Pseudomonas aeruginosa: una bella oportunista

Las bacterias son infinitamente más antiguas que el hombre y se reproducen más rápido, cada quince minutos y en una hora tienen cuatro generaciones, mientras que el hombre necesita un siglo para ello, de modo que en la larga existencia bacteriana somos apenas un minúsculo accidente. Toda la maravillosa maquinaria reunida en una sola bacteria de la especie Pseudomonas aeruginosa no fue planeada contra nosotros, incluyendo señales de quorum, bombas de expulsión, integrones, biofilm y piocinas, ya presentes en su vida natural o planctónica. Su adaptación a la vida nosocomial forzó a estudiarla y la organización de sus múltiples capacidades hace plantear que en su vida hay un propósito, una suerte de "inteligencia bacteriana" en contraposición a la tesis de Jacques Monod que estima la vida en este planeta como fruto del azar y de la necesidad.

Bacteria are infinitely older tan man and reproduce faster, every fifteen minutes and in one hour they have four generations, while man needs a century for have the same, so that in the long bacterial existence we are just a tiny accident. All the wonderful machinery assembled in a single bacterium of the species Pseudomonas aeruginosa it was not planned against us, including quorum sensing, efflux pumps, integrons, biofilm and pyocins, already presents in their natural or planktonic life. Her adaptation to hospital life forced to study this wonderful creature, and the organization of such multiple capacities suggests the existence of a vital purpose, a kind of bacterial intelligence, contrary to Jacques Monod's thesis, which estimate life in this planet as the result of chance and necessity.

Salmonella entérica serovar Enteritidis biofilm lifestyle induces lower pathogenicity and reduces inflammatory response in a murine model compared to planktonic bacteria / Salmonella entérica serovar Enteritidis en biopelícula induce una menor patogenicidad y respuesta inflamatoria en un modelo murino que su contraparte planctónica

Abstract Salmonella enterica serovar Enteritidis (S. Enteritidis) is the most frequent serovar involved in human salmonellosis. It has been demonstrated that about 80% of infections are related to biofilm formation. There is scant information about the pathogenicity of S. Enteritidis and its relationship to biofilm production. In this regard, this study aimed to investigate the differential host response induced by S. Enteritidis biofilm and planktonic lifestyle. To this purpose, biofilm and planktonic bacteria were inoculated to BALB/c mice and epithelial cell culture. Survival studies revealed that biofilm is less virulent than planktonic cells. Reduced signs of intestinal inflammation and lower bacterial translocation were observed in animals inoculated with Salmonella biofilm compared to the planktonic group. Results showed that Salmonella biofilm was impaired for invasion of non-phagocytic cells and induces a lower inflammatory response in vivo and in vitro compared to that of planktonic bacteria. Taken together, the outcome of Salmonella-host interaction varies depending on the bacterial lifestyle.

Resumen Salmonella entérica serovar Enteritidis (S. Enteritidis) es la serovariedad más frecuentemente aislada en la salmonelosis humana. Se ha demostrado que alrededor del 80% de las infecciones están relacionadas con la formación de biopelículas. Sin embargo, la información disponible acerca de la patogenicidad de S. Enteritidis y su relación con la producción de biopelículas es escasa. Este trabajo tuvo como objetivo investigar la respuesta diferencial del huésped frente a S. Enteritidis en sus 2 estilos de vida: biopelícula y planctónico. Para ello, se inocularon bacterias en estado de biopelícula o planctónico en ratones BALB/c y cultivo de células epiteliales. Los estudios de supervivencia revelaron que Salmonella en biopelícula fue menos virulenta que su contraparte planctónica. Los animales inoculados con biopelículas presentaron una mayor conservación estructural del intestino y una menor translocación bacteriana que el grupo planctónico. Asimismo, Salmonella en biopelícula mostró una capacidad deficiente para invadir células no fagocíticas e indujo una menor respuesta inflamatoria in vivo e in vitro que las bacterias planctónicas. Se concluye que el resultado de la interacción Salmonella-huésped depende del estilo de vida bacteriano.

