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Introducción: β-lactamasas de espectro extendido (BLEE) son enzimas plasmidiales que confieren resistencia a múltiples antimicrobianos. Las bacteriemias por enterobacterias productoras de BLEE restringen las opciones terapéuticas y aumentan la mortalidad. Objetivo: Realizar una descripción clínica y molecular de las bacteriemias causadas por enterobacterias productoras de BLEE. Método: Se estudiaron retrospectivamente los casos de bacteriemia por Escherichia coli, Klebsiella pneumoniae y Proteus spp. confirmadas para BLEE, en adultos ingresados en un hospital universitario durante los años 2004-2007. Se revisaron los registros clínicos y de susceptibilidad. Se realizó tipificación molecular por reacción de polimerasa en cadena y estudio de clonalidad por electroforesis de campo pulsado. Resultados: Se identificó una prevalencia de BLEE de 9,8% en enterobacterias causantes de bacteriemias. Se observó susceptibilidad disminuida a quinolonas y aminoglucósidos, sin resistencia a carbapenémicos. Los tipos de BLEE predominantes fueron CTX-M (96%), TEM (62%) y GES (28%). El 79% de las cepas presentó más de un tipo de BLEE. El análisis clínico reveló alta frecuencia de patologías de riesgo, uso previo de antimicrobianos y uso de dispositivos invasores. No se encontró clonalidad significativa. Conclusión: La presencia de BLEE en bacteriemias constituye un problema clínico que debe ser considerado al elegir la terapia empírica.

Las infecciones ocasionadas por Streptococcus pneumoniae constituyen un problema de salud pública. En nuestro país existe escasa información sobre aislados de procesos bacteriémicos en población adulta. Se estudió la susceptibilidad, serotipos y relación clonal de 56 aislados de S. pneumoniae desde hemocultivos, entre enero 2005 y agosto 2006, de pacientes adultos de la intercomuna Concepción-Talcahuano, Región del Bío-Bío, Chile. Se encontró resistencia a tetraciclina (21,4%), cotrimoxazol (18%), eritromicina (18%), cloranfenicol (7%) y a penicilina en un solo aislado procedente de un foco meníngeo (2 %). La totalidad mostró susceptibilidad a cefotaxima, levofloxacina, moxifloxacina y vancomicina. Se demostró una amplia variedad de serotipos capsulares, con predominio de los serotipos 1, 5, 23F, 7F y 3. El análisis de macrorestricción y electroforesis en campo pulsado reveló 31 patrones electroforéticos con 12 grupos clona-les, descartando un clon predominante. De acuerdo a los resultados, al menos 80% de los serotipos de aislados de S. pneumoniae de procesos bacteriémicos están incluidos en la vacuna comercial disponible. Streptococcus pneumoniae infections constitute a public health problem. In our country there is scarce information regarding isolates from bacteraemic episodes in adult population. The antibiotic susceptibility, sero-types and clonal relationship of 56 isolates of S. pneumoniae from adult patients with bacteraemic infections in Concepcion-Talcahuano, Bio-Bio Region, Chile, were studied. Resistance to tetracycline (21.4%), trimethoprim/ sulfamethoxazole (18%), erythromycin (18%), chloramphenicol (7%) and 1 penicillin resistant isolate from a meningeal focus (2%) was found. Also, all the isolates were susceptible to cefotaxime, levofloxacin, moxifloxacin and vancomycin. A wide variety of capsular serotypes was demonstrated, with predominance of serotypes 1, 5, 23F, 7F and 3. The macrorestriction analysis by pulse field electrophoresis revealed 31 electrophoretic patterns and 12 clonal groups, discarding a predominant clone. According to the results, at least, 80% of the S. pneumoniae serotypes isolated from bacteraemic adult patients are included in the available commercial vaccine.

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. AH were type VIM and were not clonally related. There was no concordance between phenotypic and genotypic MBL detecting methods. AH the strains were also multiresistant. Conclusions: The presence of MBL was detected in 19% of imipenem resistant Psae strains

Background: A progressive frequency of resistance to fluorquinolones is observed among Gram-negative bacilli. Aim: To investigate the mechanism of resistance to fluoroquinolones mediated by mutations affecting gyrA and gyrB genes in strains of Gram negative bacüli isolated from CMean hospitals. Material and method: Minimal inhibitory concentration of fluoroquinolones was determined in 91 randomly selected nalidixic acid-resistant strains of Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa, isolated from hospitals of 12 Chilean cities. Quinolone resistance determining region (QRDR) was amplified by PCR and mutations were determined by restriction fragment length polymorphism (RFLP) and DNA sequencing. Results: Strains with mutation in codon 83 of gyrA showed decreased susceptibility to ciprofloxacin with MICs ranging from 0.25 to 1024 fig/ml. The sequencing of PCR products for gyrA indicated amino acid changes in the QRDR region. One strain ofE. coli presented a double mutation, in codon 83 Ser to Leu as well as in codon 87 Asp to Asn. In strains ofK. pneumoniae, however, the change of codon 83 was Ser to Tyr, in A. baumannii was Ser to Leu and in P. aeruginosa was Thr to He. No strains with mutations affecting gyrB were found. Conclusions: Mutations in codon 83 of gyrA is a frequent genetic event involved in the mechanism leading to decreased susceptibility to fluoroquinolone in strains of Gram-negative bacilli

