The ability of pathogens to survive cheese ripening is a food-security concern. Therefore, this study aimed to evaluate the performance of two alternative methods of analysis of Listeria during the ripening of artisanal Minas cheese. These methods were tested and compared with the conventional method: Lateral Flow System™, in cheeses produced on laboratory scale using raw milk collected from different farms and inoculated with Listeria innocua; and VIDAS®-LMO, in cheese samples collected from different manufacturers in Serro, Minas Gerais, Brazil. These samples were also characterized in terms of lactic acid bacteria, coliforms and physical–chemical analysis. In the inoculated samples, L. innocua was detected by Lateral Flow System™ method with 33% false-negative and 68% accuracy results. L. innocua was only detected in the inoculated samples by the conventional method at 60-days of cheese ripening. L. monocytogenes was not detected by the conventional and the VIDAS®-LMO methods in cheese samples collected from different manufacturers, which impairs evaluating the performance of this alternative method. We concluded that the conventional method provided a better recovery of L. innocua throughout cheese ripening, being able to detect L. innocua at 60-day, aging period which is required by the current legislation.
Enteropathogenic Escherichia coli (EPEC) is a diarrheagenic pathogen that afflicts infants in developing countries. The most important virulence trait of EPEC is its ability to intimately adhere to cells in the small intestine, and to elicit diarrhea. The alternative sigma factor RpoS is involved in the virulence of several bacterial species. RpoS coordinates the general stress response and accumulates in cells under stress or in the stationary phase. RpoS levels differ across E. coli strains. High-RpoS strains are highly resistant to environmental stresses, but usually display low nutritional competence, while low-RpoS strains show the opposite phenotype. Here we investigated whether RpoS plays a role in the virulence and fitness of two different EPEC strains, E2348/69 and LRT9. A rpoS null mutation had a small positive effect on LRT9 adherence to epithelial cells, but the expression of the EPEC adhesins BfpA and intimin was not significantly affected by the mutation. E2348/69 adherence was not significantly affected by the rpoS mutation. The intrinsic level of RpoS was higher in LRT9 than in E2348/69 while the latter adhered more strongly and expressed higher levels of the adhesin BfpA than the former. Knockout of rpoS strongly impaired resistance to oxidative, osmotic and acid stress in both E2348/69 and LRT9. However, strain E2348/69 was significantly more sensitive to oxidative stress than LRT9. Finally, competition assays showed that the rpoS mutant of LRT9 displayed higher fitness under continuous culture than its isogenic wild-type strain, while E2348/69 outcompeted its rpoS mutant. In conclusion, RpoS plays mostly a positive role in EPEC biology and at least in the case of strain E2348/69 it is not constrained by the trade-off between vegetative growth and stress resistance.
Artisanal cheeses traditionally produced from raw milk have a diverse microbiota and, due the varied changes that occur in this type of food matrix during the maturation, pathogens detection's may be impaired. In this study, the conventional method established by ISO 6579:2005 to evaluate the presence of Salmonella was compared with two alternative rapid methods, PCR-BAX ® (DuPont) and VIDAS ® -SLM (BioMérieux), to analyze artisanal Minas cheese, a typical Brazilian product. Salmonella was not detected by conventional or PCR-BAX ® in 63 artisanal Minas cheese samples analyzed. Although highly specific and accurate, the immunoassay (VIDAS ® -SLM) presented 3.17% of false positives. Good manufactures practices were absent in some producers of Minas artisanal cheese and, the fact of Salmonella was not detected in analyzed samples should be related with presence of high and diverse endogenous microbiota, including approximately, 10 7 CFU.g -1 of lactic bacteria, and a low pH and water activity, conditions that can minimize pathogens growth, provide cellular injury and hamper the recovery strategies.
Controle de perdas de carotenóides em hortaliças preparadas em unidade de alimentação e nutrição hospitalar
Safe handling practices must be followed to minimize nutrient loss in fruits and vegetables. To evaluate such loss in tomatoes, storage and preparation practices were tested under storage at 10C and 24C (24 and 72 h), sanitization times (15, 45 and 75 min), type of cut (slices and cubes) and exposure time until consumption (0, 30 and 60 min). Ascorbic acid (AA), dehydroascorbic acid (DHA), lycopene andβ‐carotene were determined by high‐performance liquid chromatography. Under refrigeration, AA retention was 8% higher during 24 h storage. DHA increased at room temperature and lycopene retention was lower under refrigeration temperature. No differences were verified between cutting methods and the exposure times used. Retention after the selected storage and processing conditions ranged from 78 to 86% for vitamin C, from 53 to 81% for lycopene and from 74 to 83% forβ‐carotene. PRACTICAL APPLICATIONS Vitamin C and carotenoids are recognized as important components of healthy diet. However, the processes to which vegetables are submitted from harvest to consumption can alter vitamin content. The adoption of safe handling practices can minimize vitamin C and carotenoids losses during preparation. When the extent of the losses is known and controlled, menus can be complemented to reach the recommended vitamin daily intake. This study investigated the influence of post harvesting handling practices (storage, sanitization, slicing and the period between cooking and consumption) to select the practices that would result in greatest vitamin C and carotenoid retention.
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