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Atypical Actinobacillus pleuropneumoniae serotype 13 strains present in North America are described here for the first time. Different from serotype 13 strains described in Europe, North America strains are biotype I and antigenically related to both, serotypes 13 and 10. Chemical and structural analysis of the capsular polysaccharide (CPS) and lipopolysaccharide (LPS) of a representative strain revealed that the CPS is almost identical to that of the reference strain of serotype 13, having a slightly higher degree of glycose O-acetylation. However, it produces an O-PS within the LPS antigenically and structurally identical with that of the reference strain of A. pleuropneumoniae serotype 10. The O-PS was characterized as a homopolymer of 1,2 linked β-D-galactofuranosyl residues, a structure unrelated to that of the O-PS produced by the reference strain of serotype 13. Strains from Canada and United States are antigenically, phenotypically and genotypically similar. Animals infected by one of these strains induced antibodies that were detected by a LPS-based ELISA diagnostic test using either the homologous antigen or that of serotype 10. Based on the LPS and toxin profile, these strains might be misidentified as A. pleuropneumoniae serotype 10., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The aim of this study was to compare, by randomly amplified polymorphic DNA (RAPD), the diversity of Streptococcus suis serotypes 1/2 and 2 isolates recovered at slaughter houses from the tonsils of clinically healthy pigs. The pigs belonged to herds with or without clinical signs of S. suis disease. Overall, a low diversity was observed among isolates of serotype 1/2. A representative isolate recovered from a diseased animal presented a relatively high similarity (85%), with most isolates recovered from carrier pigs, from herds either with or without clinical signs of S. suis disease. For serotype 2 isolates, a relatively high degree of heterogeneity was observed in the whole population. Two subpopulations were observed for serotype 2 isolates, which arose from herds with clinical signs. Interestingly, the representative isolate coming from the diseased pig was included in a small closed cluster, with 2 isolates recovered from carrier pigs belonging to the same herd. On the other hand, most of the S. suis serotype 2 isolates originating from herds with no history of S. suis disease, were closely related (90% similarity). Furthermore, they presented different RAPD patterns from those originating from animals from the herd presenting S. suis clinical signs due to this serotype. Results suggest that, in the herds studied, clinical manifestations due to serotype 2 are probably related to the virulence of a specific isolate. Conversely, for the herd affected with serotype 1/2, clinical manifestations of the disease were more likely to be the result of inherent herd factors than the virulence of the specific isolate.

Isolation of specific serotypes of Streptococcus suis from the tonsils, nasal cavities, and genital tract is difficult, since low-pathogenic serotypes and untypeable strains also inhabit these sites. An immunomagnetic separation (IMS) technique for the selective isolation of S. suis serotypes 2 and 1/2 was standardized. Superparamagnetic polystyrene beads (immunomagnetic beads or IMB) were coated with either a purified monoclonal antibody (MAb) directed to a capsular sialic acid-containing epitope or purified rabbit immunoglobulin G (polyclonal antibody [PAb]), both specific for S. suis serotypes 2 and 1/2. The amount of antibodies required for optimum coating of the beads, the number of IMB required for optimum bacterial recovery, and the nonspecific carryover were considerably higher with the MAb-IMS technique than with the PAb-IMS technique. The sensitivity of the IMS technique was 10(1) CFU/0.1 g of tonsil. The presence of serotype 1/2 bacteria did not considerably affect the recovery rate of a serotype 2 strain and vice versa. To validate the technique, PAb-coated beads were used to study 192 tonsils from animals from S. suis serotype 2- or 1/2-infected herds. Results showed that significantly more positive tonsils were detected by the IMS technique than by the standard procedure. This method represents an innovative and highly sensitive approach for the isolation of S. suis serotypes 2 and 1/2 from carrier animals.

An immunomagnetic separation technique (IMS) for the selective isolation of Actinobacillus pleuropneumoniae serotype 1 was developed. Superparamagnetic polystyrene beads (immunomagnetic beads [IMBs]) were coated with purified rabbit immunoglobulin G specific for A. pleuropneumoniae serotype 1. The antibody concentration, the number of IMBs, the incubation time, and the temperature of incubation influenced the recovery of the target bacteria. The sensitivity of the IMS technique was 1,000-fold higher than that of direct culture. When tonsils from animals from infected herds were tested, significantly more positive tonsils were detected by the IMS technique (68%) than by the standard procedures (22%). The method represents an innovative and highly sensitive approach for the isolation of A. pleuropneumoniae from carrier animals.