Die komplette Dissertation im pdf-Format (4.022.867 Bytes):
The development of antimicrobial drug resistance during 1974 to 1995 of the
three most common Salmonella serovars S. enteritidis, S. typhimurium and S.
typhimurium O:5 negative is described. In general the resistance rate for
Salmonella is around 20%, peaking with 40% in 1990 when multiresistant S.
typhimurium O:5 negative DT 204 prevailed. In S. enteritidis the resistance
rate is comparably low (< 10%).
In order to gain more information on resistance in S. enteritidis, the
detailed phenotypic and genetic properties of 65 selected isolates were
investigated by genetic and molecular techniques.
It could be shown, that S. enteritidis isolates expressed resistance to
antibiotics which are commonly used in veterinary medicine, namely
tetracycline, ampicillin, chloramphenicol, kanamycin and gentamicin. The
resistance phenotypes turned out to be very stable and from the 65
investigated strains 50% were monoresistant, and 27.7% of them exhibited
resistance against tetracycline only. Another 50% of the strains were
multiresistant to 2 or more antimicrobial agents. 61% of them were resistant
against tetracycline and kanamycin.
Mating experiments were carried out, in order to detect the presence of
R-factors possessing transfer systems at 37°C and 22°C, reflecting conditions
in two habitats that Salmonella serovars accounter during their life-cycle.
High temperatures in the host and low in the environment.
83% (54) of all investigated strains transferred one or more resistances under
the mating conditions applied. The majority of 71% (46) transferred at 37°C
and 12% (8) of all strains transferred their resistances at 22°C
In order to determine a clonal structure among the strains, further strain-
differentiation was achieved by plasmid-profile-analysis and phagetyping. All
isolates carried one or more plasmids and the whole population showed a very
heterogeneous plasmid distribution. 69% carried the virulence plasmid pRQ29
and a 70-75 MD plasmid was present in 54% of the strains.
In conclusion the plasmid-profiling combined with the results of the
antibiotic resistance tests and phagetyping elucidated a very heterogeneous
population structure. The presence of clones was limited to only 6 strains.
This contrasts the results obtained with other multiresistant serotypes e.g.
the dominating multiresistant clone S. typhimurium DT104.
However, multiresistant S. enteritidis strains exist in Germany and selective
pressure could facilitate their spread. This imposes the danger, that a mainly
antibiotic sensitive S. enteritidis population might be substituted with
Since 1991 there has been an increase in the rate of Nitrofurantoin-resistance
in S. enteritidis from 0% in 1990 to 35% in 1995. 50% of the S. enteritidis
strains originated from poultry, and they showed a resistance level of 72%
against Nitrofurantoin. These strains appear to be epidemiologically related
and might be derived from a clonal spread of a single ancestor. Nevertheless
further molecular methods should be applied in order to determine the source
of these nitrofurantoin resistant strains.
600 Technik, Medizin, angewandte Wissenschaften::630 Landwirtschaft::630 Landwirtschaft und verwandte Bereiche
Genetische und molekularbiologische Untersuchungen zur Antibiotikaresistenz
bei Salmonella Enteritidis Isolaten der Jahre 1986-1995
Prof. Dr. R. Kroker
Univ.-Prof. Dr. H.M. Hafez
Genetic and molecular characterization of resistant S. enteritidis isolated
from 1986 to 1995 in Germany