population.