Prevalence and analysis of CRISPR/Cas systems in Pseudomonas aeruginosa isolates from Greece

The objective of this study was to investigate the prevalence of CRISPR/Cas systems in P. aeruginosa, isolated from a Greek hospital. Additionally, we aimed to determine the origin of the sequenced spacers. A collection of 100 nonrepetitive P. aeruginosa was analyzed. Isolates were typed by MLST. The presence of CRISPR/Cas systems, as well as amplification of CRISPR arrays, was examined by PCR using specific primers. CRISPR/Cas systems were detected in 36 isolates, of which 27 isolates exhibited resistance to carbapenems, with 10 of the later isolates producing a VIM-type MβL. The majority (n = 19) of CRISPR/Cas-positive isolates harbored a type I-F system, while I-C and I-E systems were found in 9 and 8 isolates, respectively. Based on MLST, isolates carrying I-E and I-F systems belonged to different STs and included CRISPR arrays with diverse number of spacers. Isolates with I-C systems belonged to clonal complex 235 and exhibited identical CRISPR arrays. Among 425 unique spacers, identified during this study, BLASTn search showed that they matched with P. aeruginosa chromosomal sequences (47.0%), phages (31.9%), plasmids, PAGIs, and an ICE. 16.3% of the spacers exhibited no significant similarity with sequences submitted to GenBank database. In conclusion, we observed the presence of type I-C, I-E and I-F CRISPR/Cas systems in P. aeruginosa of clinical origin. CRISPR/Cas were also observed among isolates carrying the carbapenemase-encoding bla_VIM gene, which is usually associated with integrons, questioning the defense role against mobile elements. Therefore, further experimental characterization is needed to clarify their functional role.