Science
Louis Pasteur’s Relentless Hunt for Germs Floating in the Air
Louis Pasteur was at his most comfortable when working in his Paris laboratory. It was there that he had some of his greatest scientific triumphs, including experiments that helped confirm germs can cause disease. “Everything gets complicated away from the laboratory,” he once complained to a friend.
But in 1860, years before he became famous for developing vaccines and heating milk to kill pathogens, Pasteur ventured to the top of a glacier, on a remarkable quest for invisible life.
He and a guide began at the base of Mont Blanc in the Alps, hiking through dark stands of pines. Behind them, a mule carried baskets of long‑necked glass chambers that sloshed with broth. They ascended a steep trail until they reached Mer de Glace, the sea of ice.
The wind blew briskly over the glacier, and the vale echoed with the sound of frozen boulders crashing down the slopes. Pasteur struggled to make out the path in the glare of sunlight bouncing off the ice.
When the scientist reached an altitude of 2,000 meters, he finally stopped. He removed one of the glass chambers from the mule’s pack and raised it over his head. With his free hand, he grabbed a pair of tongs and used them to snap off the end of the neck. The cold air rushed inside the container.
The sight of Pasteur holding a globe of broth over his head would have baffled other travelers visiting Mer de Glace that day. If they had asked him what he was doing, his answer might have seemed mad. Pasteur was on a hunt, he later wrote, for “the floating germs of the air.”
Now, 165 years later, scientists around the world hunt for floating germs. Some study how coronaviruses wafting through buses and restaurants spread Covid. Spores of fungi can travel thousands of miles, infecting people and plants. Oceans deliver microbes into the air with every crashing wave. Even clouds, scientists now recognize, are alive with microbes.
The sky’s ecosystem is known as the aerobiome. In Pasteur’s day, it had no name. The very idea of living things drifting through the air was too strange to imagine.
But Pasteur began to wonder about the possibility of airborne life when he was a little-known chemist teaching at the University of Lille in France. There, the father of one his students approached him for help. The man owned a distillery where he used yeast to turn beet juice into alcohol. But the juice had inexplicably turned rancid.
Inspecting the liquid under a microscope, Pasteur discovered dark rods — bacteria rather than yeast — in the sour vats. The discovery helped him work out a theory of fermentation: Microorganisms absorbed nutrients and then produced new compounds. Depending on the species, they could turn butter rancid or grape juice into wine.
The discovery won Pasteur a prestigious new post in Paris. In his account of the discovery, Pasteur suggested in passing that the bacteria might have floated through the air and settled into the vats. That notion earned him an angry letter from Félix‑Archimède Pouchet, one of France’s leading naturalists.
Pouchet informed Pasteur that the microorganisms Pasteur discovered had not dropped into the vats from the air. Instead, the beet juice had spontaneously generated them. “Spontaneous generation is the production of a new organized being that lacks parents and all of whose primordial elements have been drawn from ambient matter,” Pouchet had written earlier.
Pasteur coolly replied that Pouchet’s spontaneous generation experiments were fatally flawed. The conflict between Pasteur and Pouchet prompted the French Academy of Sciences to announce a contest for the best study addressing whether spontaneous generation was real or not. What started as a private spat had turned into a public spectacle. Pasteur and Pouchet both signed up to compete for the prize of 2,500 francs.
The public eagerly followed the competition, struggling to imagine either view of life. Spontaneous generation had the whiff of blasphemy: If life could spring into existence, it did not require divine intervention. But Pasteur’s claim that the atmosphere teemed with germs also strained the 19th‑century mind. A French journalist informed Pasteur that he was going to lose the contest. “The world into which you wish to take us is really too fantastic,” he said.
To prove that his world was real, Pasteur set out to pluck germs from the air. Working with glassblowers, he created flasks with narrow openings that stretched for several inches. He filled them with sterile broth and waited to see if anything would grow inside. If the necks were pointed straight up, the broth often turned cloudy with microorganisms. But if he sloped the necks so that the openings pointed down, the broth stayed clear. Pasteur argued that germs in the air could drift down into the flasks, but could not propel themselves up a rising path.
When Pouchet heard about Pasteur’s experiments, he sneered. Did Pasteur really believe that every germ in decaying organic matter came from the air? If that were true, every cubic millimeter of air would have been packed with more germs than all the people on Earth. “The air in which we live would almost have the density of iron,” Pouchet said.
