It is reasonable to expect that geographically/ecologically distinct populations of streptococci might be responsible for the absence of some sk gene alleles or detection of novel ones. Autophagy Compound Library screening The sk5 allele was the most commonly found variant detected in 13 (17%) of all 76 strains. The most prevalent gene alleles among GAS isolates were sk1, sk5, sk16 and sk18. GCS and GGS strains were distributed among sk5, sk6, sk10, sk11, sk16 and sk17 gene alleles (Fig. 2). Although six variants including sk5, sk10, sk11, sk12, sk13 and sk14 were previously
reported as skcg gene-specific alleles (Tewodros et al., 1996), we could identify several GAS strains among our isolates that belonged to sk5 and sk11 variants. This finding is in accordance with prior proposition on horizontal gene transfer of either the entire sk or fragments of sk between GAS and GCS/GGS strains (Kalia & Bessen, 2004). Therefore, the presence of particular gene alleles might not be restricted to GCS/GGS or GAS strains, and their detection might be solely dependent on the population of the streptococci under study and the geographical regions from where they were isolated. While
the majority of GCS/GGS isolates in the present study were classified in previously identified sk gene alleles (sk5, sk6, sk10 and sk11), most of GAS isolates belonged to the new allelic variants (sk15-sk28). This finding is consistent with the prior hypothesis for high intragenic recombination levels of ska, which accounted for the high variation rate of ska among GAS (Kapur Selleck SRT1720 et al., 1995; Kalia & Bessen, 2004). Although a number of sk gene alleles such as sk1, sk2 and sk6 were previously
proposed as SKN (Malke, 1993), in accordance with several other reports (Tewodros et al., 1993, 1996; Haase et al., 1994), identification of these alleles in our study among strains that were isolated from uncomplicated clinical diseases (Fig. 2) implies that selleck kinase inhibitor there is no association between sk allelic variants and disease manifestation. As shown in Fig. 2, a wide range of Plg activation levels displayed by different SK variants ranged from 9 to 182 IU mL−1. These results are consistent with previous observations for a wide variation of SK activity levels in a PCR/RFLP pattern (Tewodros et al., 1995) or even in a specific SK cluster (McArthur et al., 2008). In fact, beside SK variations in their primary structure, other upstream regulatory regions of SK gene were also proposed for differences in SK activities of the streptococci (Malke et al., 2000). SDS-PAGE analysis of the mid log phase proteins of the culture supernatants (as expected) did not show the presence of either the zymogene (40 kDa) or the active form (28 kDa) of the SpeB protease (Fig. S1). It indicated the reliability of SK activity data (i.e.