What Effect Do Microwaves Have on Microbes By: Matthew Scholl 9th grade Representing: Central Catholic High School, Pittsburgh 3rd year participating in PJAS
Do microwaves have an adverse impact on microbes; such as Staph and E-coli? Purpose
Implications • Is microwave cooking effective at reducing microbial contamination?
Microwaves-Long electromagnetic non-ionizing waves that range from 1mm to 1m. Frequency can reach 2.45 billion hertz.Frequency harmful to humans starts at 10,000 hertz. Thermal affect- Microwaves heat food by vibrating food molecules so fast they create friction as heat. Microwaves
Escherichia coli • Diverse and large group of bacteria • Found in the intestines of most mammals • Strains are mostly not pathogenic • Some produce shiga damaging lining of intestines • Gram (-)
Staphylococcus epidermidis • Bacteria found on healthy human skin • Most forms not pathogenic • Gram (+) • Can cause Staph infection upon entry into body
Independent Variable-Seconds of microwave exposure.Dependent-Amount of colonies that survived.Control-0 seconds of exposure time. • Variables
Null-Microwaves will have no significant effect on microbial survivorship.Alternate- Microwaves will significantly reduce microbial survivorship. Hypothesis
Materials • • 64 LB Agar Plates (0.5% yeast extract, 1% tryptone, 1% sodium chloride. • Peristaltic Pump • Flask • Sterile Dilution Fluid [SDF] (100mM KH2PO4, 100mM K2HPO4, 10mM MgSO4, 1mM NaCl) • Spreader bars • Incubator • Alcohol • Bunsen Burner • Escherichia coli (DH5-alpha) • Staphylococcus epidermidis • Micropipets • Camera (on Phone) • Notebook • Sharpie • Holding stand (For Flask) • Racks • Sterile test tubes • Old General Electric turntable oven (8,500 Watts.)
Liquid Exposure Trials • The approximate density of the initial Staph and E. coli epidermis was 10^8 cells/ml. • Bacteria were diluted to a concentration of 10^5 cells/ml. • The cells were then added to sterile dilution fluid, resulting in a final concentration of 10^3 cells/ml. • Equivalent tubes microwaved to temperatures of 0, 5, 10, 15, 20 seconds.
Sterile water tubes were microwaved for the previous exposures to determine temperature change. Thermometer Data Collection
Pipetted .1ml the first solution into 30 plates.Spread all solutions with spreader bars.Microwaved 5 plates for each exposure.0 seconds5 seconds10 seconds 15 seconds20 seconds 30 secondsPlates were incubated at 37 Celsius.Colony survivorship was recorded. Solid Exposure Trials
Not Significant P= 0.00078 Not significant T crit=3.29 Y=Surviving Colonies Significant significant
P Value 0.000124 T Crit=3.29 Not Significant Y=Surviving Colonies Significant Significant Significant
P Value=0.014 T Cit=3.62 Y=Surviving Colonies Significant Significant Significant Significant Significant
Solid Microwave Plate Staph Exposure Y=Surviving Colonies P Value=6.18E-09 T Crit=3.62 Significant Significant Significant Significant Significant
Y=Survivorship of Colonies Tube E-coli. Tube Staph. Plate E-coli. Plate Staph
Nullhypothesis rejected- both bacteria’s survivorship were significantly reduced at the higher microwave exposures.Null rejected on Staph liquid exposure for 15 and 20 seconds.Null rejected on E-coli liquid exposure for 10, 15, and 20 seconds.Null rejected on Staph solid exposure for all trials except the control.Null rejected on E-coli solid exposure For all trials except the control.Alternate accepted-Microwave exposure significantly affected the survivorship of colonies. The more seconds of exposure=less colonies that survive. Conclusion
Explanation Plate survivorship reduced most because water had a protective effect in absorbing microwave energy. Staph colonies decreased least. Gram (+), thicker peptidoglycan layer, Cell wall more resistant to heat and antibiotics. Microwaves reduced survivorship, heated microbes, destroying- mutating proteins that make reproduction possible.
Limitations • Study does not reveal other effects on the colonies health • Use different concentrations • A difficulty in synchronizing exposures and plating • Narrow ranges of exposure
Extensions/ Improvements • Use more trials • Wider range of exposures in power and time • Test on actual food • Use many other different species of bacteria, salmonella, shingella, streptococcus
Plate Staph Anova Plate E-coli Anova
Tube E-Coli Tube Staph
Average SurvivorshipIn E-coli tubes: one plate had 31 colonies and another 18 • E-coli plates 7, 13.
Background Microwaves • Microwaves for cooking-Microwaves produced by a magnetron. Two parts are opposite magnets. Create magnetism dislodge electrons from air. • Microwaves are amplified and are repeatedly bounces of the inside of the microwave. • Thermal affect- Microwaves heat food by vibrating food molecules so fast they create friction as heat.
Radiation-Movement of energy as waves or particles through a medium. Electromagnetic Radiation-Uses electrons and magnetism and consists of; Radio waves,Microwaves, visible light, x-Rays, etc.. Background-Radiation
Electromagnetic Spectrum-The entire range of wavelengths. Background-Radiation
Gram positive- Do retain Chrystal violate stain in the gram method. Prokaryotic, thick PEPTIGLOGLYCAN layer, strong cell wall, more heat resistant.Eubacteria- simple cells, round shaped, rigid cell walls, and use flagellum for movement. • Background Staphylococcus Epidermytis
Staph Infection • Staph infection- An infection on skin or respiratory tract warts or large boils. fatal when in blood stream.
Gram negative- opposite of Gram positive, weak cell wallProkaryotic- no nucleus or membrane bound organellesUnicellular and rod-shapedProteobacteria- Reproduce rapidly and have many pathogens Escherichia Coli
Lives in intestinal tract and usually harmless.Some strains produce shiga, damaging lining of intestines. food poisoning, Pneumonia, and urinary tract infections. Thermal affect- Microwaves heat food by vibrating food molecules so fast they create friction as heat E.coli Disease
Materials Continued • Staphylococcus Epidermidis • Petri dishes • Camera (on Phone) • Notebook • Sharpie • Holding stand (For Flask) • Racks • Sterile test tubes • Old General Electric turntable oven.
• 64 LB Agar Plates (0.5% yeast extract, 1% tryptone, 1% sodium chloridePeristaltic PumpFlask Spreader barsIncubatorAlcohol Burner• Escherichia Coli (DH5-alpha) Materials Peristaltic Pump
P value always less than .05- There was significant variation between groups.Dunetts test, t value greater than t crit.(significant variance)Large difference between the groupings, the radiation had an affect on survivorship.Small difference within groups scientist can trust the results. The P value, Dunetts test, and other statistics show significant variances rejecting the null. • Statistics