[Multi-drug efflux pumps and antibiotic resistance in Acinetobacter baumannii]. / Bombas de expulsión multidrogas en Acinetobacter baumannii y resistencia a antimicrobianos.

Bacterial multi-drugs systems contribute to the development of multi-resistance patterns of Acinetobacter baumannii, a nosocomial pathogen of increasing importance due to its emerging resistance to carbapenems. The multi-resistance phenomena is generated by a combination of mechanisms, one of which the efflux pump system. Many of these multiresistant isolates of A. baumannii harbor genes for the AdeABC multi-drug efflux system, related with resistance to various groups of antibacterial agents, including tygecicline and meropenem. Inhibition of these systems would allow to increase the efficacy of this antimicrobial. This review focuses on the multi-drug efflux pump system of A. baumannii with special emphasis in the AdeABC system.

[Molecular identification of aminoglycoside-modifying enzymes among strains of Enterococcus spp. isolated in hospitals of the VIII Region of Chile]. / Identificación molecular de enzimas modificantes de aminoglucósidos en cepas de Enterococcus spp. aisladas en hospitales de la Octava Región de 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 %) and 93 of these harbored at least one of the genes encoding the investigated AMEs. Three genes were detected: aac(6)Ie-aph(2")Ia (14.8%) encoding for the enzyme AAC(6)Ie-APH(2")Ia (resistance to all aminoglycosides, except streptomycin); aph(3)IIIa (26%), and ant(6)la (28.5%) 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%), 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.

[Resistance to gentamicin, amikacin and ciprofloxacin among nosocomial isolates of klebsiella pneumoniae subspecie pneumoniae producing extended spectrum beta-lactamases]. / Resistencia a gentamicina, amikacina y ciprofloxacina en cepas hospitalarias de klebsiella pneumoniae subespecie pneumoniae productoras de beta-lactamasas de espectro extendido.

BACKGROUND: Klebsiella pneumoniae is a pathogenic bacterium frequently isolated from nosocomial samples, specially the subspecie pneunonlae, with extensive antibiolic resistance profiles, including third generation cepbhalosporiis, aminoglycosides and quinolones. This is specially true for those strains producing extended spectrum beta lactamases (ESBL). AIM: To investigate the susceptibility to gentamicin, amikacin and ciprofloxacin and the presence of some aminogloycoside modifying enzyme (AMEs) among nosocomial strains of K pneumoniae subspecie pneumoniae producing ESBL. MATERIAL AND METHODS: The antibiotic resistant patterns and the level of resistance (minimal inhibitory concentration, MIC) of 100 strains, isoklted from sel ,eal bospitals of dcifferent Chilean cities, were deterl,in,ed. Tbe presence of some aminoglycosides modifying enzyme (AMEs) was investigated by PCR. RESULTS: Sixty five percent of strains were resistant to gentamicin, 47% were resistant to amikacin, and 29% were resistant to ciprofloxacin. The most frequent AMEs genes detected were the aac(6')-Ib gene (6'N-Acetyltransferase type Ib enzyme) in 69% of strains, conferring resistance to amikacin, kanamycin, tobramycin, and nieoniycin, and the gene aac(3)-IIa (3-Acetyltransferase type 3-IIa enzyme), in 36% of strains, conferring resistance to gentamlicin. CONCLUSIONS: Among nosocomial strains of K pneumoniae subspecie pneumoniae isolaterd from Chilean hospitals, there is an association between the production of ESBL and the resistance to others antimicrobial agents, especially aminoglycosides. Nevertheless, 71% of isolates are susceptible to ciprofloxacin.