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Antibiotic Resistance

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Why should I be worried about Antibiotic Resistance?  

The use of antibiotics has enabled us to cure many diseases, however, with their excessive usage, more pathogenic microbes are developing resistance to them resulting in the loss of their efficacy and necessitating invention of new ones to replace them. This poses an urgent threat to public health all over the world as the sustainability and effectiveness of antibiotics is reduced, increasing the cost of health care. This emergence of resistance is a result of the overuse of antibiotics in people and animals. The main factors leading to this widespread problem are the continued prescription of antibiotics to treat viral diseases or to promote faster growth of animals for production of food, as well as failure to complete the prescribed regimen, resulting in partial elimination of the pathogens.

Bacteria can acquire resistance to an antibiotic through inheritance of specific/broad range antibiotic resistance genes, spontaneous genetic mutations, or by taking up resistance genes from other bacterial cells in the vicinity through gene transfer mechanisms. The contamination of microbial communities that are normally susceptible to antibiotics in sewage, soil, receiving waters and other environmental compartments from hospital effluents, animals, humans and food, creates antibiotic-resistant microbes which can transfer the resistance again back into human and animal pathogens and persist for extended periods. Antibiotics are a renewable resource in that ultimately microbes will revert back to susceptibility, but the time frame required for this reversion is very long, rendering that particular antibiotic unavailable to treat infections for decades. Much can be done to sustain the efficacy of current antibiotics including reducing and regulating the use of antibiotics, and/or reducing the factors that determine the transmission and persistence of antibiotic-resistant variants, in addition to controlling infection through better sanitation, education and nutrition.

 What on earth is Antibiotic Resistance?

Antibiotics are compounds that inhibit the growth, or proliferation, of bacteria or kill them directly. The drugs typically inhibit bacterial proliferation by entering the microbes and interfering with the production of components needed to form new bacterial cells. When bacteria are continually exposed to small amounts of antibiotics, they can adapt to develop immunity to them through mutation or genetic exchange with surrounding resistant strains. When an antibiotic attacks a bacterial population, cells that are highly susceptible to the medicine will die, but cells that have some resistance may survive, especially if too little drug is given to overwhelm the cells that are present. Those cells, facing reduced competition from susceptible bacteria, will then go on to multiply. When confronted with an antibiotic, the most resistant cells in a population will inevitably out-compete all others. Over time this leads to the development of new, stronger strains of bacteria, with the antibiotic immunity passed on to subsequent generations. This adaptation change is encoded into the genetic make-up of the surviving pathogens in the form of antibiotic resistance gene(s). These are called “resistant bacteria” because they have adapted to the point where antibiotics can no longer kill them.

A pertinent example of this phenomenon and its consequence is Staphylococcus aureus, a bacterium that commonly causes pneumonia, meningitis, toxic shock, skin abscesses, heart valve infections and other serious and deadly medical conditions. In the United States, almost every strain of S. aureus is now resistant to the antibiotics oxacillin, penicillin and amoxicillin, and strains of the disease have begun developing resistance to newer drugs like methicillin and vancomycin. The threat of prolonged illness or death from an S. aureus infection has increased as it has become more resistant and fewer drugs are able to effectively control or eliminate it.

 How and why do pathogens become resistant to Antibiotics?

Excessive use of antibiotics in people and animals risks causing significant antibiotic contamination of the natural environment and consequent development of resistance in communities of non-disease organisms. Although many factors can influence whether bacteria in a person or in a community will become insensitive to an antibiotic, the two main forces are the prevalence of resistance genes and the extent of antibiotic use. If the collective bacterial flora in a community has no genes conferring resistance to a given antibiotic, the antibiotic will successfully eliminate infection caused by any of the bacterial species in the collection. But, if the bacterial population possesses resistance genes and the community uses the drug persistently, resistant bacteria which are not susceptible to eradication by the compound will emerge and multiply. Such contamination of microbial communities in septic tanks, sewers, soil, receiving waters and other environmental compartments could create a widespread pool of antibiotic-resistant microbes from which resistance could be transferred back into human and animal disease organisms.

 Antibiotics are used extensively to prevent/treat microbial infections in human and veterinary medicine. Over-prescribing antibiotics for viral-caused conditions like the flu or common cold, against which antibiotics are useless, contributes to antibiotic resistance. Most of the compounds used in medicine are only partially metabolized by patients and are then discharged into the hospital sewage system or directly into municipal waste water if used at home. Along with excreta, they flow with municipal waste water to the sewage treatment plant. They may pass through the sewage system and end up in the environment. Antibacterial substances used for livestock enter the environment when manure is applied to fields and end up in soil or sediment or in groundwater.

 Antibiotics are routinely fed to livestock, poultry, and fish on industrial farms to promote faster growth and to compensate for the unsanitary conditions in which they are raised. When drug-resistant bacteria develop at industrial livestock facilities, they can reach the human population through food, the environment, or by direct contact with animals and farm workers. Often, as much as 80 to 90 percent of all antibiotics given to animals are not fully digested and eventually pass through the body and enter the environment, where they can encounter new bacteria and create additional resistant strains. Farm waste run-off can enter rivers, lakes, and ground water, and these wastes are sometimes spread on agricultural fields as fertilizer as well. So, antibiotic resistant bacteria can leech into surface and groundwater, contaminating drinking wells and endangering the health of people living close to large livestock facilities. Antimicrobial agents are also used to treat infections in intensive fish farming where they are added directly to the water, resulting in high local concentrations in water.

