Wilhelm Alexander Tham

Prof. Dr. Wilhelm Alexander Tham


Research Focus & Metrics

Academic Career Length

21Years (2006-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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20 January 2014 in Epidemiology and Infection
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Journal Article
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GLG. Lopez-Valladares
G. Lopez-Valladares
WTWilhelm Alexander Tham
Wilhelm Alexander Tham
VPV. Singh Parihar
V. Singh Parihar
SHS. Helmersson
S. Helmersson
BAB. Andersson
B. Andersson
MDM.-L. Danielsson-Tham
M.-L. Danielsson-Tham
SUMMARY: Isolates ofListeria monocytogenes(n = 932) isolated in Sweden during 1958–2010 from human patients with invasive listeriosis were characterized by serotyping and pulsed-field gel electrophoresis (PFGE) (AscI). Of the 932 isolates, 183 different PFGE types were identified, of which 83 were each represented by only one isolate. In all, 483 serovar 1/2a isolates were distributed over 114 PFGE types; 90 serovar 1/2b isolates gave 32 PFGE types; 21 serovar 1/2c isolates gave nine PFGE types; three serovar 3b isolates gave one PFGE type; and, 335 serovar 4b isolates gave 31 PFGE types. During the 1980s in Sweden, several serovar 4b cases were associated with the consumption of European raw soft cheese. However, as cheese-production hygiene has improved, the number of 4b cases has decreased. Since 1996, serovar 1/2a has been the dominantL. monocytogenesserovar in human listeriosis in Sweden. Therefore, based on current serovars and PFGE types, an association between human cases of listeriosis and the consumption of vacuum-packed gravad and cold-smoked salmon is suggested.

2 February 2009 in Journal of Foodservice
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Journal Article
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IPInoka Priyadarshani Peiris
Inoka Priyadarshani Peiris
GLGloria Lopez‐Valladares
Gloria Lopez‐Valladares
VPVishal Singh Parihar
Vishal Singh Parihar
SHSeved Helmersson
Seved Helmersson
SBSukdevo Barbuddhe
Sukdevo Barbuddhe
MDMarie‐Louise Danielsson‐Tham
Marie‐Louise Danielsson‐Tham

17 November 2006 in Epidemiology and Infection
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Journal Article
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WTWilhelm Alexander Tham
Wilhelm Alexander Tham
GVG. Lopez Valladares
G. Lopez Valladares
SHS. Helmersson
S. Helmersson
AÖA. Österlund
A. Österlund
MDM.-L. Danielsson-Tham
M.-L. Danielsson-Tham
SUMMARY: Two variants ofListeria monocytogeneswere isolated from blood cultures from each of two patients with listeriosis. Each variant displayed a two-band difference in DNA profile from the other by pulsed-field gel electrophoresis. Although this difference in profile is insufficient to distinguish clearly between the variants, the possibility of co-infection with different strains ofL. monocytogenesneeds to be considered. We suggest that more than one colony should be selected for molecular typing to aid interpretation during investigation of the sources and routes ofListeriainfection.

1 September 2013 in Foodborne Pathogens and Disease
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Journal Article
Closed access
WTWilhelm Alexander Tham
Wilhelm Alexander Tham
GLGloria Lopez-Valladares
Gloria Lopez-Valladares
SHSeved Helmersson
Seved Helmersson
SWStefan Wennström
Stefan Wennström
AÖAnders Österlund
Anders Österlund
MDMarie-Louise Danielsson-Tham
Marie-Louise Danielsson-Tham
Isolates of Listeria monocytogenes saved from outbreaks of listeriosis, cases of sporadic listeriosis, and similar events do not always belong to a solitary genetic variant. Variants of the same strain may have evolved from a unique clone, and plasmid loss or gain and phage-mediated genetic changes are suggested as the main mechanism. Some of these reports are summarized in this short communication.

29 June 2026 in Acta Veterinaria Scandinavica
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Journal Article
Open access
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WTWilhelm Alexander Tham
Wilhelm Alexander Tham
HKHannu Korkeala
Hannu Korkeala
GVGloria Lopez Valladares
Gloria Lopez Valladares
MDMarie Louise Danielsson-Tham
Marie Louise Danielsson-Tham
The aim of the present study was to determine whether L. monocytogenes bacteria from an invasive case of listeriosis cultured in a BacT/ALERT FA bottle in 1999 have survived, and if so, whether their pulsed-field gel electrophoresis (PFGE) profiles have changed. In 2024, after more than 25 years in a refrigerator, L. monocytogenes was isolated in pure culture from the BacT/ALERT FA bottle. All 100 selected isolates showed the same by PFGE profile with the restriction enzyme Asc I as the L. monocytogenes isolates did in 1999. L. monocytogenes can apparently survive for a long time in a nutrient-poor environment, and this must be taken into account by the food industry. Persistence in clinical samples has rarely been reported; however, several authors report persistence of L. monocytogenes in the food industry, with bacteria ending up in final products.