Quantitative risk assessment of Listeria monocytogenes in traditional Minas cheeses: the cases of artisanal semi-hard and fresh soft cheeses

This study estimated the risk of listeriosis from Brazilian cheese consumption using quantitative microbial risk assessment (QMRA). Risks associated to consumption of two cheese types were assessed: artisanal ripened semihard cheese (produced with raw milk) and refrigerated fresh soft cheese (produced with pasteurized milk). The semi-hard cheese model predicted Listeria monocytogenes growth or decline during ripening, while the soft cheese model predicted pathogen growth during refrigerated storage. Semi-hard cheese modeling scenarios considered L. monocytogenes starting concentration from −2.4 to 6 log CFU/mL in raw milk and three ripening times (4, 22 and 60 days). Soft cheese modeling scenarios considered L. monocytogenes starting concentration from −2.4 to 4 log CFU/mL in milk. The inclusion of anti-listerial lactic acid bacteria (LAB) in cheeses was also examined. Risk of listeriosis due to consumption of soft cheese was 6000 and 190 times greater than that of semi-hard cheese, for general and vulnerable populations, respectively. Aging semi-hard cheese reduced risk, and risk was influenced by L. monocytogenes starting concentration. Aging cheese with inhibitory LAB for 22 days reduced risk over 4 million-fold when L. monocytogenes was assumed to be 6 log CFU/mL in raw milk. The inclusion of inhibitory LAB also reduced risk of listeriosis due to soft cheese consumption, but not as much as for semi-hard cheese. QMRA results predicted that consumption of contaminated cheeses can carry a high risk of listeriosis, especially for vulnerable populations. Scenario analyses indicated that aging of semi-hard cheese and inclusion of antimicrobial LAB mix in semi-hard and soft cheeses are effective risk mitigation measures.The authors thank to Fundação de Amparo à Pesquisa do Estado de São Paulo for the financial support (Grants 2014/14891-7 and 2016/ 09346-5) and to Conselho Nacional de Desenvolvimento Científico e Tecnológico (Grant # 302763/2014-7 and #305804/2017-0), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Grant #33003017027P1). Dr. Gonzales-Barron wishes to acknowledge the financial support provided by the Portuguese Foundation for Science and Technology (FCT) through the award of a five-year Investigator Fellowship (IF) in the mode of Development Grants (IF/00570).info:eu-repo/semantics/publishedVersio

Behavior of Listeria monocytogenes in the presence or not of intentionally-added lactic acid bacteria during ripening of artisanal Minas semi-hard cheese

The fate of Listeria monocytogenes during ripening of artisanal Minas semi-hard cheese, as influenced by cheese intrinsic properties and by autochthonous (naturally present) or intentionally-added anti-listerial lactic acid bacteria (LAB) was modeled. Selected LAB strains with anti-listerial capacity were added or not to raw or pasteurized milk to prepare 4 cheese treatments. Counts of LAB and L. monocytogenes, pH, temperature and water activity were determined throughout cheese ripening (22 days, 22±1ᵒC). Different approaches were adopted to model the effect of LAB on L. monocytogenes: an independent approach using the Huang primary model to describe LAB growth and the linear decay model to describe pathogen inactivation; the Huang-Cardinal [pH] model using the effect of pH variation in a dynamic tertiary approach; and the Jameson-effect with Nmax tot model which simultaneously describes L. monocytogenes and LAB fate. L. monocytogenes inactivation occurred in both treatments with added LAB and inactivation was faster in raw milk cheese (−0.0260 h−1) vs. pasteurized milk cheese (−0.0182 h−1), as estimated by the linear decay model. Better goodness-of-fit was achieved for the cheeses without added LAB when the Huang primary model was used. A faster and great pH decline was detected for cheeses with added LAB, and the Huang-Cardinal [pH] model predicted higher pathogen growth rate in cheese produced with raw milk, but greater L. monocytogenes final concentration in pasteurized milk cheese. The Jameson-effect model with Nmax tot predicted that LAB suppressed pathogen growth in all treatments, except in the treatment with pasteurized milk and no LAB addition. The Huang-Cardinal [pH] model was more accurate in modeling L. monocytogenes kinetics as a function of pH changes than was the Jameson-effect model with Nmax tot as a function of LAB inhibitory effect based on the goodness-of-fit measures. The Jameson-effect model may however be a better competition model since it can more easily represent L. monocytogenes growth and death. This study presents crucial kinetic data on L. monocytogenes behavior in the presence of competing microbiota in Minas semi-hard cheese under dynamic conditions.This work was supported by The São Paulo Research Foundation – FAPESP [grant numbers 2014/14891–7 and 2016/09346–5]; CNPq - The National Council for Scientific and Technological Development [grant numbers 302763/2014–7 and 305804/2017–0]; and CAPES –Coordination for the Improvement of Higher Education Personnel [Finance Code 001].info:eu-repo/semantics/publishedVersio

Modelling growth and decline in a two-species model system: Pathogenic Escherichia coli O157:H7 and psychrotrophic spoilage bacteria in milk

Producción CientíficaShiga toxin-producing Escherichia coli O157:H7 is a food-borne pathogen and the major cause of hemorrhagic colitis. Pseudomonas is the genus most frequent psychrotrophic spoilage microorganisms present in milk. Two-species bacterial systems with E. coli O157:H7, non-pathogenic E. coli, and P. fluorescens in skimmed milk at 7, 13, 19, or 25 °C were studied. Bacterial interactions were modelled after applying a Bayesian approach. No direct correlation between P. fluorescens’s growth rate and its effect on the maximum population densities of E. coli species was found. The results show the complexity of the interactions between two species in a food model. The use of natural microbiota members to control foodborne pathogens could be useful to improve food safety during the processing and storage of refrigerated foods

