Water and soil pollution has become a major concern in the world, as much of the population relies on groundwater as its major source of drinking water as well as on soil as cultivable land. Heavy-metal contamination brings a potential health harzard that can cause metal toxicoses in animals and humans (Volesky and Holan, 1995). Trace elements such as cadmium, copper, and mercury are very toxic heavy metals and have been found in the human environment at increased concentrations, because a wide variety of industrial activities have accelerated the release of these metals at higher rates than natural geochemical cycling processes can tolerate (Nriagu and Pacyma, 1988).Automobile and leather factories, and sugar mills located in Tucumán, a northwestern state of Argentine, are potential sources of effluent contamination of aquifers and rivers. Salí is one of the most important rivers of Tucumán. The Salí River flows to the Río Hondo reservoir in northeast Argentina. This reservoir is a source of drinking water, irrigation and fishing activities, and is considered an important ecological reserve in Argentina.The metal processing capacity of microorganisms can be used to concentrate, remove and recover metals from aqueous streams and enhance the efficiency of wastewater treatment processes (Brown and Lester, 1979). Different microorganisms such as fungi, yeast and bacteria were tested for the availability and biosorption potential to bind heavy metals (Volesky and Holan, 1995). However, to our knowledge little information is available about the use of actinomycetes for sequestering heavy metals from solutions (Abbas and Edward, 1989).This study deals with metal-resistant actinomycetes from polluted areas in the Salí River. From the isolates, selected strains were characterized with respect to growth in the presence of different metal ion concentrations (MICs), with the ultimate objective of utilizing these strains in bioremediation processes. Materials and MethodsSamples. Sediment samples were collected from the flow of the Salí River in the Río Hondo reservoir using a sediment grab sampler. All of the samples were kept at 0°C until use. The samples were diluted with a sterile 145 mM NaCl solution and spread onto isolation plates in duplicate.Isolation of microorganisms. The isolation and enumeration of microorganisms were carried out in SC medium that contained (per liter): starch 10 g; casein 1.0 g; K 2 HPO 4 0.5 g; and agar 15.0 g. The pH of the medium was adjusted to 7.0 prior to sterilization. The medium was supplemented with 10.0 µg ml Ϫ1 each of nalidixic acid (NA) and cycloheximide and 25 µg ml Ϫ1 of nystatin. Plates were incubated at 25°C
The inhibitory effect of lactobacilli on the growth of different pathogens was studied. The degree of inhibition was measured by disc assay in different media, showing that the inhibitory substance(s) can be extracellular and diffusible. The associative cultures were performed with lactobacilli and Escherichia coli in a relationship of 1:1 or 103:1. In the first experiments, the E. coli inhibition began at 9 h after culturing. In the experiments with lower levels of different intestinal pathogens, associative cultures were incubated for 4–6 h obtaining different degrees of inhibition with the highest being for E. coli and Klebsiella pneumoniae. After a day of incubation, we did not recover viable pathogens from the mixed cultures, while lactobacilli grew to 108–109 microorganisms per ml. The inhibition of pathogens was not due to pH alone, because the addition of different organic acids to culture media did not inhibit their normal growth. Lactobacillus casei and Lactobacillus acidophilus in this study can be considered a potential biotherapeutic treatment in patients infected with certain intestinal pathogens.
Dialyzed cell-free extract of lactobacilli was found to contain superoxide dismutase activity by using a test system in which superoxide ion is generated by xanthine oxidase. The specific activities of Lactobacillus acidophilus ATCC 4356, Lactobacillus murinus ATCC 35020, Lactobacillus acidophilus CRL 358, Lactobacillus plantarum ATCC 8014, Lactobacillus casei CRL 431, Lactobacillus plantarum CRL 353, Lactobacillus fermentum ATCC 9338, Lactobacillus buchneri NCDO 110, and Lactobacillus fermentum CRL 251 were between 0.06 and 0.43 U/mg protein. The presence of superoxide dismutase activity was demonstrated when the strains were grown in media containing Mn2+ ions. Superoxide dismutase of lactobacilli may be an Mn enzyme since it was not inhibited by either cyanide or azide ions. However, the cell-free extract of Lactobacillus murinus ATCC 35020 contains superoxide dismutase activity sensitive to both ions.
The protective effect of feeding milk fermented with a mixture of Lactobacillus casei and Lact. acidophilus against Shigella sonnei was studied. There was a 100% survival rate in mice fed for 8 d with fermented milk and then dosed orally with Sh. sonnei. The survival rate in control mice was approximately 60% after 21 d. Colonization of the liver and spleen with Sh. sonnei was markedly inhibited by pretreatment with fermented milk. Differences in cell counts of 2–3 log units between treated and control mice were always obtained, shigellas were not detected in these organs by the 10th day in treated mice, while high levels were maintained in the controls. Higher levels of anti‐shigella antibodies were found both in sera and in small intestinal fluid of mice treated with fermented milk, suggesting that the protective immunity could be mediated by the mucosal tissue. These results suggest that milk fermented with Lact. casei and Lact. acidophilus could be used as a prophylactic against gastrointestinal infections by shigellas.
Challenge studies were set up feeding Lactobacillus casei and Lactobacillus acidophilus fermented milk and two different pathogenic microorganisms: Listeria monocytogenes and enteroinvasive Escherichia coli. Mice were fed for 8 consecutive days with fermented milk and then challenged with the pathogens. The survival rate in control mice was 62% for Listeria and 83% for E. coli, while 100% protection was observed for the 20 d per vial in treated mice. Colonization of the liver and spleen by E. coli was markedly inhibited by pretreatment with fermented milk; the pathogen was not detected on the 5th day postchallenge. In the Listeria challenged mice, the pathogen was present in 1 to 2 log units lower than control up the 10th day. The levels of antipathogen sera and intestinal antibodies were 2 to 4 times higher in the treated mice, with lower values in the Listeria treated mice. The mechanism of protection in both types of infections was discussed. The results obtained suggested that milk fermented with L. casei and L. acidophilus could be used as a prophylactic against selected infections.
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