Research round-up: Hispanic style cheese and mcr-3

Traceability systems in China face many challenges​ due to the scale, diversity and complexity of food supply chains, according to researchers from the University of Portsmouth, University of Bedfordshire and China Agricultural University​.

Researchers identified laws, regulations and standards; government support; consumer knowledge and support; effective management and communication; top management and vendor support; and information and system quality as an implementation framework the Chinese government and companies can use.

Professor Mark Xu, from the University of Portsmouth and co-author, said an effective traceability system can promptly identify, single out and remove unsafe products from the market.

“We call for stronger government intervention, in particular attention should be paid to harmonizing laws and standards with international laws and standards for food safety and traceability, effective coordinating for global food risk alerts and recalls, through effective food safety monitoring and quality control systems.​

“Measures need to be taken to ensure information authenticity and accuracy. This could include traceability systems users’ training, skills development, compatibility in data collection and communication technologies, and integration of systems at different levels and regions.​

“Willingness to pay for traceable products by consumers will ultimately drive the proliferation and implementation of successful traceability systems.”​

Review of Listeria in Hispanic-style cheeses​

Better understanding of manufacturing and research on different Hispanic-style cheeses​​ are needed, according to researchers.

Consumer preferences have led to a large proportion of Hispanic-style cheeses being made from raw milk. Soft cheeses are challenging to produce due to persistence of Listeria monocytogenes in the environment and its ability to grow in a range of temperatures (up to 45°C) and under refrigerated storage and in harsh conditions such as high salt concentration.

Recent studies have suggested contamination occurs predominantly through transportation and storage of finished products and food contact surfaces rather than raw or improperly pasteurized milk.

In a review, researchers said most studies were on Queso Fresco, which is not necessarily representative of all Hispanic-style cheeses, and preservation methods fail to take into account sensory impact and consumer acceptability.

“Food safety concerns over Listeria stifle wide-spread commercial growth of fresh cheeses and especially the Hispanic-style cheese market​,” said Michael J. Miller, lead investigator, and associate professor of Food Microbiology at University of Illinois, Urbana.

“It is unclear to what extent different manufacturing steps and variations in the finished product affect listeriosis risk factors, as our knowledge of Listeria monocytogenes in commercial products is largely outdated and limited to Queso Fresco, especially in the US.”​

They also assessed antimicrobial efficacy of a Listeria bacteriophage endolysin that may address limitations of current antilisterial processes for fresh cheeses.

They showed that enzyme PlyP100 had optimal activity under pH and salt concentrations consistent with a low-acid matrix such as fresh cheese.

The leading cause of acute gastroenteritis linked to eating raw seafood paralyzes a cell's skeleton, or cytoskeleton​, according to scientists from UT Southwestern Medical Center​.

Without a working cytoskeleton, infected cells are unable to produce defensive molecules called reactive oxygen species (ROS) that normally attack bacterial DNA, said Dr Marcela de Souza Santos, lead author and a postdoctoral researcher in the lab of senior author.

"Vibrio parahaemolyticus​ bacteria deploy a needlelike apparatus called a Type III Secretion System (T3SS) that injects toxic bacterial proteins, known as effectors, into cells that line the intestine, resulting in severe gastroenteritis​," he said.

Researchers at Memorial Sloan Kettering Cancer Center​ in New York have found that bacteria living in the gut provide a first line of defense​ against Listeria infections.

The study suggests providing these bacteria in the form of probiotics could protect those particularly susceptible, including pregnant women and cancer patients undergoing chemotherapy.

Researchers identified four species of gut bacteria - members of the Clostridiales order- that together were able to limit L. monocytogenes growth in laboratory cultures.

Simone Becattini said: “Our results also raise the possibility that in other at-risk categories for listeriosis, such as infants or pregnant women, disruptions to the gut microbiome could be a contributing factor to susceptibility."​

New mobile colistin resistance gene and Salmonella detection​​

Researchers have discovered a new mobile colistin resistance gene, mcr-3​, in E. coli of pig origin.

The novel gene was discovered when a colistin-resistant E. coli isolate tested negative for mcr-1 and mcr-2.

The E. coli mcr-3 sequence is similar to those found in Enterobacteriaceae and Aeromonas, commonly found in the environment.

Genetic and dietary forms of hemochromatosis - iron overload​ - lead to divergent paths​ with respect to Salmonella infection, according to Dr Manfred Nairz and colleagues.

Salmonella feeds upon iron to move throughout the body. Many foods, such as tuna and red meat, are rich in iron.

Researchers infected two different strains of mice with Salmonella - one strain of mice had normal levels of iron, the other had an excessive amount (which is roughly analogous to humans who experience genetic hemochromatosis).

Dr Nairz said: "Inconsiderate supplementation of iron to treat anemia, without proper interpretation of lab work including iron indices, may impair the host's ability to fight off bacteria such as Salmonella.”​

Martin Loessner, ETH professor​, and colleagues have synthetically produced bacteriophage components​ to develop a universal detection method for Salmonella.

Previous methods based on antibodies recognise only a fraction of serotypes and are slower.

Loessner's team reproduced a component of the Salmonella-specific bacteriophage S16. This component - a virus tail fibre - features a spherical terminal binding protein that can adhere to two specific surface structures of all Salmonella types.

The artificial tail fibre, with the recognition structure, has been attached to the surface of microscopically small magnetic beads.

As soon as the bacteria binds to fibres on the magnetic beads, a kind of rusty aggregate forms in the test container, which can be separated using an external magnet.