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      Influencia de la concentración inhibitoria mínima de penicilina en la acción sinérgica de su combinación con gentamicina frente a estreptococos del grupo viridans Translated title: Influence of penicillin minimal inhibitory concentration in the synergy between penicillin and gentamicin in viridans group streptococci

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          Abstract

          Los porcentajes de resistencia a penicilina entre los estreptococos del grupo viridans han llegado a niveles superiores al 60% en algunos estudios realizados en la década pasada, y en recientes trabajos se los encontró asociados a un mayor índice de mortalidad en las bacteriemias. Aún no se conoce cuál es el nivel de concentración inhibitoria mínima de penicilina para el cual resulta imposible lograr un efecto sinérgico con algún aminoglucósido. Con este propósito, se estudió la sensibilidad a penicilina de 28 cepas de estreptococos del grupo viridans aisladas de materiales clínicamente significativos en el Hospital de Pediatría "Prof. Dr. Juan P. Garrahan". Se seleccionaron siete aislamientos pertenecientes al grupo mitis con distintas características de sensibilidad, y con ellos se ensayó la curva de muerte frente a penicilina, gentamicina y penicilina más gentamicina, con concentraciones de penicilina por encima y por debajo de su concentración inhibitoria mínima. En ningún caso se observó sinergia cuando la concentración de penicilina fue inferior a la concentración inhibitoria mínima, al menos en este grupo particular de estreptococos que presentaron concentraciones inhibitorias mínimas de gentamicina ³ 16 µg/ml. Se encontró sinergia en cinco de las siete cepas cuando se trabajó con concentraciones de penicilina superiores a la concentración inhibitoria mínima. En las otras dos, se detectaron enzimas modificadoras de aminoglucósidos.

          Translated abstract

          Penicillin resistance rates higher than 60% have been recorded in viridans group streptococci by some authors during the 90's and recently such resistance was associated with higher levels of mortality in bacteremia. The lowest minimal inhibitory concentration of penicillin for which synergy with aminoglycosides is not yet possible is still unknown. In order to try to dilucidate this puzzle, a study on the susceptibility to penicillin of 28 strains of viridans group streptococci isolated from significant samples in the Hospital de Pediatría "Prof. Dr. Juan P. Garrahan" was carried out. Seven mitis group isolates presenting different susceptibility patterns were selected for performing time-killing curves with penicillin, gentamicin, and penicillin plus gentamicin, using higher and lower penicillin concentrations than their minimal inhibitory concentrations. Synergy was not observed when the penicillin concentration was lower than the minimal inhibitory concentration, at least in these strains with minimal inhibitory concentrations of gentamicin ³ 16 µg/ml. When using penicillin in higher concentrations than the minimal inhibitory concentration, synergy was found in five of the seven strains. Aminoglycoside-modifying enzymes were found in the two other streptococci.

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          Most cited references 29

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          Miscellaneous catalase-negative, gram-positive cocci: emerging opportunists.

           Kathryn Ruoff (2002)
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            Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically: Approved Standard

             MJ Ferraro (2003)
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              Viridans streptococci bacteraemia in children with fever and neutropenia: a case-control study of predisposing factors.

              Viridans streptococci (VS) are an increasing cause of bacteraemia in neutropenic patients with cancer. Case-control studies of predisposing factors for acquisition of this infection in children are not published. Between January 1989 and December 1999, 168 episodes of bacteraemia in 161 children with fever and neutropenia of haemato-oncology origin were analysed. 15 cases (9%) in 15 patients were caused by VS. Each case patient was compared with 6 matched control patients; 2 with other Gram-positive cocci (group 2), 2 with gram-negative bacilli bacteraemia (group 3) and two children with fever and neutropenia without bacteraemia (group 4). The median age of patients was 4.1 years (range: 2-15 years). 87% of children had acute leukaemia or lymphomas. Pneumonia was the predominant clinical focus (70%). Shock was observed in 13% of patients. ARDS was observed in one child who died of this complication. Multivariate analysis of risk factors for the development of VS bacteraemia showed that two factors were independent predictors: high doses of cytosine-arabinoside (ARA-C) as part of the chemotherapy treatment (Odds Ratio (OR): 9.3; Confidence Interval (CI) 1.56-55.5) (P<0.014) and the presence of pneumonia (OR: 1.36: CI 2.27-81.9) (P<0.0043). We propose that further studies are warranted to confirm these results.
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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Role: ND
                Journal
                ram
                Revista argentina de microbiología
                Rev. argent. microbiol.
                Asociación Argentina de Microbiología (Ciudad Autónoma de Buenos Aires )
                1851-7617
                June 2007
                : 39
                : 2
                : 107-112
                Affiliations
                [1 ] Hospital Zonal Gral. de Agudos San Roque
                [2 ] Universidad de Buenos Aires Argentina
                [3 ] Hospital de Pediatría Prof. Dr. Juan P. Garrahan Argentina
                Article
                S0325-75412007000200011
                Product
                Product Information: website
                Categories
                MICROBIOLOGY

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