Susceptibilidad antimicrobiana y bases genéticas de la resistencia de cepas de Enterococcus causantes de infecciones en Cuba

Abstract

Objective. To identify infection-causing Enterococcus species in Cuban hospitals and 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, and glucopeptides. 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 infection surveillance, 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.