Caracterización fenotípica y genotípica de la resistencia a imipenem en Pseudomonas aeruginosa aisladas en un hospital de Buenos Aires / Phenotypic and genotypic characterization of imipenem-resistant Pseudomonas aeruginosa isolated in Buenos Aires

En el presente estudio, que tuvo por objeto analizar los mecanismos involucrados en la resistencia a carbapenemes, se incluyeron 129 aislamientos de Pseudomonas aeruginosa recuperados durante el año 2006 en el Hospital "Eva Perón" de la Provincia de Buenos Aires. La caracterización fenotípica y genotípica de la resistencia permitió reconocer la presencia de metalo-beta-lactamasas (MBL) en el 14% de esos aislamientos. En todos ellos se identificó la presencia de la enzima IMP-13; sin embargo, algunos aislamientos resultaron sensibles a carbapenemes de acuerdo con los puntos de corte establecidos por el CLSI e incluso con las sugerencias de la Subcomisión de Antimicrobianos de SADEBAC, AAM. El ensayo de detección fenotípica de MBL de sinergia con doble disco resultó útil en este estudio. Sólo aquellos aislamientos productores de IMP-13 que a su vez presentaron alteraciones en las proteínas de membrana externa resultaron completamente resistentes a imipenem. Los aislamientos productores de MBL correspondieron a varios tipos clonales, lo cual sugiere no sólo la diseminación de una cepa resistente, sino también la diseminación horizontal de este mecanismo de resistencia entre clones diferentes.

From 129 P. aeruginosa isolated at a health care centre located in Buenos Aires (Hospital "Eva Perón"), 14% produced IMP-13. Although 18 isolates were metallo-beta-lactamases (MBL) producers, only those isolates that displayed altered outer membrane protein profiles correlated with the resistant category according to CLSI or even Subcomisión de Antimicrobianos, SADEBAC, AAM. Phenotypic screening of metallo-beta-lactamases proved to be appropriate for detecting MBL producing isolates. IMP-13 producing isolates corresponded to at least five different clonal types, which not only suggests the dissemination of the resistant strain but also of the resistant marker.

Infecciones adquiridas en la comunidad por Staphylococcus aureus resistente a meticilina en un hospital de agudos / Community-acquired methicillin-resistant Staphylococcus aureus infections in a hospital for acute diseases

Staphylococcus aureus resistente a meticilina (SAMR) es uno de los principales agentes asociados a infecciones intrahospitalarias; sin embargo, en los últimos años ha surgido como un patógeno emergente de la comunidad, causando infecciones graves, principalmente en jóvenes. Se describen 33 casos de infecciones por SAMR de origen comunitario, diagnosticadas entre mayo de 2005 y junio de 2006 en el HIGA "Eva Perón". Se estudiaron retrospectivamente los aislamientos; se confirmó la resistencia a meticilina mediante la detección del gen mecA, se investigó la presencia de genes que codifican dos factores de virulencia (leucocidina de Panton-Valentine -LPV- y g-hemolisina) y el tipo de casete mec mediante PCR. Todos los pacientes se encontraban sanos previamente. Cuatro pacientes menores de 12 años presentaron bacteriemia, uno con neumonía grave y los 3 restantes con infección osteoarticular; todos los pacientes mayores de 12 años presentaron infecciones de piel y partes blandas sin compromiso sistémico. Se constató la presencia de casete mec tipo IV en todos los aislamientos; la resistencia a meticilina no se acompañó de resistencia a otros antimicrobianos; los aislamientos fueron portadores de genes que codifican para LPV y para g-hemolisina. Es importante considerar la presencia de estas cepas de origen comunitario a fin de elaborar estrategias para su correcto tratamiento.

