CRISPR-Cas, a Prokaryotic Adaptive Immune System, in Endodontic, Oral, and Multidrug-resistant Hospital-acquired Enterococcus faecalis

Introduction: Microorganisms are vulnerable to invasion by mobile genetic elements such as viruses, plasmids, and transposons. The recently discovered Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-associated system, or CRISPR-Cas, is an adaptive immunity system found in most archaea and many bacteria that targets and inactivates invading foreign genetic elements. Cells with CRISPR-cas are more likely to resist the invasion and uptake of foreign DNA such as viruses, plasmids, and transposons. The aims of this study were to (1) compare the occurrence of CRISPR-cas in collections of endodontic (n = 34), oral (n = 21), and multidrug-resistant hospital-acquired strains of Enterococcus faecalis (n = 23) and (2) evaluate the distribution of antibiotic resistance and virulence traits among strains without CRISPR-cas. Methods: E. faecalis strains were screened for CRISPR1-cas and CRISPR3-cas by using polymerase chain reaction, and products were verified by DNA sequencing. Associations were investigated between the occurrence of CRISPR-cas and the expression of phenotypic traits (antibiotic resistance, gelatinase activity, bacteriocin production, hemolysin activity, and clumping response to pheromone). Results: CRISPR-cas determinants were present in proportionally more endodontic (25 of 34) and oral (15 of 21) strains than hospital-acquired (9 of 23) strains (P = .01 and .04, respectively). Significant associations were found between the absence of CRISPR-cas and the presence of antibiotic resistance in strains overall (P = .04) and bacteriocin activity in endodontic strains (P = .01). Conclusions: Evidence for the presence of CRISPR-cas in the majority of endodontic and oral E. faecalis strains raises intriguing questions as to how prokaryotic immune systems might modulate interactions within the polymicrobial endodontic biofilm environment. (J Endod 2012;38:1511-1515)