Standardization of resazurin use in susceptibility testing of natural products against yeasts in planktonic cells and in biofilms formation

Natural products, such as the ethanolic propolis extract (PE), have been shown to be a safe and effective therapeutic alternative for the treatment of fungal skin and nail diseases. However, the presence of the resin and the physicochemical characteristics of the extract sometimes difficult the reading and determination of breakpoints of the in vitrotests, evidencing the need for alternatives that facilitate the reading. The present study aimed to standardize the use of resazurin in tests of susceptibility of PE with planktonic yeast cells and biofilm forms. The antifungal activity of PE was determined by minimum inhibitory concentration (MIC) and we observed that, for all Candida spp. tested, the most reproducible MIC results were obtained when resazurin was placed after 24 hours of incubation and remained more 24 hourswith yeasts plus PE. For encapsulated yeasts, there was no dye reduction and color transition. Resazurin was also used for the evaluation of minimal biofilm inhibitory concentration and minimal biofilm eradication concentration and it was metabolized and reproducedthe action of PE on Candida biofilms. In addition, microdilution checkerboard plates were made with the dye, which assisted reading the result of the interaction between PE and nystatin. We observed that the resin, the color and the turbidity of the PE slightly changed the color of the resazurin in high concentrations of the extract and did not impair the reading. Therefore, the resazurin standardization tests were proven to be efficient and grounds that it should be used as an auxiliary methodology for reading and interpretation of the susceptibility tests for non-encapsulated yeasts with natural products, which form turbidity or precipitation, such as propolis.

Spatio-temporal Distribution Pattern of Oyster Larvae in Guaratuba Bay, Paraná State - Brazil

HIGHLIGHTS Crassostrea oysters larvae patterns in estuarine environments. Larvae distribution patterns in Guaratuba Bay (Paraná State - Brazil).

Abstract Crassostrea oysters present planktonic/planktotrophic larval development. Thus, it is essential knowing larvae distribution patterns in estuarine environments presenting oyster farms and spat collection. The aim of the current research is to investigate the spatio-temporal distribution of oyster larvae in Guaratuba Bay (Paraná State - Brazil) based on monthly samplings conducted with a plankton net (50 cm diameter and 225 µm mesh size) from June 2003 to June 2004 in three different points (Point I - bay´s entrance; Point II - cultivation park; Point III - median sector of the bay). Plankton samples were preserved in 4% buffered formaldehyde. They were concentrated and quantified in the laboratory. The total number of larvae in the sample from each net was counted and corrected to a standard larvae/m3 collection tow. Data about sea water temperature, salinity, transparency and pluviosity were also collected. Based on results about the spatial distribution of larvae, mean density was 33.30 ±42.73 larvae/m³ in Point I; 17.84 ±16.88 larvae/m³ in Point II and 55.53 ±78.31 larvae/m³ in Point III, during the studied period. Spring and Summer were the seasons recording the most expressive mean number of larvae; the largest concentration of them was found in Point III, in the middle section of the bay.

Effect of Tanreqing Injection Combined with Imipenem-cilastatin in Inhibiting Extensively-drug Resistant Pseudomonas aeruginosa / 中国实验方剂学杂志

