STEC as a veterinary problem. Diagnostics and prophylaxis in animals.
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Animals↗
Biomedical subjects
Lothar H Wieler
Publications and source records attributed to Lothar H Wieler.
[Avian pathogenic Escherichia coli (APEC)].
Infections with avian pathogenic Escherichia coli (APEC) cause colibacillosis, an acute and mostly systemic disease resulting in significant economic losses in poultry industry worldwide. Avian colibacillosis is a complex syndrome characterized by multiple organ lesions with airsacculitis and associated pericarditis, perihepatitis and peritonitis being most typical. Environmental factors as well as the constitution of poultry or initial viral infections influence the outcome of APEC-infections. However, several challenge experiments in chickens proofed the role of virulent APEC strains as the single aetiological agent. Currently serotypes O1:K1, O2:K1 and O78:K80 are recognized as the most prevalent, however the number of published serotypes is increasing. In addition, single APEC isolates vary profoundly in virulence, and knowledge about the molecular basis of this variability is still scarce. Known virulence factors of APEC are adhesins (F1- and P-fimbriae), iron acquisition systems (aerobactin and yersiniabactin), hemolysins (hemolysinE and temperaturesensitive hemagglutinin), resistance to the bactericidal effects of serum and phagocytosis (outer membrane protein, iss protein, lipopolysaccharide, K/1)-capsule and colilcin production) as well as toxins and cytotoxins (heat stable toxin, cyto-/verotoxin and flagella toxin). Esperimental studies have shown that the respiratory tract, principally the gas-exchange region of the lung and the interstitium of the air sacs are the most important sites of entry for avian pathogenic E. coli. APEC strains adhere to the epithelial cells of air sacs presumably through F1-fimbriae. After colonization and multiplication the bacteria enter the bloodstream, and the temperature-sensitive hemagglutinin (tsh) seems to be important int his step. After invading the bloodstream APEC cause a septicemia resulting in massive lesins in multiple internal organs and in sudden death of the birds. The ability of the bacteria to acquire iron and the resistance to the bactericidal effects of serum, predominantly conferred by the increased serum survival (iss)--protein, enables APEC to multiply quickly in their hosts. Iss is regarded a specific genetic marker for avian pathogenic E. colistrains. A critical review of the literature published so far on APEC reveals, that these pathotypes are not defined appropriately. This findings urge investigations on the population structure of APEC, enabling the establishment of appropriate diagnostic tools and avoiding the obsolete use of serotyping for APEC diagnosis. So far more than 20 APEC strains have been investigated in animal experiments, explaining contrary published results. Thus, the lack of knowledge in pathogenicity and in immunity of APEC infections urges further experimental studies. As APEC share not only identical serotypes with human pathogens but also specific virulence factors, their zoonotic potential is under consideration.
Adhesins, Escherichia coli↗
[Mannheimia haemolytica and the pathogenesis of enzootic bronchopneumonia].
Mannheimia (M.) haemolytica (formerly Pasteurella [P.] haemolytica) is the primary aetiological agent of pneumonic pasteurellosis--one of the most important respiratory diseases in cattle and sheep. While bovine pneumonic pasteurellosis is regarded to be mainly caused by M. haemolytica serotype A1, and in Germany during the last years also by serotype A6, sheep can be infected by all serotypes although there is an increased prevalence of serotypes A2 and A5-7. The obligate pathogenicity of M. haemolytica is proven by isolation of pure cultures from pneumonic lungs as well as by infection studies. Knowledge about the virulence mechanisms of M. haemolytica and their molecular basis are fragmentary, most probably due to the complex gene regulation of virulence associated factors in lung tissues. This review summarizes the current literature covering virulence factors to substantiate a model of pathogenesis. After serotype A1 strains have colonized the bovine upper respiratory tract they replace other serotypes by mechanisms unknown to date. After fulminant proliferation in the upper respiratory tract the microorganisms colonize the lower respiratory tract, finally entering alveolar spaces. An inflammatory cascade is initiated by M. haemolytica LPS and Leukotoxin, causing activation of the complement system and release of cytokines. Pathognomonic for bovine pneumonic pasteurellosis is the strong influx of neutrophiles accompanied by accumulation of fibrin, finally causing necrosis of alveolar spaces. Depending on lesion size this fibronecrotizing pneumonia can result in death of the animals. In addition, possible protective antigens are discussed. There is still a great effort in the development of efficacious vaccines against pneumonic pasteurellosis in cattle and sheep caused by various M. haemolytica serotypes worldwide. The scarce knowledge concerning presence and distribution of virulence associated factors in M. haemolytica strains and their role in pathogenesis made it difficult to determine a suitable vaccine candidate in the past. In addition, there is lack of knowledge concerning the variability of virulence factors in individual isolates. Genome sequence analysis of M. haemolytica, enabling proteomics and transciptomics, hopefully will give new insight into the pathogenesis of pneumonic pasteurellosis.
Animals↗
[Plasticity of bacterial genomes: pathogenicity islands and the locus of enterocyte effacement (LEE)].
