Download - Case Study 2: Don't Swim In The Pool (Final)
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Patrick Racine
Siddarth Santhebennur
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Background Several cases of skin rash infections reported at Hotel
A in Bangor, Maine
Feb. 18-27, 2000
Infections related to low chlorine levels in the pool and hot tub
>1.0 mg/L, less than state required 1-3 mg/L
Sample of unknown pathogen taken from draining ear of 6 year old child and the pool filter
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Patient History 9 patients infected
Had rash for 7 days (or less) or an outer ear infection
All had spent time in either the pool or hot tub
7 spent time in both
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Signs and Symptoms Skin rash (folliculitis)
Outer ear infection (otitis externa)
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Possible Culprits Originally there were 6 potential bacteria that could
have caused the infections:
Escherichia coli
Pseudomonas aeruginosa
Salmonella enterica
Staphylococcus aureus
Streptococcus pyogenes
Haemophilus influenzae
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Gram Stain A Gram stain differentiates bacteria based upon
properties of their cell walls using a crystal violet stain
Separated into 2 categories:
Gram-positive (+) (dark blue/violet)
Gram-negative (-) (red/pink)
E. coli and S. aureus were Gram stained along with unknown bacteria for comparative reasons
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Results of Gram Stain Gram stain showed that the unknown bacteria is
Gram-negative
Due to its red/pink color
This eliminates 2 bacteria from being considered the cause of the outbreak
Staphylococcus aureus
Streptococcus pyogenes
Both are Gram positive
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Differential/Selective Media Two types of growth media used to inhibit or isolate
growth of a microorganism
Differential: Different microorganisms grown on the same media; distinguished by how each organism reacts to specific dyes and chemicals placed on media
Selective: Allows growth of specific organism, inhibits others
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Type of Growth Media Used Two options:
MacConkey’s Agar
Mannitol Salt Agar
Because the suspect bacteria is Gram-negative, the best option was the MacConkey Agar
Allows for growth of Gram-negative bacteria and inhibits the growth of most Gram-positive bacteria
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Determining the Culprit Bacteria At this point, there were still four potential culprits
remaining:
Escherichia coli
Pseudomonas aeruginosa
Salmonella enterica
Haemophilus influenzae
• By using the information from the results of the growth media and research into the 4 potential bacteria, it was concluded that the culprit bacteria is Pseudomonas aeruginosa
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Pseudomonas aeruginosa Rod-shaped
Aerobic respiration Due to production of arginine, undergoes anaerobic
respiration as well
Found in various environments including soil, water and hospitals Most abundant organism on Earth
Opportunistic Rarely infects healthy individuals
Prefers individuals with unhealthy immune systems
Resistant to many antibiotics
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Pseudomonas aeruginosa
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Reasons for Selecting Culprit Bacteria The infections occurred on the skin and outer ear, so
Escherichia coli and Salmonella enterica were immediately eliminated
Escherichia coli and Salmonella enterica both cause infection of the digestive system
Although Staphylococcus aureus does cause various skin infections, including folliculitis, it does not cause the outer ear infection that is also associated with the culprit bacteria
This leaves Pseudomonas aeruginosa as the only logical culprit
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Antimicrobial Susceptibility In order to choose a proper antibiotic to treat the infected
patients, an antimicrobial test was conducted The effectiveness of 6 potential antibiotics were tested on
the culprit bacteria Chlorampheicol Gentamycin Penicillin Streptomycin Tetracycline Vancomycin
Based on the results it was determined that the culprit bacteria was most sensitive to Gentamycin, making that antibiotic the best option
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Antimicrobial Susceptibility Test
The antibiotic that creates the largest zone of inhibition would be considered the most effective.