Objective:To observe the effect of combination of Tanreqing injection(Tanreqing) and imipenem-cilastatin on extensively-drug resistant Pseudomonas aeruginosa (XDPA), and study the mechanism of the combination. Method:The minimum inhibitory concentrations (MICs) of Tanreqing and imipenem-cilastatin against planktonic XDPA strain isolated in clinic were determined by the broth microdilution method. The checkerboard method was used to evaluate the combination effect. The bacterial metabolic activity in mature biofilm was studied by microtiter-plate test. The destructive effect of combination drugs on dynamic biofilm was observed by using BioFlux system, and viable cells were examined by confocal laser scanning microscope (CLSM) after treatment. The scanning electron microscopy (SEM) was used for observing Pseudomonas aeruginosa and length measurement. Result:The MIC values of imipenem-cilastatin and Tanreqing were 512 mg·L-1 and more than 16 500 mg·L-1. The checkerboard analysis showed that Tanreqing could enhance the sensitivity of imipenem-cilastatin, while the combination drugs synergistically inhibited the growth of bacteria. Compared with the control group or the imipenem-cilastatin individual group, the combined drugs significantly reduced the amount of living bacteria in the biofilm (PPPConclusion:Tanreqing and imipenem-cilastatin synergistically inhibit the bacterial growth in planktonic and biofilm states, and destruct biofilms.

Determination of optimal prey for rearing the Tropical Gar Atractosteus tropicus (Lepisosteiformes: Lepisosteidae) / Determinación de presas óptimas para la crianza del pejelagarto Atractosteus tropicus (Lepisosteiformes: Lepisosteidae)

Abstract Larval feeding studies of both ornamental and consumable fish species are important for formulating successful management, and culture strategies for conservation purposes. In the present study, we evaluated prey selectivity for the tropical gar Atractosteus tropicus in the larval stage (first 8 weeks) using the zooplankton Artemia fransiscana, Daphnia pulex and Moina macrocopa as prey following the hypothesis that prey selection of the fish species is related not only to prey species preferences but to the difference in prey densities present in the environment. Functional responses were tested at prey densities of 0.2, 0.5, 1.0, 2.0, 4.0 and 8.0 ind. mL-1 and analyzed using Manly's α. For prey selectivity, we used the three zooplankton species at three different densities. In these two experiments the fish larvae were allowed to feed for 45 min. To quantify feeding behavior (encounters, attacks, captures, ingestions, rejections) we used a density of 1 ind. mL-1 using each prey species based on 10 minutes of direct observation. Our results showed a functional response Type II for A. tropicus preying mostly on A. franciscana and M. macrocopa. The Manly's α index showed that M. macrocopa and A. franciscana are the most preys selected. The values for encounters for the three prey species were relatively constant during the eight weeks. Encounter values for the cladocerans were low in comparison to A. franciscana; however, high success in capture and ingestion was observed for all prey species used. Our results from the functional response experiments supports the hypothesis that A. tropicus is an active predator presenting a functional response of a carnivorous fish and the shift in prey selection suggests that even at low prey availability, A. tropicus is able to manipulate and feed on zooplankton of wide range in size. Also, according to our results, we suggest the use of a mix of A. franciscana and M. macrocopa to feed A. tropicus in culture systems in concentrations ≈ 2 ind. mL-1 during the first 3 weeks of age and then shift to M. macrocopa from the 4 week. Our results, in conjunction with studies on the survivorship of the juveniles would aid in conservation efforts and improve the production of gars in aquaculture. Rev. Biol. Trop. 66(3): 1018-1033. Epub 2018 September 01.

