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.

Clinical and molecular characterization of ESBL-producing enterobacteria isolated from bacteremia in a university hospitalIntroduction: Extended-spectrum--lactamases (ESBL) are plasmid-encoded enzymes that confer resistance to multiple antimicrobials. ESBL-producing enterobacteria that cause bacteremia limit therapeutic options and increase mortality. Objective: To perform a clinical and molecular description of bacteremia caused by ESBLproducing enterobacteria. Method: We retrospectively studied the cases of bacteremia due to ESBL-producing Escherichia coli, Klebsiella pneumoniae and Proteus spp in adults admitted to a university hospital during the years 2004-2007. We reviewed the clinical records and antimicrobial susceptibility patterns. Molecular typing was performed by polymerase chain reaction and study of clonality by pulsed-fi eld electrophoresis. Results: We found a prevalence of 9.8% ESBL in enterobacteria causing bacteremia. Decreased susceptibility to quinolones and aminoglycosides was observed, without resistance to carbapenems. The predominant ESBL types were CTX-M (96%), TEM (62%) and GES (28%). 79% of the strains presented more than one type of ESBL. Clinical analysis revealed high prevalence of risk factors, previous use of antimicrobials and of invasive devices. There was no signifi cant clonality. Conclusion: The presence of ESBLs in bloodstream infections is a clinical problem that must be considered when choosing empiric therapy.

The aminoglycoside-aminocyclitol antibiotics constitute one of the antibacterial agent families with greater activity upon aerobic Gram-negative bacilli. These compounds are formed by the combination of one amino-cyclic alcohol (aminocyclitol) and aminosaccharides (aminoglycosides) linked by glycosidic bonds. The strong bactericidal activity exhibited for these compounds is not only explained by their ability to inhibit the protein synthesis, but also by pleiotropic effect altering the permeability of cytoplasmatic membrane. The penetration of these antibiotics to the bacterial cells is mediated by three well defined phases, being the two latest dependant of the proton-motive force. This fact explains that this kind of compounds have no antibacterial activity upon anaerobic bacteria. Bacterial resistance to aminoglycosides is mainly due to aminoglycoside-modifying enzymes (AME), which are commonly encoded by extrachromosomal genetic elements as are plasmids and transposons. Nevertheless, new mechanisms of resistance and genetic elements participating in the resistance to these compounds have been identified. Thus, recently the methylation of the 16S rRNA binding the aminoglycosides has been described. On the other hand, the gene cassettes acquire an increasing importance, because they can host a varied of families of antibiotic resistance genes, including the aminoglycoside-aminocyclitols. These gene cassettes are associated to integrons, which are able to integrate and express these antibiotic resistance determinants.

Presence of metallo ß-lactamases in imipenem-resistant Pseudomonas aeruginosa Background: Metallo-ß-lactamases (MBL) confer high resistance to carbapenems in Pseudomonas aeruginosa (Psae). They are encoded in mobile elements of different genes (VIM, IMP, SMP, GIM), along with other resistance genes. Aim: To detect the presence of MBL in imipenem resistant Psae strains. Material and methods: Fifty-nine imipenem resistant Psae strains isolated from January 2004 to August 2005 in a University Clinical Hospital, were included. The presence of MBL was studied by Etest (phenotypic) and genotypic polymerase chain reaction (PCR) methods. To rule out a nosocomial outbreak, MBL positive strains, were studied by pulse field gel electrophoresis. Results: The presente of MBL was detected in eleven strains. All were type VIM and were not clonally related. There was no concordance between phenotypic and genotypic MBL detecting methods. All the strains were also multiresistant.

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