Big bacteria may be easier to kill, new research suggests

Image by NIAID

The size of a cell is intrinsicThe size of a cell is intrinsically linked with its genetic makeup, growth rate and other fundamental properties. What would happen if scientists could control the size of pathogens?

That possibility isn’t completely outlandish: Stanford researchers have discovered a genetic “tuning knob” that can enlarge or shrink bacteria across a wide range — and this knob can be used to fatten up the bacteria to increase their susceptibility to certain antibiotics, as recently reported in Current Biology.

The research team is led by KC Huang, an associate professor of bioengineering and of microbiology and immunology at Stanford. Huang explained in a recent Stanford Engineering  news article:

“Most strategies to killing bacteria are linear: you find a very specific target and block it with a drug. These findings point in the direction of totally orthogonal therapies, in which you predispose cells to death by tweaking a global property like size.”

The researchers found that a single protein in E. coli, called MreB, acts as a master regulator of cell size by coordinating the construction of cell walls. So they manufactured many copies of the E. coli’s DNA, changing in each copy just one of the 347 letters in MreB’s genetic code. Using fluorescence-activated cell sorting, they then separated the individual cells with different sizes to create a library of cell-size mutants.

The team used this library to study how size impacts a cell’s physiology, including how bacterium grow and survive. For instance, they treated the various E. coli mutants with several antibiotics and found that larger E. coli were more sensitive to the drugs. A larger cell has more surface area and that increases the drug uptake, they said in the paper.

Huang said he hopes their techniques can be applied to other bacteria and used to help human health in the future. He added:

“While we don’t yet know how to twist this bacterial size dial in patients, it’s good to have such an exciting new therapeutic approach as antibiotic resistance becomes increasingly prevalent.”

This is a reposting of my Scope blog story, courtesy of Stanford School of Medicine.


Stanford researchers find new bacteria in dolphins

Photo by Hans
Photo by Hans

A team of researchers co-led by David Relman, MD, professor of medicine and of microbiology and immunology, has discovered previously unknown species of bacteria in dolphins trained by the U.S. Navy.

You’ve probably heard of security dogs that help sniff out drugs, bombs or land mines — the U.S. Navy uses dolphins, the dogs’ marine equivalent, to protect ships and submarines by detecting sea mines and underwater intruders.

The researchers are cataloging the bacterial communities living inside the dolphins at the Navy’s Marine Mammal Program in San Diego. They analyzed samples from the dolphins’ mouths, stomachs, rectums and respiratory tracts. Their results were recently reported in Nature Communications.

The research team found a startling diversity of bacteria, especially from the dolphins’ mouths. “About three quarters of the bacterial species we found in the dolphins’ mouths are completely new to us,” Relman said in an online piece.

The researchers also tested the Navy’s sea lions and the surrounding seawater. The newly discovered bacteria found in the dolphins were not seen in the sea lions, even though the dolphins and sea lions were fed the same fish and swam in the same water. The bacteria in the seawater were also very different from the bacteria in the marine mammals.

Relman began working with the Navy 15 years ago to help keep the Navy dolphins healthy. However, their research may have a much wider impact, Relman explained in the story:

There’s a lot of concern about the changing conditions of the oceans and what the impact could be on the health of wild marine mammals. We would love to be able to develop a diagnostic test that would tell us when marine mammals are beginning to suffer from the ill effects of a change in their environment.

The research team plans to expand their study to include other marine mammals, including sea otters, harbor seals and elephant seals.

This is a reposting of my Scope blog story, courtesy of Stanford School of Medicine.

Bacteria Can Survive for Days inside Airplanes

Girl in seat on commercial airplane (foilman).

If you’re traveling by air on your summer vacation, you may want to think twice about what surfaces you touch inside the airplane cabin. Or better yet, you may want to drive.

Disease-causing bacteria can linger for days on surfaces in airplane cabins, according to new research results from Auburn University, Alabama. The researchers obtained common materials from the airplane cabins of a major airline – armrest, plastic tray table, metal toilet button, window shade, seat pocket cloth, and seat leather. They tested how long bacteria could survive on these surfaces under the standard airplane cabin conditions of low humidity and room temperature, when no cleaning procedures were used.

Specifically, they studied the survivability of two common pathogens: methicillin-resistant Staphylococcus aureus (MRSA) and E. coli O157:H7. They found that MRSA lasted the longest on material from the seat-back pocket, surviving for 7 days. In contrast, E. coli O157:H7 lasted the longest on the armrest material, surviving for 4 days.

Staph skin infections, including MRSA, generally start as small red bumps that often resemble spider bites but these can quickly turn into deep, painful abscesses. Different types of staph bacteria are commonly found on the skin or in the nose of about 30% of the U.S. population, while only 2% of the population are asymptomatic carriers of MRSA. You can get MRSA through direct skin-to-skin contact with an infected wound or by sharing equipment that has touched infected skin. However, these staph bacteria are generally harmless unless they enter the body through a cut or wound, so doctors recommend that you keep wounds covered with dry, clean bandages until healed.

E. coli O157:H7 is a major health problem that affects over 70,000 Americans per year. It causes nausea, vomiting, stomach cramps, fever and bloody diarrhea. The infection can be spread from person to person by fecal contamination, but it usually comes from eating food contaminated with animal or human waste. Doctors recommend eating only well cooked foods, particularly hamburger, and drinking treated pasteurized fluids.

However, MRSA and E. coli O157:H7 are not the most commonly found pathogens on airplanes based on past research studies. For instance, other researchers analyzed samples of 61 commercial airplane air filters to identify all the bacteria present.

“ There have been sequencing studies examining the HEPA filters. And MRSA and E. coli are not the dominant organisms there,” explained graduate student Kiril Vaglenov at a press conference. “But we have to remember that MRSA are often found in humans. So there is a possibility that these pathogens would actually be present in an airplane.”

In addition to testing whether MRSA and E. coli O157:H7 could survive the environmental conditions of the airplane, the University of Auborn researchers also investigated how easily the pathogens could be transferred from each surface onto skin.

“You can divide these surfaces into porous and non-porous surfaces. And the porous surfaces will protect the bacteria more,” said James Barbaree, primary investigator of the study, at the press conference. They found that the bacteria live longer on the porous surfaces like seat-back pocket fabric, but these porous surfaces are less likely to transfer to humans via surface contact. Bacteria are more likely to transfer onto skin from non-porous surfaces, like airplane armrests and tray tables. This is good news for air travelers, since non-porous surfaces are easier to disinfect.

The study was not meant to scare people about the risk. Instead, the investigators wanted to identify potential pathogens and establish a baseline. Their next research challenge is to look at how to eliminate potential pathogens or at least reduce the risk of pathogen transfer from all airplane surfaces.

“We want to look at disinfectant procedures,” said Barbaree at the press conference. “We also want to see if we can put antibacterial compounds into some of the surfaces to try to minimize the existence of the organisms on airplanes.”

Meanwhile, good hygiene is the best way to protect yourself against germs while traveling: cleaning all surfaces with antibacterial wipes, using hand sanitizer after touching surfaces, and washing your hands frequently.

This is a repost of my KQED Science blog.

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