Resumen Estudios sobre alimentación en etapa larvaria en peces ornamentales como de consumo son importantes para formular estrategias exitosas de manejo y cultivo con fines de conservación. En el presente estudio evaluamos la selectividad de presa del pejelagarto Atractosteus tropicus en etapas larvarias (primeras 8 semanas) utilizando el zooplancton Artemia fransiscana, Daphnia pulex y Moina macrocopa como presas, probando la hipótesis de que la selección de presas en peces está relacionada no solamente a la preferencia por la especie de presa sino también a la diferencia en la densidad de presas en el ambiente. También se probó la respuesta funcional con densidades de presa de 0.2, 0.5, 1.0, 2.0, 4.0 y 8.0 ind. mL-1. Para la selección de presa, utilizamos las tres especies de zooplancton en tres densidades diferentes. En ambos experimentos, las larvas de los peces se alimentaron por 45 min. Para cuantificar el comportamiento alimenticio (encuentros, ataques, capturas, ingestiones y rechazos), se usó una densidad de 1 ind. mL-1utilizando cada especie de presa mediante observación directa por 10 minutos. Nuestros resultados muestran que A. tropicus presenta una respuesta funcional Tipo II, depredando principalmente A. franciscana y M. macrocopa. El índice α de Manly mostró que las especies M. macrocopa and A. franciscana fueron las mayormente seleccionadas. Los valores de encuentros para las tres especies de presa fueron relativamente constantes a lo largo de las ocho semanas. Los valores de ataque, captura e ingestión para los cladóceros fueron bajos; sin embargo, se observó gran éxito en la captura e ingestión para todas las especias de presa utilizadas. Nuestros resultados sobre los experimentos de respuesta funcional soportan la hipótesis de que A. tropicus es un depredador activo y presenta una respuesta funcional relacionada con especies de peces carnívoras y que el cambio en la selección de presas sugiere que aún a bajas densidades y disponibilidad de presas, A. tropicus es capaz de manipular y alimentarse de presas de diferentes tamaños. También, sugerimos el uso de una mezcla de A. franciscana y M. macrocopa para alimentar a A. tropicus en sistemas de cultivo en concentraciones ≈ 2 ind. mL-1 durante las primeras tres semanas de edad y después cambiar a M. macrocopa a partir de la cuarta semana. Nuestros resultados, junto con estudios de sobrevivencia de los juveniles pueden ayudar a generar esfuerzos de conservación y mejorar la producción de pejelagarto en acuicultura.

MIC, MBIC, MBEC analyses of garlic extract (Allium sativum) from Indonesian variety against Streptococcus mutans

Garlic (Allium sativum) has been used for traditional medicine since ages. It has many uses such as an antioxidant, antiseptic, anti-viral, anti-fungal, anti-cancer, anti-aging, reduce the risk of heart disease, and antibacterial1. Aim: This study was designed to evaluate the inhibition and eradication ability for garlic against Streptococcus mutans, the bacteria that cause dental caries. Methods: Garlic extract was obtained from Ciwidey garlic maseration process in etanol 96%. MIC was a test to measure the inhibition ability of garlic extract against Streptococcus mutans in planktonic form, and MBIC in biofilms form. MBEC was a test to measure the eradication ability of garlic extract against Streptococcus mutans in biofilms form. Statistic analysis using ANOVA followed by post hoc with ρ value <0.05. Results: The garlic extract showed MIC value at 9.39 % and MBIC value at 37.5 % but was not observed to have eradication activity against Streptococcus mutans in biofilms form up to concentration 37.5%. Conclusion: Garlic extract inhibit Streptococcus mutans both in planktonic and biofilm form. Garlic extract has no eradication activity against Streptococcus mutans in biofilms form up to concentration 37.5% (AU)

Resistance of oxidative stress in biofilm and planktonic cells

This work studied the susceptibility of biofilm produced by E. coli to oxidative stress, and compared the components of free radicals defences: level of glutathione, catalase and dismutase activities in planktonic and biofilm located cells. Results showed the diversity of responses to oxidative stress in bacterial cells in log or stationary phases in both planktonic and biofilm forms. The bacteria were exposed to free-radical donors (H2O2, tBOOH, menadione, SIN-1 or peroxynitrite) in a wide range of final concentrations, from 0.5 to 10mM. Different level of toxicity of individual donors, independence of cell type (planktonic forms or biofilm) and phases of growth were observed. The highest oxidative stress resistance was observed for the cells in logarithmic phase of growth treated with H2O2, both in planktonic and biofilm forms, whereas for the cells in stationary phase, the highest resistance was observed for menadione. These results showed higher efficiency of agents based on superoxide anion donors in combating bacteria colonizing abiotic surfaces stainless steel (AISI 316L).