Methicillin- resistant Staphylococcus aureus (MRSA) is one of the most prevalent pathogens associated with nosocomial infections. However, most recently, MRSA has arisen as an emerging community pathogen, causing serious infections, mainly among young patients. We herein describe 33 cases of infections caused by community-acquired MRSA (CMRSA), diagnosed between May 2005 and June 2006, at "Eva Perón" Hospital. The isolations were retrospectively studied. Methicillin resistance was confirmed by means of the detection of the mecA gene, and the genes for two virulence factors (Panton-Valentine Leucocidin -PVL- and g-haemolysin) as well as the cassette mec type were screened by PCR. All the patients were previously healthy. Four patients under 12, presented bacteremia, one had serious pneumonia, and the three remaining patients had osteoarticular infections; all the patients over 12, had skin and soft tissue infections without systemic damage. The C-MRSA strains harboured cassette mec type IV, and the PVL and g-haemolysin genes. They were methicillin-resistant, with no other associated resistances. It is important to consider the presence of these community- acquired strains in order to develop strategies for their correct treatment.

Actividad "in vitro" de diferentes antibacterianos sobre bacilos gram-negativos no fermentadores, excluidos Pseudomonas aeruginosa y Acinetobacter spp / ‘In vitro' activity of different antimicrobial agents on gram-negative nonfermentative bacilli, excluding Pseudomonas aeruginosa and Acinetobacter spp

Los bacilos gram-negativos no fermentadores se encuentran ampliamente distribuidos en el medio ambiente. Además de causar dificultades en la identificación, a menudo presentan una marcada multirresistencia a los antimicrobianos incluyendo aquellos activos frente a Pseudomonas aeruginosa. El objetivo de este trabajo fue evaluar la actividad "in vitro" de diferentes antimicrobianos sobre 177 aislamientos de bacilos gram-negativos no fermentadores (excluidos Pseudomonas aeruginosa y Acinetobacter spp.) provenientes de especimenes clínicos. Las concentraciones inhibitorias mínimas (CIM) se determinaron por el método de dilución en agar Mueller Hinton frente a los siguientes antibacterianos: ampicilina, piperacilina, piperacilina-tazobactama, sulbactama, cefoperazona, cefoperazona-sulbactama, ceftazidima, cefepima, aztreonam, imipenem, meropenem, colistina, gentamicina, amicacina, trimetoprima-sulfametoxazol (TMS), cloranfenicol, eritromicina, rifampicina, norfloxacina, ciprofloxacina y minociclina. Sobre siete aislamientos: Sphingobacterium multivorum (2), Sphingobacterium spiritivorum (1), Empedobacter brevis (1), Weeksella virosa (1), Bergeyella zoohelcum (1) y Oligella urethralis (1) se ensayó la sensibilidad a amoxicilina-ácido clavulánico y ampicilina-sulbactama y no se determinó la actividad de cefoperazona ni de sulbactama. La multirresistencia fue comúnmente observada en los aislamientos de Stenotrophomonas maltophilia, Burkholderia cepacia, Chryseobacterium spp., Myroides spp., Achromobacter xylosoxidans y Ochrobactrum anthropi. En cambio, Pseudomonas stutzeri, Shewanella putrefaciens-algae, Sphingomonas paucimobilis, Pseudomonas oryzihabitans, Bergeyella zoohelcum, Weeksella virosa y Oligella urethralis, fueron ampliamente sensibles a los antibacterianos ensayados. Debido a la gran variabilidad observada en la sensibilidad a los antimicrobianos en las distintas especies, se hace imprescindible realizar la prueba de sensibilidad a los antibacterianos a fin de abordar la elección correcta del mismo. Debido a la marcada multirresistencia de algunas especies, surge la necesidad del desarrollo de nuevos agentes antimicrobianos que posean actividad sobre este grupo de bacterias, así como tambien la búsqueda de combinaciones sinérgicas.

