The enterococcal surface protein, Esp, originally found in Enterococcus faecalis, has been associated with increased virulence, colonization, and biofilm formation (2, 3, 5, 6). Recently, a variant esp gene was found in Enterococcus faecium isolates from humans (L. Baldassarri, L. Burtuccini, M. G. Ammendolia, G. Gherardi, and R. Creti, Letter, Lancet 357:1802, 2001; R. J. Willems, W. Homan, J. Top, M. van Santen-Verheuvel, D. Tribe, X. Manzioros, C. Gaillard, C. M. Vandenbroucke-Grauls, E. M. Mascini, E. van Kregten, J. D. van Embden, and M. J. Bonten, Letter, Lancet 357:853-855, 2001; N. Woodford, M. Soltani, and K. J. Hardy, Letter, Lancet 358:584, 2001). The esp gene encodes a protein with inferred global structural similarity to Rib and C alpha proteins from group B streptococci and R28 from group A streptococci (3, 4).
In the present study, the prevalence of esp was investigated by PCR with primers published by Woodford et al.: Esp-p1, 5′-GGT CAC AAA GCC CAA CTT GT-3′, and Esp-p2, 5′-ACG TCG AAA GTT CGA TTT CC-3′ (Woodford et al., letter). Twenty-four E. faecalis and 29 E. faecium isolates from blood culture from patients in 13 different Danish hospitals were tested together with 75 E. faecium and 75 E. faecalis isolates from Danish pigs and 66 E. faecium and 60 E. faecalis isolates from Danish poultry (Table 1).
TABLE 1.
Prevalence of the esp gene in E. faecalis and E. faecium isolates from human, pigs, and poultry
| Origin and sp. | No. of isolates tested | No. of isolates PCR positive for esp (%) |
|---|---|---|
| Humans | ||
| E. faecium | 29 | 10 (34.5) |
| E. faecalis | 24 | 10 (41.7) |
| Pigs | ||
| E. faecium | 75 | 0 (0) |
| E. faecalis | 75 | 6 (8) |
| Poultry | ||
| E. faecium | 66 | 0 (0) |
| E. faecalis | 60 | 0 (0) |
Among isolates from hospital patients, 10 of 24 (41.7%) E. faecalis isolates and 10 of 29 (34.5%) E. faecium isolates were esp positive (Table 1). The prevalence of esp-positive E. faecalis blood culture isolates was higher than that found by Shankar et al. (29%) (2) but lower than that reported by Waar et al. (45%) (6). Shankar et al. (2) did not find any esp-positive E. faecium isolates, whereas 56.5% of blood culture isolates were positive in the study by Woodford et al. (Woodford et al., letter). Among animal isolates, none of the E. faecium isolates were esp positive. This is consistent with previous studies (Woodford et al., letter; Willems et al., letter).
Six of the 75 (8.0%) E. faecalis isolates from pigs were esp positive, whereas none of the E. faecalis isolates from poultry were positive (Table 1). The 407-bp esp amplicons from two pig isolates of E. faecalis were sequenced. No variations were found in comparison with GenBank AF034779. To our knowledge, esp has not previously been reported in E. faecalis isolates of animal origin. Expression of the Esp protein was not investigated.
Willems et al. found that esp was associated with epidemic vancomycin-resistant E. faecium clones (Willems et al., letter). In our study none of the esp-positive isolates from humans and animals were resistant to vancomycin or to quinupristin-dalfopristin. However, 9 of 10 esp-positive E. faecium isolates from humans, 3 of 10 esp-positive E. faecalis isolates from humans, and 1 of 6 esp-positive E. faecalis isolates from pigs were resistant to gentamicin, encoded by aac(6′)-Ie-aph(2")-Ia. All gentamicin-resistant, esp-positive isolates were also resistant to erythromycin, streptomycin, and kanamycin, encoded by erm(B), aadE, and aphA, respectively. This suggests that a DNA element like the erm(B)-Tn5405-like element, recently found in Staphylococcus intermedius (1), could be present in some gentamicin-resistant, esp-positive enterococci.
The esp gene has been detected in 40% of E. faecalis isolates from the feces of healthy humans (6). This observation, taken together with the finding of the gene in pig isolates in this study, increases the need for more investigation of the function of this protein.
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