Antibacterial Efficacy of Dihydroxylated Chalcones in Binary and Ternary Combinations with Nalidixic Acid and Nalidix Acid-Rutin Against Escherichia coli ATCC 25 922.

In order to determine the existence of synergism, the bacteriostatic action of flavonoids against Escherichia coli ATCC 25 922 between dihydroxylated chalcones and a clinically interesting conventional antibiotic, binary combinations of 2',3-dihydroxychalcone, 2',4-dihydroxychalcone and 2',4'-dihydroxychalcone with nalidixic acid and its ternary combinations with rutin (inactive flavonoid) were assayed against this Gram negative bacterium. Using a kinetic-turbidimetric method, growth kinetics were monitored in broths containing variable amounts of dihydroxychalcone alone, combinations of dihydroxychalcone variable concentration-nalidixic acid constant concentration and dihydroxychalcone variable concentration-nalidixic acid constant concentration-rutin constant concentration, respectively. The minimum inhibitory concentrations of dihydroxychalcones alone and its binary and ternary combinations were evaluated. All chalcones, and their binary and ternary combinations showed antibacterial activity, being rutin an excellent synergizing for the dihydroxychalcone-nalidixic acid binary combination against E. coli ATCC 25 922. Thus, this synergistic effect is an important way that could lead to the development of new combination antibiotics against infections caused by E. coli.

New antimicrobial combinations: substituted chalcones- oxacillin against methicillin resistant Staphylococcus aureus

Staphylococcus aureus, the most virulent Staphylococcus species, is also the prevalent pathogen isolated from hospitalized patients and the second most common from patients in outpatient settings. In general, bacteria have the genetic ability to transmit and acquire resistance to drugs, which are utilized as therapeutic agents. Related studies of antimicrobial activity indicate that crude extracts containing flavonoids, triterpenes and steroids have showed significative activity against several Staphylococcus aureus strains. Combination effects between flavonoids and antibiotics also have been reported. The aim of the present work was to investigate in vitro synergism between several chalcones substituted in combination with oxacillin, an antibiotic used conventionally against S. aureus ATCC 43 300 that is resistant to meticillin, using the kinetic turbidimetric method developed earlier. The results were satisfactory for all assayed combinations and in accordance with the mechanism of bacteriostatic inhibition previously proposed, except for 2´,4´-dihydroxy-3´-methoxychalcone - oxacillin. The best combination was 2´,3´-dihydroxychalcone - oxacillin (MIC: 11.2 μg/mL). Further investigations are needed to characterize the interaction mechanism with antibiotics. Thus, chalcones - oxacillin combination could lead to the development of new antibiotics against methicillin resistant S. aureus infection.

New antimicrobial combinations: substituted chalcones- oxacillin against methicillin resistant Staphylococcus aureus.

Staphylococcus aureus, the most virulent Staphylococcus species, is also the prevalent pathogen isolated from hospitalized patients and the second most common from patients in outpatient settings. In general, bacteria have the genetic ability to transmit and acquire resistance to drugs, which are utilized as therapeutic agents. Related studies of antimicrobial activity indicate that crude extracts containing flavonoids, triterpenes and steroids have showed significative activity against several Staphylococcus aureus strains. Combination effects between flavonoids and antibiotics also have been reported. The aim of the present work was to investigate in vitro synergism between several chalcones substituted in combination with oxacillin, an antibiotic used conventionally against S. aureus ATCC 43 300 that is resistant to meticillin, using the kinetic turbidimetric method developed earlier. The results were satisfactory for all assayed combinations and in accordance with the mechanism of bacteriostatic inhibition previously proposed, except for 2´,4´-dihydroxy-3´-methoxychalcone - oxacillin. The best combination was 2´,3´-dihydroxychalcone -oxacillin (MIC: 11.2 µg/mL). Further investigations are needed to characterize the interaction mechanism with antibiotics. Thus, chalcones - oxacillin combination could lead to the development of new antibiotics against methicillin resistant S. aureus infection.

