Background
This laboratory exercise illustrates the critical need for proper hand washing techniques as a means of reducing the incidence of healthcare facility acquired infections. The exercise compares the effectiveness of two hand washing techniques: using water only, and using soap and water. The student is exposed to the fact that the hands harbor microorganisms that could result in transmitting disease. In addition, the microorganisms resident in the hands could result in contamination of laboratory experiments if aseptic techniques, such as wearing gloves, are not strictly followed.
Before birth, the skin of a human being is sterile. During the birthing process and subsequently, the human skin is colonized by microorganisms. The set of microorganisms that permanently colonize the human skin and do not cause harm to a healthy individual is called the residential flora. The set of microorganisms that are present only temporarily on the skin is called the transient flora. The residential flora tends to be located in the deeper layers of the epidermis and in the hair follicles. The transient flora is located superficially. The residential flora is more difficult to remove from the skin than the transient flora. The residential flora exists in a symbiotic relationship with the host. By competing for resources with pathogenic microorganisms, the resident flora can provide benefit to the host (Cappuccino 7).
Proper hand washing at healthcare facilities has the goal of removing the transient flora from the skin on the hands and also to diminish the presence of the permanent flora. A serious risk of infection exists if these microorganisms are allowed to enter the body tissues.
Materials and Methods
The materials for this laboratory experiment include: 4 nutrient agar plates; liquid antibacterial soap; 8 sterile cotton swabs, 1 test tube of sterile saline; Bunsen burner, glass marking pencil; stopwatch.
The participants in the experiment are Student 1 and Student 2.
The procedure consists of the following steps. Using the glass marking pencil, Student 1 marks the bottom of two agar plates with the label “Water” and the other two plates with the label “Soap”. The Student 1 then marks the bottom of each “Water” and “Soap” plate with a dividing middle line. Each half of a “Water” plate is labeled R1 and R2 respectively. Each half of the other “Water” plate is labeled R3 and R4 respectively. Each half of a “Soap” plate is labeled L1 and L2 respectively. Each half of the other “Soap” plate is labeled L3 and L4 respectively.
Student 1 uses aseptic technique to soak a sterile cotton swab in sterile saline solution in a test tube. The aseptic technique consists of removing the cap of the test tube, flaming the neck of the test tube using the Bunsen burner, dipping the cotton swab in saline, and putting the cap back on the test tube. Student 1 then proceeds to rub the moistened cotton swab on the pad of the right hand thumb of Student 2 and then inoculates the R1 section of the “Water” plate using a zigzag pattern from the edge of the dish towards the dividing middle line.
Student 2 proceeds to wash for one minute the thumb of the right hand under a stream of warm running water using a scrubbing motion between the thumb and the right index finger. Student 1 then proceeds to rub a sterile cotton swab on the pad of the thumb of Student 2 and then inoculates the R2 section of the “Water” plate using a zigzag motion.
Student 2 proceeds to wash for 2 minutes the thumb of the right hand under as stream of warm running water using a scrubbing motion between the thumb and the right index finger. Student 1 then proceeds to rub a sterile cotton swab on the pad of the thumb of Student 2 and then inoculates the R3 section of the “Water” plate using a zigzag motion.
Student 2 proceeds to wash for 3 minutes the thumb of the right hand under a stream of warm running water using a scrubbing motion between the thumb and the right index finger. Student 1 then proceeds to run a sterile cotton swab on the pad of the thumb of Student 2 and then inoculates the R4 section of the “Water” plate using a zigzag motion.
Student 1 uses aseptic technique to soak a sterile cotton swab in sterile saline solution in a test tube. Student 1 then proceeds to rub the moistened cotton swab on the pad of the left hand thumb of Student 2 and then inoculates the L1 section of the “Soap” plate using a zigzag pattern from the edge of the dish towards the dividing middle line.
Student 2 proceeds to add a drop of antibacterial soap to the pad of his left hand thumb and then wash for one minute the thumb under a stream of warm running water using a scrubbing motion between the thumb and the left index finger. Student 1 then proceeds to rub a sterile cotton swab on the pad of the thumb of Student 2 and then inoculates the L2 section of the “Soap” plate using a zigzag motion.
Student 2 proceeds to add a drop of antibacterial soap to the pad of his left hand thumb and then wash for 2 minutes the thumb under a stream of warm running water using a scrubbing motion between the thumb and the left index finger. Student 1 then proceeds to rub a sterile cotton swab on the pad of the thumb of Student 2 and then inoculates the L3 section of the “Soap” plate using a zigzag motion.
Student 2 proceeds to add a drop of antibacterial soap to the pad of his left hand thumb and then wash for 3 minutes the thumb under a stream of warm running water using a scrubbing motion between the thumb and the left index finger. Student 1 then proceeds to rub a sterile cotton swab on the pad of the thumb of Student 2 and then inoculates the L4 section of the “Soap” plate using a zigzag motion.
All plates are to be incubated in an inverted position at 37 degrees Celsius for a period of 48 hours.