Many bacterial virulence attributes, like toxins, adhesins, invasins, iron uptake systems, are encoded within specific regions of the bacterial genome. These in size varying regions are termed pathogenicity islands (PAIs) since they confer pathogenic properties to the respective micro-organism. Per definition PAIs are exclusively found in pathogenic strains and are often inserted near transfer-RNA genes. Nevertheless, non-pathogenic bacteria also possess foreign DNA elements that confer advantageous features, leading to improved fitness. These additional DNA elements as well as PAIs are termed genomic islands and were acquired during bacterial evolution. Significant G+C content deviation in pathogenicity islands with respect to the rest of the genome, the presence of direct repeat sequences at the flanking regions, the presence of integrase gene determinants as other mobility features,the particular insertion site (tRNA gene) as well as the observed genetic instability suggests that pathogenicity islands were acquired by horizontal gene transfer. PAIs are the fascinating proof of the plasticity of bacterial genomes. PAIs were originally described in human pathogenic Escherichia (E.) coli strains. In the meantime PAIs have been found in various pathogenic bacteria of humans, animals and even plants. The Locus of Enterocyte Effacement (LEE) is one particular widely distributed PAI of E coli. In addition, it also confers pathogenicity to the related species Citrobacter (C.) rodentium and Escherichia (E.) alvei. The LEE is an important virulence feature of several animal pathogens. It is an obligate PAI of all animal and human enteropathogenic E. coli (EPEC), and most enterohaemorrhegic E. coli (EHEC) also harbor the LEE. The LEE encodes a type III secretion system, an adhesion (intimin) that mediates the intimate contact between the bacterium and the epithelial cell, as well as various proteins which are secreted via the type III secretion system. The LEE encoded virulence features are responsible for the formation of so called attaching and effacing (AE) lesions in the intestinal epithelium. Due to its wide distribution in animal pathogens, LEE encoded antigens are suitable vaccine antigens. Acquisition and structure of the LEE pathogenicity island is the crucial point of numerous investigations. However, the evolution of the LEE, its origin and further spread in E. coli, are far from being resolved.
Bacteria↗
[Risk assessment of bluetongue disease incursion into Germany using geographic information system (GIS)].
Using a geographic information system (GIS), by analysis of the relationship between the spatial distribution of cattle density and the risk factors temperature, altitude and rainfall, we defined geographical habitats enabling optimal development and competence of Culicoides spp. to transmit Bluetongue-Virus (BTV): Risk zones (low, high, highest risk) were identified mainly in Baden-Württemberg, Hessen and Rheinland-Pfalz if persistently infected ruminants are imported into these zones in summer (June to August mainly), based on the current climatic conditions, BTD outbreaks are considered a real possibility. Overwintering of the virus seems unlikely. However, global warming will lead to a steady increase of the size of the risk zones. In addition, the possibility of primary outbreaks increases. The reason for this is not only the expected northern shift of Culicoides imicola, but in addition an increasing vector competence of domestic Culicoides species. We therefore recommend the storage of vaccines as well as conducting ecological studies analysing the presence of Culicoides vectors. Using the data from these studies, it will be possible to produce updated quantitative risk assessment via GIS.
Animals↗
[Pasteurella: insights into the virulence determinants of a heterogenous bacterial type].
Pasteurella (P.) multocida is the causative agent of numerous economically relevant diseases worldwide. These are enzootic bronchopneumonia in cattle and sheep and hemorraghic septicemia in cattle and buffaloes, Rhinitis atrophicans in swine, snuffles in rabbit, and fowl cholera. All disease complexes are associated with certain capsular and somatic antigens. Even as human pathogen P. multocida is of increasing importance, causing wound infections, and even septicemia, meningitis, and endocarditis. Despite extensive research activities including the genome analysis of one fowl cholera isolate in the year 2001 there are a lot of open questions concerning the molecular pathogenic mechanisms. Problems encountered are the high antigenic variability and the wide host spectrum of P. multocida as well as different courses of infection. In consequence there are enormous difficulties in producing vaccines. Transcriptomics and proteomics hopefully will give new insight into the pathogenesis of P. multocida infections in different hosts. A frequent problem particular in classical diagnostic laboratories is the diagnosis of P. multocida and its differentiation from other P. species and Mannheimia (M.) haemolytica. The biochemical identification of P. multocida is not reliable due to variable phenotypical characteristics often caused by different culture conditions, and it is time consuming and cost-intensive. Extensive molecular biologic studies concerning the prevalence and distribution of virulence associated genes known so far in P. species, which will be described in detail in this paper, could contribute to the establishment of a diagnostic tool, such as a multiplex polymerase chain reaction, that would provide a cheap and time-saving identification and characterization of wildtype strains.
Animal Diseases↗
[Incidence and significance of treponemes in animals].
