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.

Identificación molecular de enzimas modificantes de aminoglucósidos en cepas de Enterococcus spp. aisladas en hospitales de la Octava Región de Chile / Molecular identification of aminoglycoside-modifying enzymes among strains of Enterococcus spp. isolated in hospitals of the VIII Region of Chile

Background: Infectious diseases produced by Enterococcus spp, must be treated with a synergistic combination between a penicillin and an aminoglycoside. High level resistance to aminoglycosides is a serious therapeutic problem, since it predicts the loss of synergistic activity of this antimicrobial combination. Aim: To investigate the presence of genes encoding aminoglycoside-modifying enzymes (AMEs) among strains of Enterococcus spp with high level of resistance to aminoglycosides. Material and methods: The genes encoding some of the AMEs were investigated among 305 aminoglycoside-resistant strains of Enterococcus spp isolated in hospitals of the VIII region of Chile, by dot blot hybridization and Polymerase Chain Reaction (PCS). Results: High level resistance to some aminoglycosides was observed in 104 strains (34.1 percent) and 93 of these harbored at íeast one of the genes encoding the investigated AMEs. Three genes were detected: aac(6)Ie-aph(2")Ia (14.8 percent) encoding for the enzyme AAC(6)Ie-APH(2")Ia (resistance to all aminoglycosides, except streptomycin); aph(3)IIIa (26 percent), and ant(6)la (28.5 percent) encoding for the phosphorylating enzymes APH(3)Ilia (resistance to kanamycin, amikacin and neomycin), and ANT(6)-la (resistance only to streptomycin), respectively. None of the strains harbored the gene ant (4) which encode for the enzyme ANT (4). Conclusion: The low frequency of strains harbouring the bifunctional enzyme (<15 percent), conferring an extended resistance profile to aminoglycosides, allows us to propose the empirical use of aminoglycoside-aminocyclitols, associated to a penicillin, in the treatment of serious infections produced by species of enterococci.