Presence of virulence factors in Enterococcus faecalis and Enterococcus faecium susceptible and resistant to vancomycin

Despite the increasing importance of Enterococcus as opportunistic pathogens, their virulence factors are still poorly understood. This study determines the frequency of virulence factors in clinical and commensal Enterococcus isolates from inpatients in Porto Alegre, Brazil. Fifty Enterococcus isolates were analysed and the presence of the gelE, asa1 and esp genes was determined. Gelatinase activity and biofilm formation were also tested. The clonal relationships among the isolates were evaluated using pulsed-field gel electrophoresis. The asa1, gelE and esp genes were identified in 38%, 60% and 76% of all isolates, respectively. The first two genes were more prevalent in Enterococcus faecalis than in Enterococcus faecium, as was biofilm formation, which was associated with gelE and asa1 genes, but not with the esp gene. The presence of gelE and the activity of gelatinase were not fully concordant. No relationship was observed among any virulence factors and specific subclones of E. faecalis or E. faecium resistant to vancomycin. In conclusion, E. faecalis and E. faecium isolates showed significantly different patterns of virulence determinants. Neither the source of isolation nor the clonal relationship or vancomycin resistance influenced their distribution.

Susceptibilidad antimicrobiana y bases genéticas de la resistencia de cepas de Enterococcus causantes de infecciones en Cuba / Antimicrobial susceptibility and genetic bases for resistance of infectioncausingEnterococcus strains in Cuba

Objective. To identify infection-causing Enterococcus species in Cuban hospitalsand determine their susceptibility to antimicrobial drugs, as well as their resistance mechanisms. Methods. A total of 687 Enterococcus isolates from 30 Cuban hospitals in nine provinces of the country were studied over the period 2000–2009. The species were identified using both the conventional method and the automatic API® system.The minimum inhibitory concentration was determined for 13 antimicrobial drugs following the standards recommended by the Clinical Laboratory and Standards Institute. The polymerase chain reaction technique was used to characterize the genes that were resistant to aminoglycosides, erythromycin, tetracycline, andglucopeptides. The presence of beta-lactamase was determined by the chromogenic cephalosporin test. Results. The most prevalent species were Enterococcus faecalis (82.9%) and E. faecium (12.2%). Resistance to glucopeptides (1.0%) was mediated by the vanA and vanB genes. The strains resistant to ampicillin (6%) did not produce beta-lactamases. A high percentage of resistance to aminoglycosides was observed. Gentamicin (31.0%) and streptomycin and amikacin (29.1%) were mediated by the aac(6’)Ie-aph(2”)Ia, aph(3’)-IIIa, ant(6)Ia, and ant(3”)(9) genes. A correlation was found between resistance to tetracycline (56.0%) and presence of the tet(M) (75.1%) and tet(L) genes (7.0%), while resistance to erythromycin (34.1%) was due to the erm(B) gene (70.9%). Conclusions. Resistance to vancomycin is infrequent in Cuba, as opposed to a high level of resistance to aminoglycosides, which may be indicative of treatment failures. The microbiology laboratory is a cornerstone of Enterococcus infectionsurveillance, along with ongoing monitoring of the susceptibility of these infections to antimicrobial drugs at a time when resistance of this microorganism is on the rise.

Objetivo. Identificar las especies de Enterococcus causantes de infecciones en hospitales cubanos, su susceptibilidad a los antimicrobianos y sus mecanismos de resistencia.Métodos. Se estudiaron 687 aislamientos de Enterococcus procedentes de 30 hospitalescubanos de nueve provincias del país durante el período de 2000 a 2009. La identificación de las especies se realizó mediante el método convencional y sistema automatizado API®. Laconcentración inhibitoria mínima se determinó para 13 antimicrobianos según las recomendaciones del Instituto de Estándares Clínicos y de Laboratorio. Se determinaron los genes de resistencia a aminoglucósidos, eritromicina, tetraciclina y glucopéptidos mediante reacciónen cadena de la polimerasa. La presencia de betalactamasa se determinó por el método de lacefalosporina cromógena. Resultados. Las especies más prevalentes fueron Enterococcus faecalis (82,9%) y Enterococcus faecium (12,2%). La resistencia a los glucopéptidos (1,0%) estuvo mediada por los genes vanA y vanB y las cepas resistentes a ampicilina (6%) no produjeron betalactamasas. Se observó un alto porcentaje de resistencia a los aminoglucósidos: gentamicina (31,0%) y estreptomicina y amikacina (29,1%) mediada por los genes aac(6’)Ie-aph(2”)Ia, aph(3’)-IIIa, ant(6)Ia, ant(3”)(9). Hubo correlación entre la resistencia a tetraciclina (56,0%) y la presencia de los genes tet(M) (75,1%) y tet(L) (7,0%), mientras que la resistencia a eritromicina (34,1%) obedeció al gen erm(B) (70,9%).Conclusiones. La resistencia a vancomicina es infrecuente en Cuba, a diferencia del alto nivel de resistencia a los aminoglucósidos, que sugiere posibles fracasos terapéuticos. El laboratorio de microbiología constituye un pilar fundamental de la vigilancia de las infecciones por cepas de Enterococcus y el monitoreo continuo de su susceptibilidad a los antimicrobianos,dado el incremento de la resistencia de ese microorganismo en el tiempo.