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Sharing of a bacterium related to tooth decay among children and their families

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Research presented at the ASM Microbe research meeting provides compelling evidence that children acquire Streptococcus mutans, the bacterium most frequently associated with dental caries, from intra- and extra-familial sources besides their mother.

Children typically have more than one strain (i.e., genotype) of S. mutans and most share at least one strain with mother or a family member. However, 72% of children in this study had 1 or more S. mutans strains not found in participating household family members indicating these strains likely came from outside the home (extra-familial transmission), possibly from other children in the population.

"While the prevailing theory on S. mutans transmission suggests mother-to-child transmission as the primary route of infection, in this study 40 percent of children shared no strains with their mothers," said Stephanie Momeni, a doctoral candidate in the Department of Biology at the University of Alabama at Birmingham. Interestingly, 27 children (22.8 percent) shared 37 strains only with another child in the household (siblings or cousins), demonstrating another dimension to inter-familial transmission.

"Of the children that did not share strains with any household members, 33 percent (53/157) were found to have only 1 isolate, indicating these strains to be rare or transient," said Momeni. This is important since it suggests that approximately one-third of strains analyzed may not be clinically relevant and can confound the search for strains related to the disease. It also suggests these strains are highly transmissible but may not become established strains due to bacterial competition or host immune factors.

S. mutans is the primary bacterium most frequently associated with dental caries and is considered to be transferred from other humans. In total, S. mutans isolates (N=13,145) from 119 African American children having at least 1 household family member were evaluated. More than one family member was evaluated for 76% of children (mean=3.24, range 1-11). The strength of this study is that it evaluates interacting children as well as all participating residential household family members (including extended family). Strain types were determined using a bacterial typing method known as repetitive extragenic palindromic PCR (rep-PCR). For each rep-PCR genotype, children were evaluated as either sharing or not sharing the strain with any household members. Since children in this study had between 1-9 genotypes, a total of 315 genotype cases were evaluated.


Paper-based test could help prevent food poisoning

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Food poisoning is a stomach-churning, miserable condition that sends thousands of Americans to hospital emergency rooms every year. Now scientists report in ACS' journal Analytical Chemistry a simple, paper-based test that could help detect pathogens hitchhiking on food before they reach store shelves, restaurants and, most importantly, our stomachs.

According to one estimate by the U.S. Department of Agriculture, the foodborne bacteria Salmonella alone led to nearly 20,000 hospitalizations and almost 400 deaths in 2013. Economists estimate that the treatment of all these patients and the related productivity losses cost more than $3 billion annually. And those numbers account for just one of the 15 pathogens responsible for most of the food poisoning cases. Current testing for pathogens in food requires complicated machinery and trained personnel. But these tests don't provide the simple results needed in large-scale food manufacturing. So Je-Kyun Park and colleagues set out to find a more practical way to detect foodborne pathogens.

The researchers developed a paper-based test that can handle the multistep reactions necessary for this kind of analysis by controlling the pore size of the paper. When dipped into solutions containing the E. coli strain O157:H7, Salmonella typhimurium or both, lines appeared on the dipstick indicating a positive result within 15 minutes. Because the method requires dipping the device into a solution once and produces an easy-to-read result, it could be performed by workers without special training, the researchers say.

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Dentistry Infectious Diseases / Bacteria / Viruses Penn team uses nanoparticles to break up plaque and prevent cavities

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Penn team uses nanoparticles to break up plaque and prevent cavities

MNT Knowledge Center
Adapted Media Release
Published: Thursday 28 July 2016

The bacteria that live in dental plaque and contribute to tooth decay often resist traditional antimicrobial treatment, as they can "hide" within a sticky biofilm matrix, a glue-like polymer scaffold.

A new strategy conceived by University of Pennsylvania researchers took a more sophisticated approach. Instead of simply applying an antibiotic to the teeth, they took advantage of the pH-sensitive and enzyme-like properties of iron-containing nanoparticles to catalyze the activity of hydrogen peroxide, a commonly used natural antiseptic. The activated hydrogen peroxide produced free radicals that were able to simultaneously degrade the biofilm matrix and kill the bacteria within, significantly reducing plaque and preventing the tooth decay, or cavities, in an animal model.

