We have long known that bacteria can become resistant to antibiotics. Now, British researchers have found that germs multiply much faster after becoming resistant, than they did before.
World Health Day 2015 is about highlighting food security. So what's the role of microorganisms in our food? We take a look at mold, bacteria and viruses that can spoil your appetite - but are also be useful.
Image: imago/Gerhard Leber
Ewww!
Just scrape the mold off, right? Wrong. A moldy old sandwich like this one is anything but harmless. While there are some harmless kinds of mold - like on Camembert cheese - many molds are toxic. Furthermore, mycelium spores can trigger allergies. Through contact with highly toxic types of mold, humans with weakened immune defenses could even die as a result of an extended exposure.
Image: imago/imagebroker
Mold as a biocatalyst
Mold can also be useful: Fungi is able to break down carbon hydrates, fats and proteins - more efficiently than any other organism. Industry makes use of a genetically modified Aspergillus niger fungus, which produces enzymes that can be used in food processing and production of detergents - like a living factory.
Image: BASF
Salami tactics
"Botulus" is Latin for "sausage." If mistakes are made in the production of sausage, or if meat or vegetables get contaminated during canning, this can cause botulism. The bacteria Clostridium botulinum causes this life-threatening poisoning.
Image: picture-alliance/dpa
Life without oxygen
Clostridium botulinum thrives in anaerobic, or oxygen-free, environments. It produces the nerve agent botox - used among cosmetic surgeons to help smooth skin. But in food, it leads to paralysis. At first, certain body parts get paralyzed, resulting in symptoms like slurred speech. But later, also the muscles responsible for breathing and heartbeat freeze up - eventually resulting in death.
Image: picture alliance/OKAPIA
Fresh vegetables not always healthy
Fenugreek sprouts were a favorite among Germans trying to eat healthy - until 2011. That year, seeds contaminated with the bacteria Escherichia coli (EHEC) caused an outbreak that killed 53 people - hundreds more were sickened. EHEC produces a toxin that destroys intestinal wall cells, and later attacks brain and kidney cells. Cooking raw vegetables and meat kills the harmful bacteria.
Image: picture-alliance/dpa
A useful relative
But not all varieties of E. coli are dangerous. Inside the human large intestine, the bacteria are usually responsible for producing vitamin K - important for the development of bones and cells, and for blood coagulation. In biotechnology, the bacteria play a role in producing insulin and growth hormones. They can even be used for turning microalgae into alcohol-based biofuel.
Image: Harvard’s Wyss Institute
Bacteria preserves foods
Thousands of years ago, humans learned to use lactic acid bacteria - for the production of yoghurt, kefir, sourdough bread and cheese. Raw milk warmed to 20 degrees Celsius is heaven for bacteria: Within 10 hours, the milk will go sour. Milk fermented with the help of bacteria, however, can stay edible for much longer.
Image: ZDF
Too much of a good thing
One of the many varieties of lactic acid bacteria are streptococci, which play a role in producing sauerkraut and fermented milk products. Although streptococci are everywhere - on humans, animals and plants - some of them are unhealthy. Some strains of strep can trigger tooth decay or sepsis, commonly known as blood poisoning.
Image: picture-alliance/OKAPIA
Dangerous diarrhea
Rod-shaped bacteria like Campylobacter and Salmonellae cause illness and death the world over. Undercooked beef, pork or chicken containing Campylobacter is a common cause of diarrhea wordwide. Typhus is the most dangerous form of salmonellae, triggering high fever, weak heartbeat and constipation. Every year, about 32 million people are sickened from typhus - mainly by drinking impure water.
Also viruses can contaminate food
Norovirus or stomach flu is transmitted person-to-person through traces of vomit or feces. Just 100 tiny norovirus particles are enough to infect someone. The virus can easily pass into the food chain via infected drinking water.
Image: Foto: Gudrun Holland/Robert-Koch-Institut
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Researchers at the University of Exeter exposed Escherichia coli (also known as E.coli) bacteria to eight rounds of antibiotic treatment over a period of four days.
In the process, the germs, which usually cause stomach pain and diarrhea and in worse cases kidney failure, increased antibiotic resistance with each treatment.
This was a mutation the scientists expected. What they were not prepared for was the observed speed with which the resistant germs multiplied after being treated. In one case the bacteria populations grew three times as big as in the case of normal E.coli bacteria within the same timeframe.
Bacterial mutants are sustainable
Even after removing the antibiotics, the mutated bacteria maintained its ability to multiply faster.
"Our research suggests, there could be added benefits for E.coli bacteria when they evolve resistance to clinical levels of antibiotics," lead author Prof. Robert Beardmore said. "It is often said that Darwin evolution is slow, but nothing could be further from the truth, particularly when bacteria are exposed to antibiotics."
He described the ability of bacteria to rearrange their DNA as "remarkable." This could stop drugs from working sometimes in a matter of days. "While rapid DNA change can be dangerous to a human cell, to a bacterium like E.coli it can have multiple benefits, provided they hit on the right changes."
In 2011 it became clear, how dangerous mutated forms of E.coli can be, when several people died of EHEC.Image: picture-alliance/dpa
Finding the source by DNA sequencing
As part of the study, which was published on January 30th 2017 in the journal Nature Ecology & Evolution, the scientists exposed the bacteria to the antibiotic doxicycline. Then, they froze the bacteria at minus 80 degrees Celsius and conducted gene sequencing to find out exactly which genetic changes were responsible for the observed resistance.
Some of the changes were well known and described in clinical patients. One of them is the ability of the bacteria to produce more "antibiotic pumps". These are segments called "pump DNA", which literally pump antibiotics out of the bacterial cell with the result of ensuring that the drugs can not do their work.
But the scientists also discovered that the mutated bacteria were lacking part of the DNA that is known to describe a dormant virus.
Several parallel evolutionary processes at work
What that means exactly is not clear, but Dr. Carlos Reding - a co-author of the study - has an idea. "Our best guess is that losing viral DNA stops the E.coli destroying itself, so we see more bacterial cells growing once the increase in pump DNA allows them to resist the antibiotic in the first place," Reding said. "This creates an evolutionary force for change on two regions of the E.coli genome".
Usually, bacteria tend to use self destruction as a means to colonize surfaces. That's how a biofilm develops - the slimy substance found, for instance, in the drains of sinks.
"But our study used liquid conditions, a bit like a bloodstream, so the E.coli could give up its biofilm lifestyle in favor of increasing cell production", the researcher suggests.
Using antibiotics in a targeted way
Dr. Mark Hewlett - also from Exeter University - added: "It is said by some that drug resistance evolution doesn't take place at a high dosage but our paper shows that it can and that bacteria can change in ways that would not be beneficial for the treatment of certain types of infection."
Anyhow, he concludes, that it is important to use "the right antibiotic on patients as soon as possible. So we don't see adaptations like these in the clinic."
