Cyanobacterial blooms and hepatotoxic microcystins (MCs) usually occur in summer, constituting a sanitary and environmental problem in Salto Grande Dam, Argentina. Water sports and recreational activities take place in summer in this lake. We reported an acute case of cyanobacterial poisoning in Salto Grande dam, Argentina, which occurred in January 2007. Accidentally, a young man was immersed in an intense bloom of Microcystis spp. A level of 48.6 μg·L−1 of microcystin-LR was detected in water samples. Four hours after exposure, the patient showed nausea, abdominal pain and fever. Three days later, dyspnea and respiratory distress were reported. The patient was hospitalized in intensive care and diagnosed with an atypical pneumonia. Finally, a week after the exposure, the patient developed a hepatotoxicosis with a significant increase of hepatic damage biomarkers (ALT, AST and γGT). Complete recovery took place within 20 days. This is the first study to show an acute intoxication with microcystin-producing cyanobacteria blooms in recreational water.

The aims of this work were to couple both the silver nanoparticles (AgNPs) synthesis, and filmogenic suspensions preparation, to characterize the obtained AgNPs and the derived nanocomposite films studying their antimicrobial capacity and developing an active packaging. One of the new approaches to this work is the use of low concentrations of AgNPs at which no adverse cytotoxic effects have been observed. Nanoparticles were characterized by spectrophotometric techniques and electron microscopy, finding that they are spherical with diameters varying between 5 and 20 nm and detecting the formation of agglomerates. The addition of AgNPs did not affect the filmogenic capacity of gelatinized starch suspension. The content of AgNPs caused a slight increase in film thickness and opacity, keeping the material UV-barrier capacity. A decrease in water vapor permeability with increasing AgNPs concentration was observed. Besides, AgNPs allow the matrix reinforcement, developing a more resistant and tough material, with smooth and homogeneous surfaces, as evidenced by SEM, and maintaining their heat sealing capacity. Nanocomposite films containing AgNPs concentrations greater than 71.5 ppm inhibited the growth of E. coli ATCC and Salmonella spp., which are responsible for most foodborne diseases. However, films containing 143 ppm AgNPs were selected since they better maintained their integrity to microbial attack. These active films were able to extend the shelf-life of fresh cheese samples for 21 days. Thus, it was possible to develop and characterize nanocomposite films based on corn starch and containing AgNPs, which confers them antimicrobial properties.

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Microcystis are known for their potential ability to synthesize toxins, mainly microcystins (MCs). In order to evaluate the effects of temperature on chlorophyll a (Chl a), growth, physiological responses and toxin production of a native Microcystis aeruginosa, we exposed the cells to low (23°C) and high (29°C) temperature in addition to a 26°C control treatment. Exponential growth rate was significantly higher at 29°C compared to 23°C and control, reaching 0.43, 0.32 and 0.33 day −1 respectively. In addition, there was a delay of the start of exponential growth at 23°C. However, the intracellular concentration of Chl a decreased significantly due to temperature change. A significant increase in intracellular ROS was observed in coincidence with the activation of enzymatic antioxidant catalase (CAT) during the first two days of exposure to 23°and 29°C in comparison to the control experiment, decreasing thereafter to nearly initial values. in cells exposed to 29°C. The same trend was observed for all other MCs except for the least abundant MC-LR which showed a continuous increase during exposure time. Our results suggest a high ability of M. aeruginosa to perceive ROS and to rapidly initiate antioxidant defenses with a differential response on MC production.

The effect of yeast concentration on ultraviolet (UV) inactivation of five strains of Escherichia coli O157: H7 from different sources, inoculated both individually and simultaneously in orange juice, was analyzed and mathematically modeled. The presence of yeast cells in orange juice decreases the performance of UV radiation on E. coli inactivation. UV absorption coefficients in the juice increased with increasing yeast concentration, and higher UV doses were necessary to inactivate bacterial strains. UV intensities of I=3.00±0.3 mW/cm 2 and exposure times (t) between 0 and 10 min were applied; radiation doses (energy, E=I×t) ranging between 0 and 2 J/cm 2 were measured using a UV digital radiometer. All the tested individual strains showed higher resistance to the treatment when UV radiation was applied at 4°C in comparison to 20°C. UV inactivation of E. coli O157:H7 individual strain was satisfactory fitted with a first order kinetic model. A linear relationship was found between UV absorptivities and D values (radiation doses required to decrease microbial population by 90%) for each strain. The dose required to reach 5-log reduction for the most unfavorable conditions that is the most UV resistant strain, and maximum background yeast concentration was 2.19 J/cm 2 at 4°C (corresponding to 11 min of UV treatment) and 2.09 J/cm 2 at 20°C (corresponding to 10.55 min of UV treatment). When a cocktail of strains was inoculated in orange juice, the logistic equation was the best model that fits the experimental results due to the deviation from the log-linear kinetics. The UV resistance between strain cocktail and single strain were mathematically compared. Slopes of the decline curves for strain cocktail at high UV doses were lower than the slopes of the log-linear equation calculated for the individual strains, even for the most resistant one. Therefore, microbial inactivation tests using a cocktail of strains are particularly important to determine the performance of the UV inactivation treatment.

The effect of sub-chronic exposure of intraperitoneal (i.p.) injections of microcystin-LR (MC-LR) on microscopic tissue architecture, hepatic function and lipid peroxidation has been studied in liver and kidney of mice. Mice were treated i.p. with 25 microg of pure MC-LR/kg body weight or saline solution for 1 month (every 2 days) with the aim of producing an inflictive stage with evident damage. Histopathological analysis of dissected livers of mice showed a disrupted lobar architecture and the development of cytoplasmatic vacuoles. According to this, a significant increase in hepatic lipid content and in lipid peroxidation levels in liver and kidney was found in MC-LR-treated animals when compared with controls. Moreover, serum alkaline phosphatase and aspartate aminotransferase activities showed a significant alteration in MC-LR-treated animals. After damage, progression or recovery was studied for 1 and 2 months of wash-out. The recovery from liver damage was evident at the cytological and physiological level, only the recovery of lobar architecture was incomplete along the period investigated. In conclusion, the present study demonstrates the ability of hepatic tissue to recover from damage produced by sub-chronic MC-LR administration. The dynamic interplay between damage and tissue-repairing response in determining the ultimate outcome of toxicity should be considered in risk-assessment studies.

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