"Even using a very low concentration of hydrogen peroxide, the process was incredibly effective at disrupting the biofilm," said Hyun (Michel) Koo, a professor in the Penn School of Dental Medicine's Department of Orthodontics and divisions of Pediatric Dentistry and Community and Oral Health and the senior author of the study, which was published in the journalBiomaterials. "Adding nanoparticles increased the efficiency of bacterial killing more than 5,000-fold."

The paper's lead author was Lizeng Gao, a postdoctoral researcher in Koo's lab. Coauthors were Yuan Liu, Dongyeop Kim, Yong Li and Geelsu Hwang, all of Koo's lab, as well as David Cormode, an assistant professor of radiology and bioengineering with appointments in Penn's Perelman School of Medicine and School of Engineering and Applied Science, and Pratap C. Naha, a postdoctoral fellow in Cormode's lab.

The work built off a seminal finding by Gao and colleagues, published in 2007 in Nature Nanotechnology, showing that nanoparticles, long believed to be biologically and chemically inert, could in fact possess enzyme-like properties. In that study, Gao showed that an iron oxide nanoparticle behaved similarly to a peroxidase, an enzyme found naturally that catalyzes oxidative reactions, often using hydrogen peroxide.

When Gao joined Koo's lab in 2013, he proposed using these nanoparticles in an oral setting, as the oxidation of hydrogen peroxide produces free radicals that can kill bacteria.

"When he first presented it to me, I was very skeptical," Koo said, "because these free radicals can also damage healthy tissue. But then he refuted that and told me this is different because the nanoparticles' activity is dependent on pH."

Gao had found that the nanoparticles had no catalytic activity at neutral or near-neutral pH of 6.5 or 7, physiological values typically found in blood or in a healthy mouth. But when pH was acidic, closer to 5, they become highly active and can rapidly produce free radicals.

The scenario was ideal for targeting plaque, which can produce an acidic microenvironment when exposed to sugars.

Gao and Koo reached out to Cormode, who had experience working with iron oxide nanoparticles in a radiological imaging context, to help them synthesize, characterize and test the effectiveness of the nanoparticles, several forms of which are already FDA-approved for imaging in humans.

Beginning with in vitro studies, which involved growing a biofilm containing the cavity-causing bacteria Streptococcus mutans on a tooth-enamel-like surface and then exposing it to sugar, the researchers confirmed that the nanoparticles adhered to the biofilm, were retained even after treatment stopped and could effectively catalyze hydrogen peroxide in acidic conditions.

They also showed that the nanoparticles' reaction with a 1 percent or less hydrogen peroxide solution was remarkably effective at killing bacteria, wiping out more than 99.9 percent of the S. mutans in the biofilm within five minutes, an efficacy more than 5,000 times greater than using hydrogen peroxide alone. Even more promising, they demonstrated that the treatment regimen, involving a 30-second topical treatment of the nanoparticles followed by a 30-second treatment with hydrogen peroxide, could break down the biofilm matrix components, essentially removing the protective sticky scaffold.

Moving to an animal model, they applied the nanoparticles and hydrogen peroxide topically to the teeth of rats, which can develop tooth decay when infected with S. mutans just as humans do. Twice-a-day, one-minute treatments for three weeks significantly reduced the onset and severity of carious lesions, the clinical term for tooth decay, compared to the control or treatment with hydrogen peroxide alone. The researchers observed no adverse effects on the gum or oral soft tissues from the treatment.

"It's very promising," said Koo. "The efficacy and toxicity need to be validated in clinical studies, but I think the potential is there."

Among the attractive features of the platform is the fact that the components are relatively inexpensive.

"If you look at the amount you would need for a dose, you're looking at something like 5 milligrams," Cormode said. "It's a tiny amount of material, and the nanoparticles are fairly easily synthesize, so we're talking about a cost of cents per dose."

In addition, the platform uses a concentration of hydrogen peroxide, 1 percent, which is lower than many currently available tooth-whitening systems that use 3 to 10 percent concentrations, minimizing the chance of negative side effects.

Looking ahead, Gao, Koo, Cormode and colleagues hope to continue refining and improving upon the effectiveness of the nanoparticle platform to fight biofilms

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