SafePork 2011 196 back to index Proceedings - Posters back to index A retrospective analysis of Salmonella isolation trends from pigs in Great Britain since 1994, with special reference to monophasic S. Typhimurium and antimicrobial resistance trends D. Mueller-Doblies*, K. Speed, R. H. Davies Bacteriology Department, Animal Health and Veterinary Laboratories Agency Weybridge Woodham Lane, New Haw, Addlestone, Surrey, KT15 3NB, United Kingdom *corresponding author : doris.mueller-doblies@ahvla.gsi.gov.uk Abstract The numbers of Salmonella reports from pigs in Great Britain have reduced considerably since the mid- 1990s, when up to 384 positive epidemiological group reports (incidents) per year were recorded, and numbers have been relatively stable since 2003 with less than 200 incidents reported per year. S. Typhimurium has been the most common serovar throughout the study period (between 58 and 75% of incidents). S. Derby, which was the second most common serovar for many years, has shown a downward trend since 2007, accounting only for 5% of incidents in 2009. At the same time, monophasic strains of S. Typhimurium have been on the rise since 2006. S. 4,5,12:i:- went from 0% in 2005 up to 6.2% of incidents in 2009, whereas S. 4,12:i:-, after showing a small peak in 1997, has also increased since 2007 and accounted for 1.2% of incidents in 2009. Throughout the 1990s, the most commonly seen phage type among S. Typhimurium isolates was DT104, but numbers declined sharply from 1998 onwards. Since 2002, U288 has been the most commonly seen phagetype in S. Typhimurium with up to 67.7% of all S. Typhimurium incidents being U288. DT193 has been increasing since 2003, with up to 41.5% of S. Typhimurium incidents in 2008. At the same time as the number of DT193 incidents in S. Typhimurium increased, an increase in the number of monophasic strains of S. Typhimurium oc- curred, with the majority of those isolates being DT193. The percentage of S. Typhimurium isolates from pigs showing resistance to six or more antimicrobials has increased from 19.7% in 1995 to 47.6% in 2009, with a peak of 76.8% in 2007. Resistance of S. Typhimurium to compound sulphonamides, ampicillin, streptomycin and chloramphenicol increased considerably between 2002 and 2007, while resistance to tetracycline has been at a high level since the beginning of the study period. The most common resistance pattern observed in S. 4,5,12:i:- (ampicillin, streptomycin, compound sulphonamides, tetracycline) was seen in 72.7% of isolates in 2009. In species other than pigs, S. 4,5,12:i:- has, so far, shown a signifcant increase in cattle only, and the frst isolates from poultry were only reported in 2010. Introduction Human salmonellosis is one of the most common foodborne diseases in the UK, and contaminated pork may be an im- portant source of infection for humans. It has been estimated in various European countries that 10–20% of all cases of salmonellosis in humans are related to the consumption of pork (Borch et al., 1996; Berends et al., 1998; Steinbach & Hartung, 1999; EFSA, 2010). Pigs can be infected by several Salmonella serovars but symptoms are rarely seen, making infection diffcult to recognize, thus risking the spread of infection to the rest of the herd and causing Salmonella to enter the food chain. The majority of Salmonella serovars are biphasic and express two distinctive agellar phases but some isolates do not express either phase 1 or phase 2 agella and are therefore classed as monophasic. In recent years, such monophasic strains of S. Typhimurium (namely S. 4,5,12:i:- and S. 4,12:i:-) have been observed in several animal species including pigs. Material and Methods The Salmonella Unit at The Animal Health and Veterinary Laboratories Agency is the Salmonella Reference Laboratory for Veterinary Salmonellosis in the UK. The data for this study period was sourced from Salmonella surveillance data from Great Britain from 1994 to 2009. Characterisation of the Salmonella isolates in this study was done by serotyping according to the White-Kauffmann-LeMi-