The genus Treponema consists of various species. Currently most of them are not cultivable because respective cultivation conditions are unknown. Therefore the biodiversity of treponemes was only appreciated recently by applying comparative 16S rRNA sequence analysis. Treponemes are mainly representatives of the gastrointestinal autochthonal flora, especially in termites, but they have also been described in swine and cattle. On the other hand treponemes are involved in different infectious diseases, the most well known being syphilis in humans or venereal spirochetosis in rabbits. Furthermore, treponemes are associated with several infectious periodontal diseases, e.g. gingivitis or periodontitis, where they can be detected regularly. Culture has not been successful for most of the oral treponemes, so the major part can only be identified by their 16S rRNA sequence. Similar to these oral disorders treponemes are also associated with digital dermatitis (DD), a chronic inflammatory disease of the bovine skin, where different treponemal phylotypes were found in large numbers. Treponema brennaborense was first identified and isolated in DD biopsies. Unravelling the pathogenic potential and aetiological significance of treponemes in chronic infectious diseases like peridontitis or DD remains a costly task. Although treponemes can be frequently detected in such lesions, it is often unclear to what extent treponemes are involved in pathogenesis of these diseases. The possession of various virulence features like high motility, the ability to adhere and invade as well as to cause cytopathic effects in eukaryotic cells are highly indicative of the aetiological relevance of treponemes.
Animals↗
Racing, ornamental and city pigeons carry shiga toxin producing Escherichia coli (STEC) with different Shiga toxin subtypes, urging further analysis of their epidemiological role in the spread of STEC.
Pigeons are known to shed zoonotic pathogens. Therefore, in this study a total of 366 droppings from pigeons were analysed using PCR and DNA-DNA-hybridization for Shiga toxin producing E. coli (STEC). Specimens were collected from three different groups of pigeons: 247 collective and 3 individual droppings from racing pigeons, 26 collective and 40 individual from ornamental pigeons as well as 50 collective droppings from city pigeons. Initial screening experiments revealed a total 245 (66.9%) droppings to be Shiga toxin gene positive. Of these 36% were positive for stx1, 9% for stx2 and 37% for stx2f. Prevalence significantly (p < 0.001) differed in regard to the pigeon groups examined. Droppings from racing pigeons showed prevalence of 45.6% for stx1, 3.2% for stx2, and 33.2% for stx2f, while the distribution of stx-positive specimens was more even in ornamental pigeons (15% stx1, 27% stx2, and 26% stx2f). In specimens from city pigeons, stx2f was found to be most prevalent with 76% (2% stx1, 16% stx2). In 161 samples, stx genes were detected by PCR as well as DNA-DNA-hybridization. From these 161 samples, 20 were randomly chosen for isolation of STEC. A total of 27 STEC strains were isolated from 13 of these 20 samples. Six of the STEC were positive for stx1, 21 harbored stx2f. Further typing for virulence factor genes revealed the existence of eae in 4 of the 6 stx1-positive strains, as well as in 19 of the 21 stx2f-positive strains. eae is known to be crucially involved in the ability of E. coli strains to cause the "attaching and effacing" lesion in the gut, while stx2fSTEC are assumed to be host specific for pigeons. Here we report the first description of stx1- and eae-positive STEC strains in pigeons from Germany, especially in racing and ornamental pigeons. Taking into account the close contact between fanciers and pigeons, these findings warrant a more critical appraisal of these zoonotic pathogens in pigeons.
Animals↗
[Methicillin-resistant Staphylococcus aureus (MRSA) in veterinary medicine: a "new emerging pathogen"?].
The problem of nosocomial infections is of increasing importance in veterinary medicine. As an example, this review summarizes current knowledge regarding methicillin-resistant Staphylococcus aureus (MRSA) as a typical example, as these pathogens are the most important agents of nosocomial infections in human medicine worldwide and are being increasingly reported in veterinary medicine. MRSA are classified by their ability to be resistant against oxacillin/methicillin, this feature being confered by mecA, a gene which was acquired by horizontal gene transfer of the staphylococcal gene cassette (SCCmec). It is this genetic information that enables MRSA to be resistant against all penicillins, cehalosporins and carbapenems. In addition, MRSA are often resistant against a variety of other antiinfectives, i.e. aminoglycosides, macrolides, lincosamide, streptomycins, tetracyclin, chloramphenicol, but also against fluorquinolones and rifampicin. Presumably, these highly adapted strains are particularly able to acquire resistance genes located on plasmids or transposons. They are also able to develop point mutations, further leading to resistant phenotypes. If these pathogens are leading to infectious diseases, veterinarians may be confronted with a worst-case scenario, being left without any antiinfective therapeutic. As Staphylococcus aureus is highly tenacid, professional hygiene management is of utmost importance. The increasing number of published sporadic MRSA infections, MRSA-infectious diseases as well as MRSA outbreaks in veterinary medicine justifies their recognition as a "New Emerging Pathogen". So far, horses and dogs are mostly affected by MRSA. Although transmission between humans and animals has been reported occasionally, the sources, routes of transmission or the epidemiological relevance of MRSA infections in animals are far from being understood. Therefore, epidemiological investigations utilizing molecular typing tools are mandatory. Typing tools like multilocus-sequence-typing (MLST), pulsefield-gelelectrophoresis (PFGE), sequence analysis of the gene encoding protein A (spa-typing) as well as SCCmec-typing are all at hand.
Animals↗