Almut Liesegang

Short Communication - Modified pulsed-field gel electrophoresis method for DNA degradation-sensitive Salmonella enterica and Escherichia coli strains

A number of S. enterica and E. coli strains appeared sensitive to a rapid DNA degradation during the course of PFGE pattern analysis. This kind of DNA degradation could not be stopped by intensive treatment with proteinase K, formalin treatment, or other modifications of the protocol for the isolation of intact chromosomal DNA. However, the application of 100 microM thiourea into the running buffer gave rise to clear-cut PFGE patterns and in turn to an overall typeability.

Clonal Relationship of Salmonella enterica Serovar Typhimurium Phage Type DT104 in Germany and Austria

A new epidemic clone of Salmonella enterica serovar Typhimurium designated definitive phage type (DT) 104 has been emerging since 1990 to become most common type among S. Typhimurium isolates in Germany and Austria. Molecular fingerprinting (PFGE-pattern, plasmid profiles, IS200 pattern, ribotype, ERIC-type, OMP and MLE patterns) revealed the majority of the DT104 isolates to have clonal identity; they were designated as type 1 (about 95%). Moreover, clonal type 1 of DT104 was found to occur in sensitive as well as in a range of multiply drug-resistant variants and in a variety of plasmid profile types (in particular with small cryptic plasmids in the range of 1.0 to 5.0 Md). Since the clonal type 1 of DT104 has been identified among isolates from other countries, too, including such from the United Kingdom, the United Arab Emirates, the Philippines, and the Netherlands, its pandemic spread in man indicates that the import/export of this pathogen continues. About 5% of the DT104 isolates have been identified as genetically diverse indicating the independent appearance of the same multiple drug resistance and phage pattern phenotype among different Salmonella ancestor strains.

Clonal diversity of Shiga toxin-producing Escherichia coli O103 : H2/H^- in Germany

Shiga toxin producing Escherichia coli O103:H2/H(-) belong to the third most frequently isolated EHEC serotypes in Germany following isolates of O157:H7/H(-) and O26:H11/H(-). A total of 145 respective E. coli 103 isolates from single cases of diarrhoea and haemolytic uremic syndrome (HUS) in 1997-2000 were characterised by a range of molecular subtyping methods (PFGE, P-gene profiling, ribotyping, electrotyping) and phage typing in order to analyse their genetic relatedness and the practicability for new epidemiological tracing back. All isolates cluster into a distinct EHEC subgroup and reveal a high clonal diversity together with a considerable stability. Since strains of this serotype rank up to the third most frequently isolated EHEC in Germany a large population of this serotype, and therefore, a great supply of such strains may exist in this country.

Clonal diversity of Shiga toxin-producing Escherichia coli O157:H7/H- in Germany — A ten-year study

Two hundred and ten E. coli O157:H7/H- strains isolated from single cases and outbreaks of diarrhoea and haemolytic uraemic syndrome (HUS) in Germany between 1988 and 1998 were characterised by a range of molecular subtyping methods and phage typing in order to analyse their clonal nature. A high clonal heterogeneity, together with a considerable clonal stability, has been identified among the bacterial isolates and no single clonal type appeared to be geographically dominant. It is recommended to apply pulsed-field gel electrophoresis (PFGE) together with P gene profile determination (number and genomic positions of lambdoid bacteriophages) as laboratory tools for an extended epidemiological surveillance of E. coli OOFF phage typing will remain helpful as a first line of analysis, particularly in outbreak situations.

