Microbiology of Kitchen Sponges

1. Microbiology of Kitchen Sponges Jim Abshire, Maggie Crenshaw May 10, 2006 BSCI 223H

2. 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

3. 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

4. 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

5. Materials • 2 used, wet sponges • TSA • SS Agar (Salmonella-Shigella) • Vogel-Johnson Agar (Staphylococcus) • MacConkey’s Agar • Sterile saline • Sterile flasks, test tubes

6. Methods • Squeeze out liquid into sterile flask • Serial dilutions on TSA for viable cell counts • 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 • Spread 0.1 mL original culture onto 4 of each type of plate

7. Methods • 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

8. Results Before Microwaving (TSA) After Microwaving (TSA)

9. Results • Growth on all media • Viable Plate Counts (CFU / mL)

10. Results SS agar before and after microwaving sponges

11. Results MacConkey’s agar before and after microwaving sponges

12. Results VJ agar before and after microwaving sponges

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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