They were truly the master warriors of the 1940s and 1950s, charging forth on a determined mission to seek and destroy all those infectious diseases that had once struck down untold millions long before their time.

As in any battle, little thought was given to the long-term consequences. Few questioned whether these armies of antibiotics could continue in their battle against evil hordes of bacteria without their defences weakening, leaving them open to counter-attack by colonies that, in an odd paradox, were growing stronger as the war waged on.

Evidence of the ability of bacteria to evolve and adapt to changes in their environment - something that includes the presence of antibiotics - presented itself to scientists as long ago as 1941. By 1982, penicillin was effective against only ten percent of the strains of staphylococcus aurea that just thirty years previously it had the power to vanquish.

From the 1950s, antibiotics were prescribed for almost every ailment known to mankind, with safe, simple but effective home remedies abandoned in favour of these wonder drugs. Newer, more powerful antibiotics were continually marketed - in total, some 150 since the 1940s - which ensured they kept a step ahead of the problem of bacterial resistance.

The initial rumblings about ever-increasing evidence of bacterial resistance created by cavalier use of antibiotics were initially dismissed by the medical profession. With those rumblings now a volcanic roar resounding throughout the world, doctors are at last acknowledging that uncontrolled dispensing of antibiotics has created alarming problems, such as the emergence of Enterococci and Staphylococcus bacteria resistant to the most powerful broad-spectrum antibiotic now available - vancomycin.

However, even with this, the message still has not fully sunk in. This was evidenced in a recent US study, involving 1500 doctors and 28,000 patient visits, and reported in the Journal of the American Medical Association (1997; 278:901-904;944-945). This study found that many doctors still prescribe antibiotics for virus-induced respiratory ailments such as colds, upper respiratory tract infections (URTI), and bronchitis, even though antibiotics are effective only against infections caused by bacteria.

The researcher, Dr Ralph Gonzales, Assistant Professor of Medicine at the University of Colorado Health Services Centre in Denver, stressed the point that too-frequent use of antibiotics led to bacterial resistance that eventually rendered drugs useless against future infections with those bacteria. He attributed improper and unnecessary prescribing of antibiotic drugs to the increasing emergence of antibiotic-resistant bacteria. He also counselled doctors and hospitals to examine their hygiene practices, such as washing hands after attending each patient, as this was clearly contributing to the problem.

Another, major, factor in the creation of ‘supergerms’ - as antibiotic-resistant bacteria have been dubbed - is the widespread use of antibiotics down on the farm.

When animals develop infections, they are given antibiotics promptly, for crowded feedlots mean that infections spread instantaneously through the rest of the herd. However, antibiotics are also routinely administered as a growth-promoting agent, primarily in pig and poultry production in Australia. Dr Thomas H. Jukes, PhD was the first to discover the growth-enhancing property of antibiotics during the late 1940s. What he thought was a nutritional growth factor related to vitamin B12 proved to be traces of the antibiotic chlortetracycline. Research conducted on this drug revealed that minuscule amounts of the antibiotic - between five and ten parts per million - dramatically increased both growth and weight gain in chickens. The reason for this action has never been established, but scientists believe its because antibiotics kill or immobilise bacteria that would normally utilise nutrients for their own metabolism. With so many bacteria knocked out, the nutrients are utilised by the animal.

Chlortetracycline was made available to farmers in 1950, with recommended dosages of two to ten milligrams per kilogram of animal weight. These subtherapeutic doses - generally 1/10 to 1/100 of the therapeutic dose - encourage the survival of antibiotic-resistant species because they kill only the most susceptible bacteria, sparing those with resistance. Humans are exposed to resistant bacteria when they handle raw meat, when they eat meat that is not properly cooked, and when they come in contact with farmers who administer antibiotics. People at greatest risk of acquiring a serious antibiotic-resistant infection are those who are either taking a course of antibiotics when they make contact, or who have taken them recently.