Quantitative Microbial Risk Assessment of Antibacterial Hand Hygiene Products on Risk of Shigellosis

ABSTRACT There are conflicting reports on whether antibacterial hand hygiene products are more effective than nonantibacterial products in reducing bacteria on hands and preventing disease. This research used new laboratory data, together with simulation techniques, to compare the ability of nonantibacterial and antibacterial products to reduce shigellosis risk. One hundred sixtythree subjects were used to compare five different hand treatments: two nonantibacterial products and three antibacterial products, i.e., 0.46% triclosan, 4% chlorhexidine gluconate, or 62% ethyl alcohol. Hands were inoculated with 5.5 to 6 log CFU Shigella; the simulated food handlers then washed their hands with one of the five products before handling melon balls

Selection of indigenous lactic acid bacteria presenting anti-listerial activity, and their role in reducing the maturation period and assuring the safety of traditional Brazilian cheeses

Artisanal raw milk cheeses are highly appreciated dairy products in Brazil and ensuring their microbiological safety has been a great need. This study reports the isolation and characterization of lactic acid bacteria (LAB) strains with anti-listerial activity, and their effects on Listeria monocytogenes during refrigerated shelf-life of soft Minas cheese and ripening of semi-hard Minas cheese. LAB strains (n ¼ 891) isolated from Minas artisanal cheeses (n ¼ 244) were assessed for anti-listerial activity by deferred antagonism assay at 37 C and 7 C. The treatments comprised the production of soft or semi-hard Minas cheeses using raw or pasteurized milk, and including the addition of selected LAB only [Lactobacillus brevis 2-392, Lactobacillus plantarum 1-399 and 4 Enterococcus faecalis (1-37, 2-49, 2-388 and 1-400)], L. monocytogenes only, selected LAB co-inoculated with L. monocytogenes, or without any added cultures. At 37 C, 48.1% of LAB isolates showed anti-listerial capacity and 77.5% maintained activity at 7 C. Selected LAB strains presented a bacteriostatic effect on L. monocytogenes in soft cheese. L. monocytogenes was inactivated during the ripening of semi-hard cheeses by the mix of LAB added. Times to attain a 4 log-reduction of L. monocytogenes were 15 and 21 days for semi-hard cheeses produced with raw and pasteurized milk, respectively. LAB with anti-listerial activity isolated from artisanal Minas cheeses can comprise an additional barrier to L. monocytogenes growth during the refrigerated storage of soft cheese and help shorten the ripening period of semi-hard cheeses aged at ambient temperature.The authors thank the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for financial support (Grants 13/ 20456-9, 14/14891-7, 15/25641-4, 16/21041-5, 16/12406-0 and 16/ 09346-5). Dr. Gonzales-Barron also acknowledges the financial support provided by the Portuguese Foundation for Science and Technology (FCT) through the award of an Investigator Fellowship (IF) in the mode of Development Grants (IF/00570). A.S. Sant'Ana acknowledges the financial support of “Conselho Nacional de Desenvolvimento Científico e Tecnológico” (CNPq) (Grant #302763/ 2014-7) and CAPES (Grant #33003017027P1).info:eu-repo/semantics/publishedVersio

A comparison of dynamic tertiary and competition models for describing the fate of Listeria monocytogenes in Minas fresh cheese during refrigerated storage

This study compares dynamic tertiary and competition models for L. monocytogenes growth as a function of intrinsic properties of a traditional Brazilian soft cheese and the inhibitory effect of lactic acid bacteria (LAB) during refrigerated storage. Cheeses were prepared from raw or pasteurized milk with or without the addition of selected LAB with known anti-listerial activity. Cheeses were analyzed for LAB and L. monocytogenes counts, pH and water activity (aw) throughout cold storage. Two approaches were used to describe the effect of LAB on L. monocytogenes: a Huang-Cardinal model that considers the effect of pH and aw variation in a dynamic kinetic analysis framework; and microbial competition models, including Lotka-Volterra and Jameson-effect variants, describing the simultaneous growth of L. monocytogenes and LAB. The Jameson-effect with γ and the Lotka-Volterra models produced models with statistically significant coefficients that characterized the inhibitory effect of selected LAB on L. monocytogenes in Minas fresh cheese. The Huang-Cardinal model [pH] outperformed both competition models. Taking aw change into account did not improve the fit quality of the Huang-Cardinal [pH] model. These models for Minas soft cheese should be valuable for future microbial risk assessments for this culturally important traditional cheeseAuthors are grateful to Fundação de Amparo à Pesquisa do Estado de São Paulo for the financial support (Grants 2014/14891-7 and 2016/ 09346-5). Dr. Gonzales-Barron acknowledges the financial support provided by the Portuguese Foundation for Science and Technology through the award of an Investigator Fellowship (IF) in the mode of Development Grants (IF/00570). A. S. Sant’Ana acknowledges Conselho Nacional de Desenvolvimento Científico e Tecnológico (Grant # 302763/2014-7, 305804/2017-0), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Finance Code 001”.info:eu-repo/semantics/publishedVersio

The Physics of the B Factories

This work is on the Physics of the B Factories. Part A of this book contains a brief description of the SLAC and KEK B Factories as well as their detectors, BaBar and Belle, and data taking related issues. Part B discusses tools and methods used by the experiments in order to obtain results. The results themselves can be found in Part C