Gram-negative nonfermentative bacilli (NFB) are widely spread in the environment. Besides of difficulties for identification, they often have a marked multiresistance to antimicrobial agents, including those active against Pseudomonas aeruginosa. The objective of this study was to evaluate the ‘in vitro' activity of different antimicrobial agents on 177 gram-negative nonfermentative bacilli isolates (excluding Pseudomonas aeruginosa and Acinetobacter spp.) isolated from clinical specimens. Minimum inhibitory concentrations (MIC) were determined according to the Mueller Hinton agar dilution method against the following antibacterial agents: ampicillin, piperacillin, piperacillin-tazobactam, sulbactam, cefoperazone, cefoperazone-sulbactam, ceftazidime, cefepime, aztreonam, imipenem, meropenem, colistin, gentamicin, amikacin, trimethoprim-sulfamethoxazole, chloramphenicol, erythromycin, rifampin, norfloxacin, ciprofloxacin and minocycline. Seven isolates: Sphingobacterium multivorum (2 ), Sphingobacterium spiritivorum (1), Empedobacter brevis (1), Weeksella virosa (1), Bergeyella zoohelcum (1) and Oligella urethralis (1), were tested for amoxicillin-clavulanic acid and ampicillin-sulbactam susceptibility, and susceptibility to cefoperazone or sulbactam was not determined. Multiresistance was generally found in Stenotrophomonas maltophilia, Burkholderia cepacia, Chryseobacterium spp., Myroides spp., Achromobacter xylosoxidans, and Ochrobactrum anthropi isolates. On the other hand, Pseudomonas stutzeri, Shewanella putrefaciens-algae, Sphingomonas paucimobilis, and Pseudomonas oryzihabitans, Bergeyella zoohelcum, Weeksella virosa and Oligella urethralis were widely susceptible to the antibacterial agents tested. As a result of the wide variation in antimicrobial susceptibility shown by different species, a test on susceptibility to different antibacterial agents is essential in order to select an adequate therapy. The marked multiresistance evidenced by some species, prompts the need to develop new antimicrobial agents active against this group of bacteria and to search for synergistic combinations.

Bacteriemia por Brucella canis. Aislamiento con el sistema Bact-Alert / [Bacteremia by Brucella canis. Isolation with the Bact-Alert system]

Brucella canis and other species of the genus Brucella can cause human disease. However, this species infrequently cause human disease, including in countries where dogs population is highly infected. A 15 years old male was admitted to the hospital with 15 days history of fever without visible focus. Physical examination revealed pain at liver palpation and axillar, cervical and inguinal lymphoadenomegalies. Abdominal ultrasonography showed spleenomegally, the chest Rx and the trans thoracic echocardiogram were normal. Five blood samples were obtained and cultured in 2 standards bottles (time of positivization 72 - 64.8 hours), and 3 pediatric FAN bottles (time of positivization 74.5; 72 and 67.2 hours) (Bact-Alert system, Biomerieux, Marcy, l’Etolie, France). The microorganism was presuntive identified as B. canis, and then was confirmed in the National Reference Center Instituto ANLIS [quot ]Carlos G. Malbran[quot ]. After 14 days of initiating ceftriaxone treatment the patient was afebrile. When the confirmation of Brucella was made, he was discharged and ambulatory was prescribed with doxycycline and rifampin for 21 days. Bones were not compromised and the outcome was good with complete resolution of his illness.

Sistema automatizado de hemocultivos Bact-Alert: 5 vs 7 dias de incubación. Primer estudio multicéntrico argentino / [Bact-Alert automatized system for blood cultures: 5 vs 7 days of incubation. First Argentine multicentre study]

Bact-Alert automatized system for blood cultures: 5 vs 7 days of incubation. First Argentine multicentre study. Between January and December 2001, we analyzed 80,141 blood cultures by the Bact-Alert system (14,960 FAN aerobics, 3,855 FAN anaerobic, 11,114 standards aerobics, 11,367 standards anaerobic, 12,054 pediatrics and 26,791 FAN pediatrics bottles) and 44.235 series from 27.615 patients at eight hospitals of Buenos Aires city, one of La Plata city and three of the Buenos Aires province. A total of 13,657 blood cultures yielded a positive result. Only 181 of them had been detected as positive between the 5th and 7th day of incubation and only 26 (0.19

