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

• 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 countsa. 0.9 mL saline into each tube

b. 0.1 mL culture into first tube

c. Serial dilutions to 10-6

d. 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. Microwaved sponges until dry (3.5 min)

5. Re-wetted with 30 mL sterile saline

6. Squeezed out into new flasks

7. Repeated dilution and plating procedure

8. 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

• 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