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.

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

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.

[Community-acquired methicillin-resistant Staphylococcus aureus infections in a hospital for acute diseases]. / 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. 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 (C-MRSA), 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 gamma-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 gamma-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.

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.

[Bact-Alert automatized system for blood cultures: 5 vs 7 days of incubation. First Argentine multicentre study]. / 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. 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% coagulase negative staphylococci), 31.2% by the FAN aerobic (33.3% difphteroids and 28.9% Bacillus spp), 11.8% by the pediatric, 9% by FAN pediatric, 8.33% 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.

[Dog bite infections associated with CDC group EF-4a. Report of 2 cases]. / Infecciones por mordedura de perro asociadas a CDC grupo EF-4a. Comunicación de 2 casos.

BACKGROUND: Group EF-4 bacteria make up part of the normal flora of the oral cavity of dogs and cats. Few reports have been published on the incidence of human infections by this group of bacteria and these are associated with animal bite or scratch. Two cases of infections by CDC group EF-4 by dog bite were diagnosed in 1996 by the Bacteriology Laboratory of the authors' hospital. These cases are herein described and the biochemical analysis and profile of sensitivity of this little known group of bacteria evaluated. METHODS: Two clinical cases of infection by CDC group EF-4a by dog bite are described. Identification of the bacteria was performed by conventional biochemical tests and quantitative antibiotic sensitivity to 12 antibiotics was carried out by the seried broth macrodilution method. RESULTS: The two strains isolated corresponded to biovar "a" of group EF-4 being sensitive to: ampicillin, ceftriaxone, aminoglycosides, chloramphenicol, rifamipicin, TMS and ciprofloxacin, intermediate sensitivity to erythromycin and were resistant to cefalotine, oxacillin and vancomycin. With respect to penicillin, one of the strains was sensitive and the other presented intermediate sensitivity. Neither of the strains produced beta lactamase. CONCLUSIONS: Although Pasteurella sp. is usually considered in dog bite wounds, the possible presence of group EF-4 should be taken into account since the sensitivity of both microorganisms against penicillin and cefalotin, which are effective against Pasteurella but less active against group EF-4 bacteria differ.

Relationship between lactate arteriovenous gradient and tissue lactate content in subendocardial and subepicardial layers of the ischaemic in situ heart.

Myocardial lactate content and simultaneous evolution of a lactate arteriovenous gradient associated with incomplete obstruction of the left coronary bed were studied in dog hearts. Samples of blood were taken from a peripheral artery and the coronary sinus; transmural samples of myocardial tissue were obtained from the left ventricular wall by drill biopsy in animals under total cardiopulmonary by-pass. Lactate content was assessed in subendocardial and subepicardial layers separately. A 40 to 70% reduction in coronary flow induced a quick reduction and even an inversion of the positive lactate gradient while the tissue content, which was similar to the arterial content, rose considerably, chiefly in the subendocardial layer. Lactate accumulating in tissue was released into the blood approximately in proportion to the tissue concentration. The value of employing the lactate concentration difference between arterial blood and coronary sinus blood as an index of the severity and duration of myocardial ischaemia is discussed.

[Comparison of myocardial metabolic effects of in subendocardial and subepicardial layers ischaemia and beta-adrenergic stimulation (author's transl)]. / Comparison des effets métaboliques myocardiques de la stimulation beta-adrénergique et de l'ischémie effectuée dans les zones sous-endocardique et sous-épicardique.

The influence of beta-adrenergic stimulation on myocardium carbohydrate and lipid metabolism has been compared with the influence of ischemia in anesthetized dog heart in situ. Transmural samples necessary to the repeated determination of tissular substrates were taken from left ventricular wall according to the "drill biopsy" technique: they were made possible by a total cardiopulmonary by-pass system. The beta-adrenergic stimulation was obtained by infusion of isoproterenol (1 microgram/kg/min.) and the ischemia by injection into left coronary artery before its division of a viscous mixture, reducing coronary flow by 40 to 70%. In both subendocardial and subepicardial layers, but mainly in the former: --beta-adrenergic stimulation lowers glycogen content and raises lactate content immediately, lowers free fatty acid concentration more progressively without modifying triglyceride concentration significantly; --ischemia decreases glycogen content and increases lactate content in the same way, but raises free fatty acid and triglyceride concentration. Consequently, beta-adrenergic stimulation and ischemia are likely to add their effects on anaerobic glycolysis, whereas they exert an opposite influence on lipid metabolism.

Modifications by ischemia of carbohydrate and lipid metabolism of the dog heart in situ from circulating and endogenous substrates.

The uptake of circulating substrates, lactate, glucose and free fatty acids (FFA) has been investigated concurrently with the tissular contents of these principles and the glycogen and triglyceride stores in the dog heart in situ submitted to incomplete obstruction of left coronary bed. Transmural samples necessary for the repeated determination of tissular substrates were taken from left ventricular wall by means of a total cardiopulmonary by-pass system, then divided to allow the analysis separately in subendocardial and subepicardial layer. A 40 to 70% reduction in coronary blood flow gave rise to decrease or suppression of uptake of all the substrates or even to conversion of uptake into output. The modifications of uptake are chiefly related to the deficiency of breakdown by oxidation, though lessened in the case of FFA by incorporation into triglycerides and enhanced in the case of glucose by glycogenolysis. Glycogenolysis and consequent anaerobic glycolysis appear to be the main process available against the energy cellular defect linked with oxygen lack which affects notably more subendocardial than subepicardial layer.