Pasteur responded by changing his hypothesis. Germs were not everywhere, he said. Instead, they drifted in clouds that were more common in some places than others.
To prove his claim, Pasteur took his straight-necked flasks out of his lab and began collecting germs. In the courtyard of the Paris Observatory, all 11 of his flasks turned cloudy with multiplying germs. But when he traveled to the countryside and ran his experiment again, more of his flasks stayed sterile. The farther Pasteur got from human settlements, the sparser airborne life became. To put that idea to an extreme test, Pasteur decided to climb Mer de Glace.
His first foray to the glacier ended in failure. After holding up a flask, he tried using the flame from a lamp to seal its neck shut, but the glare of the sun made the flame invisible. As Pasteur fumbled with the lamp, he worried that he might be contaminating the broth with germs he carried on his skin or his tools. He gave up and trudged to a tiny mountain lodge for the night.
He left his flasks open as he slept. In the morning they were rife with microorganisms. Pasteur concluded that the lodge was packed with airborne germs that travelers had brought from around the world.
Later that day, Pasteur modified his lamp so that the flame would burn bright enough for him to see it under the glacier-reflected sun. When he climbed back up Mer de Glace, the experiment worked flawlessly. Only one of the flasks turned cloudy with germs. The other 19 remained sterile.
In November 1860, Pasteur arrived at the Academy of Sciences in Paris with the 73 flasks he had used on his travels. He entered the domed auditorium, walked up to the table where the prize committee sat, and laid out the flasks. The judges peered at the broth as Pasteur described his evidence, saying it gave “indubitable proof” of floating germs in inhabited places.
Pouchet refused to accept the evidence, but nevertheless withdrew from the contest. Pasteur was awarded the prize.
Still, the two continued to spar. The rivalry remained so intense that the Academy set up a new commission to evaluate their latest experiments. Pouchet dragged out the proceedings, demanding more time for his research.
Pasteur decided to seize public opinion and put on a spectacle. On the evening of April 7, 1864, in an amphitheater filled with Parisian elites, Pasteur stood surrounded by lab equipment and a lamp to project images on a screen. He told the audience it would not leave the soiree without recognizing that the air was rife with invisible germs. “We can’t see them now, for the same reason that, in broad daylight, we can’t see the stars,” he said.
At Pasteur’s command, the lights went out, save for a cone of light that revealed floating motes of dust. Pasteur asked the audience to picture a rain of dust falling on every surface in the amphitheater. That dust, he said, was alive.
Pasteur then used a pump to drive air through a sterile piece of cotton. After soaking the cotton in water, he put a drop under a microscope. He projected its image on a screen for the audience to see. Alongside soot and bits of plaster, they could make out squirming corpuscles. “These, gentlemen, are the germs of microscopic beings,” Pasteur said.
Germs were everywhere in the air, he said — kicked up in dust, taking flights of unknown distances and then settling back to the ground, where they worked their magic of fermentation. Germs broke down “everything on the surface of this globe which once had life, in the general economy of creation,” Pasteur said.
“This role is immense, marvelous, positively moving,” he added.
The lecture ended with a standing ovation. Pasteur’s hunt for floating germs elevated him to the highest ranks of French science.
By the time he died 31 years later, Pasteur had made so many world-changing discoveries that his many eulogies and obituaries did not mention his trip to Mer de Glace.
But scientists today recognize that Pasteur got the first glimpse of a world that they are only starting to understand. They now know that life infuses the atmosphere far more than he had imagined, all the way to the stratosphere. Our thriving aerobiome has led some scientists to argue that alien aerobiomes may float in the clouds of other planets. Ours is not the only world that seems too fantastic to believe.
Science
Commentary: My toothache led to a painful discovery: The dental care system is full of cavities as you age
I had a nagging toothache recently, and it led to an even more painful revelation.
If you X-rayed the state of oral health care in the United States, particularly for people 65 and older, the picture would be full of cavities.
“It’s probably worse than you can even imagine,” said Elizabeth Mertz, a UC San Francisco professor and Healthforce Center researcher who studies barriers to dental care for seniors.
Mertz once referred to the snaggletoothed, gap-filled oral health care system — which isn’t really a system at all — as “a mess.”