Determination of the responsible molecular zone for the chalcones bacteriostatic activity

Foi estudada a bioatividade de compostos com estrutura de acetofenoma e benzadeído pela metodologia cinético-turbidimétrica. Os agentes testados näo inibiram o desenvolvimento de S. aureus ATCC 25.923, mas foram eficientes para E. coli ATCC25.992. Os resultados foram satisfatoriamente interpretados, a partir da fórmula anteriormente proposta, para estudo do mecanismo de açäo bacteriostática. Na comparaçäo de substâncias de estruturas similares, definiu-se a Eficácia Bacteriostática Percentual (Ebp) de um fármaco com Ebp = 100/CIM, em que 100 é o fator percentual arbitrário e CIM é a concentraçäo inibitória mínima do fármaco, em ug/ml. Na comparaçäo das Ebp dos pares de acetofenonas e benzaldeídos apropriados, encontra-se que: Ebp (acetofenona) + Ebp (benzaldeído) <<<< Ebp (chalcona) A maior Ebp, observada para as chalconas deve-se à presença na estrutura de chalcona da ligaçäo dupla Calfa=Cbeta, que possibilita a intensificaçäo do deslocamento eletrônico no anel B da molécula, aumentando a polarizaçäo do grupo carbonila e a oxidrila vizinha (2) é a responsável pela presença da atividade bacteriostática destas substâncias

Determinación de la concentración inhibitoria mínima a partir de parâmetros cinéticos de crecimiento / Minimum inhibitory concentration determination by kinetic parameters of growth

Se evaluó la actividad bacteriostática de 2',4-dihidroxichalcona y 7-hidroxiflavanona frente a Staphylococcus aureus ATCC 25 923 y Escherichia coli ATCC 25 922, utilizando una técnica cinética turbidimétrica original y comparando los resultados logrados por otras metodologías tradicionales (difusión en agar, dilución en agar, macrodilución en caldo). El nuevo procedimiento propuesto comprende la determinación de curvas de crecimiento de los microorganismos en medios aireados: una serie de erlenmeyers de 500 ml provistos de cortacorrientes, conteniendo 100 ml de caldo nutritivo fueron acicionados de las soluciones de las drogas en concentraciones crecientes desde 10 a 200 ug/ml agregando a uno de ellos el diluyente sin droga como control; cada enlenmeyer fue sembrado con 2 ml de inóculo y colocado en mesa agitadora dentro de una cámara de cultivo. Alícuotas de los cultivos fueron extraídas durante 5 h cada 20 min y se efectuó la lectura de transmitancia a 720 nm. La concentración celular a diferentes tiempos se obtuvo por medio de la relación 1n N = 27,4 - 10,3.T, para S. aureus y 1n N = 27,1 - 8,56.T para E. coli (N:ufc/ml y T: transmitancia). A partir de las representaciones gráficas de 1n N ante tiempo, se midieron las velocidades específicas de crecimiento de las bacterias u para cada concentración de droga (C), determinándose por medio de regresión no lineal la ecuación: µT-A.[C]/(1+B;[C] (µt: velocidad específica de crecimiento para [C]=0 (testigo); A y B: constantes empíricas propias de cada sistema droga-microrganismo). La concentración inhibitoria mínima se calculó con la expresión: CIM = µT/(A - µT.B), obtenida de la anterior, haciendo µ=0. Los valores de CIM obtenidos de esta forma son en general mayores que los determinados con las metodologías tradicionales. La metodología propuesta, en apariencia más laboriosa, presenta las siguientes características: fácil estandarización de los inóculos; cálculo de la CIM con pocas determinaciones de µ en presencia de distintas concentraciones de droga; interpretación de la inhibición total o parcial de diversos microorganismos con ecuaciones sencillas; útil para la evalación de la actividad antibacteriana de nuevos compuestos sintéticos y naturales; económica; resultados altamente reproducibles y un tiempo adecuado de duración del ensayo.

Actividad bacteriostatica de 2', 4'- dihidroxi 3'-metoxichalcona / Bacteriostatic activity of 2', 4'- dihydroxy 3'-methoxychalcone

Continuando la realización de ensayos microbiológicos con sustancias naturales de propiedades desconocidas, se investigó y cuantificó el efecto ejercido por 2',4' -dihidroxi-3' -metoxichalcona (aislada de la Zuccagnia Punctata Cav., San Luis, Argentina), sobre el crecimiento de cepas de Staphylococcus aureus y Escherichia coli. Utilizando un método cinétido turbidimétrico se determinó la CMI (58,6 microng/ml) y se interpretó la actividad bacteriostática del compuesto mediante un mecanismo de inhibición que implica la complejación de metales indispensables para el metabolismo del microorganismo