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Title: The phenotypic and genotypic characterisation of Streptococcus suis from diseased pigs in Scotland
Author: MacLennan, Mairiead A.
ISNI:       0000 0001 3615 750X
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2006
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This work provides new information on the prevalence of the serotype of S. suis in Scotland and relates the serotype distribution to the population genetics of the organism. The 519 isolates included in the Study Group were gathered over a ten-year period, predominantly from diseased pigs examined during routine post mortems, as part of the disease surveillance remit of Scottish Agricultural College, Veterinary Services (SACVS). The phenotypic and genotypic characteristics of the strains are described, as well as their serotype prevalence.  The serotypes found in this Study Group included 1/2, 2, 3, 4, 7, 8, 9, 10, 12, 1/14, (generally known as serotype 1), 14, 15, 16, 21, 22, 24, 28, 31, 33 and 34.  The biochemical characterisation of the bacterial isolates, in the routine laboratory, remains the most common method of identification and in the case of S. suis can be so variable that the potential for misidentification exists.  I confirmed useful markers for identification of streptococci as S. suis as; negative Voges Proskauer (VP), negative, hydrolysis of hippuric acid (HIP), negative fermentation of ribose, arabinose and sorbitol, positive lactose fermentation, positive amygdalin (AMD), and positive for the enzyme leucine aminopeptidase (LAP).  However, no strong links could be made between these biochemical characteristics and the serotype of the isolates. Further, contrary to some published data; no strong links were made between the fermentation of raffinose and specific serotypes of S. suis. Serotyping provides some definition between strains.  Certain serotypes are always associated with disease (serotype 1/2) whilst others are rarely, if ever (serotype 22).  Other serotypes, serotype 2 in particular, produce both pathogenic and non-pathogenic strains.  An Outbreak Group provides strong evidence for a serotype switch during the course of an outbreak.  These 45 pathogenic, genetically indistinguishable strains were 50% serotype 2 and 50% serotype 1/2.  One particular genotype (ET-Sfi-1) is observed in several serotypes, further suggesting the occurrence of serotype switching. Molecular studies using pulsed field gel electrophoresis (PFGE) and amplified fragment length polymorphism (AFLP) demonstrated that S. suis is a widely diverse organism.  Within this diversity, a clonal complex was identified and named ET-SfiComplex A.  This complex constituted 36% of the Study Group and is commonly associated with disease in pigs.  ET-SfiComplex A includes all serotype 1/14 (known generally as serotype 1) and serotype 14 isolates as well as the majority of serotype 2 isolates.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available