Penicillin tactics revealed by scientists

Penicillin, the wonder drug discovered in 1928, works in ways that are still mysterious almost a century later. One of the oldest and most widely used antibiotics, it attacks enzymes that build the bacterial cell wall, a mesh that surrounds the bacterial membrane and gives the cells their integrity and shape. Once that wall is breached, bacteria die -- allowing us to recover from infection.

That would be the end of the story, if resistance to penicillin and other antibiotics hadn't emerged over recent decades as a serious threat to human health. While scientists continue to search for new antibiotics, they still don't understand very much about how the old ones work.

Now Thomas Bernhardt, associate professor of microbiology and immunobiology at Harvard Medical School, and his colleagues have added another chapter to the story.

Their findings, published Dec. 4 in Cell, reveal how penicillin deals bacteria a devastating blow -- which may lead to new ways to thwart drug resistance.

Looking beyond penicillin's known targets in the cell wall, he and his team have shown that these drugs do more than simply block cell-wall assembly. Penicillin and its variants also set in motion a toxic malfunctioning of the cell's wall-building machinery, which dooms the cell to a futile cycle of building and then immediately destroying that wall. This downstream death spiral depletes cells of the resources they need to survive.

"It seems to be a common theme with some of the best antibiotics that we have: They don't just inhibit the enzyme they are targeting; they actually convert that target so that whatever activity it has left becomes toxic," Bernhardt said. "I think it's important in understanding how the drug works, but it also teaches us fundamentally about how bacteria build a wall so we can find news way we might throw a wrench in that process."

Penicillin and similar drugs -- a class called beta-lactams -- are derived from natural antibiotics produced by fungi that evolved effective ways to kill bacteria. The drugs prevent the bacteria from properly building their cell walls.

There are two parts to the wall-assembly process: synthesizing new strands of linked sugars and then linking them into the expanding matrix. Beta-lactam drugs work by blocking the enzymes that build cross-links, weakening the wall. The wall can't hold together, so the bacterial cell bursts and dies.

This general framework of the bacteria-penicillin battle is well known, but the molecular details were missing. What happens after blockage of the cross-linking process to promote the death of the bacterial cell?

To find out, Bernhardt and Hongbaek Cho, a postdoctoral fellow in the Bernhardt Lab and lead author of the Cell paper, used a specific derivative of penicillin that targets only one enzyme in cell-wall assembly. Their trick was to genetically manipulate their study subject E. coli to make this enzyme dispensable for the life of the cell.

To their surprise, the scientists saw that targeting the nonessential enzyme with the penicillin still killed the cell. This finding was quite a conundrum. The enzyme could be removed from cells completely without harm. Yet, when it was present and bound by the drug, the cells would die.

The investigators discovered that the root cause of the problem was that the drug not only inhibited the enzyme, but it also caused it to malfunction in such a way that its activity became toxic. They found that the bacteria still made new cell wall strands, but because linking was blocked, they were immediately degraded, which set up a futile cycle of building up and breaking down the cell wall.

This suggested that while the cell has many molecular machines building the wall, the drugs need to hit only a few of them to drain resources from the rest.

"You inhibit some of the machines and, by going through the futile cycle, they deplete cell resources to inhibit even the ones that haven't been targeted by the drug yet. Your drug becomes much more potent at that point, rather than just being a simple inhibitor that blocks cell-wall synthesis," Bernhardt said. "You get more bang for your buck with the drug this way."

Penicillin is powerful, but it's still vulnerable to resistance. When the cell walls of bacteria are disintegrating, they fight back with enzymes called beta-lactamases that slice the beta-lactam molecules and keep them from attaching to their targets.

Seeing how penicillins work, the scientists have also learned more about how bacteria turn on their beta-lactamases to resist penicillin. An enzyme called Soluble Lytic Transglycosylase (Slt) has been a suspect in recruiting beta lactamases to the struggle. Now it has been directly shown to cause the futile cycle of building and degrading new cell-wall material, creating the alarm signal the bacterium uses to start the production of beta-lactamases.

Knowing in greater detail just how Slt recruits beta-lactamases may lead to ways to block this form of resistance. Bernhardt has already launched new chemical screens at the medical school's ICCB-Longwood Screening Facility to look for new antibiotic candidates.

"Now that we know more about beta-lactams being toxic, it gives us a hook to look for new molecules that target the cell wall," he said. "The more we understand how these processes like cell wall synthesis work in bacteria, the better position we'll be in to find new ways to disrupt it."

Friendly bacteria are protective against malaria

In a breakthrough study to be published on the December 4th issue of the scientific journal Cell, a research team led by Miguel Soares at the Instituto Gulbenkian de Ciência (IGC; Portugal) discovered that specific bacterial components in the human gut microbiota can trigger a natural defense mechanism that is highly protective against malaria transmission.

Over the past few years, the scientific community became aware that humans live under a continuous symbiotic relationship with a vast community of bacteria and other microbes that reside in the gut. These microbes, know as the gut microbiota, do not necessarily cause disease to humans and instead can influence a variety of physiologic functions that are essential to maintain health. Some of these microbes, including specific strains of Escherichia coli (E. coli) that are usual inhabitant of the human gut, express on their surface sugar molecules (known as carbohydrates or glycans). These glycans can be recognized by the human immune system, which results in the production of high levels of circulating natural antibodies in adult individuals. It has been speculated that natural antibodies directed against sugar molecules expressed by the microbiota may also recognize perhaps similar sugar molecules expressed by pathogens, that is, parasites that can cause diseases in humans.

