(2007) Bacterial Survivability and Transferability on Biometric Devices

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The purpose of this study was to investigate bacterial recovery and transfer from three biometric sensors and the survivability of bacteria on the devices. The modalities tested were fingerprint, hand geometry and hand vein recognition, all of which require sensor contact with the hand or fingers to collect the biometric. Each sensor was tested separately with two species of bacteria, Staphylococcus aureus and Escherichia coli. Survivability was investigated by sterilizing the sensor surface, applying a known volume of diluted bacterial culture to the sensor and allowing it to dry. Bacteria were recovered at 5, 20, 40 and 60 minutes after drying by touching the contaminated device with a sterile finger cot. The finger cot was re-suspended in 5 mL of saline solution, and plated dilutions to obtain live cells counts from the bacterial recovery. The transferability of bacteria from each device surface was investigated by touching the contaminated device and then touching a plate to transfer the bacteria to growth medium to obtain live cell counts. The time lapse between consecutive touches was one minute, with the number of touches was n = 50. Again, S. aureus and E. coli were used separately as detection organisms. This paper will describe the results of the study in terms of survival curves and transfer curves of each bacterial strain for each device.

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(2007) Bacterial Survivability and Transferability on Biometric Devices

  1. 1. BACTERIAL SURVIVABILITY AND TRANSFERABILITY ON BIOMETRIC DEVICES Christine R. Blomeke Researcher Biometrics Standards, Performance, & Assurance Laboratory Purdue University 401 N. Grant Street West Lafayette, IN 47906 USA Stephen J. Elliott Associate Professor Biometric Standards Performance, & Assurance Laboratory Purdue University 401 N. Grant Street West Lafayette, IN 47906 USA Thomas M. Walter Continuing Lecturer Department. Of Biological Sciences Purdue University 915 W. State Street West Lafayette, IN 47906 USA Abstract - The purpose of this study was to investigate bacterial recovery and transfer from three biometric sensors and the survivability of bacteria on the devices. The modalities tested were fingerprint, hand geometry and hand vein recognition, all of which require sensor contact with the hand or fingers to collect the biometric. Each sensor was tested separately with two species of bacteria, Staphylococcus aureus and Escherichia coli. Survivability was investigated by sterilizing the sensor surface, applying a known volume of diluted bacterial culture to the sensor and allowing it to dry. Bacteria were recovered at 5, 20, 40 and 60 minutes after drying by touching the contaminated device with a sterile finger cot. The finger cot was re-suspended in 5 mL of saline solution, and plated dilutions to obtain live cells counts from the bacterial recovery. The transferability of bacteria from each device surface was investigated by touching the contaminated device and then touching a plate to transfer the bacteria to growth medium to obtain live cell counts. The time lapse between consecutive touches was one minute, with the number oftouches was n = 50. Again, S. aureus and E. coli were used separately as detection organisms. This paper will descrbe the results of the study in terms of survival curves and transfer curves of each bacterial strain for each device. Index Terms - biometrics, hygiene, bacterial transmission 1. Introduction As the concerns over infectious diseases grow, so do the concems over the hygiene of surfaces in public areas. This is of interest to the biometric community as efforts are made to implement the use of biometric technologies in the public arena, specifically in airports, retail stores, and various financial institutions. The motivation to conduct the current study arises from antidotal evidence from previous studying in the Biometrics Standards, Performance and Assurance Laboratory. During previous studies, specifically with fingerpfint and hand geometry, subjects would ask questons about the cleanliness ofthe sensor. Latent prints left on the platen glass of a device by the deposition of finger moisture, sweat, or oils, can make it appear to be unclean [1]. In 2006, s survey yielded responses about the perception of the cleanliness of biometric devices. Seventy-five percent of surveyed subjects responded that they felt that biometric devices were somewhat sanitary, neutral, or somewhat unsanitary. This indicates that the subject population does not view biometric devices as being overwhelmingly sanitary nor unsanitary [2]. In addition, the development of touchless sensors has prompted the question whether or not bacteria and other disease causing organisms are a potential hazard that can be transferred from person to person through touching a common device. Studies have shown that human pathogens can be transmitted between nonliving objects by direct hand contact [31. Contactless sensors eliminate the possibility of latent prints and decrease the hygiene concerns because the fingertip never comes into contact with the device [4. Although this lessens concems with the cleanliness of using common devices, there is a need to investigate whether using a common biometric device is any different that touching common surfaces in public areas. For instance, in many workplaces, individuals touch common items without a second thought. Doorknobs, elevator buttons, pens on a countertop, are a few items that are touched throughout the day by various people. However, recent media attention regarding the implementation of biometric devices in the work place has cited that employees have concerns about the hygiene of touching the devices, and has prompted the installation of hand sanitizer stations next to the biometric devices [51. It is important to note that the skin surface serves as the habitat of a flora of microorganisms, predominately consisting of gram-positive bacteria. These are naturally occurring organisms living on the skin, and normally do not cause disease or infection. Temperature, humidity, and skin physiology all play a role in maintaining the skin microflora [6]. 1-4244-1129-7/07/$25.00 ©2007 IEEE 80
