Citation
Ooi, Wai Ling
(2000)
Molecular Characterization of Escherichia Coli Serotype 0157:H7 Utilising Contemporary PCR Techniques and PFGE-Genotyping.
Masters thesis, Universiti Putra Malaysia.
Abstract
A total of 28 strains of Escherichia coli 0157:H7 which were originally
isolated from beef and chicken samples from various locations in Malaysia were
examined and further characterized by various molecular techniques. These
techniques include the plasmid profiling, antibiotic resistance, multiplex PeR, RAPD
pattern, PFGE, and also ERIC fingerprinting. All the strains utilized in this study were
found to exhibit a multiple antibiotics resistance pattern to the fourteen antibiotics [
bacitracin (100%), penicillin G (100%), sulphafurazole (82%), ampicillin (61%),
cephalothin (57%), carbenicillin (50%), ceftazidime (39%), erythromycin (32%),
streptomycin (18%), nalidixic acid (14%), chloramphenicol (11%), kanamycin (7%),
latamoxef (7%), and tetracycline (7%)] used. The plasmid profile obtained ranged in
sizes from 3.23 MDa to 60 MDa. Development of a PCR identification assay for
Escherichia coli 0157:H7 is based on the isolation of species-specific DNA. Two
types of specific primer encoding the Shiga-Like Toxin gene, the SLnI (584 bp) gene
and SLn (348 bp) were utilized in the multiplex PCR assay. Analysis carried out demonstrated that Escherichia coli 0157:H7 strains were positive for the presence of
single SLm gene (17.9 %) or both the SLlI and SLlII genes (82.1%). Three 50%
G+C contents 10-mer random primers, the Gen 1-50-01 (5'-GTGCAATGAG-3'), Gen
1-50-06 (5'-AGGTTCTAGC-3'), and Gen 1-50-09 (5'-AGAAGCGATG-3') were
chosen after screening through ten random primers. In PFGE technique carried out,
two kinds of restriction enzymes, the SpeI (5'-A-l,CTAGT-3') and XbaI (5'T
-l,CTAGA-3') were used to check for the in-situ DNA digestion pattern due to their
inherit advantages of the short sequence of these enzymes. Both the RAPD
polymorphism pattern and the PFGE profile obtained showed a significant
discriminatory fingerprinting among the 28 isolates under studied. A respective
dendrogram was constructed from the binary data matrix obtained from the RAPD,
PFGE and ERIC fingerprints to compare the diversity relationship among the 28
isolates. All the dendrograms were constructed utilising the RAPDistance software
package based on the data retrieved from the presence or absence of banding pattern.
ERIC genotyping technique was used as an additional molecular typing method to
further assists in the molecular characterization of the Escherichia coli 0157:H7.
Interestingly, all the three molecular techniques of RAPD, PFGE, and ERIC
genotyping showed a significant correlation whereby the first 14 and the second 14
isolates of Escherichia coli 0157:H7 used in this study showed a closer relationship in
the respective cluster groups as shown in the constructed dendrograms. From the
overall results obtained both the RAPD and PFGE analysis showed greater
discriminatory power compared to the other phenotypic and molecular
characterization techniques used in this study. Our results demonstrate that the
plasmid profiling, multiplex PCR, RAPD-PCR fingerprinting, PFGE and ERIC
profiling methods are able to act as one of the most appropriate and suitable analysistools for a rapid and reliable molecular typing and identification of Escherichia coli 0157:H7.
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