Research round-up: Listeria, GBS and “smart” compounds

We start with findings by scientists at UCSF Benioff Children’s Hospital in San Francisco that listeriosis is unrelated to lowered immunity in pregnancy.

Researchers, led by senior author Anna Bakardjiev​, looked at pregnant guinea pigs, because the placentas and responses to Listeria closely resemble humans.

Previous research by Bakardjiev found a single bacterium was responsible for infection that grew to very high numbers in the placenta, indicating another factor played a role in listeriosis.

Researchers performed a genomic screen in pregnant guinea pigs that identified 201 Listeria genes implicated in infection of the placenta.

They identified a protein secreted by Listeria that promotes placental infection, while having only a minor role in the infection of other organs.

In research with guinea pigs and mice, the team discovered that the protein, which they named InlP, increased the amount of bacteria in the placenta by 1,000-fold.

Bakardjiev said findings challenge current beliefs that pregnant women are susceptible to listeriosis because of immune compromise.

“Instead, placental pathogens need specific virulence factors that allow them to grow and survive in ​this niche,” said the associate professor at UCSF Benioff Children’s Hospital San Francisco.

“InlP presents a novel tool that we can use to better understand the course of placental infections, which is necessary for the development of new strategies to prevent and treat listeriosis and other infection-related pregnancy complications.”​

Listeria during pregnancy​

In a separate work, researchers in Wisconsin discovered how Listeria monocytogenes travels through the mother's body to attack the placenta and fetus during early pregnancy in a macaque monkey.

Listeria may pose a greater risk of miscarriage​ in the early stages of pregnancy than appreciated.

Infection in pregnancy may go unnoticed as the few recognizable symptoms are nearly indistinguishable from the discomfort most newly pregnant women feel, said the researchers.

Ted Golos, professor of reproductive sciences at the School of Veterinary Medicine at the University of Wisconsin-Madison, and his team exposed four pregnant macaques to a moderate dose of Listeria by tube-feeding them tainted whipped cream on days 36-46 of gestation-corresponding to about week six or seven of a human pregnancy.

The team found the infection rapidly spread to the fetus: by days seven-13 after exposure, all four fetuses had died in the womb.

Graduate student Bryce Wolfe tracked infections in the mothers through blood and fecal sampling and in fetuses via ultrasound. All of the mothers showed signs of bacterial infection in their bloodstream, but displayed few to no symptoms.

Next, the team will investigate what is happening with the immune cells that survey and protect the maternal-fetal interface.

Golos and Wolfe will attempt to better define how the bacterium targets the reproductive tract, its incubation time and the problems it causes leading up to miscarriage.

Model of GBS and “smart” compounds​

Next, a Michigan State University research team has shown how Campylobacter causes Guillain-Barre Syndrome (GBS).

Linda Mansfield, lead author and MSU College of Veterinary Medicine professor, said it takes a certain genetic makeup​ combined with a particular Campylobacter strain to cause this disease.

“The concerning thing is that many of these strains are resistant to antibiotics and our work shows that treatment with some antibiotics could actually make the disease worse,” ​she said.​

“We have successfully produced three preclinical models of GBS that represent two different forms of the syndrome seen in humans.​

“Many patients with GBS are critically ill and they can’t participate in clinical trials. The models we identified can help solve this.”​

Meanwhile, a research team in Sweden have synthesized a new “smart” compound that changes shape​ when it comes in contact with components of bacteria and emits light at a specific wavelength.

The compound is non-toxic and binds to very specific components of the bacterial biofilm.

As soon as bacterial cells start producing the slime associate with the biofilm, the smart compound will bind and it can be detected.

The hope is the molecule will be used by researchers trying to tackle the problem of infectious bacteria living in biofilms.

“The molecules we have developed are unique in that they can send out different colours, depending on how they twist and bend​,” said Professor Peter Nilsson from Linköping University, who developed the molecules.

“We usually call them molecular chameleons, because they change colour according to the environment. When the molecules binds to the biofilm they actually turn on their fluorescence, we can see that as a red light.”​

Finally, Liesbeth Jacxsens of the University of Ghent et al assessed the exposure to Salmonella​ by consumption of boiled milk and Gouda cheese in Musanze town, Rwanda.

A previous study by Oliver Kamana at the University of Rwanda revealed that 8.3% (n=96) of Gouda cheese and 11.4% (n=96) of boiled milk were contaminated by Salmonella at consumption level.

Although Salmonella is eliminated by milk boiling, the risk of infection persists due to post-contamination in the milk shops (8.4% of consumers infected per year), but is decreased by additional boiling in households to 4.9% (children) and 4.6% (adults) per year.

For cheese consumption, the risk of infection was lowered by multiple food safety interventions for cheese producers such as training on food hygiene and provision of modern equipment improving the situation by 30%% per year in the case of adults.

The study developed a probabilistic shop-to-consumer exposure model to provide information and to serve as a case study for future mitigation strategies.