Efecto del cloruro de benzalconio sobre comunidades microbianas en lodos activados y Aeromonas hydrophila
Fecha
2023-09-14
Tipo
tesis doctoral
Autores
Chacón Jiménez, Luz María
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Resumen
La limpieza, como actividad cotidiana, incluye el uso de una gran cantidad de desinfectantes que terminan siendo descargados en aguas residuales domésticas e industriales, en plantas de tratamiento (PTAR) y finalmente en ríos y mares. La contaminación generada por estas sustancias impacta fuertemente las comunidades de microorganismos en los ecosistemas acuáticos. En este contexto esta investigación tuvo como objetivo general estudiar el efecto de estos contaminantes emergentes sobre los microorganismos asociados a las PTAR a través de diferentes modelos microbianos. Par esto el abordaje se realizó en tres ámbitos, en el primero se examinaron los efectos del cloruro de benzalconio (BAC) en una comunidad microbiana proveniente de lodos activados, en el segundo se examinaron los mecanismos de Aeromonas hydrophila (aislamientos de baja susceptibilidad), proveniente de una PTAR, para resistir el BAC y en el tercero se caracterizaron aislamientos de Escherichia coli en función de su resistencia a los antibióticos. Entre nuestros principales hallazgos destaca que la comunidad microbiana de los lodos activados, después de exponerse al BAC, presenta una disminución en la diversidad bacteriana, en paralelo con un aumento en la carga del gen qacE/qacEΔ, asociado directamente con la resistencia a aminas cuaternarias como el BAC. Sin embargo, la diversidad funcional de la comunidad se mantuvo intacta hasta las concentraciones de 25 µg/mL - 50 µg/mL. En el segundo trabajo se determinó que la cepa A. hydrophila INISA09 presenta un alto número de mutaciones puntuales en comparación con otras cepas de la misma especie. La respuesta observada frente al BAC, estudiada a través de ensayos de proteómica, indicó que la resistencia es modulada a través de dos mecanismos: el primero a nivel de la membrana, con disminución en la expresión de ciertas porinas y citocromos, y aumento en la expresión de bombas de eflujo y otros citocromos; y el segundo, a nivel citoplasmático, con aumento en reacciones metabólicas de tipo redox. En el tercero fue posible encontrar aislamientos de E. coli multirresistentes capaces de transferir horizontalmente genes de resistencia de forma exitosa en los afluentes y efluentes de las PTAR estudiadas. Los resultados demuestran que el uso continuo de productos biocidas disminuye la diversidad de las comunidades microbianas, las cuales pueden adaptarse fácilmente a este sin perder su perfil funcional, entendido como su capacidad de respiración de sustratos. Además, especies como E. coli y A. hydrophila también se han adaptado a ambientes contaminados, desarrollando mecanismos de supervivencia que incluyen desde transferencia horizontal de genes hasta modificaciones en estructura y metabolismo. Estos hallazgos proporcionan ejemplos de adaptación microbiana a sustancias tóxicas; sin embargo, sus implicaciones a medio y largo plazo en los cuerpos receptores de aguas e incluso sobre la salud deben ser investigadas en profundidad.
Cleaning, as a daily activity, involves the use of a large number of disinfectants that end up being discharged into domestic and industrial wastewater, in wastewater treatment plants (WWTPs), and finally into rivers and seas. The pollution generated by these substances strongly impacts the communities of microorganisms in aquatic ecosystems. In this context, the overarching objective of this research was to study the effect of these emerging contaminants on microorganisms associated with WWTPs using various microbial models. To achieve this, the investigation was approached in three main areas. Firstly, the effects of benzalkonium chloride (BAC) on a microbial community originating from activated sludge were examined. Secondly, the mechanisms of Aeromonas hydrophila (an isolate with low susceptibility), obtained from a WWTP, to resist BAC were investigated. Thirdly, Escherichia coli isolates were characterized based on their antibiotic resistance. Among our main findings, it was observed that the microbial community from activated sludge, after exposure to BAC, exhibited a decrease in bacterial diversity, concurrently with an increase in the qacE/qacEΔ gene load, which is directly associated with resistance to quaternary amines like BAC. However, the functional diversity of the community remained intact up to concentrations of 25 µg/mL - 50 µg/mL. In the second study, it was determined that the strain A. hydrophila INISA09 presented a high number of point mutations compared to other strains of the same species. The response observed against BAC, studied through proteomic assays, indicated that resistance is modulated through two mechanisms: firstly, at the membrane level, with decreased expression of certain porins and cytochromes, and increased expression of efflux pumps and other cytochromes; and secondly, at the cytoplasmic level, with an increase in redox-type metabolic reactions. In the third study, it was possible to identify multi-resistant E. coli isolates capable of successfully horizontally transferring resistance genes in the influents and effluents of the studied WWTPs. The results demonstrate that the continuous use of biocidal products reduces the diversity of microbial communities, which can easily adapt to this situation without losing their functional profile, understood as their substrate respiration capacity. Furthermore, species like E. coli and A. hydrophila have also adapted to contaminated environments, developing survival mechanisms that include horizontal gene transfer and modifications in structure and metabolism. These findings provide examples of microbial adaptation to toxic substances. However, their medium and long-term implications on water receiving bodies and even on health should be thoroughly investigated.
Cleaning, as a daily activity, involves the use of a large number of disinfectants that end up being discharged into domestic and industrial wastewater, in wastewater treatment plants (WWTPs), and finally into rivers and seas. The pollution generated by these substances strongly impacts the communities of microorganisms in aquatic ecosystems. In this context, the overarching objective of this research was to study the effect of these emerging contaminants on microorganisms associated with WWTPs using various microbial models. To achieve this, the investigation was approached in three main areas. Firstly, the effects of benzalkonium chloride (BAC) on a microbial community originating from activated sludge were examined. Secondly, the mechanisms of Aeromonas hydrophila (an isolate with low susceptibility), obtained from a WWTP, to resist BAC were investigated. Thirdly, Escherichia coli isolates were characterized based on their antibiotic resistance. Among our main findings, it was observed that the microbial community from activated sludge, after exposure to BAC, exhibited a decrease in bacterial diversity, concurrently with an increase in the qacE/qacEΔ gene load, which is directly associated with resistance to quaternary amines like BAC. However, the functional diversity of the community remained intact up to concentrations of 25 µg/mL - 50 µg/mL. In the second study, it was determined that the strain A. hydrophila INISA09 presented a high number of point mutations compared to other strains of the same species. The response observed against BAC, studied through proteomic assays, indicated that resistance is modulated through two mechanisms: firstly, at the membrane level, with decreased expression of certain porins and cytochromes, and increased expression of efflux pumps and other cytochromes; and secondly, at the cytoplasmic level, with an increase in redox-type metabolic reactions. In the third study, it was possible to identify multi-resistant E. coli isolates capable of successfully horizontally transferring resistance genes in the influents and effluents of the studied WWTPs. The results demonstrate that the continuous use of biocidal products reduces the diversity of microbial communities, which can easily adapt to this situation without losing their functional profile, understood as their substrate respiration capacity. Furthermore, species like E. coli and A. hydrophila have also adapted to contaminated environments, developing survival mechanisms that include horizontal gene transfer and modifications in structure and metabolism. These findings provide examples of microbial adaptation to toxic substances. However, their medium and long-term implications on water receiving bodies and even on health should be thoroughly investigated.
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Palabras clave
biocidas, resistencia a los antimicrobianos, comunidades microbianas, aguas residuales