Staphylococcus aureus microcapsule expression attenuates bacterial virulence in a rat model of experimental endocarditis.
The virulence of the Staphylococcus aureus strains that differed only in capsule expression was compared in a rat model of catheter-induced experimental endocarditis. The ID50 of all the strains was low (less than 3 x 10(3) cfu of S. aureus), suggesting that this model may be more sensitive than other animal models to differences in bacterial virulence. Compared with the wild-type strains that expressed type 5 or type 8 capsular polysaccharides, mutant strains devoid of capsule had significantly lower ID50 values. In contrast, a mutant that produced scant amounts of the type 5 polysaccharide had an ID50 similar to that of the parental type 5 isolate. As the bacterial inoculum was increased, each of the S. aureus strains reached final concentrations of 10(10)-10(11) cfu/g of vegetation; however, the nonencapsulated mutants colonized the left-sided vegetations at lower inocula than did the wild-type strains. This study indicates that microcapsule expression attenuates bacterial virulence in a rat model of catheter-induced endocarditis.
Baddour
L M
LM
Department of Medicine, University of Missouri-Columbia.
Lowrance
C
C
Albus
A
A
Lowrance
J H
JH
Anderson
S K
SK
Lee
J C
JC
D000818:Animals; D016667:Bacterial Capsules / Q000096:biosynthesis / Q000502:physiology*; D004195:Disease Models, Animal; D004697:Endocarditis, Bacterial / Q000382:microbiology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000472:pathogenicity*; D014774:Virulence