Percentage of invasion of A549 cell line by MRSA clones ST22-IV and ST228-I.

Three to six different strains for each predominant variant of the two clones (ST22-IV variants A and B, ST228-I variants B2 and B5) were tested. For ST22-IV strains tested originated from lower respiratory tract (LRT, 37%), pus (37%) and blood (26%); for ST228-I strains tested were isolated from LRT (55%) and blood (45%). The percentage of invasion was determined by plating cellular lysates after 2 hours contact between bacteria and cells’ monolayer, followed by 1 hour treatment with lysostaphin to kill extracellular bacteria. Each symbol represents a single strain; the black bar indicates the average percentage of invasion. Statistically significant differences are indicated by symbols when present: * indicates a p value <0,05; ***: p<0,001.