Hyaluronic acid capsule: strategy for oxygen resistance in group A streptococci

Unencapsulated variants of encapsulated, M-protein-positive group A streptococci are oxygen sensitive and secrete inhibitory concentrations of hydrogen peroxide when grown in aerated broth cultures. The organisms were equally sensitive to hydrogen peroxide, and neither exhibited catalase or peroxidase activity, suggesting that differences in oxygen sensitivity reflect dissimilarity in oxygen uptake. The encapsulated parental culture was found to grow in aggregates that take up oxygen more slowly than unencapsulated, oxygen-sensitive derivatives. Moreover, the latter grow in an unaggregated, homogenous suspension. The enzyme hyaluronidase was able to disrupt aggregates of the encapsulated strain increase the rate that these cells take up oxygen, and cause the accumulation of toxic concentrations of hydrogen peroxide earlier in their growth cycle. The evidence presented shows that the aggregation of streptococcal cells by their hyaluronic acid capsule provides this organism with a novel means to avoid self-destruction by oxygen metabolites--cells are shielded from oxygen. The reduced surface-to-volume ratio and limited diffusion of oxygen into the interior of aggregates are proposed as the protective mechanism.