A study on the mechanism of biofilm formation of Pseudomonas aeruginosa and its relationship with drug resistance / 预防医学

Objective To compare antibiotic resistance of pseudomonas aeruginosa in biofilms and in planktonic state,so as to provide practical guidance and theoretical support for clinical treatment of drug. Methods pseudomonas aeruginosa were divided into control culture group( group A),medium group of biological membrane after culture( group B) and the biofilm culturing silica film adhesion group( group C). Three groups were observed by silver staining,extracellular sugar staining and scanning of electron microscope. These groups were cultured with different antibiotic medium,and the situation of bacterial resistance was observed by the method of k-B. Results There was no significant difference in drug resistance and minimum inhibitory concentration(MIC)between group A and B(p >0. 01). Compared with group A, group C showed that their drug resistance on meropenem,cefepime,ceftazidime,ceftriaxone,amoxicillin and levofloxacin were much higher(p<0. 01). The minimal biofilm eradication concentration(MBEC)of group C was about 100 times than that of group A and group B. Conclusion The assay of establishment of pseudomonas aeruginosa biofilm and the methods observed by silver stainingin vitro is convenient and feasible. At the same time,pseudomonas aeruginosa in biofilm exhibits far more resistance to antimicrobial than its planctonic counterparts does.

Studies on Limnological Characteristics of Ramankere Tank, Honalli, Davangere, Karnataka, India.

An investigation was carried out in Ramankere tank near Honalli of Davangere on physico-chemical characteristics and Planktonic composition during January to December 2011. The results of physico-chemical parameters were compared with the standard values prescribed by the Bureau of India Standards (BIS) and World Health Organization (WHO). The study revealed that, tank water is polluted as it possesses high BOD, CO2, phosphate and nitrogen. A total of 36 species belonging to 27genera of phytoplanktons were recorded, of which Bacillariophyceae and chlorophyceae were dominant. Eight zooplanktons and six macrophytes were also recorded. In the light of standard of water quality recommended by WHO, the tank water should not be used by human beings especially for drinking and cooking.

Spatial and temporal patterns of ciliate species composition (Protozoa: Ciliophora) in the plankton of the Upper Paraná River floodplain / Padrões espaciais e temporais da composição de espécies de ciliados (Protozoa: Ciliophora) no plâncton da planície de inundação do Alto Rio Paraná

Spatial and temporal patterns of plankton ciliates species composition in the Paraná River floodplain were investigated. Samplings were carried out in twelve environments in two distinct hydrological periods (limnophase and potamophase). A total of 61 species of ciliates were recorded, and among them 21 are classified as pelagic while 40 are considered preferentially as littoral species. The registered species belong to eleven orders, and among them, Prostomatida was the most specious followed by Hymenostomatida and Peritrichida. The ciliate species composition was significantly distinct between periods, but not among environments. In this way, typically pelagic species characterized the ciliate community during the limnophase period, while the littoral species were predominant during the potamophase period. Our results strongly support the idea of the flood pulse as the main factor driving the composition pattern of the planktonic ciliates community in the Paraná River floodplain.

No presente estudo foram investigados os padrões espaciais e temporais da composição de espécies de ciliados planctônicos na planície de inundação do Alto Rio Paraná. As amostras foram obtidas em 12 ambientes, em dois períodos hidrológicos distintos (limnofase e potamofase). Foram registradas 61 espécies de ciliados entre as quais 21 foram classificadas como pelágicas enquanto 40 foram consideradas preferencialmente litorâneas. As espécies registradas pertencem a 11 ordens, sendo Prostomatida foi a mais especiosa, seguida por Hymenostomatida e Peritrichida. A composição de espécies de ciliados foi significativamente distinta entre os períodos hidrológicos, enquanto que entre os ambientes, diferenças na composição não foram evidenciadas. Dessa forma, espécies tipicamente pelágicas caracterizaram a comunidade de ciliados na limnofase, enquanto que espécies litorâneas foram preponderantes para a composição de ciliados na potamofase. Os resultados suportam a idéia do pulso de inundação como principal fator controlador dos padrões de composição da comunidade de ciliados planctônicos na planície de inundação do Alto Rio Paraná.