But let me get back to my toothache, while I reach for some painkiller. It had been bothering me for a couple of weeks, so I went to see my dentist, hoping for the best and preparing for the worst, having had two extractions in less than two years.
Let’s make it a trifecta.
My dentist said a molar needed to be yanked because of a cellular breakdown called resorption, and a periodontist in his office recommended a bone graft and probably an implant. The whole process would take several months and cost roughly the price of a swell vacation.
I’m lucky to have a great dentist and dental coverage through my employer, but as anyone with a private plan knows, dental insurance can barely be called insurance. It’s fine for cleanings and basic preventive routines. But for more complicated and expensive procedures — which multiply as you age — you can be on the hook for half the cost, if you’re covered at all, with annual payout caps in the $1,500 range.
“The No. 1 reason for delayed dental care,” said Mertz, “is out-of-pocket costs.”
So I wondered if cost-wise, it would be better to dump my medical and dental coverage and switch to a Medicare plan that costs extra — Medicare Advantage — but includes dental care options. Almost in unison, my two dentists advised against that because Medicare supplemental plans can be so limited.
Sorting it all out can be confusing and time-consuming, and nobody warns you in advance that aging itself is a job, the benefits are lousy, and the specialty care you’ll need most — dental, vision, hearing and long-term care — are not covered in the basic package. It’s as if Medicare was designed by pranksters, and we’re paying the price now as the percentage of the 65-and-up population explodes.
So what are people supposed to do as they get older and their teeth get looser?
A retired friend told me that she and her husband don’t have dental insurance because it costs too much and covers too little, and it turns out they’re not alone. By some estimates, half of U.S. residents 65 and older have no dental insurance.
That’s actually not a bad option, said Mertz, given the cost of insurance premiums and co-pays, along with the caps. And even if you’ve got insurance, a lot of dentists don’t accept it because the reimbursements have stagnated as their costs have spiked.
But without insurance, a lot of people simply don’t go to the dentist until they have to, and that can be dangerous.
“Dental problems are very clearly associated with diabetes,” as well as heart problems and other health issues, said Paul Glassman, associate dean of the California Northstate University dentistry school.
There is one other option, and Mertz referred to it as dental tourism, saying that Mexico and Costa Rica are popular destinations for U.S. residents.
“You can get a week’s vacation and dental work and still come out ahead of what you’d be paying in the U.S.,” she said.
Tijuana dentist Dr. Oscar Ceballos told me that roughly 80% of his patients are from north of the border, and come from as far away as Florida, Wisconsin and Alaska. He has patients in their 80s and 90s who have been returning for years because in the U.S. their insurance was expensive, the coverage was limited and out-of-pocket expenses were unaffordable.
“For example, a dental implant in California is around $3,000-$5,000,” Ceballos said. At his office, depending on the specifics, the same service “is like $1,500 to $2,500.” The cost is lower because personnel, office rent and other overhead costs are cheaper than in the U.S., Ceballos said.
As we spoke by phone, Ceballos peeked into his waiting room and said three patients were from the U.S. He handed his cellphone to one of them, San Diegan John Lane, who said he’s been going south of the border for nine years.
“The primary reason is the quality of the care,” said Lane, who told me he refers to himself as 39, “with almost 40 years of additional” time on the clock.
Ceballos is “conscientious and he has facilities that are as clean and sterile and as medically up to date as anything you’d find in the U.S.,” said Lane, who had driven his wife down from San Diego for a new crown.
“The cost is 50% less than what it would be in the U.S.,” said Lane, and sometimes the savings is even greater than that.
Come this summer, Lane may be seeing even more Californians in Ceballos’ waiting room.
“Proposed funding cuts to the Medi-Cal Dental program would have devastating impacts on our state’s most vulnerable residents,” said dentist Robert Hanlon, president of the California Dental Assn.
Dental student Somkene Okwuego smiles after completing her work on patient Jimmy Stewart, 83, who receives affordable dental work at the Ostrow School of Dentistry of USC on the USC campus in Los Angeles on February 26, 2026.
(Genaro Molina / Los Angeles Times)
Under Proposition 56’s tobacco tax in 2016, supplemental reimbursements to dentists have been in place, but those increases could be wiped out under a budget-cutting proposal. Only about 40% of the state’s dentists accept Medi-Cal payments as it is, and Hanlon told me a CDA survey indicates that half would stop accepting Medi-Cal patients and many others will accept fewer patients.
