Identification of the clonal complexes of Staphylococcus aureus strains by determination of the conservation patterns of small genomic islets

Abstract

To investigate the clonality of Staphylococcus aureus isolates, it is important to identify their clonal complexes (CCs) with multilocus sequence typing (MLST). However, it is expensive to carry out MLST analyses for many isolates. The aim of this study, therefore, was to develop a cost-effective method to identify CCs by determining the conservation pattern of 'small genomic islets' (SGIs). SGIs are nonconserved regions between strains and have single or multiple open-reading frames (ORFs). The whole-genome sequences of nine strains were compared in order to select 16 SGIs. The conservation patterns of the 16 SGIs (islet patterns) were investigated in 136 S. aureus isolates, which were classified into 21 CCs. The islet patterns (IPs) exhibited a one-to-one correspondence with the CCs, except for isolates belonging to CC1, CC5 and CC8. The IPs typical of strains belonging to CC1, CC5 and CC8 differed between those of sequence type 1 (ST1) and ST188 (CC1), ST5 and ST6 (CC5) and ST8 and ST239 (CC8). The CCs of many isolates can be identified in an easy and inexpensive manner by detecting these 16 SGIs. Emergent clones, particularly methicillin-resistant ones, can be identified by examining numerous islets by IP analysis.