Implications of bacterial biofilms in chronic rhinosinusitis

The recognition of sessile form of bacteria with particular features, known as biofilm, has given new insights to the understanding of pathogenesis of several chronic diseases, including Chronic Rhinosinusitis (CRS). In this article we review the main characteristics of biofilms, describe the current methods used to demonstrate biofilms in chronic rhinosinusitis and discuss the future directions of research in the field.

Spatial and temporal patterns of ciliate species composition (Protozoa: Ciliophora) in the plankton of the Upper Paraná River floodplain

Spatial and temporal patterns of plankton ciliates species composition in the Paraná River floodplain were investigated. Samplings were carried out in twelve environments in two distinct hydrological periods (limnophase and potamophase). A total of 61 species of ciliates were recorded, and among them 21 are classified as pelagic while 40 are considered preferentially as littoral species. The registered species belong to eleven orders, and among them, Prostomatida was the most specious followed by Hymenostomatida and Peritrichida. The ciliate species composition was significantly distinct between periods, but not among environments. In this way, typically pelagic species characterized the ciliate community during the limnophase period, while the littoral species were predominant during the potamophase period. Our results strongly support the idea of the flood pulse as the main factor driving the composition pattern of the planktonic ciliates community in the Paraná River floodplain.

No presente estudo foram investigados os padrões espaciais e temporais da composição de espécies de ciliados planctônicos na planície de inundação do Alto Rio Paraná. As amostras foram obtidas em 12 ambientes, em dois períodos hidrológicos distintos (limnofase e potamofase). Foram registradas 61 espécies de ciliados entre as quais 21 foram classificadas como pelágicas enquanto 40 foram consideradas preferencialmente litorâneas. As espécies registradas pertencem a 11 ordens, sendo Prostomatida foi a mais especiosa, seguida por Hymenostomatida e Peritrichida. A composição de espécies de ciliados foi significativamente distinta entre os períodos hidrológicos, enquanto que entre os ambientes, diferenças na composição não foram evidenciadas. Dessa forma, espécies tipicamente pelágicas caracterizaram a comunidade de ciliados na limnofase, enquanto que espécies litorâneas foram preponderantes para a composição de ciliados na potamofase. Os resultados suportam a idéia do pulso de inundação como principal fator controlador dos padrões de composição da comunidade de ciliados planctônicos na planície de inundação do Alto Rio Paraná.

Atividade antimicrobiana e antiaderente in vitro do extrato de Rosmarinus officinalis Linn. sobre bactérias orais planctônicas / In vitro antimicrobial activity and antiadherence of Rosmarinus officinalis Linn. against oral planktonic bacteria

Neste estudo foi investigada a ação antimicrobiana e a inibição de aderência in vitro do extrato hidroalcoólico de Rosmarinus officinalis Linn. (alecrim) sobre cepas padrão de Streptococcus mitis ATCC 98811, Streptococcus sanguinis ATCC 10556, Streptococcus mutans ATCC 25175, Streptococcus sobrinus ATCC 27609 e Lactobacillus casei ATCC 7469. Os ensaios foram realizados pelas técnicas de ágar-difusão em placas de Petri para determinação da Concentração Inibitória Mínima (CIM) e técnica de tubos inclinados para determinação da Concentração Inibitória Mínima de Aderência (CIMA) ao vidro, na presença de 5 por cento de sacarose. Os mesmos procedimentos foram realizados com a clorexidina à 0,12 por cento. As CIMs (mg/mL) do extrato de Rosmarinus officinalis sobre S. sanguinis ATCC 10556, S. mutans ATCC 25175, S. sobrinus ATCC 27609 e L. casei ATCC 7469 foram 1:1, 1:4, 1:1 e 1:4, respectivamente. Não houve inibição de crescimento de S. mitis ATCC 98811. As CIMAs do extrato de Rosmarinus officinalis frente a S. mitis ATCC 98811, S. mutans ATCC 25175 e S. sobrinus ATCC foram 1:8, 1:16 e 1:8, nessa ordem. Os resultados sugerem a possibilidade de uso do extrato de alecrim como antimicrobiano oral. No entanto, modelos de estudo que possam reproduzir situações mais próximas àquelas encontradas na cavidade oral são requeridas para avaliação de agentes antimicrobianos no tratamento e prevenção de infecções orais biofilme-dependentes.

