A preliminary study of the molecular epidemiology of Brachyspira hyodysenteriae isolates in Australia

Abstract

Swine dysentery (SD) is a mucohaemorrhagic colitis of grower-finisher pigs. Affected pigs have faeces ranging from soft, yellow-grey to mucoid, bloody diarrhoea. Swine dysentery is one of the most economically significant enteric diseases of pigs in Australia due to its effect on growth rate, feed efficiency, mortality and the associated medication control costs. The classical causative agent is a strongly β-haemolytic anaerobic intestinal spirochaete Brachyspira hyodysenteriae. Diagnosis of SD requires bacterial isolation and (or) identification using polymerase chain reaction (PCR). A number of PCR methods have been described for identifying B. hyodysenteriae. In this study, a multiplex PCR for B. hyodysenteriae, B. pilosicoli, L. intracellularis and Salmonella spp. including primers described by Elder et al. (1997) was compared with the PCR targeting NADH oxidase (nox) as described by La et al. (2006). Multi-locus sequence typing (MLST) was used to determine the relatedness of the B. hyodysenteriae isolates (La et al. 2009). The hypothesis was that isolates that were test-negative using the multiplex PCR but test-positive using the simple PCR were related but different to those positive on both PCR tests.A total of 11 B. hyodysenteriae isolates from grower pigs from 11 farms having clinical signs of SD and collected over the period 2010-2014 was tested. Isolates were cultured to demonstrate pure cultures for MLST. The pigs originated from three genetic sources (Sources A, B and C). Isolates 1-3 were from three different farms supplied by Source A. Isolates 4, 5 and 6 were from three farms supplied by Source B. Isolates 7-11 were from five different farms supplied by Source C.The multiplex PCR detected six (55%) of the nox PCR positive isolates. There was no clear relationship between the enteric PCR positive and negative isolates (Fig. 1). Isolates from different farms that obtained pigs from the same source generally were closely related, with isolates 1-3