An Update on Streptococcus Suis Identification

Streptococcus suis is a worldwide cause of a variety sular type 2 isolate was recovered in pure culture from of porcine infections. It has been isolated from cases lungs and kidneys of a 41⁄2-month-old aborted bovine of meningitis, bronchopneumonia, arthritis, pericarfetus and its placenta. This suggests that S. suis may ditis, endocarditis, polyserositis, septicemia, rhinitis, be pathogenic for more than 1 animal species. and abortion.20,22,24 Different alpha-hemolytic strepIn Canada, it was reported that 94% of 4-8-weektococci were ascribed to Lancefield groups R, S, RS, old clinically healthy piglets harbored S. suis in their and T in 1963.5 Other investigators working with capnasal cavities, and 79% of these isolates did not belong sulated streptococci similar to de Moor’s groups S and to the 9 capsular types.3 Recently, we demonstrated R realized that the polysaccharides involved in serothat almost 90% of these untypeable isolates belong to typing originated from the capsular material rather than only 4 of the new capsular types (types 17, 18, 19, and from the cell wall. They considered these isolates as a 21, unpublished data). Other investigators have atnew species (Streptococcus suis) within the Lancefield tributed the development of rhinitis4,7,22 to untypeable group D, with 2 capsular types: 1 and 2, respectively. S. suis isolates. At this time, it is not possible to know The de Moor’s group RS was also added as S. suis type whether any of the capsular types of S. suis belong to 1⁄2.26 In 1983, 6 new capsular types of S. suis origithe normal flora of the nasal cavity or whether they nating from diseased pigs were described. 20 In 1987 represent real pathogens. Of the new capsular types, the species was officially recognized, l4 but the authors types 9 and 22 are more frequently found in diseased demonstrated by DNA hybridization that S. suis was pigs than in healthy ones. An outbreak of S. suis type not closely related to group D streptococci. 9 infection recently occurred in swine in Canada? Despite the presence of 9 capsular types of S. suis, Although 22 of 23 capsular types of S. suis are present untypeable isolates were still frequently reported. These in North America, our studies revealed that almost isolates were recovered from diseased4,10,12,13,22,24,25 and 30% of isolates recovered from diseased pigs are still clinically healthy pigs.2,3,21 More recently, 14 new capuntypeable (unpublished data). sular types have been described.9 Some of the reference As the number of capsular types increases, serotypstrains originated from diseased pigs, whereas others ing becomes more complicated, and it could soon bewere from the nasal cavities of clinically healthy pigs. come limited to reference laboratories. Even biochemOne strain was isolated from a diseased calf (capsular ical identification, when used alone, can be misleading. type 20) and another from a human case of meningitis Thus, veterinary diagnostic laboratories face a difficult (capsular type 14). Isolates belonging to capsular type situation. There is an urgent need for a standardization 14 have recently been recovered from diseased pigs in of both the biochemical identification of S. suis and our laboratory as well as in Denmark and Belgium (Dr. the techniques for capsular typing. The purpose of this J. Henrichsen, personal communication, 1989). This paper is to summarize the knowledge of biochemical confirms that types other than capsular type 2 could characterization and serotyping of S. suis and to suggest be involved in a zoonosis.9 In addition to the bovine means to facilitate the proper identification of this incapsular type 20, several other S. suis isolates have fectious agent of growing importance. been recovered from ruminants.9,12 Capsular type 16 Streptococcus suis is a gram-positive coccus that ocwas recently isolated in our laboratory from lungs of curs singly, frequently in pairs, or occasionally in short a calf suffering from bronchopneumonia, and a capchains. The organism grows well in aerobiosis, but growth is often enhanced by microaerophilic condiFrom the Research Group in Swine Infectious Diseases, Faculty of Veterinary Medicine, University of Montreal, Saint-Hyacinthe, tions. The majority of strains are alpha-hemolytic on