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TRANSCRIPT
The Culturing of Staphylococcus epidermidis and Streptococcus salivarius with Escherichia coli Does Not Increase Antibiotic Resistance in Escherichia coli
By: Sarah Weber
INTRODUCTION
• Antibiotic resistance is important -- antibiotics are used to treat bacterial infections
• When testing effectiveness of an antibiotic -- performed on individual strains
• Not realistic -- hundreds of strains interact in the environment
• Bacteria intermingle and transfer genes between each other in order to survive
INTRODUCTION
• Escherichia coli– Member of a large and diverse group of gram
negative bacteria– Normally live in human and animal intestines– Most strains are harmless, some are pathogenic– Can be used to indicate if water is contaminated– Rod-shaped (bacillus) bacteria
INTRODUCTION
• Streptococcus salivarius – Gram positive– Principal bacterium living in human oral cavity
without causing harm – Pioneer in colonizing dental plaque– Can cause disease if it enters the blood stream– Spherical shaped (coccus) bacteria
INTRODUCTION
• Staphylococcus epidermidis– Gram positive– Part of normal skin flora in humans– Leading cause of hospital born infections in
immune compromised patients– Spherical shaped (coccus) bacteria in grape-like
clusters
INTRODUCTION
• Penicillin– One of the earliest discovered and widely used
antibiotics– Used to treat many different types of infections
caused by bacteria– Kills bacteria by interfering with the ability to
synthesize the cell wall
INTRODUCTION
• Erythromycin– Macrolide antibiotic– Used to treat many different types of infections
caused by bacteria– Slows the growth of sensitive bacteria – Reduces the production of important proteins
needed by the bacteria to survive
INTRODUCTION
• Streptomycin– Aminoglycoside antibiotic– Used to treat many different kinds of bacterial
infections– Cannot be given orally; injected intramuscularly– Prevents growth of bacteria by protein synthesis
inhibition
INTRODUCTION
• Mutation rate– Bacteria mutate at a rapid rate, some faster than
others– Bacteria that survive in the presence of antibiotics
acquire resistance through:• Resistance genes• Recombination with foreign DNA
– Presence of antibiotics induces mutations causing a slow mutation rate
AIM
• The aim of the research was to study the speed at which bacterial resistance occurred in a pure culture versus mixed cultures.
HYPOTHESIS
• I hypothesized that the antibiotic resistance in the E. coli with S. epidermidis and E. coli with S. salivarius would increase faster than in the E. coli alone.
METHODS• Cultures made of parent strains • Parent strains plated to see zone of inhibition • Plates were made of E. coli only, mixtures of E. coli
with S. salivarius, and mixtures of E. coli with S. epidermidis
• Test plates of individual strains– Left to Right: E. coli, S. epidermidis, S. salivarius
METHODS• Every other day a culture was made using the
previous growth plate to make a new generation using only the E. coli with S. salivarius and E. coli with S. epidermidis plates
• The cultures were incubated, then plated onto blood agar with one disk each of penicillin, erythromycin, and streptomycin
E. coli S. salivarius S. epidermidis0
0.5
1
1.5
2
2.5
3
3.5
4
Diameter of the Zone of Inhibition for the Parent Generation
PenicillinErythromycinStreptomycin
Parent Generation
Zon
e of
Inh
ibiti
on(m
m)
• Generation Number 1‾ Left to right: E. coli, E. coli with
S. salivarius, E. coli with S. epidermidis
• Generation Number 16‾ Left to right: E. coli, E. coli with
S. salivarius, E. coli with S. epidermidis
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 170
0.2
0.4
0.6
0.8
1
1.2
1.4
Diameters of the Zone of Inhibition for E. coli Con-trol
PenicillinStreptomycin
Generations
Zon
e of
Inh
ibiti
on (m
m)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 170
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Diameters of the Zone of Inhibition for S. salivarius and E. coli
PenicillinErythromycinStreptomycin
Generations
Zon
e of
Inh
ibiti
on (m
m)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 170
0.5
1
1.5
2
2.5
Diameters of the Zone of Inhibition for S. epidermidis and E.coli
PenicillinErythromycinStreptomycin
Generations
Zon
e of
Inh
ibiti
on (m
m)
RESULTS
• An ANOVA (General Linear Model) was performed• No significant difference between the two different
bacterial combinations on the rate of change in the zone of inhibition (p> 0.05)
• Significant difference in generations (p< 0.05)
Generation Mean (mm)
1 0.5875a
17 0.3167c,d
RESULTS
• Significant difference with respect to inhibition of bacterial growth (p< 0.05)
Antibiotic Mean (mm)
Streptomycin 0.4371a
Erythromycin 0.3400a,b
Penicillin 0.2961b
CONCLUSION
• Hypothesis of antibiotic resistance in the E. coli with S. epidermidis and E. coli with S. salivarius would increase faster than in the E. coli alone was rejected
• Significance: two bacteria grown together did not selectively mutate any faster than individual strains
• Change in the zone over time showed the antibiotics are not as effective as when first introduced
LIMITATIONS OF RESEARCH
• Too many similarities between the two treatment bacteria (S. salivarius and S. epidermidis)
• Too many similarities in the zones of inhibition• The number of generations was insufficient • The recombination of the two bacteria did not
occur
FURTHER RESEARCH
• Allow for more generations to determine how many are needed for the bacteria to become completely desensitized to the antibiotics
• Change the bacteria used • Change the antibiotics used
QUESTIONS