ABILITY OF CLINICAL ISOLATES OF GROUP-A STREPTOCOCCI TO ADHERE TO ANDINVADE HEP-2 EPITHELIAL-CELLS

Individual strains of group A streptococci (GAS) differ in virulence, but the reasons for these differences are incompletely understood. To determine if the ability of GAS to cause invasive disease corresponded with their capacity to adhere to or invade epithelial cells, 63 clini cal isolates of GAS (40 from patients with systemic infection and 23 f rom superficial disease) were examined in quantitative assays of bacte rial adhesion to and invasion of HEp-2 cells, a continuous line of hum an pharyngeal epithelial cells. The results showed that individual iso lates of GAS varied considerably in their ability to adhere to and pen etrate HEp-2 cells, However, on the whole, strains from patients with invasive disease adhered to cells in numbers c,1,5 greater than those from superficial infection. Paradoxically, strains from patients with invasive disease invaded HEp-2 cells to a significantly lesser extent than those from superficial sites, with a two-fold difference in invas ion index (defined as the percentage of cell-associated bacteria locat ed intracellularly), To determine if these differences were caused by differences in the production of hyaluronic acid capsule or M protein by the two groups of bacteria, the adherence and invasive capacities o f bacteria carrying defined mutations in the genes for these factors w ere examined. Although M18-protein-deficient bacteria were less adhere nt to HEp-2 cells than the wild-type, neither the hyaluronic acid caps ule nor the M protein had a significant influence on the ability of GA S to adhere to or invade HEp-2 cells. The results of this study demons trate that there are biological differences between GAS isolates assoc iated with invasive and superficial diseases and that these difference s can be demonstrated by an assay of bacterial adherence to and invasi on of HEp-2 epithelial cells.