One of the most concerning examples of animal-human transmission is Escherichia coli, a bacterium that aids digestion present in the intestines of all humans and many mammals. In 1982, a mutant form appeared, one that was capable of causing haemorrhages of the kidneys and colon in people of all ages. All known cases of infection were caused by contaminated meat. Many scientists believe that agricultural use of antibiotics is even more damaging than medical use. Every day throughout the world millions of tonnes of faeces, laden with antibiotic-resistant bacteria, are dropped and scattered great distances on the winds. Microbiologist Cedric A. Mims, PhD of Guy’s Hospital Medical School in London, has said that pigs with foot-and- mouth disease daily release 100 million viruses on their breath. If the humidity is right, 65% of those viruses survive and may be transported in the air across the Channel from France to England, to infect cow herds there. Mims says that outbreaks of foot-and-mouth disease can often be explained by studying air trajectories.

Dr Stuart Levy, MD of Tufts University is another who has expressed grave concern about the use of agricultural antibiotics. Dr Levy conducted an experiment at a private farm on which antibiotics had not been used for the previous seven years. Subtherapeutic doses of tetracycline were given to 150 chickens in their feed. Another group of chickens was fed only grain, without drugs.

When the experiment began, only 10% of E. Coli obtained from (all) birds’ faeces showed tetracycline resistance, with samples from the farmer’s family demonstrating similarly low levels. Two days after eating their first ‘drugged’ meal, 60% of the chickens’ faecal E.Coli were tetracycline resistant. In two weeks, this figure rose to 90%. Four months later, 30% of chickens in the non-antibiotic group were excreting large quantities of antibiotic-resistant E.Coli. The same thing occurred with the eight family members, with 80% of the E.Coli proving drug resistant in three members. It was also found that the E. Coli in both chickens and humans were resistant to a whole range of antibiotics, even though tetracycline was the only drug used.

Avoparcin, the animal antibiotic used in Australia, is similar to vancomycin. Some 15 years ago, the NHMRC banned all animal antibiotics similar to human drugs, but approved avoparcin for use. In those days, vancomycin was not widely prescribed by doctors, nor was it expected to be in the future. However, because of avoparcin’s similarity to the human drug, Enterococci which become resistant to avoparcin also fight off vancomycin.

With the global emergence of vancomycin-resistant Enterococci, (which are bacteria that cause intestinal infections), vancomycin became a restricted antibiotic in the US. Such drastic action was taken in an attempt to preserve the effectiveness of this drug that has been called “one of our most precious miracles”. The major pharmaceutical companies, believing that infectious diseases were conquered, stopped researching new antibiotics during the 1980s. Whilst they have been hard at work ever since the appearance of methicillin-resistant bacteria, it will be several years before a drug as strong and wide-acting as vancomycin appears on the market. Recently, a number of cases of vancomycin-resistant staphylococcus have come to light, something that is particularly concerning as staph is the number one cause of infection in the US. It can produce anything from a pimple to deadly septic shock when the bloodstream becomes infected.

The consensus of opinion is that the indiscriminate use of antibiotics must be curbed in order to curtail the trend of ever-increasing antibiotic resistant bacteria. However, it is pointless regulating medical use of antibiotics while unregulated sales of the drugs continue in the agricultural industry. It’s a problem that cannot be tackled in isolation: international tactics and co-operation are essential.

Not surprisingly, there is universal resistance to banning the use of antibiotics in animal husbandry everywhere, although Germany, Finland and Denmark have banned avoparcin. Farming bodies claim there is no evidence that Australia’s incidence of vancomycin-resistant Enterococci has arisen from using avoparcin in animal husbandry, that it is purely the result of human antibiotic use. They warn that, if antibiotics were no longer used to promote growth, food would become more expensive.

We can only wonder whether that increased cost - which surely must be slight considering the extremely low doses of antibiotics fed to the animals - would be a cheap price to pay to prevent a return to the dark dies when infectious diseases ran rampant.

Copyright © by The Australian Vegetarian Society All Right Reserved.

Published on: 2007-04-17 (641 reads)