Background: A progressive frequency of resistance to fluorquinolones is observed among Gram-negative bacilli. Aim: To investigate the mechanism of resistance to fluoroquinolones mediated by mutations affecting gyrA and gyrB genes in strains of Gram negative bacüli isolated from CMean hospitals. Material and method: Minimal inhibitory concentration of fluoroquinolones was determined in 91 randomly selected nalidixic acid-resistant strains of Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa, isolated from hospitals of 12 Chilean cities. Quinolone resistance determining region (QRDR) was amplified by PCR and mutations were determined by restriction fragment length polymorphism (RFLP) and DNA sequencing. Results: Strains with mutation in codon 83 of gyrA showed decreased susceptibility to ciprofloxacin with MICs ranging from 0.25 to 1024 fig/ml. The sequencing of PCR products for gyrA indicated amino acid changes in the QRDR region. One strain ofE. coli presented a double mutation, in codon 83 Ser to Leu as well as in codon 87 Asp to Asn. In strains ofK. pneumoniae, however, the change of codon 83 was Ser to Tyr, in A. baumannii was Ser to Leu and in P. aeruginosa was Thr to He. No strains with mutations affecting gyrB were found. Conclusions: Mutations in codon 83 of gyrA is a frequent genetic event involved in the mechanism leading to decreased susceptibility to fluoroquinolone in strains of Gram-negative bacilli

La resistencia de Acinetobacter baumannii a antimicrobianos ß-lactámicos se debe fundamentalmente a la síntesis de ß-lactamasas. Del punto de vista clínico se considera que esta bacteria, y otras agrupadas en el acrónimo SPACE (Serratia, Pseudomonas, Acinetobacter, Citrobacter, Enterobacter), son predominantemente productoras de ß-lactamasas tipo AmpC. No hay información en nuestro país sobre presencia de ß-lactamasas de espectro extendido (BLEE) en Acinetobacter. Se estudió la producción de BLEE en cepas de Acinetobacter, mediante una modificación de la técnica de Ho y col adicionando cloxacilina como inhibidor de ß-lactamasas cromosomales. De 69 cepas con resistencia al menos a una cefalosporina de tercera generación, sólo siete presentaron sinergia positiva. Cuatro cepas amplificaron por RPC un fragmento intragénico de genes de familia TEM y una de ellas amplificó, además, para el gen de la familia OXA. Se evidenció un bajo porcentaje de producción de BLEE, lo que confirma que la producción de Amp-C es el principal mecanismo de resistencia de A. baumannii a ß-lactámicos. Sin embargo, la descripción de BLEE en esta bacteria, enfatiza su capacidad de albergar múltiples mecanismos de resistencia The resistance of Acinetobacter baumannii to ß-lactam antibiotics is mainly due to the synthesis of ß-lactamases. From a clinical point of view, this bacteria and others, grouped under the acronym SPACE (S: Serratia, P: Pseudomonas, A: Acinetobacter, C: Citrobacter, E: Enterobacter) are essentially Amp-C ß-lactamases producers. There is no local information about ESBL presence in Acinetobacter. We studied ESBL production using the Ho and col. technique modified by adding cloxacillin as chromosomal ß-lactamases inhibitor. From 69 isolates, with resistance to at least one third generation cephalosporin, only 7 showed positive synergy test. Four of these amplified for TEM family gene, and one of these amplified also for the OXA family. Our study found a low ESBL production percentage, which agrees with the premise of Amp-C as the main mechanism of resistance to ß-lactam antibiotics in A. baumannii. However, the ESBL description in these bacteria emphasizes the capacity of expressing multiple resistance mechanisms

