Susceptibilidad antimicrobiana, serotipos capsulares y relación clonal entre cepas invasoras de Streptococcus pneumoniae aisladas de pacientes adultos de la Región del Bío-Bío, Chile: Período 2005-2006 / Antimicrobial susceptibility, capsular serotypes and clonal relationship of invasive Streptococcus pneumoniae isolates in adult population of the Bio-Bio Region, Chile: 2005-2006

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 por ciento), cotrimoxazol (18 por ciento), eritromicina (18 por ciento), cloranfenicol (7 por ciento) y a penicilina en un solo aislado procedente de un foco meníngeo (2 por ciento). 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 por ciento 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 percent), trimethoprim/ sulfamethoxazole (18 percent), erythromycin (18 percent), chloramphenicol (7 percent) and 1 penicillin resistant isolate from a meningeal focus (2 percent) 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 percent of the S. pneumoniae serotypes isolated from bacteraemic adult patients are included in the available commercial vaccine.

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

Los sistemas multidrogas bacterianos contribuyen al desarrollo del fenotipo de multi-resistencia presentado por cepas de Acinetobacter baumannü, patógeno intrahospi-talario, que durante los últimos años ha incrementado su importancia por la creciente resistencia a carbapenémicos. El fenotipo de multi-resistencia está otorgado por la combinación de varios mecanismos de resistencia entre los cuales se encuentran estos sistemas de bombas de expulsión. El sistema multidroga AdeABC se ha detectado en muchas de estas cepas multi-resistentes de A. baumannü y, se ha relacionado con resistencia a diversos grupos de antimicrobianos, incluidos tigeciclina y meropenem. La inhibición de dichos sistemas multidrogas permitiría aumentar la eficacia de la terapia antimicrobiana. La siguiente revisión se enfoca en las bombas de expulsión multidrogas presentes en A. baumannü, con particular énfasis en el sistema AdeABC.

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 oí A. baumanni with special emphasis in the AdeABC system.

Mutaciones en genes gyrA y gyrB en cepas de bacilos Gram negativos aisladas en hospitales chilenos y su relación con la resistencia a fluoroquinolonas / Mutations in gyrA and gyrB genes among strains of Gram-negative bacilli isolated from Chilean hospitals and their relation with resistance to fluoroquinolones

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.

Impacto de la evaluación infectológica en el uso racional de antimicrobianos en pacientes con bacteriemia por Streptococcus pneumoniae / Impact of infectious diseases specialist evaluation on the rational use of antibiotics in patients with Streptococcus pneumoniae bacteremia

The increasing reporting of Streptococcus pneumoniae resistance to penicillin has lead to the recommendation of third generation cephalospirins for the treatment of serious pneumococcal infections. As a consequence, clinicians usually do not prescribe first line antibiotics despiste the availability of susceptibility studies. Whit the aim to evaluate the impact of the infectious diseases specialist evaluation in the apropriate use oh the susceptibility studies, two series were compared: a historic control one (1998-2002, n = 50) and a prospectuve group that had the advisement of one infectious diseases specialist (2003-2006, n = 60). In both series, pneumonia stood out as the source of the bacteremia, and -alcoholism/hepatic insufficiency as associated factor. In the first series, 48 isolates resulted susceptible to penicillin by agar diffusion, and 1 out of 36 patients with pneumonia had a change in the antibiotic therapy to penicillin. In the prospective series, we found 56 susceptible isolates, and the remaining four were classified as intermediate susceptibility according to the MIC value. Antibiotics were changed in 36 out of 50 patients with bacteremic pneumococcal pneumonia (p < 0.05). The infectious diseases specialist evaluation had a positive impact on the use of the microbiological information for therapeutics purposes.

La descripción creciente de Streptococcus pneu-moniae resistente a penicilina, ha llevado a la recomendación de emplear cefalosporinas de tercera generación para el tratamiento de las infecciones neumo-cócicas graves. Como consecuencia, los médicos clínicos no prescriben, usualmente, antimicrobianos de primera línea, a pesar de disponer de estudios de susceptibilidad in vitro. Con el propósito de evaluar el impacto de la asesoría del infectólogo para el uso adecuado de los estudios de susceptibilidad, se compararon dos series: un control histórico (1998-2002, n = 50) y un grupo prospectivo en que sí hubo asesoría infectológica (2003-2006, n = 60). En ambas series, la neumonía fue el foco principal de bacteriemia y alcoholismo/falla hepática los factores asociados más frecuentes. En el primer grupo, 48 aislados resultaron susceptibles a penicilina por prueba de difusión en agar y en uno de 36 pacientes con neumonía, se efectuó cambio en la terapia antimicrobiana a bencilpeni-cilina. En el grupo prospectivo, hubo 56 cepas susceptibles y las cuatro restantes fueron clasificadas como de susceptibilidad intermedia, de acuerdo con los valores de CIM. Se cambió de antimicrobiano en 36 de 50 pacientes con neumonía neumocóccica bacteriémica (p < 0,05). La evaluación hecha por el infectólogo tuvo un impacto positivo en el uso de información micro-biológica con fines terapéuticos.

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.

Producción de ß-lactamasas de espectro extendido (BLEE) en cepas de Acinetobacter baumannii aisladas en hospitales de la VIIIª Región, Chile / Extended spectrum ß-lactamases (ESBL) production in Acinetobacter baumannii strains isolated from Chilean hospitals belonging to VIII Region

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.

