Infectious Disease Case Study 4 Learning Objectives antibiotic apocolypse Draw a picture to illustrate the effect of antibiotics on a population of bacteria Distinguish between antibiotic resistance and an antibioticresistant infection ID: 928160
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Slide1
Antibiotic resistanceDoes antibiotic use on farms contribute to resistant infections in humans?
Infectious Disease
Case Study 4
Slide2Learning Objectivesantibiotic apocolypse
Draw a picture to illustrate the effect of antibiotics on a
population
of bacteria.
Distinguish between antibiotic resistance and an antibiotic-resistant infection.
Analyze and make predictions using data on antibiotic resistance.
Develop a model to explain how human antibiotic resistant infections may be linked to antibiotic use on animal production farms.
Slide3Denmark 1998
Outbreak of 25 cases of food poisoning.
All were infected with a strain of
Salmonella
that is treated with
cipro antibiotic. The antibiotic wasn’t effective. Two patients died.
How did the Salmonella strain become resistant to cipro?
We will develop a model to answer this question by the end of this case study
Source:
Molbak
et al. (1999) New England Journal of Medicine 341:1420-1425.
Slide4Do NowUnderstanding the Evolution of Antibiotic Resistance
What is the role of “selection pressure” in the acquisition of antibiotic-resistance?
Answer the first question on the worksheet then
choose the correct scenario on the following slides
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1. Bacteria are exposed to antibiotic
2. Presence of antibiotic puts pressure on the bacteria to become resistant
3. Resistant bacteria can then pass the resistance trait onto other bacteria
antibiotic
Bacterial cell
Scenario #1: Is this correct?
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Slide62. The non-resistant cells die in presence of antibiotic
3. Resistant bacteria can then pass the resistance trait onto other bacteria
Scenario #2: Is this correct?
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1. Bacteria are exposed to antibiotic; a rare cell is resistant
antibiotic
Bacterial cell
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Slide72. The non-resistant cells die in presence of antibiotic
3. Resistant bacteria can then pass the resistance trait onto other bacteria
Scenario #2 is correct
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1. Bacteria are exposed to antibiotic; a rare cell is resistant
antibiotic
Bacterial cell
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Selective pressure occurs when antibiotics are present.
The bacteria that possess the resistance trait are selected to live—survival of the fittest!
Slide8Acquisition of resistance is a process of evolution.There is usually a selection pressure that drives the outcome. Those organisms with the beneficial trait survive while others do not.
Slide9Pew Charitable Trusts
http://
www.pewhealth.org
/other-resource/record-high-antibiotic-sales-for-meat-and-poultry-production-85899449119
Activity: Developing a model to link antibiotic use on farms with human infections
A lot of antibiotics are used on meat-producing farms in the U.S.
What do you predict about bacteria isolated from those farms?
Slide10Farm
type
Number of antibiotic-resistant
samples
Total number of samples
testedPercent resistant
Conventional (antibiotics (
Ab
)
used)
10
13
77%
Organic (no
antibiotics
)
0
16
0%
Determine if the data support your prediction
Conventional farms supplement daily animal feed with antibiotic.
Aarestrup (1995) Microbial Drug Resistance 1:255-257.
Do these data support your prediction?
Intestinal microbes present in feces of healthy chickens on farms
Slide11The data show an association between antibiotic use on farms and carriage of resistant bacteria by animals on those farms.
(Many different types of studies have shown the same result)
What does this mean for human health?
Slide12An early sign that there might be reason for concern
In a revolutionary study in 1976:
Part 1
Studied a farm in which antibiotics had not been used.
Took stool samples from chickens, farm family members and neighbors.
Part 2
Added tetracycline (antibiotic) to the feed of chickens on the farm.
Over time, measured the percent of bacteria from stool samples that were resistant to tetracycline.
Measured samples from chickens, farm families and neighbors.
Source: Levy et al. (1976) New England Journal of Medicine 295:583-588.
Slide13Predict the results
Adapted from results in Levy et al. (1976) New England Journal of Medicine 295:583-588.
What percent of stool bacteria are resistant to antibiotic 48 hour and 3 months after adding it to chicken feed?
Graph for each group sampled (chickens, farm family and neighbors)
chickens
farm family
neighbors
Percent antibiotic resistant
Prior to antibiotic
48 hours
6 months
Slide14Predict the results
Adapted from results in Levy et al. (1976) New England Journal of Medicine 295:583-588.
What percent of stool bacteria are resistant to antibiotic 48 hour and 3 months after adding it to chicken feed?
Graph for each group sampled (chickens, farm family and neighbors)
chickens
farm family
neighbors
Percent antibiotic resistant
Prior to antibiotic
48 hours
6 months
Slide15Association was made between antibiotic use on farms and carriage of resistant bacteria by
humans
who live on those farms.
(Many different types of studies have shown the same result)
Slide16Does having antibiotic-resistant bacteria on your skin or in your intestinal tract make you sick?
Slide17What is the result of having tetracycline-resistant bacteria in/on your body?
A. You will be sick and treatment with tetracycline won’t cure the infection.
B. You will be sick, but treatment with tetracycline should clear the infection.
C. You are not necessarily going to get sick.
D. You will not get sick because you are resistant to tetracycline infections.
Slide18What is the result of having tetracycline-resistant bacteria in/on your body?
A. You will be sick and treatment with tetracycline won’t cure the infection.
B. You will be sick, but treatment with tetracycline should clear the infection.
C. You are not necessarily going to get sick.
D. You will not get sick because you are resistant to tetracycline infections.
Slide19Which is an accurate statement?
A) Humans can become resistant to antibiotics.
B) Humans can get infected with bacteria that are resistant to antibiotics.
C) Both are true.
D) Neither is true.
Slide20Which is an accurate statement?
A) Humans can become resistant to antibiotics.
B) Humans can get infected with bacteria that are resistant to antibiotics.
C) Both are true.
D) Neither is true.
Animals do not become resistant to antibiotics, bacteria do.
Some of the normal flora in or on our bodies can be resistant but we may never know it.
We can become infected with resistant types of bacteria.
Slide21What is the link between antibiotic-resistant microbes that were found on the farm and the antibiotic-resistant human food poisoning outbreak?
Slide22Read part 2 of background reading
Slide23Patients with the
cipro
-resistant infections were interviewed.
Most had eaten pork, worked at the slaughterhouse, or had been in contact with the infected patients.
Pork was traced to a single herd of pigs.
Pigs from that herd tested positive for the same strain of Salmonella as in the patients.
Source: Molbak et al. (1999) New England Journal of Medicine 341:1420-1425.
Slide24Wrap UpProvide a model to explain our original question
How did the deadly
Salmonella
strain become resistant to
cipro
?
an antibiotic was usedSelection pressure (from the antibiotic) took place leaving behind resistant forms of Salmonella
The resistant bacteria remained on the pork after slaughter and deliveryPatients ingested the Salmonella either through handling or consumption of raw pork
Slide25Proving causation is difficult
This single story is not
proof
that antibiotic use on farms causes resistant infections in humans.
But an accumulating number of reports like this are creating consensus amongst scientists that there is a link.
For many areas of science, an accumulation
of evidence compels adoption of a particular model. For example:Smoking and lung cancerHuman activity and global warming