Don’t Swim in the PoolPatrick Racine

Siddarth Santhebennur

Background Several cases of skin rash infections reported

at Hotel A in Bangor, MaineFeb. 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

Patient History9 patients infectedHad rash for 7 days (or less) or an outer ear

infectionAll had spent time in either the pool or hot

tub7 spent time in both

Signs and SymptomsSkin rash (folliculitis)

Outer ear infection (otitis externa)

Possible CulpritsOriginally there were 6 potential bacteria

that could have caused the infections:Escherichia coliPseudomonas aeruginosaSalmonella entericaStaphylococcus aureus Streptococcus pyogenes Haemophilus influenzae

Gram StainA 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

Results of Gram StainGram stain showed that the unknown

bacteria is Gram-negativeDue to its red/pink color

This eliminates 2 bacteria from being considered the cause of the outbreakStaphylococcus aureus Streptococcus pyogenes

Both are Gram positive

Differential/Selective MediaTwo types of growth media used to inhibit or

isolate growth of a microorganismDifferential: 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

Type of Growth Media UsedTwo options:

MacConkey’s AgarMannitol Salt Agar

Because the suspect bacteria is Gram-negative, the best option was the MacConkey AgarAllows for growth of Gram-negative bacteria

and inhibits the growth of most Gram-positive bacteria

Determining the Culprit BacteriaAt this point, there were still four potential

culprits remaining:Escherichia coliPseudomonas aeruginosaSalmonella entericaHaemophilus 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

How did we eliminate?Escherichia coli

Severe stomach cramps and stomach tenderness. Diarrhea, watery at first, but often becoming very bloody. Nausea and vomiting

Pseudomonas aeruginosa Eye infection: Pain in the eye, reduced vision, swollen eyelids. Cystic fibrosis: Cough, reduced appetite, fast breathing,

enlargement of abdomen. Skin infections: Ulcer that can result in bleeding

Salmonella enterica Gastrointestinal Symptoms

Haemophilus influenzae Meningitis Affects eyes

Pseudomonas aeruginosaRod-shapedAerobic respiration

Due to production of arginine, undergoes anaerobic respiration as well

Found in various environments including soil, water and hospitalsMost abundant organism on Earth

OpportunisticRarely infects healthy individualsPrefers individuals with unhealthy immune systems

Resistant to many antibiotics

Pseudomonas aeruginosa

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

Antimicrobial SusceptibilityIn order to choose a proper antibiotic to treat the

infected patients, an antimicrobial test was conductedThe effectiveness of 6 potential antibiotics were tested

on the culprit bacteria ChlorampheicolGentamycinPenicillinStreptomycinTetracyclineVancomycin 

 Based on the results it was determined that the culprit bacteria was most sensitive to Gentamycin, making that antibiotic the best option

Antimicrobial Susceptibility TestThe antibiotic that creates the largest zone of inhibition would be considered the most effective.