Genetic diversity of cell-invasive erythromycin-resistant and -susceptible group A streptococci determined by analysis of the RD2 region of the prtF1 gene.
The RD2 region of the internalization-associated gene prtF1, which encodes the
fibronectin-binding repeat domain type 2 of protein F1, plays a crucial role in
the entry of group A streptococci (GAS) into epithelial cells. A molecular study
of the variability of the RD2 region was carried out with 77 independent Italian
GAS, 66 erythromycin resistant (ER) and 11 erythromycin susceptible (ES), which
had previously been investigated for the association between erythromycin
resistance and ability to enter human respiratory cells. The amplicons obtained
from PCR analysis of the RD2 region were consistent with a number of RD2 repeats
ranging from one to five, more frequently four (n = 30), three (n = 27), and one
(n = 18). A new method to type cell-invasive GAS (RD2 typing) was developed by
combining PCR analysis of the RD2 region and restriction analysis of PCR products
with endonucleases HaeIII, DdeI, and HinfI. Overall, 10 RD2 types (a to j) were
distinguished (all detected among the 66 ER isolates, four detected among the 11
ES isolates). Comparison and correlation of RD2 typing data with the genotype and
phenotype of macrolide resistance and with data from PCR M typing and SmaI
macrorestriction analysis allowed us to identify 41 different clones (31 among
the 66 ER isolates and 10 among the 11 ES isolates). Three major clones accounted
for 40% of the isolates (47% of ER strains). Some ES isolates appeared to be
related to ER isolates with identical combinations of RD2 type and emm type.
While simultaneous use of different typing methods is essential for a thorough
investigation of GAS epidemiology, RD2 typing may be especially helpful in typing
cell-invasive GAS