Background: Klebsiella pneumoniae is an important pathogenic bacterium, frequently isolated from nosocomial samples, that exhibits wide antimicrobial resistance profiles, including third generation cephalosporins (3GC), aminoglycosides and quinolones. The resistance to 3GC is mainly due to the synthesis of extended spectrum beta lactamases (ESBL), encoded by conjugative plasmids. Aim: To investigate the potential transference of resistance to 3GC from nosocomial strains of K. pneumoniae to other clinical strains of various species of Enterobacteriaceae. Material and methods: The mating experiments were carried out in liquid media and three nosocomial strains of K. pneumoniae were used as donors. These strains were ESBL-producers and resistant to, at least, one of the 3GC assayed. One strain of Citrobacter freundii, Salmonella typhimurium, Serratia marcescens and Escherichia coli, isolated from clinical specimens, were used as recipients. The presence of bla genes was investigated by PCR. Results: The three nosocomial strains of K. pneumoniae were able to transfer the resistance to 3GC and the genes encoding the ESBL to the susceptible recipient strains of enterobacteria. The frequency of transference was as high as 3.2 x 10-2 transconjugants/recipient cell when the strain of Citrobacter freundii was used as recipient. All transconjugants exhibited high level of resistance to the 3GC assayed. Conclusions: Strains of K. pneumoniae isolated from Chilean hospitals are able to disseminate the ESBL genes to clinical strains of others species of Enterobacteriaaceae

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.

Background: Klebsiella pneumoniae is a pathogenic bacterium frequently isolated from nosocomial samples, specially the subspecie pneumoniae, with extensive antibiotic resistance profiles, including third generation cephalosporins, 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 aminoglycoside 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, isolated from several hospitals of different Chilean cities, were determined. The 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 neomycin, and the gene aac(3)-IIa (3-Acetyltransferase type 3-IIa enzyme), in 36% of strains, conferring resistance to gentamicin. Conclusions: Among nosocomial strains of K pneumoniae subspecie pneumoniae isolated 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 (Rev Méd Chile 2004; 132: 1173-8)

Bacteria have developed sophisticated and successful genetic mechanisms to evade the action of antimicrobials. Bacterial multiresistance has caused serious problems in the treatment of nosocomial infections. Integrons and gene cassettes are considered the main genetic elements in the evolution of plasmids and transposons that actively participate in the mobilization of genes, codifying different bacterial resistance mechanisms. This article reviews the historical and structural aspects of integrons and resistance gene cassettes and the presence of these structures in Gram negative bacteria isolated from Chilean hospitals in the last ten years (Rev Méd Chile 2004; 132: 619-26).

Background: The resistance of Shigella flexneri to antimicrobial agents can be associated to the presence of integrons that may contain and express antimicrobial resistance gene cassettes. Aim: To study antimicrobial resistance and the presence of integrons and antimicrobial gene cassettes in Shigella flexneri strains. Material and methods: In vitro susceptibility to 27 antimicrobials was studied in twenty four Shigella flexneri strains isolated from stools. The presence of integrons class 1, 2 and 3 and antimicrobial resistance gene cassettes was investigated by polymerase chain reaction (PCR) using specific primers for each gene. Results: Most strains were resistant to one of the following antimicrobials: ampicillin, sulphonamide, trimethoprim, tetracycline, streptomycin, sulfamethoxazole-trimethoprim or chloramphenicol. Twenty nine percent were simultaneously resistant to all these antimicrobials. Integrons class 1 and 2 were found in 19 strains (79%). Class 3 integrons were not found. Gene cassettes dfrA1 and ant(3")I were associated to integrons class 2 in most strains (15/20, 75%). Genes cat, tetB and blarTEM were detected in 18/24 (75%), 7/24 (29%) and 4/24 (17%) of the strains, respectively and were not associated to any of the studied integrons. Genes that codify enzymes AAC(6')Ib and APH(3')VI were not detected in any strain. Conclusions: The high frequency of integrons found in the studied strains, could partly explain the increasing antimicrobial resistance of Shigella flexneri strains, isolated in Chile (Rev Méd Chile 2003; 131: 727-33)

La resistencia bacteriana a los agentes antimicrobianos ha aumentado durante las últimas décadas. De particular importancia es la descripción de aislamientos de Enterococcus resistente a vancomicina (EVR), de reciente y progresiva descripción en nuestro país. Comunicamos el aislamiento de dos cepas de E. faecium resistentes a vancomicina de pacientes colonizados por este microorganismo en el Hospital Clínico Regional de Concepción. El estudio feno y genotípico fue positivo para vanB, además ambos aislamientos presentaron similitud genética en un estudio de tipificación molecular por rep-PCR. Interesantemente el aislamiento de estas cepas precedió al aislamiento de EVR según el protocolo ministerial. Esta diferencia puede explicarse por los factores de riesgo que presentaron los pacientes estudiados. The antibiotic resistance among bacteria has increased during the last decades. Of particular importance was the report of vancomycin-resistant Enterococcus isolates (VRE), recently described in our country. In this work we report the isolation of two strains of E. faecium resistant to vancomycin from colonized patients admitted to the Hospital Regional de Concepción. The phenotyping and genotyping studies gave positive results for VanB type of vancomycin resistance. Both strains showed genetic similarity when were molecular typed by rep-PCR. Interestingly, the isolation of this strains was previous to the isolation of VRE according to the protocols delineated by the Health Ministry. This difference may be explained by the risk factors exhibited by the colonized patients.