The Science Bit – Part 11: Resisting Antibiotic Resistance

30 04 2011

There’s been a recurrent trending topic in the scientific community’s Twitter feed in the last week or so – the increasing problem of antibiotic resistance and in particular, the isolation of a new superbug gene that could be coming to a hospital near you very soon. But what are these so-called superbugs, how did they get here, and how are we going to stop them?

Superbugs are, in short, strains of bacteria that have evolved the ability to be unaffected by antibiotics – the drugs that we use to kill them and prevent the spread of infection. The superbug that most people are most familiar with is MRSA. This stands for “methicillin-resistant Staphylococcus aureus”. Staphylococcus aureus is a very common bacterium that is often found living happily on our skin and up our noses without giving us any grief. It usually only causes problems if it gets somewhere that it shouldn’t be, like into a wound, and if that happens, a trip to the GP and a course of penicillin will usually see you right. MRSA however is a strain of this normally docile bacterium that doesn’t die when treated with bog standard antibiotics, or even with some of the more expensive ones that you might be given if you were in hospital with a more serious infection.

Superbugs evolve in the same way that any organism evolves – through the Darwinian process of natural selection, leading to “survival of the fittest”. The difference with bacteria however, is that bacteria don’t just reproduce sexually or asexually like the majority of other organisms – they also have a weird and wonderful way of sharing and swapping genes with other bacterial cells, simply by passing them through the cell membrane as they float past. As well as this, they reproduce so darn quickly – doubling in numbers every few minutes or hours – that natural selection takes place on an accelerated scale. Compare this with the 5 or 10 years that it takes scientists to identify and process new drugs through clinical trials to the open market, and it’s no wonder that our antibiotics are getting out of date.

The thing that’s been getting the scientific community in a tizzy lately is the fact that bacteria carrying a gene that gives antibiotic resistance against a group of antibiotics called carbapenems has been found in the drinking water supplies of the Indian city New Delhi (The Lancet Infectious Diseases (11)70059-7, 2011). The gene, NDM-1, has the ability to transfer into several different bacterial strains, which means that it is likely to spread very quickly, and carbapenems are used to treat the most serious and stubborn, hard-to-treat infections. Thanks to the large amount of international travel to and from India, NDM-1 has already found its way to the UK and healthcare providers are bracing themselves for a crisis.

So what can we do about antibiotic resistance? Well, firstly, we need to stop using antibiotics as a cure-all for the slightest of infections. We humans are just a little bit antibiotic-mad and the fact that Fleming’s wonder-drugs have traditionally been so effective means that we’re happy to pop pills for all manner of small, non-urgent infections, especially in those countries where strong antibiotics can be bought over the counter without a prescription.

Secondly, we need to embrace organic farming and put an end to the practice of feeding our livestock with antibiotics in order to produce bigger and fatter animals for meat. In any battle, if you try the same tactic too many times, the enemy will eventually get wise to it and beat you at your own game. So it is with bacteria. By bombarding our animals with the same varieties of antibiotics over and over again – often needlessly – bacteria are now becoming more and more able to evade our weapons. In fact, a recent study published in BioMed Central’s very own BMC Environmental Health found that flies and cockroaches living in pig poo were an important vector in the transmission of antibiotic resistant bacteria from animals to humans.

Thirdly, we need to stay healthy. Obviously this is easier said than done, but most serious infections with antibiotic resistant bacteria occur in hospitals – not necessarily because hospitals are germ-ridden, but because when we’re in hospital, we’re often immunosuppressed. When our immune systems are weakened, bacteria can take hold and our natural defences are less able to cope, resulting in infections that spread rapidly and can overwhelm us.

Lastly, of course, we need new antibiotics, and new, faster approaches to antibiotic development. A Taiwanese group of researchers have recently published findings in Nature Chemical Biology that demonstrate the potential for tweaking the chemical structure of existing antibiotics in order to improve efficacy. Results have been promising in the Petri dish and rat models, but further tests and trials will need to be done before these drugs can be developed for human use. The question is, will it be too late by then?

The Science Bit – Part 10: Pigs lead the way in Cystic Fibrosis research

1 04 2011

Cystic Fibrosis (CF) is a recessive genetic disorder that affects approximately 8,500 people in the UK. It’s the most common life-shortening inherited disease in the world, with around 1 in 20 people being a carrier for the condition.

CF is caused by a mutation in the gene for a protein called the cystic fibrosis transmembrane conductance regulator or (thankfully) CFTR for short. This protein, in its normal state, is a channel protein that controls the movement of salts from the inside of the cell to the fluid surrounding the cells in the lungs, pancreas and other affected organs. In the sweat glands, CFTR usually works by moving salt from the sweat on the skin back into the body. When CFTR does not work properly however, too much salt and not enough water accumulates in the lungs, pancreas etc, and remains on the skin. The lack of water means that the normally lubricating tissue fluid in these organs becomes thick and sticky mucus.

The most recognisable symptoms of CF are to do with the build up of mucus in the airways, which causes unrelenting, mucusy coughing and a difficulty in breathing. Bacteria thrive on the thickened mucus, so lung infections including pneumonia are common, leading to damage of the airways and general poor health because of the inability to exercise properly to maintain fitness.

Mutated CFTR has effects elsewhere in the body, too. In the intestines, severe, chronic constipation caused by a lack of water to soften stools in the bowel can often lead to infection and rectal prolapse. Food cannot be digested properly in the small intestine, so CF patients often have difficulty in maintaining their weight and growth is stunted. The bile ducts may become blocked and cause damage to the liver. Cystic Fibrosis-related diabetes may occur as a result of the blockage of insulin in the pancreas. 97% of CF men are infertile because of an absence of the vas deferens, the tube that supplies sperm to the penis.

Given all these complications, it’s perhaps not surprising that until only a few decades ago, an infant born with CF would have been lucky to reach its first birthday. Now, although still a relatively short life expectancy, a CF sufferer might live well into their 30s and 40s, and with a successful lung transplant, even longer. Advances in treatment, including respiratory therapy, antibiotics, physiotherapy, diet and lifestyle changes have all made significant improvements to the quality of life for CF patients. But while the symptoms of CF can now be more effectively managed, there is still no cure for the disease.

A key to finding a targeted cure for CF is to understand the genetic and molecular processes that go on at the cellular level. Recently, a team of researchers from the University of Iowa made an important discovery that brings us a little step closer to the end goal of curing this disease. Pigs.

Pigs have long been used as an animal model for human disease research because in many organ systems, they have a very similar anatomy. Of course, there is much about a pig that is different, but by genetically engineering a pig model that mimics the faulty CFTR gene, the research team have been able to discover that the mutated protein has the same pathological effects in their pig model as in humans. This breakthrough means that pigs may now be used in further research to more accurately pinpoint what exactly happens to the mutated CFTR protein, and to find a way to treat it or correct it.

Using their new model, the team, whose findings were published in Science Translational Medicine last week, have already identified that the faulty CFTR protein is “misprocessed” in the cell and ends up in the wrong place, compared to the normal protein. Now that we know that pigs are analogous to humans in the manifestation of CF, they can be used to test a variety of potential new treatments, including gene therapy techniques that replace the faulty gene with a working copy, and “corrector” drugs, which aim to move the faulty protein to its proper position in the cell. The development of a pig model for studying this disease opens new doors to finding a way to beat cystic fibrosis, and new hope to its victims.

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