by Rosemary Ann Ogilvie
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
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
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
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.
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