As a college microbiology instructor, I teach a lab about microbial control, how to kill microbes. There are various control methods available to students: physical (heat and UV radiation), antibiotics and chemical agents.
Article Summary: Many steam mops use both physical (heat) and chemical (cleaner) means to sanitize, and claim nearly 100% effectiveness. But how clean do steam mops really get floors?
sanitized his kitchen floor and got very impressive results, so impressive that I bought my first steam mop that same day.
In contrast to the Shark Light & Easy, which uses only steam to clean and sanitize floors, I chose a model of steam mop that employs both steam (heat) and spray cleanser (chemicals), the Shark® PRO Steam and Spray™ Mop. Steam mops typically generate steam at more than 200 degrees Fahrenheit, a temperature that will kill most microbes.
With the Shark Steam & Spray mop, steam is only generated when the mop is plugged in. The cleanser sprayer is battery operated. The Shark Steam Energized™ cleanser comes with the mop, costs approximately $7 per 20 fl. oz. bottle separately, and makes no claims regarding sanitizing. This cleanser was used for all of our Shark® PRO Steam and Spray™ Mop experiments. However, as it is expensive, when cleaning my floors I typically refill the bottle with my own cleaning solution (although doing so is, not surprisingly, against the manufacturer's recommendation).
Changes to Original Experimental Design
There were some elements of the original experimental design that I wanted to change, and further tests I wanted to perform. In the original Shark Light and Easy steam mop experiment, one kitchen floor tile was steam cleaned for one minute. That is not a realistic amount of time to clean a floor tile. Few people will spend an entire minute cleaning each small section of floor. So the following experiment was designed with a shorter cleaning time and with three comparisons: steam only, cleanser only, and a combination of steam and cleanser.
The steam mop was used to clean three adjacent dirty areas of kitchen floor in front of the stove. Each area cleaned was as wide as the mop head in a vertical 2 foot swipe. Cleaning was accomplished using five back-and-forth “swipes” (a total of 10 passes), each swipe lasting 1 second. When the mop is plugged in, steam is released every time the mop is pushed forward.
1. Separate sterile swabs were used to sample the dirty areas of floor, and those “before cleaning” samples were plated on ½ of a TSY plate and ½ of a MacConkey’s agar plate. (TSY is an all-purpose bacterial growth media that will grow a wide variety of bacteria. MacConkey's is a specialized bacterial growth media that only grows Gram-negative bacteria and will indicate if coliform bacteria are present.)
2.The steam mop was run over each area in five 1-second back-and-forth “swipes”, a total of 10 passes over each area cleaned. A new, dry cleaning pad was used for each section of floor:
a. In strip 1a, only steam was used, one burst of steam each of the 5
times the mop was pushed forward.
b.In strip 1b, the steam was turned off and the cleanser
sprayed each of the 5 times the mop moved forward.
c.In strip 1c, with the steam on, the cleaner was sprayed each
of the 5 times the mop moved forward.
3.The floor was allowed to dry.
4. A separate sterile swab was used to sample each of the three cleaned areas of the floor and that “after cleaning” sample was plated on the other ½ of a TSY agar plate and ½ of a MacConkey’s agar plate.
5. The plates were left in a warm location for one week, then examined for growth.
For all three sections of floor, cleaning dramatically reduced the amount of bacteria present, however, there was not a dramatic difference between the three sections. In other words, steam only, cleanser only and combined steam and cleanser worked equally well. See photos and summary of results below.
Equipment used for Shark PRO Steam & Spray Mop Sanitation Experiment #1:
-3 TSY agar plates
-3 MacConkey's agar plates
- permanent marker
Shark PRO Steam & Spray Sanitation Experiment Results
"Before cleaning" floor samples plated on left side of plates, "after cleaning" samples plated on right side of plates. TSY agar on left, MacConkey's agar on right, in each photo.
For all three experimental conditions, cleaning dramatically reduced the amount of bacteria on the floor, regardless of whether steam alone (1), cleanser alone (2) or a combination of steam and cleanser (3) were used. There were no bacterial colonies growing on any of the MacConkey's agar plates, neither before nor after cleaning, indicating the absence of Gram-negative coliform bacteria.
Although cleaning the floor did reduce the number of bacteria present, none of the experimental conditions (steam alone, cleanser, alone or a combination of steam and cleanser) resulted in a level of sanitation that I'd like to see after cleaning my floors. There was still too much bacteria present.
However, the the mopping method I used in this experiment did not feel like what I would normally use when cleaning the floor. There were too few strokes over each area of the floor (a total of 10 for each section) and too much cleanser left on the floor to dry in the sections that used cleanser. It took more than a half hour for the floor to dry after mopping.
Please read this section carefully before carrying out the experiment outlined above. Although these plates will be growing bacteria present on hands, once the bacteria begin growing on the agar plates, they will be present in much higher numbers than a person would normally encounter. Therefore, there are some important safety precautions to keep in mind:
Wear safety goggles and protective gloves when handling plates that are growing bacteria.
Never open the plates after placing the sample on the agar. Bacteria will be present in large numbers. Some can become airborne and be breathed in or land on areas of the body close to an open plate.
Keep plates out of the reach of small children and pets. Talk to children about these safety precautions and make sure they know not to ever handle the plates without adult supervision.
You may place a rubber band around the plates to reduce the likelihood that they will accidentally fall open.
The top of the refrigerator can be a good place to store incubating plates, as it is up high and usually a bit warm.
Placing incubating plates in open plastic bag (so aerobic bacteria can get oxygen) is a good measure to keep them safer and reduce odor (bacteria are stinky).
When the experiment is finished, and you are done with the plates, place them in a zipped up plastic bag (Zip-loc) in the trash. They will run out of food and water eventually and die, but not before generating a lot of stink.