antimicrobial use and antimicrobial resistance · antimicrobial use and antimicrobial resistance...
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Antimicrobial use and antimicrobial resistance
Peter Smith
peter.smith @nuigalway.ie
Aquatic AMR Workshop 1: 10-11 April 2017, Mangalore, India
FMM/RAS/298: Strengthening capacities, policies and national action plans on
prudent and responsible use of antimicrobials in fisheries
Antibiotics are chemicals
that kill or inhibit the growth of bacteria
but
have very much less effect
on animals and plants
The availability of antibiotics
produced a total revolution in our thinking about the
control of infectious diseases
We now had a “magic bullet”
A drug that attacked invading bacteria but had no effect
on the host
If we are to protect our
“magic bullet”
we must learn how to use it
We will have to learn the values of
wisdom,
prudence
and
restraint
We need to understand bacteria
Bacteria are the oldest life form on this planet
They have survived 4 billion years because they
have a remarkable ability to adapt to changes in
their environment
They are protean
Mutable, flexible, versatile, adaptable and capable of
adopting many forms
Proteus
A sea god in Greek mythology.
He had to reveal the future but
changed his appearance to
avoid having to.
He revealed the truth only to
those who were wise enough to
see through his shape-
changing to his real nature
Bacteria adapt to their environment
If their environment contains a chemical agent that
is harmful to them, bacterial populations will adapt.
Strains and species that are not affected by that
chemical will emerge.
ALL uses of antibiotics release these agents into the
environment
It is absolutely inevitable
that bacteria will adapt to the presence of antibiotics in
their environment
The emergence of bacteria that can function in the
presence of antibiotics will follow the use of antibiotics as
night follows day
Where does ‘resistance’ come from
Bacterial genes that encode reduced susceptibility to
antibiotics existed before antibiotics were discovered,
developed and used by humans
The use of antibiotics by humans has resulted in a selective
pressure for an increase in the frequency of bacteria
containing these genes
The use of antibiotics has also increased the range of species
where these genes are found
Bacterial communication
Within the microbiome genetic data including ‘resistance’
genes are continually being exchanged
All bacteria have access to their Google and Facebook
They are continuously ‘on-line’
Any ‘resistance’ gene present in any member of any species in
the microbiome has the potential to transfer to any other
species
GENERAL RULE 1
The more
antibiotics are used to control disease
the more likely
the target bacteria will be resistant
and the less likely
they will have any therapeutic value
GENERAL RULE 2
The increase in the frequency of resistance genes anywhere
on the planet increases the probability that a similar increase
will occur anywhere else
Antibiotic use in human medicine could impact the frequency
of resistance genes in bacteria that infect aquatic animals
Antibiotic use in aquatic animals could impact the frequency
of resistance genes in bacteria encountered in human
medicine
Use and resistance
The relationship between
use and the emergence of resistance
is not simple or linear
In some species resistance to some antibiotics emerged
rapidly
In others resistance appeared only very slowly
Percentage ‘resistance’ in Flavobacterium psychrophilum
Denmark UK Chile USA
Quinolones 76 82 40 0
Oxytetracycline 40 54 56 76
Florfenicol 0 0 1 0
The threat of re-entering the pre-antibiotic age
The global rainbow trout industry is currently dependent on
the continued susceptibility of Flavobacterium psychrophilum
to florfenicol.
All our experience suggests that this resistance will emerge
sometime soon and then …………..
During the furunculosis epizootic of the 1980s in northern
Europe strains of Aeromonas salmonicida were isolated that
were resistant to all available antibiotics
Avoiding the threat
If we wish to avoid re-entering the pre-antibiotic age we must learn
how to use antibiotics wisely
1. Although we have very little idea about how much we use in
aquaculture we do know that we must use less.
2. We need antibiotics but we must learn to use antibiotics only when
that use is necessary, prudent and rational.
3. When we use antibiotics we must learn the most effective and
efficient methods to administer them
My experience
The majority of antibiotic use in aquaculture is imprudent,
irrational, inefficient and not even economically justifiable
This is a problem for not just aquaculture
The majority of antibiotic use in human and veterinary
medicine is also imprudent and irrational
Control of bacterial disease
1. Prevent infections
Limit the contact between the host and the pathogenic
bacterium
2. Increase the hosts resistance to infection
Improve hosts general heath
Vaccinate to limit specific infections
3. Treat the infected hosts
Antibiotics are a last resort
Prevention is better than cure
When animals are dying the only option is (antibiotic) therapy
But when animals are dying the factors that led to their
disease have already happened
It is too late to correct these factors
But control of these factors is always the most efficient
method of controlling disease
Deciding to apply antibiotic therapy is always a gamble
Is the money that will be lost if no treatment is given
greater than the cost of the therapy?
The potential loss must always be a guess
The direct cost can be quantified by individual farmers
The long term indirect costs, associated with the
selection for resistance, cannot.
These long term costs will be borne by the wider industry, the
wider community and ultimately everybody on the planet
Antibiotic therapy cannot
1. Control industry-wide epizootics
1. Compensate for poor husbandry
1. Function as a growth promoter
1. Have any effect on limiting losses associated with
infections by resistant bacteria
Antibiotic therapy works best when
1. The general health of the treated population is good and their
environment suitable
1. The target bacterium plays a major role in the disease process
1. The dose is correct and its administration is efficient
1. The antibiotic is administered in time
1. The target bacterium is susceptible
Resistance and treatment
To initiate a course of antibiotic treatment in the absence of any
information on the susceptibility of the target bacterium is
irresponsible
imprudent
and a potential waste of money
We must design systems that allow health care professionals access
to susceptibility data
The way forward
Data requirements
How much antibiotic are we using?
How much resistance has resulted?
Actions
Provision of education in prudent use
Provision of appropriate technical support