Jörg Hacker

Properties of Escherichia coli strains of serotype O6.

SummaryEscherichia coli isolates of serotype O6 show a broad spectrum of virulence: virulent strains often cause urinary tract infections; other strains are considered nonpathogenic. In order to analyze the properties ofE. coli O6 strains, different phenotypic and genotypic test systems were used. Our data indicate that O6 strains represent a rather heterogenous group of bacteria, which differ in the genotypic presence as well as in the phenotypic expression of virulence factors. In contrast to the isolates 536 (O6:K15) and RZ 475 (O6:K5) the strain DSM 6601, belonging to serotype O6:K5:H1, produces neither toxins nor mannose-resistant hemagglutinating (MRHA) adhesins. However, the strain possesses chromosomally located gene clusters coding for F1C (foc) and type I fimbriae (fim). In addition, the strain secretes the iron-uptake substances aerobactin and enterobactin and produces at least one microcin. The strain is serum-sensitive and is less virulent inin vivo animal tests.ZusammenfassungEscherichia coli-Isolate des Serotyps O6 zeigen ein breites Virulenzspektrum. Virulente Isolate sind häufig Ursache von Infektionen des Urogenitaltrakts (UTI), andere Stämme werden als apathogen bezeichnet. Zur Untersuchung der Eigenschaften derE. coli O6-Stämme wurden verschiedene phänotypische und genotypische Testsysteme herangezogen. Die Daten belegen, daß es sich bei den O6-Stämmen um eine sehr heterogene Stammgruppe handelt, die sich hinsichtlich des Vorkommens und der Expression von Virulenzfaktoren unterscheidet. Im Gegensatz zu den Stämmen 536 (O6:K15) und RZ 475 (O6:K5) ist der Stamm DSM 6601 (O6:K5:H1) nicht in der Lage, Toxine oder Mannose-resistent hämagglutinierende (MRHA) Adhäsine zu produzieren, er besitzt jedoch chromosomal kodierte F1C- (foc) und ein Typ I-Fimbrien (fim) Gencluster. Zusätzlich produziert der Stamm die Eisenaufnahmesysteme Aerobaktin und Enterobaktin sowie mindestens ein Microcin. Der Stamm ist serumsensitiv und ist inin vivo Tiermodellen wenig virulent.

Genome dynamics and its impact on evolution of Escherichia coli.

The Escherichia coli genome consists of a conserved part, the so-called core genome, which encodes essential cellular functions and of a flexible, strain-specific part. Genes that belong to the flexible genome code for factors involved in bacterial fitness and adaptation to different environments. Adaptation includes increase in fitness and colonization capacity. Pathogenic as well as non-pathogenic bacteria carry mobile and accessory genetic elements such as plasmids, bacteriophages, genomic islands and others, which code for functions required for proper adaptation. Escherichia coli is a very good example to study the interdependency of genome architecture and lifestyle of bacteria. Thus, these species include pathogenic variants as well as commensal bacteria adapted to different host organisms. In Escherichia coli, various genetic elements encode for pathogenicity factors as well as factors, which increase the fitness of non-pathogenic bacteria. The processes of genome dynamics, such as gene transfer, genome reduction, rearrangements as well as point mutations contribute to the adaptation of the bacteria into particular environments. Using Escherichia coli model organisms, such as uropathogenic strain 536 or commensal strain Nissle 1917, we studied mechanisms of genome dynamics and discuss these processes in the light of the evolution of microbes.