Swine dysentery (SD) is an economically important disease of pigs worldwide, which results from infection with the anaerobic spirochaete Brachyspira hyodysenteriae (Taylor and Alexander 1971). Clinically the disease is characterised by a mucohaemorrhagic diarrhoea. Due to its severity and lack of vaccination antibiotics such as pleuromutilins, macrolides and lincosamides were widely used in the control of SD. However, treatment is increasingly hampered by a lowered susceptibility of field strains to antibiotics (Lobova and others 2004, Hidalgo and others 2011). Thus, antimicrobial susceptibility testing is a desirable step towards an improved treatment of SD. Unfortunately, there is no approved protocol provided by the Clinical Laboratory Standards Institute (CLSI). Alternatively, the agar dilution method that was mainly used to determine antimicrobial susceptibility of B hyodysenteriae isolates can be used as a reference method (Taylor 1976, Ronne and Szancer 1990, Karlsson and others 2002, 2003). Moreover, despite the fastidious and anaerobic character of B hyodysenteriae , a broth dilution assay was established, which makes a valid minimum inhibitory concentration (MIC) identification possible (Karlsson and others 2002). However, to date, no broth microdilution assay has been reported. Such a test, geared as closely as possible towards international standards such as CLSI, could be applied for valid MIC analyses and also …