Archive for the ‘Disease’ Category
Sometimes you find a paper with a title so intriguing you just have to find out a little more about it. Recently, I came across a paper about ‘entombed pigs’, so how could I possibly ignore it? I learned a fair bit about animal-disease control methods in Asia and the use of quicklime to decompose corpses , a fairly standard weekend for me.
The work centres on foot-and-mouth disease (FMD), a viral infection of hoofed animals caused by Aphthovirus. It causes significant suffering in animals and has serious economic consequences: a 2001 outbreak is estimated to have cost the UK £8 billion.
Millions of infected animals were culled in South Korea in 2010/11, then buried (rather than burnt, as they are in the UK). The slaughtered animals were placed in five-metre-deep pits and covered with quicklime and copious amounts of soil to prevent the FMD spreading. Problem solved? Well, perhaps not.
The hepatitis B virus (HBV) causes potentially life-threatening diseases, including cirrhosis and liver cancer. The virus is transmitted by bodily fluids and is thought to infect around two billion people, causing approximately 600 000 deaths a year.
HBV has at least ten genotypes. Each genotype, which refers to the arrangement of genetic material in a virus, is divided into multiple subgenotypes, each localised to a particular area or population.
In Korea, where HBV infection is endemic, most viruses isolated are from the C2 (HBV/C2) genotype. The big question is, ‘Where did HBV/C2 come from?’ Now, remarkably, a 16th-century mummy is helping scientists solve the mystery.
As we’ve discussed before, Mycobacterium tuberculosis is the major cause of tuberculosis, a disease that has plagued humans for millennia. The oldest recorded case of TB is in a 500 000-year-old fossil of Homo erectus. Despite the best efforts of modern medicine, we have so far failed in our fight against this disease, which kills up to two million people every year.
The problem is that M. tuberculosis infections are both hard to detect and hard to treat. Mycobacteria have a waxy coating of fats called mycolic acids that make them naturally resistant to many antibiotics and helps them hide inside human immune cells. Because the immune system can’t attack itself, this is a pretty ingenious hiding place. It typically takes six months of multidrug therapy to cure an active TB infection and nine months to kill a latent infection (that is, the TB cells that are hiding). Some of the cells that are hiding are known as ‘persisters’, and it’s these cells that take longer to kill in a latent infection.
In a recent study, scientists developed a new way to study persister cells in the lab. They found that in a large collection (or population) of TB cells, a small number form a distinct subgroup of persisters. Weirdly, despite all the cells being genetically identical, the persisters are more resistant to antibiotics than all the other normal TB cells.
Most of us have at some point in our life received a course of antibiotics to treat a bacterial infection. However, treatment options are becoming limited for many infections, as some bacteria have developed resistance to multiple antibiotics, such as the ‘superbug’ methicillin-resistant Staphylococcus aureus (MRSA), or the recently emerged totally drug-resistant (TDR) TB.
With drug resistance making bacterial infections increasingly difficult to treat, the search for new antibiotics has become more urgent than ever. This makes the discovery of acyldepsipeptides, a new class of antibiotics, very welcome indeed. Acyldepsipeptides are effective against some of the most prominent human-disease causing bacteria, including MRSA, and have attracted a great deal of attention as potential new drugs. They are distinct from all of the antibiotics currently used in the clinic as they have a novel target in the bacterial cell, as described in a paper published in PNAS.
Most antibiotics target one of four essential bacterial processes: cell wall biosynthesis; nucleic acid biosynthesis; protein synthesis; or folic acid biosynthesis (required for making DNA, RNA and proteins). Acyldepsipeptides work differently, blocking cell division – vital for bacterial survival.
Normally, bacteria multiply by dividing in two, producing identical copies of themselves. Acyldepsipeptides stop this process by binding to a bacterial enzyme called ClpP: a protease that destroys unwanted or damaged proteins. Acyldepsipeptides change the action of ClpP so that it specifically targets and destroys FtsZ, a protein that marks the site at which bacterial cell division should occur.
