Evaluation of Mycobacterium avium subsp. paratuberculosis survival during the manufacturing process of Italian raw milk hard cheeses (Parmigiano Reggiano and Grana Padano).

Mycobacterium avium subsp. paratuberculosis (MAP), the agent of paratuberculosis in ruminants, is suspected to be involved in the aetiology of some human diseases. Notably, the consumption of milk and dairy products is considered to be the main route of human exposure to MAP because of its ability to survive during pasteurization and manufacturing processes. The aim of this study was to investigate, through a microbiological challenge test, the survival of MAP during the manufacturing and ripening period of two Italian hard cheeses, Parmigiano Reggiano and Grana Padano, made from raw bovine milk. The challenge test was performed in two different phases: the creaming phase and the manufacturing phase. The creaming phase, which is the first step of cheese production, was reproduced in the laboratory employing raw cow's milk spiked with a MAP reference strain at a final concentration of 5.58 log10 CFU/mL. After the creaming at 18 °C and 27 °C for 12 h, a decrease of 0.80 log10 and 0.77 log10 was observed in partially skimmed milk, respectively. In the second phase, two batches of raw cow's milk (1000 L each) were inoculated with MAP reference and wild strains, respectively. Then, the entire manufacturing process for Parmigiano Reggiano and Grana Padano, both of Protective Designation of Origin (PDO), was reproduced in an experimental cheese factory, starting from a concentration in milk of 5.19 ±â€¯0.01 and 5.28 ±â€¯0.08 log10 CFU/mL of MAP reference and wild strains, respectively. Heating the curd at 53 °C for 20 min did not affect MAP survival, however a significant decrease (p < 0.05) in MAP viability was observed during the moulding phase and after salting in brine, regarding the wild strains and the reference strain, respectively. In addition, a significant decrease was observed during the ripening period, at which time the MAP concentration dropped below the limit of detection from the second and the third month of ripening, for the wild and reference strains, respectively. Taking into account the poor data availability about MAP survival in hard cheeses, this study may improve the knowledge regarding the effect of the cheese manufacturing process on the MAP dynamics, supporting also the safety of traditional raw milk hard cheeses.

Paediatric HUS Cases Related to the Consumption of Raw Milk Sold by Vending Machines in Italy: Quantitative Risk Assessment Based on Escherichia coli O157 Official Controls over 7 years.

A quantitative risk assessment (RA) was developed to estimate haemolytic-uremic syndrome (HUS) cases in paediatric population associated with the consumption of raw milk sold in vending machines in Italy. The historical national evolution of raw milk consumption phenomenon since 2008, when consumer interest started to grow, and after 7 years of marketing adjustment, is outlined. Exposure assessment was based on the official Shiga toxin-producing Escherichia coli O157:H7 (STEC) microbiological records of raw milk samples from vending machines monitored by the regional Veterinary Authorities from 2008 to 2014, microbial growth during storage, consumption frequency of raw milk, serving size, consumption preference and age of consumers. The differential risk considered milk handled under regulation conditions (4°C throughout all phases) and the worst time-temperature field handling conditions detected. In case of boiling milk before consumption, we assumed that the risk of HUS is fixed at zero. The model estimates clearly show that the public health significance of HUS cases due to raw milk STEC contamination depends on the current variability surrounding the risk profile of the food and the consumer behaviour has more impact than milk storage scenario. The estimated HUS cases predicted by our model are roughly in line with the effective STEC O157-associated HUS cases notified in Italy only when the proportion of consumers not boiling milk before consumption is assumed to be 1%. Raw milk consumption remains a source of E. coli O157:H7 for humans, but its overall relevance is likely to have subsided and significant caution should be exerted for temporal, geographical and consumers behaviour analysis. Health education programmes and regulatory actions are required to educate people, primarily children, on other STEC sources.

Short communication: Arcobacter butzleri and Arcobacter cryaerophilus survival and growth in artisanal and industrial ricotta cheese.