Results
The agar plates were visually examined after the period of incubation and the observations appear in Table 1.1. The growth for the “Water” plates starts heavy and progressively diminishes to slight growth. The growth for the “Soap” plates starts at heavy and also diminishes to slight growth but shows lag in the rate of decrease at the beginning.
Table 1.1 Macroscopic observations of microorganism growth
| Section(Water-RightThumb) | Time (min) | Growth(0 = none,1+ = slight,2+ = moderate,3+ = heavy,4+ = maximum) | Section(Soap – LeftThumb) | Time (min) | Growth(0 = none,1+ = slight,2+ = moderate,3+ = heavy,4+ = maximum) |
| R1 | 0 | 3+ | L1 | 0 | 3+ |
| R2 | 1 | 2+ | L2 | 1 | 3+ |
| R3 | 2 | 1+ | L3 | 2 | 1+ |
| R4 | 3 | 1+ | L4 | 3 | 1+ |
The number of colonies were counted by visual inspection of the plates. The percent of microorganism growth was calculated as: percent reduction = [colonies (section 1) – colonies (section x)] – colonies (section 1), where x = plate sections 2, 3, 4 for each hand. Table 1.2 show the results of the calculations. The percent reduction for the right hand shows a linear rate. The percent reduction for the left hand shows initially an increase and then a linear rate of decline.
Table 1.2 Percent microorganism growth reduction
| Section(Water – Right Thumb) | Time (min) | Number of Colonies | Percent Reduction | Section (Soap – Left Thumb) | Time (min) | Number of Colonies | Percent Reduction |
| R1 | 0 | 36 | – | L1 | 0 | 68 | – |
| R2 | 1 | 16 | 55.6 | L2 | 1 | 94 | -38.2 |
| R3 | 2 | 8 | 77.8 | L3 | 2 | 11 | 83.8 |
| R4 | 3 | 1 | 97.2 | L4 | 3 | 1 | 98.5 |
Figure 1.1 shows an image of the agar plates for the right hand. Figure 1.2 shows an image of the agar plates for the left hand.
Figure 1.1 Agar plates inoculated with microorganisms from the right hand thumb.
Figure 1.2 Agar plates inoculated with microorganisms from the left hand thumb.
Conclusions
The results from the hand washing experiment indicate that washing with water is effective. Also, washing with antibacterial soap appeared to be effective also but initially lagged in removing microorganisms. One reason for this lag may be that the soap was effective in loosening the microorganisms at deeper layers of the epidermis. The results from this experiment are somewhat misleading since there is documented evidence that the best methods for infection control involve the use of antimicrobial agents (Kampf). There is also evidence that “a hygienic hand disinfection with an alcohol-based hand rub is the preferred treatment to be carried out after patient care activities that could lead to contamination of the hands of the health care workers” (Kamp).
The experiment should be modified to have a better starting condition for the hand contamination. Both hands should be used to contact the same surfaces where microorganisms are known to be present.
Review Questions:
1. Compare the effectiveness of hand washing with water, with soap, and with soap and surgical scrubbing.
According to research literature, hand washing with water only is ineffective. Using soap for extended periods of time is a better alternative to using only water. However, this allows some transient flora to cling deeply to hair and to remain protected by oil and dead skin cells. Soap with surgical scrubbing is a good way to remove transient flora and some residential flora.
2. How does the presence of residential flora influence the infectious process?
Residential flora is at a deeper layer of the skin as compared with transient flora. Residential flora is harder to remove than transient flora. Normally, residential flora exists symbiotically with the skin. It can present a risk for infection in individuals whose immune system is compromised. Residential flora can cause infections if they gain entrance to the human tissues.
3. How does hand washing affect residential versus transient flora?
Residential flora is difficult to remove with simple hand washing. Transient flora is easier to remove. Surgical scrubbing is the best way to remove transient flora and reduce the presence of residential flora.
4. Why do you think hand washing is necessary when medical and surgical personnel wear gloves during surgery or when examining patients?
It is necessary to wash hands when wearing gloves during surgery or when examining patients because the gloves can have defects that allow microorganisms to pass through them. In addition, there is risk that the glove may become damaged during surgery and the patient become exposed to the microorganisms resident on the hands. It is advisable to perform hand washing after removing gloves to reduce the risk that microorganisms might have been transferred from the glove surface to the hands. (cdc.gov)
Works cited
Cappuccino, James, and Natalie Sherman. Microbiology: A Laboratory Manual. Tenth Edition. Boston: Pearson, 2014. Print.
Cdc.gov. “Infection control in dental settings,” cdc.gov. Centers for disease control and prevention. 10 July 2013. Web. 5 April 2014.
Kampf, Gunter. “Epidemiologic background of Hand Hygiene and Evaluation of the Most Important Agents for Scrubs and Rubs,” Clinical Microbiology Reviews, Oct. 2004. Web. 5 April 2014.
Last updated on 7-April-2014 at 2:30 PM
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