, 2010; Hu et al., 2010). Serotyping, a procedure that relies on the composition of capsular material, is an important

step in the identification of S. suis. While initially classified in the early 1960s under the Lancefield scheme (S, R, and RS), strains of S. suis have subsequently been classified into PI3K inhibitor serotype 1 (group S), serotype 2 (group R), and serotype 1/2 (RS) (Gottschalk et al., 2001). Currently, there are 35 serotypes of S. suis (1 to 34 and 1/2) (Messier et al., 2008). All serotypes are not responsible for serious diseases and pathogenicity may vary within the same serotype. Serotype 2 is most frequently associated with pathology (Gottschalk et al., 2001), although other serotypes are also the source of many infections (Tian et al., 2004; Costa et al., 2005; Zhang

et al., 2008). The existence of nontypeable isolates of S. suis has been reported (Marois et al., 2007; Wei et al., 2009). More specifically, Wei et al. (2009) characterized 407 strains of S. suis isolated from diseased pigs in China and recovered 5.4% of nontypeable isolates, while serotype 2 represented 43.2% of the isolates. In Canada, between 12% and 20% of strains recovered from diseased pigs are untypeable (Higgins & Gottschalk, 2001). In the present study, seven nontypeable strains selleck products of S. suis isolated from infected animals were characterized with regard to their cell surface properties and compared with serotype 2 strains. The S. suis strains used in this study and their origins are listed in Table 1. Bacteria were routinely grown aerobically in Todd Hewitt Broth (THB, BBL Microbiology Systems, Cockeysville, MA) without agitation at 37 °C. Bacteria used in the assays described below were harvested from overnight (16–18 h) cultures. Wells of a flat-bottomed microtitre plate (Nunc-Immuno® MaxiSorp; Nalge Nunc International, Rochester, NY) were filled with 100 μL of fibronectin (0.1 mg mL−1; Chemicon International, Danvers, MA) or bovine serum albumin (BSA) as a control (1 mg mL−1; Fisher Scientific, check Ottawa, ON, Canada), and the plate was incubated overnight at room temperature. The

protein solution was then removed by aspiration and 0.05% glutaraldehyde (100 μL) was subsequently added. After 45 min at room temperature, glutaraldehyde was removed and the wells were washed twice with distilled water. Cells of S. suis harvested from an overnight culture were suspended in 50 mmol L−1 phosphate-buffered saline (PBS; pH 7.2) to an OD660 nm of 1 and 100 μL was added to each well. The plate was incubated at 37 °C for 90 min under agitation. Unbound bacteria were then removed by aspiration and the wells were washed three times with PBS containing 0.01% Tween 20 to minimize nonspecific hydrophobic interactions. Adherent bacteria in the wells were fixed with 100 μL of methanol for 15 min, washed extensively with distilled water and then stained with 0.