Ricotta cheese is a ready-to-eat product with properties (pH >6.0, aw >0.98-0.99) and moisture content (75-80%) that may pose a risk to public health due to postprocess contamination by several bacterial pathogens, including Arcobacters. The objective of the study was to evaluate the behavior of Arcobacter butzleri and Arcobacter cryaerophilus in ricotta cheese during its shelf life assuming postprocessing contamination. Two types of ricotta cheese, artisanal water buffalo (WB) and industrial cow milk ricotta cheese, were experimentally contaminated with A. butzleri and A. cryaerophilus and the count was monitored at 2 different temperatures (6°C and 12°C) during shelf life of 5 d for WB cheese and 22 d for industrial ricotta cheese. In WB ricotta cheese the A. butzleri count remained stable during the 5 d of storage at 6°C, whereas a moderate but significant decrease was observed in A. cryaerophilus count. The counts of both species increased when WB ricotta cheese was stored at 12°C. In industrial ricotta cheese stored at 6°C, a significant reduction was observed both in A. butzleri and A. cryaerophilus counts during the 22-d storage period; at 12°C storage, a count increase was observed for both Arcobacter species up to d 14 of storage after which the log cfu/g count resulted constant until d 22 of storage. The ability of A. butzleri and A. cryaerophilus to survive at 6°C and to grow at 12°C in ricotta cheese has significant food safety implications.

Quantitative risk assessment of verocytotoxin-producing Escherichia coli O157 and Campylobacter jejuni related to consumption of raw milk in a province in Northern Italy.

A quantitative risk assessment was developed to describe the risk of campylobacteriosis and hemolytic uremic syndrome (HUS) linked to consumption of raw milk sold in vending machines in Northern Italy. Exposure assessment considered the microbiological status of dairy farms, expected milk contamination, storage conditions from bulk tank to home storage, microbial growth during storage, destruction experiments, consumption frequency of raw milk, age of consumers, serving size, and consumption preference. The differential risk between milk handled under regulation conditions (4°C throughout all phases) and the worst field handling conditions was considered. The probability of Campylobacter jejuni infection was modeled with a single-hit dose-response beta-Poisson model, whereas for HUS an exponential dose-response model was chosen and two probabilities were used to model the higher susceptibility of children younger than 5 years old. For every 10,000 to 20,000 consumers each year, the models predicted for the best and worst storage conditions, respectively, 2.12 and 1.14 campylobacteriosis cases and 0.02 and 0.09 HUS cases in the 0- to 5-year age group and 0.1 and 0.5 HUS cases in the >5-year age group. The expected pediatric HUS cases do not differ considerably from those reported in Italy by the Minister of Health. The model developed may be a useful tool for extending the assessment of the risk of campylobacteriosis and HUS due to raw milk consumption at the national level in Italy. Considering the epidemiological implications of this study, the risk of illness linked to raw milk consumption should not be ignored and could be reduced by the use of simple measures. Boiling milk before consumption and strict control of temperatures by farmers during raw milk distribution have significant effects on campylobacteriosis and HUS and are essential measures for risk management.

Behaviour of Listeria monocytogenes in packaged water buffalo mozzarella cheese.

AIMS: The aim of the study was to evaluate the behaviour of Listeria monocytogenes in the conditioning liquid of packaged water buffalo mozzarella cheese (WBMC). METHODS AND RESULTS: The conditioning liquid was contaminated with L. monocytogenes, and the contaminated samples were stored at four different storage temperatures: 5 and 10 °C for 22 days; 20 °C for 9 days; 20 °C for 3 days and then at 5 °C for 6 days. The results showed that L. monocytogenes concentration decreased when contaminated samples were stored at 5 °C. When WBMC was stored at 20 °C and at 10 °C, L. monocytogenes started to grow after a lag phase of 3 and 10 days, respectively. When samples were stored at variable temperature conditions, L. monocytogenes numbers showed a lag phase of 5 days. CONCLUSIONS: Use of a conditioning liquid characterized by acidity and a correct storage temperature is able to counteract pathogen replication during shelf life. A high concentration of lactic acid bacteria was associated with effective control of L. monocytogenes but the role of lactic acid bacteria in WBMC conditioning liquid requires further investigation. SIGNIFICANCE AND IMPACT OF THE STUDY: According to European regulations, food producers should be able to justify decision-making on the shelf life assigned to their products, taking into account reasonable storage conditions and use by consumers. The results of the trial yielded information for producers of WBMC and similar cheeses for decision-making on product shelf life.