Download Microbiology of Kitchen Sponges

Microbiology of Kitchen Sponges
Jim Abshire, Maggie Crenshaw
May 10, 2006
BSCI 223H
Introduction
• Kitchen sponges can be effective growth
environments for bacteria
– Continually wet environment provides ideal
growing conditions
– Repeated contact with food and [mess] adds
nutrients and new bacteria
• Most common bacteria found on sponges
– E. coli (from fecal matter, meat)
– S. aureus (normal flora on some people’s skin)
– Salmonella enterica
Introduction
• Sponges are sometimes microwaved in order
to reduce bacterial concentrations
– Heat (boils water)
– Steam from evaporating water
– Dries out sponge
• Must microwave until sponge is dry
– Remaining bacteria can survive and multiply in
greater numbers when sponge is wet
Research Questions
• How “dirty” are communal sponges used in
residence halls?
– What kind of bacteria are found in kitchen
sponges used in Anne Arundel Hall?
– How many?
• What effect does microwaving sponges have
on bacterial counts?
• Hypothesis: Sponges will contain Salmonella,
E. coli, and Staphylococcus
Materials
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2 used, wet sponges
TSA
SS Agar (Salmonella-Shigella)
Vogel-Johnson Agar (Staphylococcus)
MacConkey’s Agar
Sterile saline
Sterile flasks, test tubes
Methods
1. Squeeze out liquid into sterile flask
2. Serial dilutions on TSA for viable cell counts
a.
b.
c.
d.
0.9 mL saline into each tube
0.1 mL culture into first tube
Serial dilutions to 10-6
Plated 0.1 mL from each tube on TSA
3. Spread 0.1 mL original culture onto 4 of
each type of plate
Methods
4.
5.
6.
7.
8.
Microwaved sponges until dry (3.5 min)
Re-wetted with 30 mL sterile saline
Squeezed out into new flasks
Repeated dilution and plating procedure
Incubated all cultures for 48 hours at 37˚C
Results
Before Microwaving (TSA)
After Microwaving (TSA)
Results
• Growth on all media
• Viable Plate Counts (CFU / mL)
Before
After
Reduction
Sponge 1 7.7 x 107
2.3 x 103
99.995%
Sponge 2 1.2 x 108
5.6 x 103
99.997%
Results
SS agar before and after microwaving sponges
Results
MacConkey’s agar before and after microwaving sponges
Results
VJ agar before and after microwaving sponges
Discussion
• Presence of Salmonella, E. coli,
Staphylococci, and other enterobacteria on
sponges
• Microwaving dramatically decreased
concentrations of enterobacteria
– Concentration of staphylococci increased
– Contact with hands shortly before incubation
E. coli
• Member of enterobacteriaceae
– Gram negative, lactose fermenting,
– Found commonly in intestinal tracts of animals
• As a pathogen: best known for causing
intestinal infections
• Most infectious strain: E. coli O157:H7
– 73,000 cases of infection each year in the US
– 61 deaths per year
– Symptoms include bloody diarrhea, abdominal
cramps, occasionally kidney failure
– Most people recover without antibiotics within 5-10
days
Salmonella
• Members of enterobacteriaceae
– 99% of diseases caused by S. enterica
– Live in intestinal tracts of animals
– Gram-negative, oxidase-negative, motile
• Cause self-limiting gastroenteritis
– Rehydrate patient (diarrhea)
– Only treat with antibiotics if spread outside intestines
• Each year 40,000 cases reported
– Only most severe cases reported
– About 600 fatal cases per year
Staphylococcus
• Gram-positive cocci
• Normal flora in humans
• Some are pathogenic: S. aureus
– Gastrointestinal illness: nausea, vomiting, cramps,
diarrhea
– Fast-acting toxin: illness within 30 min
– Self-limiting, toxin not affected by antibiotics
– Cause > 90% of reported food poisoning cases in US
Concluding Comments
• Protocol was sound: may have introduced
staphylococcus by hand-squeezing sponges
– May have been out-competed on sponges before microwaving
• Results supported hypothesis
• Further research would evaluate pathogenicity of
bacteria found
• Kitchen sponges should be replaced frequently
– Contain enteric (possibly pathogenic) bacteria
– Microwaving is useful technique to reduce bacterial
concentrations
References
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Josephson, K.L., Rubino, J.R., and Pepper, I.L, 1997. Characterization
and quantification of bacterial pathogens and indicator organisms in
household kitchens with and without the use of a disinfectant cleaner.
Journal of Applied Microbiology. 83(6): 737-750.
Sharp, K., and Walker, H., 2003. A microbiological survey of communal
kitchens used by undergraduate students. International Journal of
Consumer Studies. 27(1): 11-16.
Ikawa, J., and Rossen, J., 1999. Reducing Bacteria in Household
Sponges. Journal of Environmental Health. 62(1): 18-22.
http://www.cdc.gov
http://medinfo.ufl.edu/year2/mmid/bms5300/bugs/esccoli.html
http://textbookofbacteriology.net/e.coli.html