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|Title: ||Differentiation of selected Salmonella Serovars in Malaysia by Macrorestriction analysis, plasmid profiling and antimicrobial susceptibility testing|
|Authors: ||Lai, Kin Seng|
Antimicrobial Susceptibility Testing
|Issue Date: ||2009 |
|Publisher: ||University Malaya|
|Abstract: ||Seven hundred and six Salmonella enterica strains from nine serotypes namely Salmonella Agona, Albany, Bareilly, Corvallis, Kentucky, Matopeni, Muenchen, Typhi, and Virchow were included into this study. Strains have been subjected to phenotyping (Antibiotic Susceptibility Testing) and genotyping (plasmid profiling and Pulsed-Field
Gel Electropheresis) methods. Serotyping was used as a method for reconfirming the identity of strains whenever in doubt. Strains were isolated from various sources from humans, foods and environmental samples. Majority of the strains were isolated from
stool samples. However, a handful of strains had also been isolated from cerebrospinal fluid (CSF), urine, wound, sputum and blood samples.
In this study, PFGE was able to highlight strains that have been wrongly serotyped. For example, 169 strains which were all serotyped as S. Corvallis were separated into S. Corvallis (n=83) and S. Albany (n=86) as Pulsed-Field Profiles (PFPs)
of the two serotypes were of vast difference.
Geographical association of certain serotypes was observed. For example, S.
Albany, S. Bareilly, S. Matopeni, and S. Muenchen were mainly found in Kuala Lumpur
while S. Typhi was obviously more prevalent in Kelantan. A higher incidence of salmonellosis was recorded for patients from 1 month to 7 years old in infections caused by S. Agona, S. Albany, S. Bareilly, S. Corvallis, S. Matopeni, S. Muenchen and S. Typhi.
Different serotypes were found to display different resistance phenotypes. For example, all the S. Muenchen and S. Virchow strains were resistant to tetracycline. Most of the S. Albany strains exhibited multidrug-resistant profiles which were co-resistant to ampicillin, chloramphenicol, co-trimozaxole, kanamycin, nalidixic acid, sulphonamides, streptomycin, tetracycline and trimethoprim. Majority of S. Corvallis strains were only resistant to treptomycin and tetracycline. Multidrug resistant phenomenon was observed for S. Albany, S. Kentucky and S. Typhi while S. Matopeni is a drug susceptible serotype. Two S. Agona strains were resistant to ciprofloxacin and ceftriaxone, individually and this is the first reporting in Malaysia.
Plasmid profiling presents serious limitations as it was not able to differentiate most of the strains as not all strains, of particular S. Agona, S. Albany, S. Matopeni and S. Virchow, harbour plasmid. However, all the S. Muenchen strains harboured plasmid and plasmid profiling is applicable for differentiating S. Muenchen strains. Plasmid harbouring strains were varied in the number of plasmids and molecular weight. Common plasmids were observed in S. Corvallis and S. Muenchen.
PFGE was used to investigate the extent of genetic diversity in Salmonella serotypes. Three restriction enzymes (AvrII, SpeI and XbaI) were used for typing S. Albany, Corvallis, Kentucky, Matopeni, Muenchen, and Virchow while S. Agona, Bareilly, and Typhi were only analyzed using XbaI. This is because XbaI was more discriminative and cost effective.
PFGE was able to differentiate outbreak related strains from sporadic strains. PFGE revealed that many outbreaks might have gone undetected. For example, 12 S. Kentucky strains (SKE 5 to SKE 16) which were obviously originated from a common source was being over looked. Strains from a single outbreak could exhibit 2-6 PFPs with 1-9 bands difference as exemplified by a S. Typhi Bachok outbreak in 2003.
Strains from different serotypes displayed different degrees of heterogeneity. For example, PFPs of S. Typhi strains were highly diverse while many conserved restriction fragments were observed in S. Corvallis strains. Dual infections of a single patient with different strains or serotypes either from the same site or different sites were observed exemplified by S. Matopeni (SMP 9 and SMP 10) and S. Typhi (STP 125 and STP 127).
Except for S. Corvallis, PFGE has been proven to be more discriminative than plasmid profiling and antimicrobial susceptibility testing. Strains with a common PFP were found to have more than 1 phage type or plasmid profiles and vice versa. Many conserved fragments were observed among strains of the same serotype resulting in clustering of strains of the same serotype. It was clear that a PFP pattern is highly specific for a Salmonella serotype. In short, PFGE has been proved to be useful for typing Salmonella strains and delineating outbreak related strains from sporadic cases. PFPs generated are serotype specific.|
|Description: ||Dissertation (M.C.S.) -- Faculty of Science, University of Malaya, 2009.|
|Appears in Collections:||Masters Dissertations : Science|