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Infection and Immunity, August 2002, p. 4312-4322, Vol. 70, No. 8
0019-9567/02/$04.00+0 DOI: 10.1128/IAI.70.8.4312-4322.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Streptococcus suis Interactions with the Murine Macrophage Cell Line J774: Adhesion and Cytotoxicity
Mariela Segura and Marcelo Gottschalk*Groupe de Recherche sur les Maladies Infectieuses du Porc (GREMIP) and Canadian Research Network on Bacterial Pathogens of Swine, Faculté de médecine vétérinaire, Université de Montréal, St-Hyacinthe, Québec, Canada
Received 8 March 2002/ Returned for modification 18 April 2002/ Accepted 22 May 2002
Streptococcus suis capsular type 2 is an important etiological agent of swine meningitis, and it is also a zoonotic agent. Since one hypothesis of the pathogenesis of S. suis infection is that bacteria enter the bloodstream and invade the meninges and other tissues in close association with mononuclear phagocytes, the objective of the present study was to evaluate the capacity of S. suis type 2 to adhere to macrophages. An enzyme-linked immunosorbent assay technique was standardized to simply and accurately measure the rate of bacterial attachment to phagocytic cells. Results were confirmed by plate counting. Adhesion was dependent on bacterial concentration and incubation time and was not affected by cytochalasin pretreatment of macrophages. Inhibition studies showed that the sialic acid moiety of the S. suis capsule would be, at least in part, responsible for bacterial recognition by macrophages. Serum preopsonization of bacteria increased adhesion levels. Complement would be partially implicated in the serum-enhanced binding of S. suis to cells. Adhesion varied among different S. suis type 2 isolates. However, high bacterial concentrations of several isolates were cytotoxic for cells, and these cytotoxic effects correlated with suilysin production. Indeed, hemolytic strain supernatants, as well as purified suilysin, reproduced cytotoxic effects observed with live bacteria, and these effects were inhibited by cholesterol pretreatment. Bacterial adhesion and cytotoxicity were confirmed by scanning and transmission electron microscopy. We hypothesize that attachment of bacteria to phagocytes could play an important role in the pathogenesis of S. suis infection by allowing bacterial dissemination and causing a bacteremia and/or septicemia. This interaction could also be related to the activation of the host inflammatory response observed during meningitis.
* Corresponding author. Mailing address: GREMIP, Faculté de médecine vétérinaire, Université de Montréal, 3200 rue Sicotte, C.P. 5000, St-Hyacinthe, Québec, J2S 7C6, Canada. Phone: (450) 773-8521, ext. 8374. Fax: (450) 778-8108. E-mail: gottschm{at}medvet.umontreal.ca.
Infection and Immunity, August 2002, p. 4312-4322, Vol. 70, No. 8
0019-9567/02/$04.00+0 DOI: 10.1128/IAI.70.8.4312-4322.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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