Species belonging to the genus Salmonella are an important cause of enteric fevers, gastroenteritis, and septicemia, and the pathogens are commonly transmitted through contaminated food. In this study, polymerase chain reaction (PCR) amplification of a 287-bp region of the invA gene was compared to a microbiological technique to determine the presence of Salmonella in retail beef and in cantaloupe rinse samples. Both methods showed the same level of sensitivity, detecting 1 CFU/25 g of meat after enrichment for 24 h at 42• C. The presence of Salmonella was determined in 50 commercial top sirloin beef samples that were not artificially inoculated. Three samples were positive by the microbiological method, and these samples and an additional sample were positive by the PCR. Both methods were also used to test surface rinses of cantaloupes collected from 4 farms in Nayarit, Mexico. Salmonella was detected by the microbiological method in 9 of 20 samples (45%), whereas the pathogen was detected by the PCR in 11 samples (55%). This study demonstrates the utility of the PCR targeting the invA gene to determine the presence of Salmonella spp. in beef and cantaloupe samples.
Contamination caused by heavy metals in wastewater has a high potential of risk because they easily penetrate in to the trofic chain accumulating as organometallic compounds. In this work, the expression of mice metallothionein in E. coli (pMt-Thio) was examined as a strategy to enhance metal biosorption efficiency of bacterial biosorbents for Pb(II) and Cd(II) ions. The results showed that pMt-Thio led to significant increase in overall biosorption capacity, especially for biosorption of Pb. Isotherms and kinetic of biosorption were evaluated in this designed system. The influence of metal concentration in solution is discussed in terms of Langmuir and Freundlich isotherm and constants. The Langmuir model was found to correlate better with the experiment data. The biomass showed maximum capacities according to Langmuir adsorption model of 28.14 mgPb/gpMt-Thio and 24.27 mgCd/gpMt-Thio. The study proved that pMt-Thio is a suitable material for the removal of the heavy metal ions studied from aqueous solutions, achieving removal efficiencies higher than 90% for Pb(II) and higher than 40% for Cd(II), and could be considered as a potential material for treating effluent polluted with Cd(II) and Pb(II) ions.
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