Bahtiyar Yilmaz, a PhD student of the Instituto Gulbenkian de Ciência PhD programme in Miguel Soares' laboratory, found that the Plasmodium parasite, the causative agent of malaria, expresses a sugar molecule called alpha-gal, which is also expressed at the surface of a strain of E. coli that is part of the human gut microbiota. In a series of experiments performed in mice, Bahtiyar Yilmaz went on to find that expression of alpha-gal by these bacteria, when resident in the gut, is sufficient to induce the production of natural antibodies that can recognize the same sugar molecule when expressed at the surface of Plasmodium parasites. He then found that these antibodies attach to the alpha-gal sugar at the surface of Plasmodium parasites, immediately after the inoculation in the skin by a mosquito, the vector of malaria transmission. When this occurs the anti-alpha-gal antibodies activate an additional arm of the human immune system, called the complement cascade, which goes on to punch holes and kills the Plasmodium parasite before it can move out of the skin. The protective effect is such that when present at high levels at the time of the mosquito bite, anti-alpha-gal antibodies manage to arrest the transition of the parasite from the skin into the blood stream and by doing so block malaria transmission.

It was well established before these studies, that only a fraction of all adult individuals that are confronted to the bite of mosquitoes in endemic areas of malaria do become infected by the Plasmodium parasite and eventually go on to contract malaria. This argued that adults might have a natural defense mechanism against malaria transmission, which is in sharp contrast with children under 3-5 years old that are much more susceptible to contract malaria. When analyzing individuals from an endemic area of malaria in Mali, in collaboration with a research team lead by Peter D. Crompton at National Institute of Allergy and Infectious Diseases (Maryland; USA) and at the University of Sciences, Techniques and Technologies of Bamako (Bamako, Mali), the research team lead by Miguel Soares established that those individuals that have the lowest levels of circulating anti-alpha-gal antibodies are also those that are the most susceptible to contract malaria. In contrast those individuals that have the highest levels of circulating anti-alpha-gal antibodies are less susceptible to be infected and to develop malaria. They conclude that the reason why young infants are so susceptible to contract malaria is probably due to the fact that they have not yet generated sufficient levels of circulating natural antibodies directed against the alpha-gal sugar molecule.

With the goal of overcoming this shortcoming, Bahtiyar Yilmaz found that when mice are vaccinated against a synthetic form of alpha-gal that is rather easy and inexpensive to produce, they produced high levels of circulating anti-alpha-gal antibodies that are highly protective against malaria transmission by mosquitoes. Whether the same "trick" can be applied to humans and in particular to young infants to confer protection against malaria transmission is a "burning question" that remains to be answered.

It is estimated that 3.4 billion people are at risk of contracting malaria and WHO data from 2012 reveal that about 460,000 African children died from malaria before reaching their fifth birthday. The present study argues that if one can induce the production of antibodies against alpha-gal in those children one may be able to revert these grim numbers.

Miguel Soares adds: "We observed that children under 3 years old do not have sufficient levels of circulating anti-alpha-gal antibodies, which might be one of the reasons for their exquisite susceptibility to malaria. One of the beauties of the protective mechanism we just discovered is that it can be induced via a standard vaccination protocol, leading to the production of high levels of anti-alpha-gal antibodies that bind and kill the Plasmodium parasite. If we can vaccinate these young children against alpha-gal, many lives might be saved."

Story Source:

The above story is based on materials provided by Instituto Gulbenkian de Ciencia . Note: Materials may be edited for content and length.

Gadget Lab Podcast: Saying Goodbye to Friends Is Sad. But Hello CES!

It's almost time for CES, and it's the holidays. The madness has begun.

It’s almost time for CES, and it’s the holidays. The most maddening time of the year. Jim Merithew

It’s the holidays, otherwise know to us at the Gadget Lab as “buying stuff season.” The hosts exchange their gift-giving plans. Also on the horizon is the big event happening in one month: the Consumer Electronics Show in Las Vegas. Hundreds of thousands of attendees and vendors will descend upon the desert oasis the first week in January to touch each other’s electronic devices and to distribute biological viruses. Is CES still relevant? (Yes.) And what’s the most interesting tech advancement this year? (We’ll tell you when we see it.) Lastly, maybe you’ve heard: Mat is leaving the flock. He tells us a little bit about his new job, which starts in a few weeks.

Listen to this week’s episode or subscribe in iTunes.

Send the hosts feedback on their personal Twitter feeds (Mat Honan is @mat and Michael Calore is @snackfight) or to the main hotline at @GadgetLab.

Sony Celebrates PlayStation’s 20th Anniversary With a Limited-Edition PS4

To celebrate the 20th anniversary of PlayStation, Sony is releasing a limited number of specially designed PlayStation 4 consoles that use the original PlayStation’s color scheme.

And no, that doesn’t just mean “gray.” The $499 PlayStation 4 20th Anniversary Edition is also covered in the classic PlayStation circle-cross-square-triangle symbols, plus a numeral 2 next to the circle symbols to suggest the number 20.

The console includes similarly-colored editions of the PlayStation 4’s controller, camera, vertical stand and headset.

Sony will sell 12,300 of these consoles through its online Sony Store, beginning Saturday, December 6. At 10 a.m. Pacific time, it will announce details about the preorder program via the live-stream of its keynote address at PlayStation Experience, a fan expo to be held this weekend in Las Vegas.

The original PlayStation console was released on December 3, 1994 in Japan. It was not released in the United States until September 9, 1995.