In this study was investigated the antimicrobial activity and in vitro adherence inhibition of a hydro alcoholic Rosmarinus officinalis Linn. (alecrim) on standard strains of Streptococcus mitis ATCC 98811, Streptococcus sanguinis ATCC 10556, Streptococcus mutans ATCC 25175, Streptococcus sobrinus ATCC 27609 and Lactobacillus casei ATCC 7469 extract. The test was carried out by inundation tecniques in Petri dishes to determine the Minimum Inhibitory Concentration (MIC) and inclined tubes techniques the Minimum Inhibitory Concentration of Adherence to glass (MICA) at the presence of 5 percent sucrose. Tests with gluconate of chlorexidine 0.12 percent were performed as controls. MICs of the Rosmarinus officinalis extract dilutions (mg/mL) against S. sanguinis ATCC 10556, S. mutans ATCC 25175, S. sobrinus ATCC 27609 and L. casei ATCC 7469 were 1:1, 1:4, 1:1 e 1:4, respectively. The extract from alecrim inhibited all the standard strains growth tested, except for S. mitis ATCC 98811. MICAs of the Rosmarinus officinalis extract dilutions (mg/mL) against S. mitis ATCC 98811, S. mutans ATCC 25175 e S. sobrinus ATCC were 1:8, 1:16 e 1:8, respectively. The results suggest that there is a possibility of the alecrim use as an oral antimicrobial. Nevertheless, study models which could reproduce situations similar to those seen in bucal caries are necessary for the antimicrobial agents evaluation in the treatment and biofilm dependant oral infections prevention.

Planktonic ciliates from an oligotrophic South Andean lake, Morenito Lake (Patagonia, Argentina)

In this contribution we have studied the planktonic ciliates from Morenito Lake, an oligotrophic lake situated in the South Andes of Argentina. Six species that are new records for South America or Argentina are described and illustrated. Besides, population dynamics of the ciliate species were studied during a spring--summer period. Strobilidium lacustris and Balanion planctonicum were the most abundant species, showing a maximum in mid summer. Paradileptus elephantinus was present all over the period while Urotricha furcata was observed in late summer samples. Strobilidium lacustris and S. humile were found to be occasional species during the studied period. The recorded ciliate assemblage with oligotrichs and prostomates as dominant indicate the oligotrophic condition of the lake.

Nesta contribuição estudamos os ciliados planctônicos do Lago Morenito, um lago oligotrófico localizado nos Andes do Sul (Argentina). São descritas e ilustradas seis espécies registradas pela primera vez na Argentina e na América do Sul. Durante o período de primavera--verão foram estudadas as dinâmicas populacionais dessas espécies de ciliados. Strobilidium lacustris e Balanion planctonicum foram as espécies mais abundantes, mostrando um máximo na metade do verão. Paradileptus elephantinus esteve presente durante todo o período e Urotricha furcata foi observado em amostras no final do verão. Strobilidium lacustris e S. humile foram espécies ocasionais durante o período estudado. O grupo de ciliados registrados com dominância de oligotricos e prostomados indica a condição oligotrófica do lago.