Longitudinal study of an Australian pig farm infected with monophasic Salmonella Typhimurium-like PT193 (1,4,,12:i:- PT193) using MLVA
An Australian weaner-to-finish pig herd with a history of entrenched Salmonella infection (>10 months in duration) was sampled on 5 occasions over a 15 month period commencing in 2011. On each occasion, either 12 or 18 individual pen faecal samples were collected from pigs between 6 weeks and 22 weeks of age (n=71). From the Salmonella positive samples (n=42), a total of 346 isolates were further processed (up to 10 colony picks per sample). All of the 123 isolates typed were identified as monophasic S. Typhimuriumlike PT193 (mSTm193). Results of antibiotic sensitivity testing found 336 of 346 isolates were resistant to ampicillin, streptomycin, sulphathiozole and tetracycline (ASSuT). In addition, all 346 isolates were examined by MLVA and 13 different closely-related MLVA profiles were identified. Only 2 MLVA profiles persisted throughout the 15 month study. This study is the first report of monophasic S. Typhimurium-like PT193, its persistence and associated clinical disease in an Australian pig herd.