More than half of hospital infections were caused by antibiotic resistant bacteria In 2004. Antibiotic resistance means that the bacterial infection can't be stopped by the drugs that would normally be able to cure it.
Antibiotics were first discovered in 1923 by Alexander Fleming. Fleming, as the story goes, was not a very tidy scientist and left a petri dish uncovered on his desk while he was on holiday. When he got back, he found that a kind of mold had started growing on the dish, pushing out the bacteria that had been growing there. He reasoned that the mold was secreting some chemical that killed the bacteria and that it may be able to stop bacterial infections. He was able to isolate a chemical compound from the Penicillium mold that he called penicillin. In 1945 penicillin was developed as the first anti-biotic drug. Often considered the beginning of modern medicine, the development of penicillin has changed the way humanity deals with microbes. Immediately after that first exhilarating success, however, we discovered that microbes develop a resistance to antibiotics under certain circumstances.
To understand more about antibiotic resistance and how we can stop it, we have to delve a little deeper into the subject of evolution. Weather or not we believe in it, natural selection acts on the genes of disease-causing bacteria. "The evolution debate" has stirred up a lot of controversy in schools but ignoring it has resulted in millions of deaths in hospitals. The reason is that species change over time. Though we have evidence that dinosaurs may have evolved into birds, that was long ago and the evidence is mostly from fossils. Bacteria, however, change right in front of us, often in a matter of days. The change is impossible to ignore. One week an antibiotic may stop a bacterial infection but the next week, the infection may become antibiotic resistant and the patient could die. This is no longer a matter of fossil evidence, it's a matter of life and death!
Bacterial cells divide very quickly, some in as little as 12 hours. When bacterial cells copy their genes they make a lot of mistakes. Many of these mistakes, known as mutations, are harmful to the cells and they die. Because the bacterial colony grows so quickly, these deaths don't effect the size of the colony very much. Even more mutations have no effect. Some mutations benefit the cells and the cells with beneficial mutations survive much better and reproduce much faster than the previous generation. This kind of change is easily witnessed in a lab on a petri dish but it happens all the time in nature.
When an antibiotic is given to a patient with a bacterial infection almost all of the bacterial cells die right away. Some of the cells, however, survive in a weakened state because they naturally have a very slight resistance to the antibiotic. This is called selection. The antibiotic exerts "selective pressure" on the bacteria. Bacteria that are susceptible to the antibiotic are "selected against" (they die) and those with a slight resistance are "selected for" (they live and reproduce). These bacteria with a slight resistance would probably be killed by another course of antibiotics but in many cases, they only get a small dose of antibiotics, not enough to kill them. The resistant bacteria reproduce and their offspring are also slightly resistant to the antibiotic. If this second generation of bacteria are confronted with the antibiotic they will survive and their offspring will be even more resistant. The third generation of bacteria to experience selective pressure are often completely resistant to the antibiotic and thrive in its presence. Selection works both ways, once the bacteria are no longer in the presence of an antibiotic their resistance fades over the course of several generations and eventually they are just as susceptible to the antibiotic as they were in the beginning.
There are many ways that antibiotics are misused that can result in resistant bacteria. In feed lots where animals are kept very close to eachother with very poor hygiene, antibiotics are used to prevent widespread disease. The antibiotics are given in very large doses to the animals and are secreted in the animals feces. When the antibiotics are watered down, disease causing bacteria can become resistant to them and infect the animals. The wastes from these infected animals can be both extremely toxic and also resistant to antibiotics. Most food poisoning deaths and food recalls in the US stem from contamination of foods with animal waste from feed lots. The antibiotic resistant strains of bacteria from these feed lots enter hospitals when humans become sick and can go on to infect other people in the hospital.
Antibiotics are used by doctors to cure bacterial infections. Doctors prescribe a "course" of antibiotics that lasts several days or even a week after it seems that the infection is gone. Many people stop taking antibiotics or feeding them to a pet once they have recovered. This has the effect of driving the infection to the brink of death but leaving several antibiotic resistant cells alive. Many times, these cells become the beginning of the next infection that is now resistant to the antibiotic. The patient returns to the doctor with a second infection that is unresponsive to an antibiotic and the doctor prescribes another antibiotic. If the second infection happens the same way the first one did, a population of bacteria are now resistant to two antibiotics. In hospitals, multi-drug resistant strains of bacteria cause many people to die even with the best care because our antibiotics are useless against them. Infections that people get in hospitals are called "nosocomial" and kill 90,000 people a year in the United States.
Another problem is that since antibiotics have been so effective, patients get the idea that they can cure anything. Many patients go to physicians with viral infections demanding antibiotics and doctors prescribe them antibiotic medications. Antibiotics are also used in ordinary products such as hand soaps and disinfectant wipes that are labeled "antibacterial". These products may reduce the number of bacteria over all but increase the number of resistant strains. The bacteria that we encounter on a day to day basis don't generally cause any kind of disease and the bacteria on our skin may actually help us cope with the environment by protecting us from disease causing bacteria. Hand washing with regular, not antibacterial, soap is sufficient to keep us from getting and spreading diseases. The bottom line is that It's not a good idea to use antibiotics for anything other than a bacterial infection and then use them exactly as they are prescribed.
Saturday, May 2, 2009
Lactose Intolerance
The FDA recommends that people drink three cups of milk a day for bone health and essential nutrients. This is a problem for a lot of people who can’t digest milk. Usually this is because of lactose intolerance, a condition where the gut doesn’t make the right enzymes to break down the sugar in milk, called lactose.