“It’s appalling that when the cost of providing healthcare is at an all-time high, the state is considering cutting program funding back to 1990s levels,” Hanlon said. “These cuts … will force patients to forgo or delay basic dental care, driving completely preventable emergencies into already overcrowded emergency departments.”
Somkene Okwuego, who as a child in South L.A. was occasionally a patient at USC’s Herman Ostrow School of Dentistry clinic, will graduate from the school in just a few months.
I first wrote about Okwuego three years ago, after she got an undergrad degree in gerontology, and she told me a few days ago that many of her dental patients are elderly and have Medi-Cal or no insurance at all. She has also worked at a Skid Row dental clinic, and plans after graduation to work at a clinic where dental care is free or discounted.
Okwuego said “fixing the smiles” of her patients is a privilege and boosts their self-image, which can help “when they’re trying to get jobs.” When I dropped by to see her Thursday, she was with 83-year-old patient Jimmy Stewart.
Stewart, an Army veteran, told me he had trouble getting dental care at the VA and had gone years without seeing a dentist before a friend recommended the Ostrow clinic. He said he’s had extractions and top-quality restorative care at USC, with the work covered by his Medi-Cal insurance.
I told Stewart there could be some Medi-Cal cuts in the works this summer.
“I’d be screwed,” he said.
Him and a lot of other people.
steve.lopez@latimes.com
Science
Diablo Canyon clears last California permit hurdle to keep running
Central Coast Water authorities approved waste discharge permits for Diablo Canyon nuclear plant Thursday, making it nearly certain it will remain running through 2030, and potentially through 2045.
The Pacific Gas & Electric-owned plant was originally supposed to shut down in 2025, but lawmakers extended that deadline by five years in 2022, fearing power shortages if a plant that provides about 9 percent the state’s electricity were to shut off.
In December, Diablo Canyon received a key permit from the California Coastal Commission through an agreement that involved PG&E giving up about 12,000 acres of nearby land for conservation in exchange for the loss of marine life caused by the plant’s operations.
Today’s 6-0 vote by the Central Coast Regional Water Board approved PG&E’s plans to limit discharges of pollutants into the water and continue to run its “once-through cooling system.” The cooling technology flushes ocean water through the plant to absorb heat and discharges it, killing what the Coastal Commission estimated to be two billion fish each year.
The board also granted the plant a certification under the Clean Water Act, the last state regulatory hurdle the facility needed to clear before the federal Nuclear Regulatory Commission (NRC) is allowed to renew its permit through 2045.
The new regional water board permit made several changes since the last one was issued in 1990. One was a first-time limit on the chemical tributyltin-10, a toxic, internationally-banned compound added to paint to prevent organisms from growing on ship hulls.
Additional changes stemmed from a 2025 Supreme Court ruling that said if pollutant permits like this one impose specific water quality requirements, they must also specify how to meet them.
The plant’s biggest water quality impact is the heated water it discharges into the ocean, and that part of the permit remains unchanged. Radioactive waste from the plant is regulated not by the state but by the NRC.
California state law only allows the plant to remain open to 2030, but some lawmakers and regulators have already expressed interest in another extension given growing electricity demand and the plant’s role in providing carbon-free power to the grid.
Some board members raised concerns about granting a certification that would allow the NRC to reauthorize the plant’s permits through 2045.
“There’s every reason to think the California entities responsible for making the decision about continuing operation, namely the California [Independent System Operator] and the Energy Commission, all of them are sort of leaning toward continuing to operate this facility,” said boardmember Dominic Roques. “I’d like us to be consistent with state law at least, and imply that we are consistent with ending operation at five years.”
Other board members noted that regulators could revisit the permits in five years or sooner if state and federal laws changes, and the board ultimately approved the permit.
Science
Deadly bird flu found in California elephant seals for the first time
The H5N1 bird flu virus that devastated South American elephant seal populations has been confirmed in seals at California’s Año Nuevo State Park, researchers from UC Davis and UC Santa Cruz announced Wednesday.
The virus has ravaged wild, commercial and domestic animals across the globe and was found last week in seven weaned pups. The confirmation came from the U.S. Department of Agriculture’s National Veterinary Services Laboratory in Ames, Iowa.