 In agriculture, antibiotics are applied as aerosols to cover acres of fruit trees, for controlling or preventing bacterial infections. Some antibiotics such as streptomycins are used in fruit growing, others in bee-keeping. Disinfectants and antimicrobials are also widely used in the food and glue industries. High concentrations of the antibiotic may kill all the bacteria on the targeted trees at the time of spraying, but lingering antibiotic residues can promote the growth of resistant bacteria that later colonize the fruit during processing and shipping. Here, again, resistant bacteria can make their way into people through the food chain, finding a home in the intestinal tract after the produce is eaten.

 Antibiotics affect the mixed population of resistant and nonresistant bacteria both in the individual being treated, and in that individual’s environment. This is because the rise of resistant bacteria in treated individuals spread readily to the surrounding populations and to new hosts. Also, regular use of antimicrobials in such settings as hospitals, day care centers and even in the household (cleaning products, disinfectants etc.), increases the levels of resistant bacteria in people and others, who are not being treated – including in individuals who live near those epicenters of high consumption or who pass through the centers. So, these drugs also affect the kinds of bacteria in the environment and people around the individual being treated, resulting in a widespread societal effect. On a larger scale, antibiotic resistance that emerges in one place can often spread far and wide. The ever increasing volume of international travel has hastened transfer to the U.S. of multidrug-resistant tuberculosis from other countries. And investigators have documented the migration of a strain of multidrug-resistant Streptococcus pneumonia (a cause of pneumonia and meningitis), and other diseases from Spain to the U.K., the U.S., South Africa and elsewhere.

 How did we get here?

Regardless of how bacteria acquire resistance genes today, commercial antibiotics can promote the survival and propagation of antibiotic-resistant strains. Excessive and unnecessary use of antibiotics favours rapid selection of antibiotic resistant organisms in the microbial population.

 Human treatment accounts for roughly half the antibiotics consumed every year in the U.S. Perhaps only half that use is appropriate, meant to cure bacterial infections and administered correctly – in ways that do not strongly encourage resistance. Researchers have estimated that some 50 million of the 150 million outpatient prescriptions for antibiotics every year are unneeded.

 In the developed world, most antibiotics are available only by prescription, but this does not ensure proper use. People often fail to finish the full course of treatment. Patients then often store the leftover doses and medicate themselves, or their family and friends, in less than therapeutic amounts. In both circumstances, the improper dosing will fail to eliminate the disease agent completely and will encourage growth of the most resistant strains, which may later produce hard-to-treat disorders. In the developing world, antibiotic use is even less controlled and a large number of these drugs are available over the counter. Unfortunately, when resistance becomes a clinical problem, these countries may have no substitutes available.

 Why is it my problem?

Antibiotic resistance is threatening to undermine the effectiveness of infectious disease treatment in every country of the world. It is as much a societal problem as it is an individual one; if mass behaviour change across the population does not occur, the problem of resistance cannot be mitigated at community levels. Antibiotic-resistant bacteria are a growing public health crisis because infections from resistant bacteria are increasingly difficult and expensive to treat. It has been estimated that at least 18,000 Americans die every year from drug-resistant infections. Although everyone is at risk when antibiotics stop working, the threat is greatest for young children, the elderly, and people with weakened immune systems, including cancer patients undergoing chemotherapy, organ transplant patients and, in general, people whose health is compromised in some way. Industrialized countries have the highest antibiotic use, and so could be the first to see the development of environmental pools of resistance. However, with global travel and widespread commerce, drug resistance can be expected to spread steadily to all parts of the world. Developing countries might thus suffer the worst consequences because of the poor state of their health services and their inability to pay for alternatives to cheap antibiotics.

 There is a constant race between microbes and medical researchers to come up with newer antibiotics as the existing ones become ineffective due to resistance. For the moment it seems like we are losing – according to the data reported by the Infectious Disease Society of America, which estimates that 70% of hospital-acquired infections in the United States are resistant to one or more antibiotics. Based on studies of the costs of infections caused by antibiotic-resistant pathogens versus antibiotic susceptible pathogens, the cost to the U.S. health care system of antibiotic resistant infections is $21 billion to $34 billion each year and more than 8 million additional hospital days.

 What can I do about it?

The alarming scenario of a pathogen resistant to all available antibiotic classes is a major global public health concern today. In order to address the problem of antibiotic resistance, manifold attempts have to be made on a wider, international scale. A global effort to sustain the efficacy of currently available antibiotics is needed in addition to increased research and development of newer antibiotics. As a step in this direction, various groups are now attempting to track the emergence of resistant bacterial strains. For example, an international organization, the Alliance for the Prudent Use of Antibiotics (http://www.tufts.edu/med/apua), has been monitoring the worldwide emergence of such strains since1981. The group shares information with members in more than 90 countries and tries to spread awareness among the public and health professionals. Reversal of resistance requires a new awareness of the broad consequences of antibiotic use – a perspective that concerns itself not only with curing bacterial disease at the moment but also with preserving microbial communities in the long run, so that bacteria susceptible to antibiotics will always be there to outcompete resistant strains. Public health officials, policymakers, physicians, patients, farmers, researchers and pharmaceutical manufacturers have to work together to overcome antibiotic resistance. While the search for new drugs continues, there is an urgent need to preserve the effectiveness of available medications by reducing and regulating the use of antibiotics, monitor the factors that determine the transmission and persistence of antibiotic-resistant variants in the environment as well as through improvement of sanitation.

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