Bacterial Resistance to Antibiotics (page 4)
(This chapter has 4 pages)
© 2008 Kenneth Todar, PhD
Societal,
medical and agricultural practices that lead to antibiotic resistance
In the face of a microbe's inherent ability to develop antibiotic
resistance, many societal. medical and agricultural practices
contribute to this process, foremost of which are discussed below.
Antibiotics in food and water
Prescription drugs
are not the only source of antibiotics in the environment. In the
United States,
antibiotics can be found in beef cattle, pigs and poultry. The same
antibiotics then find their way into municipal water systems when the
runoff from housing facilities and feedlots contaminates streams and
groundwater. So it's a double hit: we get antibiotics in our food and
drinking water, and we meanwhile promote bacterial resistance.
Routine
feeding of antibiotics to animals is banned in the European Union and
many other industrialized countries. Maybe they know something we don't.
Indiscriminate use of antibiotics in agriculture and veterinary
practice
The non-therapeutic use of antibiotics in livestock production makes up
at least 60 percent of the total antimicrobial production in the United
States. Irresponsible use of antibiotics in farm animals can lead
to the development of resistance in bacteria associated with the animal
or with people who eat the animal. Such
resistance can then be passed on to human
pathogens by mechanisms of HGT.
Of major concern is the use of antibiotics as feed additives given to
farm animals to promote animal growth and to prevent infections (rather
than cure infections). The use of an antibiotic in this way contributes
to the
emergence of antibiotic-resistant pathogens and reduces the
effectiveness of the antibiotic to combat
human infections.
Antibiotic resistance in genetically
modified crops
Antibiotic-resistance genes are used as "markers" in genetically
modified crops. The genes are inserted into the plant in early stages
of development to in order to detect specific genes of interest . e.g.
herbicide-resistant genes or insecticidal toxin
genes. The antibiotic-resistance genes have no further role
to play, but they are not removed from the final product. This practice
has met with criticism because of the potential that the
antibiotic-resistance genes could be acquired by microbes in the
environment. In
some cases these marker genes confer resistance to front-line
antibiotics such as the beta-lactams and aminoglycosides.
Inappropriate use of antibiotics in the medical environment
One problem is the casual use of antibiotics in medical situations
where they are of no value. This is the fault of both health care
workers and patients. Prescribers sometimes thoughtlessly prescribe
'informed' demanding patients with antibiotics. This leads to use of
antibiotics
in circumstances where they are of not needed, e.g. viral upper
respiratory infections such as cold
and flu,
except when there is
serious threat of secondary bacterial infection. Another problem
is patient failure
to adhere to regimens for prescribed antibiotics.
Patients and doctors need to realize their responsibility when they
begin an antibiotic regimen to combat an infectious disease. There are
several measures that should be considered.
� Patients should not take antibiotics for which there is no medical
value (corollary: doctors should not prescribe antibiotics for
which there is no medical value).
� Patients should adhere to appropriate prescribing guidelines and take
antibiotics until they have finished.
� Patients should be give combinations of antibiotics, when necessary,
to minimize the development of resistance to a single antibiotic (as in
the case of TB).
� Patients need to be given another antibiotic or combination of
antibiotics if the first is not working.
Combating
antibiotic resistance
The following are recommendations to combat the development of
antibiotic resistance in bacteria and other microorganisms.
Search for new antibiotics. To combat the
occurrence of resistant bacteria, biotechnology and pharmaceutical
companies must
constantly research, develop and test new antimicrobials in order to
maintain a pool of effective drugs on the market.
Stop the use of antibiotics as growth-promoting substances in farm
animals. Of major concern is the use of antibiotics as feed additives
given to
farm animals to promote animal growth and to prevent infections rather
than cure infections. The use of such antibiotics contributes to the
emergence of antibiotic-resistant bacteria that threaten human health
and decreases the effectiveness of the same antibiotics used to combat
human infections.
Use the right antibiotic in an infectious situation as determined by
antibiotic sensitivity testing, when possible.
Stop unnecessary antibiotic prescriptions. Unnecessary antibiotic
prescriptions have been identified as causes for an enhanced
rate of resistance development. Unnecessary prescriptions of
antibiotics
are made
when antibiotics are prescribed for viral infections (antibiotics have
no effect on viruses). This gives the opportunity for indigenous
bacteria (normal flora)
to acquire resistance that can be passed on to pathogens.
Finish antibiotic prescriptions. Unfinished antibiotic prescriptions
may leave some bacteria alive or
may expose them to sub-inhibitory concentrations of antibiotics for a
prolonged period of time. Mycobacterium tuberculosis is a slow
growing bacteria which infects the lung and causes tuberculosis. This
disease kills more adults than any other infectious disease. Due to the
slow growing nature of the infection,
treatment programs last for months or even years. This has led to many
cases on unfinished prescriptions and 5% of strains now observed are
completely resistant to all known treatments and hence incurable.
Several other possible solutions have been proposed or implemented to
combat antibiotic resistance.
In the pharmaceutical industry, past and current strategies to combat
resistance have not been effective. Pharmaceutical companies are
seeking new,
less costly strategies to develop antibiotics.
A decrease in the number of prescriptions for
antibiotics, especially in small children, is occurring.
Several countries
such as the UK have regulations concerning the use of
antibiotics in animal feed.
Large scale public health
education efforts are underway to stress the importance of
finishing prescriptions. Indeed, in many places, failure to finish
tuberculosis prescriptions can result in jail time.
Summary
The discovery of antibiotics was a leap in modern medicine. They have
been able to stop the growth or
kill many different kinds of microorganisms. However, bacteria have
proven to be much more innovative and adaptive than we
imagined and have developed resistance to antibiotics at an ever
increasing pace. Bad practices and mismanagement have only
exacerbated the situation. We could soon return to a state of medical
health that was as dire as that which occurred prior to antibiotic use.
However, with more research, education of the public, and well thought
out regulations, the problems
can be solved. Several
strategies are currently used to find new antibacterial compounds and
new strategies are in development and trial.
Not only is there a problem in finding new antibiotics to fight old
diseases (because resistant strains of bacteria have emerged), there is
a parallel problem to find new antibiotics to fight new diseases. In
the past three decades, many "new" bacterial diseases have been
discovered (E. coli O157:H7 gastric ulcers, Lyme disease, toxic
shock syndrome, "skin-eating" streptococci). Already broad patterns of
resistance
exist in these pathogens, and it seems likely that we will soon
need new antibiotics to replace the handful that are effective now
against these bacteria, especially as resistance begins to emerge among
them in the selective environment antibiotic chemotherapy.
It is said that the discovery and use of antibiotics and immunization
procedures against infectious disease are two developments in the field
of microbiology that have contributed about twenty years to the average
life span of humans in developed countries where these practices are
employed. While the greater part of this span in time is probably due
to vaccination, most of us are either
still alive or have family members or friends who are still alive
because
an antibiotic conquered an infection that otherwise would have killed
them.
If we want to retain this medical luxury in our society we must be
vigilant
and proactive We must fully understand how and why antimicrobial
agents
work, and why they don't work, and realize that we must maintain a
stride
ahead of microbial pathogens that can only be contained by antibiotic
chemotherapy.
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