Capsular antibodies select for loss of capsule production by Staphylococcus aureus during infection in a mastitis mouse model. Abstract P-012.

TUCHSCHERR, LORENA P. LEE JC AND SORDELLI DO.; BUZZOLA, FERNANDA R.; ALVAREZ, LUCIA P.; CALVINHO, LUIS F.; LEE, JEAN C.; SORDELLI, DANIEL O.

Maastricht, Holanda

Simposio; 12th International Symposium on Staphylococci and Staphylococcal Infections (ISSSI); 2006

ISSSI

The prevalence of encapsulation among S. aureus isolates from bovines with mastitis in Argentina is only 14%. We reported previously that a non-typeable (NT) S. aureus mutant persisted longer in the infected mammary glands of lactating mice than isogenic serotype 5 or 8 strains. This study was designed to test whether antibodies to the serotype 5 (CP5) or 8 (CP8) capsules would select for non-encapsulated S. aureus during infection. Groups of mice were injected intraperitoneally with 0.3 ml of a rabbit antiserum to CP5 or CP8 previously adsorbed with the corresponding NT isogenic mutant. After 24 h mice were challenged by the intramammary route with 106 CFU of a CP5 or CP8 S. aureus strain. Control animals received non-immune rabbit serum. Mice were euthanized 4 d after challenge, the infected mammary glands were homogenized, and the homogenates plated quantitatively. The bacterial burden in the mammary glands of mice treated with CP antiserum was decreased by 4 orders of 10 when compared with those of control animals (p<0.01).  CP5 or CP8 S. aureus strains were serially passaged through the mammary glands of lactating mothers that were pretreated with CP antiserum.  Colonies recovered from the infected glands were evaluated for CP production by a colony immunoblot assay. Approximately 11% and 50% of the S. aureus colonies recovered from mice given CP5 antiserum were CP5-negative after 4 and 5 mouse passages, respectively. Likewise, 40% and 95% of the colonies were CP8-negative after the 6 or 7 passages, respectively, of the CP8 S. aureus strain in mice given CP8 antiserum. NTS. aureus colonies were not detected in control animals after 10 passages. Our experiments demonstrate that antibodies to the S. aureus capsule (CP5 or CP8) may select for non-encapsulated variants in vivo, and this may contribute to persistence of S. aureus in the infected host.