Genetic Variation and Evolution of the Pathogenicity Island of Enterococcus faecalis

Abstract

Enterococcus faecalis is a leading cause of nosocomial infections and is known for its ability to acquire and transfer virulence and antibiotic resistance determinants from other organisms. A 150-kb pathogenicity island (PAI) encoding several genes that contribute to pathogenesis was identified among antibiotic-resistant clinical isolates. In the current study, we examined the structure of the PAI in a collection of isolates from diverse sources in order to gain insight into its genesis and dynamics. Using multilocus sequence typing to assess relatedness at the level of strain background and microarray analysis to identify variations in the PAI, we determined the extent to which structural variations occur within the PAI and also the extent to which these variations occur independently of the chromosome. Our findings provide evidence for a modular gain of defined gene clusters by the PAI. These results support horizontal transfer as the mechanism for accretion of genes into the PAI and highlight a likely role for mobile elements in the evolution of the E. faecalis PAI.Enterococcus faecalis is a core constituent of the intestinal flora of humans and a leading cause of nosocomial infections worldwide (35). Enterococci are associated with a variety of pathologies, including pelvic infections, intra-abdominal abscesses, postsurgical infection, bacteremia, endocarditis, and urinary tract infections (12,20,30). The ability of E. faecalis to cause serious infection is connected to the inherent hardiness of the bacterium, which enables it to tolerate desiccation, persist in the hospital environment, and then endure host defenses (20,22). In addition, enterococci are particularly adept at acquiring resistance to antibiotics and disseminating these elements within and beyond the genus (30, 48).Pathogenicity islands (PAIs) are large, horizontally transmitted elements found in many gram-positive and gram-negative pathogens (14). They are believed to contribute to the rapid evolution of nonpathogenic organisms into pathogenic forms (2, 26). The PAI of E. faecalis is approximately 150 kb and encodes multiple factors that contribute to its virulence, including the cytolysin toxin (3, 18), the enterococcal surface protein Esp (40), and Gls-24-like proteins (44), as well as traits suspected of contributing to pathogenicity or altering its relationship with the host, including a bile acid hydrolase, carbohydrate utilization pathways, and many additional genes of unknown function (38). The PAI, or parts thereof, has been identified in hundreds of E. faecalis isolates, and variation in genetic content has been noted (25,30,32,39). It is enriched among infection-derived isolates (38) and highly clonal lineages containing multiple antibiotic resistance elements (30). Variation has been found in the occurrence of genes within the PAI, even within a genetic (clonal) lineage, suggesting that segments of the island can vary independently of the whole (38). Indeed, movement of genes derived from an internal portion of the PAI has been det...

Comparative Genomics and Transduction Potential of Enterococcus faecalis Temperate Bacteriophages

“…Their actual contribution to infection awaits more defined experiments with animals and a systematic analysis of the impact that lysogeny has upon gene expression during growth. The integration sites of the phages were performed by PCR using primers for the integrase of each phage and genes adjacent to phage integration sites identified by comparative genome hybridization studies (26,34). In addition PCR amplifications across these integration sites were performed using the primer pairs listed in Table 1.…”

“…Chromosomal integration sites of phages were determined via two PCR screens. First, JH2-2 lysogen DNA was amplified using primers for integrase (primers int1-1 or int1-3 for phages FL1A to C, ⌽FL2A and B, and ⌽FL3A and B, or primers int4-1 or int4-3 for phage ⌽FL4A) ( Table 1) with primers for genes adjacent to phage insertion sites that were identified by comparative genome hybridization studies (26,34). Second, amplification was performed across the phage junction sites using primers for EF0302/EF0358, EF1275/EF1292, EF1416/EF1490, EF1987/EF2044, EF2083/ EF2146, EF2797/EF2856, and EF2935/EF2956 (Table 1) for the JH2-2 lysogens and JH2-2.…”

“…A proposed pathogenicity island identified with E. faecalis V583 (49) is composed of a variable gene set encoding the virulence determinants enterococcal surface protein, cytolysin, and aggregation substance. This highly variable 150-kb mobile element contains many components of unknown function that are hypothesized to facilitate survival and/or transmission in the health care setting (34,40,49).…”

Complete Genome Sequence of the Commensal Enterococcus faecalis 62, Isolated from a Healthy Norwegian Infant

“…Notably, a Tn916 element is found in the chromosome of E. faecalis 62. EF62pC (55,393 bp) resembles pAM737-type plasmids associated with the pathogenicity island (PAI) element (11,12,19).…”

Complete Genome Sequence of the Porcine Isolate Enterococcus faecalis D32

“…High-level resistance to streptomycin is chromosomally encoded by an aminoglycoside 6-adenyltransferase gene (aadK). The pathogenicity island (PAI) in D32 contains a bile acid hydrolase (cbh) and lactose metabolic pathway genes (lacABCDEFG) but lacks common markers such as the enterococcal surface protein gene (esp) and the cytolysin operon (8,15) present in the original PAI in MMH594 (9,14). Additionally, a previously novel and uncharacterized genomic island (138 kb) is integrated at the attachment site of the conjugative vanB transposon in V583 (12).…”