Lactose is a disaccharide meaning a two part sugar. It’s made out of two simple sugars that need to be broken apart before the body can use them. Lactose is broken down by an enzyme called lactase. People who are lactose tolerant produce the enzyme Lactase in their guts. When people who are lactose intolerant drink milk, their gut bacteria eat the lactose causing cramps and “intestinal distress.” (do you really wanna know?)
An infant needs the enzyme lactase to digest her mother’s milk. Although almost all children are born with the gene for lactase production, gene regulation begins turning the gene “off” as children mature, beginning around the age of two, when children are generally beginning to wean. Children are able to digest less and less milk until they become lactose intolerant around the age of six.
***
Digression:
In the United States it’s very unusual for a child to be nursing by age 2. Most infants are weaned early here, but in other cultures children nurse for much longer and even older toddlers may nurse infrequently though they regularly eat solid food. Mother’s milk is not only an important source of calories and nutrients; it also offers immune protection and a safe source of liquid for children. In the United States and other developed nations we can afford to wean infants early because of our clean public water. In developing nations, however, mother’s milk keeps children alive in very harsh conditions: children’s immune systems are challenged by parasites and disease, and their water is unsafe to drink. A child would die of diarrhea except for a regular infusion from her mother’s immune system and safe hydration. When mothers in developing nations feed their children formula, they have to use dirty water to mix it and many children die of water borne diseases. UNICEF recommends all mothers “breastfeed exclusively for the first six months and continue to breastfeed for two years or more.” They estimate that exclusive breastfeeding would prevent 1.4 million infant deaths a year in the developing world.
***
In some populations with a history of milk drinking, a mutation occurred allowing the lactase gene to stay “on”, resulting in lactose tolerant adults. The ability to digest milk would have been very helpful because milk allows us to obtain more nutrition from our domesticated animals (moo!) than just their meat. In places where sanitation is poor, cow’s milk is a safe source of water as well as calories and nutrients. People with a mutation that lets them to digest milk would have a genetic advantage over their peers, and they could produce more offspring. The mutation eventually became widespread in certain populations such as northern Europe and southern Africa. This is one of the most recent examples of natural selection acting on the human genome.
Dairy is an important source of calories in some areas but not in others; not all populations developed lactose tolerance. Although most people in the United States and Europe can digest milk, the majority of people on earth can’t. Lactose tolerance (the ability to digest milk) in adulthood is actually less common than lactose intolerance and it’s only a problem in areas where people drink milk. Lactose intolerance is quite variable with some people unable to digest even the slightest bit of lactose and others able to consume up to a glass of milk. In Japan, for instance, one study shows that most Japanese can digest up to 200ml of milk without digestive distress. They also found that people who drink milk habitually can tolerate much more milk. The researchers speculate that continuous exposure to milk can extend lactose tolerance into adulthood.
Lactose is a disaccharide meaning a two part sugar. It’s made out of two simple sugars that need to be broken apart before the body can use them. Lactose is broken down by an enzyme called lactase. People who are lactose tolerant produce the enzyme Lactase in their guts. When people who are lactose intolerant drink milk, their gut bacteria eat the lactose causing cramps and “intestinal distress.” (do you really wanna know?)
An infant needs the enzyme lactase to digest her mother’s milk. Although almost all children are born with the gene for lactase production, gene regulation begins turning the gene “off” as children mature, beginning around the age of two, when children are generally beginning to wean. Children are able to digest less and less milk until they become lactose intolerant around the age of six.
***
Digression:
In the United States it’s very unusual for a child to be nursing by age 2. Most infants are weaned early here, but in other cultures children nurse for much longer and even older toddlers may nurse infrequently though they regularly eat solid food. Mother’s milk is not only an important source of calories and nutrients; it also offers immune protection and a safe source of liquid for children. In the United States and other developed nations we can afford to wean infants early because of our clean public water. In developing nations, however, mother’s milk keeps children alive in very harsh conditions: children’s immune systems are challenged by parasites and disease, and their water is unsafe to drink. A child would die of diarrhea except for a regular infusion from her mother’s immune system and safe hydration. When mothers in developing nations feed their children formula, they have to use dirty water to mix it and many children die of water borne diseases. UNICEF recommends all mothers “breastfeed exclusively for the first six months and continue to breastfeed for two years or more.” They estimate that exclusive breastfeeding would prevent 1.4 million infant deaths a year in the developing world.
***
In some populations with a history of milk drinking, a mutation occurred allowing the lactase gene to stay “on”, resulting in lactose tolerant adults. The ability to digest milk would have been very helpful because milk allows us to obtain more nutrition from our domesticated animals (moo!) than just their meat. In places where sanitation is poor, cow’s milk is a safe source of water as well as calories and nutrients. People with a mutation that lets them to digest milk would have a genetic advantage over their peers, and they could produce more offspring. The mutation eventually became widespread in certain populations such as northern Europe and southern Africa. This is one of the most recent examples of natural selection acting on the human genome.
Dairy is an important source of calories in some areas but not in others; not all populations developed lactose tolerance. Although most people in the United States and Europe can digest milk, the majority of people on earth can’t. Lactose tolerance (the ability to digest milk) in adulthood is actually less common than lactose intolerance and it’s only a problem in areas where people drink milk. Lactose intolerance is quite variable with some people unable to digest even the slightest bit of lactose and others able to consume up to a glass of milk. In Japan, for instance, one study shows that most Japanese can digest up to 200ml of milk without digestive distress. They also found that people who drink milk habitually can tolerate much more milk. The researchers speculate that continuous exposure to milk can extend lactose tolerance into adulthood.
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