) had clinical significance (Staphylococcus aureus 3; coagulase negative staphylococci 2; Enterococcus faecalis 1; Streptococcus pneumoniae 2; Campylobacter spp 1; Escherichia coli 1; Enterobacter cloacae 1; Enterobacteraerogenes 1; Citrobacter freundii 1; Klebsiella pneumoniae 1; Proteus mirabilis 1; Serratia marcescens 4; yeasts 7, including one strain of Cryptococcus neoformans). Of the total of contaminants, 38

were isolated by the anaerobic standard (65

were Propionibacterium spp and 29

by the FAN aerobic (33.3

difphteroids and 28.9

by the pediatric, 9

by aerobic standard and 1.4

by FAN anaerobic bottle. Our results show that the prolonged incubation of blood cultures for more than 5 days using the Bact-Alert system is unnecessary.

Evaluación de API 20 NE (versión 6.0) en bacilos gram-negativos no fermentadores de glucosa infrecuentes / [Evaluation of API 20 NE (version 6.0) in rare Gram-negative non-glucose-fermenting bacilli]

The ability of the API 20 NE method (6.0 version, bio-Mérieux, Marcy L’Etoile, France) to identify 188 strains of gram negative nonfermentative bacilli (NFB) was evaluated (Fenazinic pigment producing Pseudomonas aeruginosa and Acinetobacter spp. were excluded). These were isolated from patients treated at the Hospital de Clínicas José de San Martín of the University of Buenos Aires during the period 1996-2001. Strains were identified according to the Schreckenberger P testing method. Out of 188 NFB strains, 175 (93.09

) were correctly identified by the API 20 NE method at the genus and species level (IC95 = 88.47-96.27) while 61 (32.45

) required additional testing for correct identification. Thirteen strains (6.91

; IC95 3.73-11.53) could not be correctly identified and none of them were classified as [quot ]non identified[quot ]. The API 20 NE method is a practical, easy to handle, fast and useful system for the identification of NFB since conventional manual methods take longer and require many biochemical, enzymatic and physiological tests which are sometimes not available depending on the size and capability of the laboratory. Although it is easy to handle, the API 20 NE identification system must be interpreted by an expert microbiologist who must compare the results obtained by this system with the information provided by the distinctive cultures and mobility patterns of these organisms.

Actividad de catorce antimicrobianos sobre Eikenella corrodens / [Activity of 14 antimicrobials against Eikenella corrodens]

Eikenella corrodens is a gram-negative bacillus that colonizes as normal flora of the mouth, the upper respiratory tract and the gastrointestinal tract. The aim of this study was to determine the susceptibility patterns against fourteen antibiotics of 25 E. corrodens strains isolated at our hospital. MICs were determined by the agar dilution technique using M³eller-Hinton agar with sheep blood (5

v/v) to penicillin, ampicillin, ampicillin-sulbactam, cephalotin, cefoxitin, ceftiaxone, colistin, gentamicin, amikacin, erythromycin, rifampin, ciprofloxacin and clindamycin. The most active antibiotics were ciprofloxacin and ceftriaxone (MIC90 = 0.008 and 0.125 microgram/ml, respectively), whereas eritromycin, gentamicin and amikacin showed less activity. Only one strain was beta lactamase positive, and it was inhibited by sulbactam. Erithromycin, gentamicin and amikacin had poor activity (MIC90 = 16.8 and 64 micrograms/ml, respectively), whereas all the strains were uniformly resistant to clindamycin (MIC > or = 32 micrograms/ml). We suggest about the need of periodical surveys of E. corrodens susceptibility patterns, since strains have been found with decreased susceptibility against antibiotics which are currently being used for the treatment of infectious diseases.