dc.contributor.author
Muschkowitz, Christine
dc.date.accessioned
2018-06-07T15:17:32Z
dc.date.available
2000-12-14T00:00:00.649Z
dc.identifier.uri
https://refubium.fu-berlin.de/handle/fub188/854
dc.identifier.uri
http://dx.doi.org/10.17169/refubium-5056
dc.description
Die komplette Dissertation im pdf-Format :
diss.pdf
dc.description.abstract
Food products are subject to various influencing factors possibly leading to a
microbial contamination during production, treatment and entry into
circulation. A possible ensuing germ multiplication within the food product
involves a high risk of food poisoning or food perishing.
Of great importance for germ multiplication - during which log phase
generation time can be determined - are milieu conditions such as temperature
and pH-value. An accumulation of bacteria and/or their toxins can be prevented
by appropriate manipulation of milieu conditions. To achieve this, increased
measurements, for example of the pH-value, temperature or temperature-
variation, are carried out within the framework of quality assurance systems
(HACCP).
It is essential to have exact knowledge of the breeding and multiplication
behaviour of microbes in order to arrange pH-value / temperature /
temperature-variation parameters effectively and / or to allow predictions of
multiplication or of stagnation in the breeding of microorganisms (and finally
to allow predictions as to how long food can be safely kept [predictive
microbiology]).
The speed at which multiplication takes place is manifested by the generation
time. The international literature on aspects of growth and multiplication of
bacteria as well as on generation time and milieu conditions has been
collected and analysed in the literature review of the present study. It is
evident that the information on generation time of microorganisms so far been
available is still insufficient because of methodical problems.
Efforts to complete data material have only been made in the 1990s, and were
facilitated by the use of rapid new methods amongst which impedance
measurement has proved to be especially suitable.
Impedance measurement offers the possibility of quickly and effectively
determining generation times indirectly under various conditions and in
greater scales.
Previous culture methods involved determination of germ counts and were
therefore costly as far as time and materials were concerned. Impedance
measurement measures the change of conductivity (impedance) within 2 samples
with differing germ numbers. Generation time is determined on the basis of the
difference of the initial germ numbers in proportion to the difference of the
impedimetrically determined detection time.
Within the framework of this project, generation intervals of 30 different
strains of food-hygienically relevant Enterobacteriaceae-species and -genera
were determined. The model strains belonged to 10 genera and differed in their
characteristics and in their origins.
The importance of these microbes was explained in the literature review, in
which special attention was given to the clinical and epizootiological factors
of Enterobacteriaceae-infections and -intoxications in humans as well as the
possibility of perishability caused by these germs. Various illnesses caused
by these bacteria in humans and animals have also been listed.
The aim of the experiments was the determination of generation times of
Enterobacteriaceae in relation to different milieu conditions (with
temperatures ranging from 12°C to 40°C and pH-values between 5.0 and 7.3).
In view of the generation intervals of the examined genera it was essential to
check to what extent generation intervals differed between the strains of one
species or between the species of one genus, especially at low temperatures.
Clear relations could be established between the length of generation time and
temperature. Within the examined temperature sector it was ascertained that
the mean of the generation times of the model strains (except the Yersinia
spp. strain) was, as expected, shortest with 22 min at 35°C and 37°C
respectively and grew steadily with the deviation of temperature from the
optimum.
Under favourable milieu conditions (temperatures from 30°C to 37°C, pH-value
from 6.0 to 7.3) the generation times of the model strains were almost
homogenous.
Only temperatures, especially those under 25°C, and acid initial pH-values
such as pH 5.0 and partly even pH 5.5 caused a slow in growth and
multiplication processes.
With the reduction of incubation temperatures, the generation times of the
model strains grew disproportionally. Generation time at 20°C was triple of
that at 37°C, increasing at 18°C to quadruple, at 15°C to six-fold and at 12°C
to nine-fold.
Below 12°C an impedimetric determination of generation time was only possible
with a few of the strains and over a considerable period of time.
Temperatures under 15°C or a pH-value of 5.0 (or considered together a
temperature ? 20°C in interaction with a pH of ? 5.5) lead to a considerable
slowing down of growth and multiplication processes.
Upon evaluation of the results, it was conspicuous that the majority of the
generation times of the examined Enterobacteriaceae-strains were almost
identical, but that the Yersinia showed significally longer generation
intervals and therefore had to be analysed separately.
Under unfavourable milieu conditions, the mean variation of results increased,
whereby for example, the genera Salmonella and Shigella were more restricted
in their speed of growth and multiplication, their generation time increasing
in contrast to the other genera.
The acquired results complete and broaden the knowledge of multiplication
speed of microbes, especially those from the Enterobacteriaceae-family. These
results can contribute to a better assessment of possible hazards to the human
health and to the minimization of food perishing.
en
dc.rights.uri
http://www.fu-berlin.de/sites/refubium/rechtliches/Nutzungsbedingungen
dc.subject
food-microbiology
dc.subject.ddc
600 Technik, Medizin, angewandte Wissenschaften::630 Landwirtschaft::630 Landwirtschaft und verwandte Bereiche
dc.title
Impedimetrische Bestimmung von Generationszeiten bei Stämmen
lebensmittelhygienisch relevanter Enterobacteriaceaespezies und -genera
dc.contributor.firstReferee
Priv.-Doz. Dr. Th. Bergann
dc.contributor.furtherReferee
Univ.-Prof. Dr. K. Fehlhaber
dc.contributor.furtherReferee
Univ.-Prof. Dr. R. Staufenbiel
dc.date.accepted
1998-01-30
dc.date.embargoEnd
2001-02-06
dc.identifier.urn
urn:nbn:de:kobv:188-1998000722
dc.title.subtitle
Koadsorption von K und CO auf Pt(111); Li, Na, K auf Pt111); N auf Cu(110)
sowie Untersuchungen von der reinen Ga(001)-Oberfläche
dc.title.translated
Impedimetric determination of generation times of strains of food-hygienically
relevant Enterobacteriaceae-species and -genera
en
dc.title.translatedsubtitle
Investigation of the Coadsorption of K and CO on Pt(111); Li, Na, K on
Pt(111);N on Cu(110) as well the clean Ga(001)-surface
en
refubium.affiliation
Veterinärmedizin
de
refubium.mycore.fudocsId
FUDISS_thesis_000000000017
refubium.mycore.transfer
http://www.diss.fu-berlin.de/1998/72/
refubium.mycore.derivateId
FUDISS_derivate_000000000017
dcterms.accessRights.dnb
free
dcterms.accessRights.openaire
open access