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.

Transferecia de de ß-lactamasas de espectro extendido desde cepas hospitalarias de Klebsiella pneumoniae a otras especies de enterobacterias / Transference of extended-spectrum ß-lactamases from nosocomial strains of Klebsiella pneumoniae to other species of Enterobacteriaceae

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.

Aminoglucósidos-aminociclitoles: características estructurales y nuevos aspectos sobre su resistencia / Aminoglycosides-aminocyclitols: structural characteristics and new aspects on resistance

Los antimicrobianos aminoglucósidos-aminociclitoles constituyen una de las familias de agentes antibacterianos de mayor actividad sobre bacilos gramnegativos aeróbicos. Estos compuestos están característicamente formados por la combinación de un alcohol cíclico aminado (aminociclitol) y aminoazúcares (aminoglucósidos) unidos por enlaces glucosídicos. La potente actividad bactericida de estos compuestos parece no sólo explicarse por su capacidad de inhibición de la síntesis proteica, sino que también por un efecto sumatorio y pleiotrópico que altera la permeabilidad de la membrana citoplasmática. La penetración de estos antibacterianos en células bacterianas ocurre mediante tres fases bien definidas, siendo las dos últimas dependientes de la fuerza protón motriz (FPM). Este hecho explica la ausencia de actividad de estos compuestos sobre bacterias anaeróbicas. La resistencia bacteriana a este grupo de antibacterianos se debe, principalmente, a la producción de enzimas modificantes de aminoglucósidos. Estas enzimas son normalmente codificadas por elementos extracromosomales tales como plßsmidos y transposones. Sin embargo, se han identificados nuevos mecanismos y elementos genÚticos que participarían en los fenómenos de resistencia. Recientemente se ha descrito la metilación de bases involucradas en la unión entre el ARN 16S y el aminoglucósido, lo que implicaría un nuevo mecanismo de resistencia contra esta familia de antimicrobianos. Por otra parte, los cassettes genéticos adquieren una creciente importancia ya que albergan genes de resistencia a múltiples familias de antibacterianos, entre ellos, los aminoglucósidos-aminociclitoles. Estos cassettes genÚticos se encuentran asociados a integrones, los cuales son capaces de captar estos determinantes de resistencia.

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

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.

Integrones y cassettes genéticos de resistencia: estructura y rol frente a los antibacterianos / Integrons and resistance gene cassettes: structure and role against antimicrobials

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 MÚd Chile 2004; 132: 619-26).

Metodología clásica y molecular en la identificación de especies de enterococcus spp / Classic and molecular methodologies for the identification of enterococcus species

Background: Enterococcus is a bacterial genus with low virulence. However, in the last years, the importance of some enterococcus species as nosocomial pathogens has increased, specially due to their resistance to some antimicrobial. Aim: To identify enterococcus strains using classical biochemical techniques and genomic amplification with Polymerase Chain Reaction (PCR). Material and methods: Three hundred and five enterococcus strains, isolated between 1996 and 1999, from different clinical specimens in hospitals and other centers of the VIIIth Region of Chile, were studied. The isolates were identified, to the species level, according to the scheme proposed by Carvalho et al. Identification of some strains was confirmed by PCR. Results: Eighty nine percent of isolates were identified as E fócalis, 10.2 percent as E fócium and 3.3 percent as other species. Conclusions: PCR is a fast and promising technique, useful in the identification of Enterococcus species

Propiedades microbiológicas, clasificación y relación estructuras-actividad de cefalosporinas e importancia de las cefalosporinas de cuarta generación / Microbiological properties, classification and structure-activity relationships of cephalosporins and the importance of fourth generation cephalosporins

Las cefalosporinas son uno de los grupos de mayor importancia dentro de los ß-lactámicos. Existen diversas clasificaciones de esta moléculas, siendo la más utilizada aquella que agrupa a estos compuesto de acuerdo a propiedades estructurales, microbiológicas y desarrollo histórico: primera a cuarta generación. Las cefalosporinas de tercera generación han sido ampliamente utilizadas, pero la emergencia de resistencia bacteriana fundamentalmente derivada de la producción de ß-lactamasas tanto cromosomales como plasmidiales, ha limitado el uso de estos compuestos. Las cefalosporinas de cuarta generación se caracterizan por la presencia de un nitrógeno cuaternario en C, además de mantener el grupo metoxi-imino aminotiazolil en C. Presentan una elevada penetración intracelular a través de la membrana externa de bacilos Gram negativos y tienen una baja afinidad por enzimas que degradan cefalosporinas de tercera generación. Cefepime, una cefalosporina de cuarta generación, demostró una mayor actividad inhibitoria sobre cepas chilenas de Klebsiella pneumoniae y Escherichia coli productoras de ß- lactamasa de espectro extendido, que cefotaxima y ceftazidima

Consideraciones generales sobre el uso de agentes antimicrobianos en pacientes hepáticos / General remarks: antimicrobial agents use in hepatic patients

El hígado juega un papel fundamental en el metabolismo de las drogas, incluyendo los antimicrobianos. En los pacientes con enfermedad hepática, se deben monitorizar cuidadosamente los efectos adversos y toxicidad de estos medicamentos. En este artículo se analizan los aspectos del metabolismo de los antimicrobianos, particularmente relacionados a los cambios farmacocinéticos en los pacientes hepáticos. Además, se dan algunas recomendaciones prácticas sobre su uso en estos pacientes