Biological Properties of the Encapsulated Staphylococcus aureus M

Abstract

Strain M, classified as a Staphylococcus aureus, behaves like the other rare encapsulated staphylococcal strains. It was clumping-factor negative, grew in diffuse-type colonies in serum-soft agar, and produced rapidly fatal disease in mice. Strain M was highly resistant to phagocytosis by human or mouse leukocytes and required both specific antibody and heat-labile serum factor(s) for efficient ingestion by human polymorphonuclear leukocytes. Electron micrographs confirmed the presence of a large capsule. Agglutination studies, active or passive mouse protection experiments, and opsonic studies revealed that strain M represents a new, immunologically distinct strain of encapsulated staphylococcus. Strain M differs from other known encapsulated staphylococci in several other respects: its cellular and colonial morphology is atypical; its LD50 in the mouse peritoneal model is 100 times less than that of other mouse lethal strains; it is poorly opsonized by normal human serum; and, finally, it possesses an unusually large capsule as seen in electron micrographs. MATERIALS AND METHODS Cultures. Strain M. This encapsulated strain was isolated from a human infection in 1962 and has been described by Scott (20). The organism (NCTC 10649) was obtained from the National Collection of Type J. Bacteriol, in press). Smith diffuse. This variant has been previously described and has been used extensively as the prototype of an encapsulated mouse-virulent staphylococcus in this laboratory (9). T mutant. This is a mutant of S. aureus H possessing an additional surface polysaccharide antigen (24). The organism was kindly supplied by J. T. Park, Tufts University, Boston, Mass. Wiley. This strain (Wound) was kindly supplied by B. B. Wiley. When grown under certain conditions this strain has been reported to undergo a specific capsular reaction (23). Giorgio. This strain of S. aureus has been previously described (14) and is a prototypic non-ecapsulated S. aureus. All cultures were maintained on brain heart infusion agar (Difco) slants at 4 C. Unless otherwise noted, 18-h subcultures in brain heart infusion broth were used in all experiments.

Transcriptional analysis of type 1 capsule genes in Staphylococcus aureus

“…Because of the large amount of capsule synthesized, strains producing type 1 or 2 capsule are mucoid on an agar surface, non-typeable with respect to phage, clumping-factor negative and exhibit a halo around the cells during negative staining with India ink. These strains have been shown to be antiphagocytic and virulent to mice (Lee et al, 1987;Melly et al, 1974;Peterson et al, 1978), although they are rarely isolated. In contrast, type 5 and 8 strains are the predominant isolates which account for approx.…”

“…The presence of taurine in the capsule is dependent on the presence of taurine in the growth medium (Wilkinson et al, 1979). The production of capsule in strain M has been correlated with its virulence properties in both in vitro phagocytic assays and in vivo mouse lethality assays (Melly et al, 1974;Peterson et al, 1978). It has been shown that the mechanism of resistance to opsonization is due to the masking of the bacterial surfacebound C3b complement by capsule, thus preventing interaction with the receptors on phagocytic cells by capsule.…”

Increased Sensitivity to Phagocytosis of Staphylococcus E‐46 after Growth in Artificial Media

“…These results confirm that Staphylococcus E-46 is highly resistant to phagocytosis (4, 5), probably because it is poorly opsonized. The capsule-like structure on the cell surface of Staphylococcus E-46 was initially postulated to confer resistance to phagocytosis (3)(4)(5) as reported for other encapsulated S. aureus (7,11,12). During storage of Staphylococcus E-46 on HI slants, the surface component seemed to change.…”

“…In some strains, cell surface components seem to contribute to the virulence. Encapsulated Staphylococcus aureus was reported to exhibit high virulence for mice, and it was shown that the presence of a polysaccharide capsule interferes with opsonization (7,11,12). M protein, the surface antigen of group A streptococci, is also known to participate in resistance to phagocytosis.…”

Encapsulation, slime production and surface hydrophobicity of coagulase-negative staphylococci

“…Staphylococcus aureus, the pathogenic counterpart of CNS, can be encapsulated [4]. Such strains possessed increased virulence in comparison with their non-encapsulated variant strains [5,6]. Characterization of CNS has been advocated [7,8], but no special attention has been given to the presence of a capsule, although encapsulated CNS have been reported [9].…”