Destruction of FtsZ leads to the formation of long, filamentous bacteria that continue to grow but cannot divide. Crucially, this means that the bacteria cannot multiply and spread to cause infection.
The discovery of a new class of antibiotics, with a new cellular target, provides us not only with potentially lifesaving drugs, but also a glimmer of hope of unearthing yet more novel antibiotics and targets for the treatment of multi-drug resistant bacteria.
Claire is an undergraduate student at the University of East Anglia
Sass, P., Josten, M., Famulla, K., Schiffer, G., Sahl, H., Hamoen, L., & Brotz-Oesterhelt, H. (2011). Antibiotic acyldepsipeptides activate ClpP peptidase to degrade the cell division protein FtsZ Proceedings of the National Academy of Sciences, 108 (42), 17474-17479 DOI: 10.1073/pnas.1110385108
Image Credit: Wellcome Images on Flickr
Last year, I was lucky enough to visit the Wellcome Collection’s Dirt exhibition, which featured several microbiology treasures. Among other objects, I saw an original van Leeuwenhoek microscope and a first edition of Robert Hooke’s Micrografia. I also had the chance to get close to an original copy of John Snow’s cholera map.
Snow, who is commonly considered to be the father of modern epidemiology, is most famous for identifying where cases of cholera were occurring during an epidemic in London in 1854. This allowed him to trace the source of the outbreak – a contaminated water pump on Broad Street.
Today, very few cases of cholera are reported in the UK; however, it is endemic in many other countries and resulted in more than 100 000 deaths in 2010. It is caused by the bacterium Vibrio cholerae, which produces toxins in the small intestine of an infected person, causing them – if untreated – to produce more than ten litres of diarrhoea a day. Death comes as a result of dehydration.
As shown by Snow in 1854, people get the disease through drinking contaminated water. This is a real problem in much of the world, where clean drinking water is not accessible for local populations.
Neisseria meningitidis is a very nasty bug that can cause life-threatening bacterial meningitis; however, many people have the bacteria living harmlessly in their nasopharynx (the area at the back of your nose). The problems begin when the bacteria enter the bloodstream, after which rapid disease progression is likely. Even if it’s not fatal, meningitis can have serious consequences, including deafness or limb amputation. The specific warning signs that can help you identify a N. meningitidis infection are definitely worth a read.
The bacterium is not only nasty but also very crafty. I’ve been reading a paper from PLoS ONE that explains how it can evade being destroyed by macrophages, the ‘first line of defence’ for the body’s immune system. These immune cells engulf invading bacteria through a process known as phagocytosis. The bacteria are then broken down inside the macrophage using a series of enzymes and toxic molecules, and the broken fragments of microbe are passed on to specialised immune cells that attack any remaining bacteria.
Stopping the macrophages doing their job is an important step for an invading pathogen. Some bacteria, such as Mycobacterium tuberculosis, do this by preventing the macrophages breaking them down. They get engulfed, but they just stay dormant and hide within the immune cells until they’re ready to emerge and cause the tuberculosis disease. N. meningitidis has a very different tactic: it makes the macrophages commit suicide. The proper name for this is apoptosis, or ‘programmed cell death’, a very important cellular pathway that usually happens in a highly regulated manner (you don’t want your cells dying for no reason).
Fungal diseases in plants cause huge economic problems for farmers worldwide, either by reducing crop yield or by killing plants outright. These disease-causing fungi produce an array of compounds, known as ‘virulence factors’ that they use to breach plant defences. The two are locked in a constant arms race, with the plant trying to produce defences that let it stay one step ahead of the pathogen. This is often described as the Red Queen Hypothesis.
A new paper by Djamei et al. has revealed the nature of one of the virulence factors of Ustilago maydis, the fungal agent that causes maize smut. U. maydis requires live plants to survive, secreting many protein effectors that suppress the plant’s defence response and alter its metabolic pathways to suit the fungus. Most of these proteins are of unknown function.
Read the rest of this entry »