“This is exceptionally rapid detection of an outbreak in free-ranging marine mammals,” said Professor Christine Johnson, director of the Institute for Pandemic Insights at UC Davis’ Weill School of Veterinary Medicine. “We have most likely identified the very first cases here because of coordinated teams that have been on high alert with active surveillance for this disease for some time.”
Since last week, when researchers began noticing neurological and respoiratory signs of the disease in some animals, 30 seals have died, said Roxanne Beltran, a professor of ecology and evolutionary biology at UC Santa Cruz. Twenty-nine were weaned pups and the other was an adult male. The team has so far confirmed the virus in only seven of the dead pups.
Infected animals often have tremors convulsions, seizures and muscle weakness, Johnson said.
Beltran said teams from UC Santa Cruz, UC Davis and California State Parks monitor the animals 260 days of the year, “including every day from December 15 to March 1” when the animals typically come ashore to breed, give birth and nurse.
The concerning behavior and deaths were first noticed Feb. 19.
“This is one of the most well-studied elephant seal colonies on the planet,” she said. “We know the seals so well that it’s very obvious to us when something is abnormal. And so my team was out that morning and we observed abnormal behaviors in seals and increased mortality that we had not seen the day before in those exact same locations. So we were very confident that we caught the beginning of this outbreak.”
In late 2022, the virus decimated southern elephant seal populations in South America and several sub-Antarctic Islands. At some colonies in Argentina, 97% of pups died, while on South Georgia Island, researchers reported a 47% decline in breeding females between 2022 and 2024. Researchers believe tens of thousands of animals died.
More than 30,000 sea lions in Peru and Chile died between 2022 and 2024. In Argentina, roughly 1,300 sea lions and fur seals perished.
At the time, researchers were not sure why northern Pacific populations were not infected, but suspected previous or milder strains of the virus conferred some immunity.
The virus is better known in the U.S. for sweeping through the nation’s dairy herds, where it infected dozens of dairy workers, millions of cows and thousands of wild, feral and domestic mammals. It’s also been found in wild birds and killed millions of commercial chickens, geese and ducks.
Two Americans have died from the virus since 2024, and 71 have been infected. The vast majority were dairy or commercial poultry workers. One death was that of a Louisiana man who had underlying conditions and was believed to have been exposed via backyard poultry or wild birds.
Scientists at UC Santa Cruz and UC Davis increased their surveillance of the elephant seals in Año Nuevo in recent years. The catastrophic effect of the disease prompted worry that it would spread to California elephant seals, said Beltran, whose lab leads UC Santa Cruz’s northern elephant seal research program at Año Nuevo.
Johnson, the UC Davis researcher, said the team has been working with stranding networks across the Pacific region for several years — sampling the tissue of birds, elephant seals and other marine mammals. They have not seen the virus in other California marine mammals. Two previous outbreaks of bird flu in U.S. marine mammals occurred in Maine in 2022 and Washington in 2023, affecting gray and harbor seals.
The virus in the animals has not yet been fully sequenced, so it’s unclear how the animals were exposed.
“We think the transmission is actually from dead and dying sea birds” living among the sea lions, Johnson said. “But we’ll certainly be investigating if there’s any mammal-to-mammal transmission.”
Genetic sequencing from southern elephant seal populations in Argentina suggested that version of the virus had acquired mutations that allowed it to pass between mammals.
The H5N1 virus was first detected in geese in China in 1996. Since then it has spread across the globe, reaching North America in 2021. The only continent where it has not been detected is Oceania.
Año Nuevo State Park, just north of Santa Cruz, is home to a colony of some 5,000 elephant seals during the winter breeding season. About 1,350 seals were on the beach when the outbreak began. Other large California colonies are located at Piedras Blancas and Point Reyes National Sea Shore. Most of those animals — roughly 900 — are weaned pups.
It’s “important to keep this in context. So far, avian influenza has affected only a small proportion of the weaned at this time, and there are still thousands of apparently healthy animals in the population,” Beltran said in a press conference.
Public access to the park has been closed and guided elephant seal tours canceled.
Health and wildlife officials urge beachgoers to keep a safe distance from wildlife and keep dogs leashed because the virus is contagious.
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