Phage typing and PFGE pattern analysis as tools for epidemiological surveillance of Salmonella enterica serovar Bovismorbificans infections

Some years ago, an increase in the number of sporadic cases and outbreaks of salmonellosis due to S. enterica serovar Bovismorbificans was observed in several European countries including Finland, Sweden, England/Wales, Austria, and Germany. In order to understand the recent spread of this serovar and to trace the route of infection back to its source, it was considered necessary to subtype S. Bovismorbificans isolates. Using phage typing (newly described here) and molecular fingerprinting (PFGE-pattern, plasmid profiles and ribotype) the isolates of European origin could be subtyped and compared to S. Bovismorbificans isolates that originated in overseas countries such as Australia, Thailand, India, etc. where this serovar was isolated more frequently. Significant clonal diversity was identified but some of the clonal types of S. Bovismorbificans dominated the epidemics and single cases in Europe as well as in overseas countries. The clonal identity among these isolates indicates an international distribution, new sources of infection, and highlights the urgent requirement for standardized laboratory based surveillance networks (e.g. Enter-Net). Moreover, it is suggested that strains of S. Bovismorbificans will continue to be of concern in public health and that phage typing together with PFGE typing can be applied as reliable and rapid tools for their future monitoring.

Occurrence of Salmonella enterica serovar Dublin in Austria

SummaryIn Austria, Salmonella enterica serovar Dublin, a bovine-adapted serovar, rarely causes human infections. In the year 2000, Austria was within the European mean with an incidence of 0.1 per million inhabitants. Our data show that the vast majority of all Austrian serovar Dublin infections can be traced to two Tyrolian districts. This concentration of cases can be explained by a particularly traditional aspect of cattle farming in Tyrol, the alpine pasture. There is increased risk of cross-infection due to the communal keeping of animals from various farms. Infected cattle are a source of infection for people, and contagion usually occurs from eating beef and drinking cow’s milk. Using pulsed-field gel electrophoresis and automated ribotyping, 3 out of 5 available isolates from human infections could be traced to characteristic Tyrolian S. Dublin clones. Bacteriological screening of herds with a known history of S. Dublin infection would be a start to prevent future contamination of alpine pastures through latently infected cattle excreting potentially infectious feces. Bacteriological screening for fecal carriage before the return of cattle from pastures known to be connected with infections could prevent cross-contamination of large mixed herds.ZusammenfassungBei Salmonella enterica serovar Dublin handelt es sich um ein im hohen Maß auf das Rind adaptiertes Serovar, welches beim Menschen nur selten Infektionen verursacht. Mit 0,1 humanen Erkrankungen pro 1 Million Bevölkerung lag die Inzidenz humaner Erkrankungen im Jahr 2000 im europäischen Durchschnitt. Unsere epidemiologischen Untersuchen ergaben, daß der überwiegende Teil aller österreichischen Infektionen mit Serovar Dublin auf zwei Bezirke im Bundesland Tirol zurückgeführt werden kann. Diese ungewöhnliche Konzentration läßt sich mit einer Besonderheit der alpenländischen Landwirtschaft, der Almwirtschaft, erklären. Die gemeinsame Haltung von Tieren aus verschiedenen Beständen birgt ein erhöhtes Risiko von Kreuzinfektionen. Infizierte Rinder stellen dann die Infektionsquelle für den Menschen dar, wobei der Konsum von kontaminiertem Rindfleisch und der Genuß von unpasteurisierter Kuhmilch die wesentlichsten Infektionswege sind. DNA-Fingerprinting mittels Pulsed-Feld-Gelelektrophorese und automatisierter Ribotypisierung zeigte, daß 3 von 5 zur Verfügung stehenden Isolaten von humanen Erkrankungen einem charakteristischen Tiroler Salmonella enterica serovar Dublin Klon zuzuordnen sind. Ein jährliches bakteriologisches Screening von Kotproben der Rinder aus betroffenen Beständen vor Almauftrieb und Almabtrieb wäre ein erster Ansatz, um Kreuzinfektionen sowie Rekontaminationen der Sommerweiden zu verhindern.

Increased occurrence of KCN-resistant Salmonella strains

104 KCN-resistant Salmonella strains were detected among 1391 strains typed (7.4%) during the first 7 months in 1993. In particular Salmonella enterica strains of subspecies I isolated from humans and foods exhibited this character. Those KCN-resistant Salmonella strains did not belong to a special antigen formula. The second flagellar phase could not be detected in most of these strains. KCN resistance does not seem to be plasmid-encoded.