  2. 2. Each bacterial species has a different infectivity level. As a result, different numbers of each bacterium must enter the body for that particular species to cause an infection or disease. They can enter the body through the thin tissues in the eyes, nose, and mouth, or at injury sites where the skin is broken. The literature focuses on studies conducted on the survivability of bacteria on non-porous inanimate surfaces are limited to health care and domestic environments, but do not consider public surfaces. Thus, this paper examines bacterial survival and transfer on biometric devices that could be used in public environments. II. Methodology The three biometric devices tested in this study were the Recognition Systems HandKey Ill, Crossmatch Venfier 300 LC, and TechSphere VP-Il S. Each device was tested separately with two strains of bacteria. Each bacterial strain was tested independently of the other. The test organisms utilized were Staphylococcus aureus and Escherichia coli. The two organisms were common teaching laboratory strains of bacteria that contain genetic mutations so not to cause infection, but were used as tracer organisms. Staphylococcus aureus is a representafive of gram positive bacteria, and in contrast, Eschenchia coli represent gram negative species. A. Survivability of Bacteria on a Biometric Device The survivability of the bacteria on the device was determined by contaminating each device with a known concentration of bacteria and recovering organisms over a period of time. Just prior to contamination, the device was sterilized with a 70 percent ethanol solution and control samples were collected. The control samples ensured that the sterilization was complete, and only bacteria on the device surface were the intentional contaminates. Sterile finger cots were worn over sterilized laboratory latex gloves. This ensured that the inside of the finger cot remained sterile, and prevented the naturally occurring bacteria on the skin's surface from being introduced into the experiment. After the collection ofthe control samples, 50 microliters of the bacterial suspension were applied to the device surface. The solution was allowed to dry. Bacteria were recovered by a single touch to the device surface with a sterile finger cot after five, twenty, forty and sixty minutes of dry time. The finger cots were resuspended in 5 milliliters of saline solution. Systematic dilutions of the solution were plated onto Tryptic Soy Agar (TSA) agar plates and allowed to grow for 24 hours at 37 degrees Celsius. Tryptic soy agar is a growth medium that contains all essential nutrents for bacterial growth. The colony growth on the plate allowed for the quantification of the number of surviving cells recovered at each time point. B. Transfer of Bacteria from Biometric Device The transferability of bacteria over tme from biometric devices was investigated by intentionally contaminating the device surface with one species of bacteria at a time. Prior to contamination, the device surface was sterilized with a 70 percent ethanol solution. Sterilized gloves were worn, and the device surface was touched by a sterile finger, and then touched to a TSA agar plate. The sterilized surface was touched ten times with a different sterile glove fingertip, and touched to the TSA agar plate as the control samples. The agar plates were labeled to indicate the touch number, with an average number oftouches to a plate being 12, see Figure 1 below. Bacterial colonies will only grow where they have been placed, and do not migrate over the surface; therefore the touches to the plate were non- overlapping to ensure that the colonies could be quantified for each touch. Immediately pror to touch 11 on the device, the device surface was contaminated with one species of bacteria, and allowed to dry. The remaining 40 touches were collected after contamination of the device. A sterile glove fingertip was used to collect each successive touch to the device. Successive touches lasted for 10 seconds were collected and plated at 20 second intervals. Touches 20, 30, 40, and 50 were collected with a sterile fingercot worn over the sterile glove, and was placed into 5 milliliters of saline solution. Serial dilutions ofthe saline solution were plated and grown over night to quantify the number of live cells that were recovered from touching the contaminated device. Figure 1: Transferability collection of bacteria on the Techsphere VP-Il S Vein Reader. 111. Conclusions 81
  3. 3. The survivals of S. aureus and E. coli over time were measured by quantifying the number of cells recovered from the biometric devices over time. Below in Figure 2, the survival of S. aureus is graphically represented in terms of the percentage of cells surviving over time for all three of the biometric devices. At five minutes past the dry time, the survival ofthe bacteria on the devices had decreased to 40 percent, 20 percent, and 15 percent for the hand geometry reader, vein reader, and fingerprint sensor respectively. After 20 minutes, the survival rate had approached zero for all three devices, yet even at 60 minutes a small quantity of bacteria were still recoverable. Survival of S. aureus F'- k . . . _, . . _ _. . , 4 ... .. _ _ . ..... .I 0 5 10 15 20 25 30 35 40 45 50 55 60 Time (mlnutMs) Figure 2: Survival of S. aureus, presented as the percentage of survival over time in minutes. In contrast to S. aureus, the survival of E. coli, the drop off in survival rate is not nearly as steep in the first five minutes. The percent survival at five minutes is 50, 40, and 28 percent for the vein reader, hand geometry reader, and fingerprint reader respectively. Similar to the test with S. aureus, the survival rate approached zero for all three devices at 20 minutes for E. coli. Figure 3 depicts the survival curves over a one hour time period. Survival of E. coli I -FP HG I-*,VR The results of the survivability experiment can be reported as a rate of the log of the survival. The survival rate of the bacteria decreases over tme, and hence can be considered a death curve. Table 1 illustrates the rate at which the survival decreases over time by device and bacterial species. TABLE 1 RATE OF LOG SURVIVAL OF BACTERIA BY DEVICE S. aureus E. coi l Hand Geometry0.904 Reader T 09004 ---- Fingerprint 0.10 Sensor ___ 0.14_T___I Vein Recognition 0.14 0.05 Device__ _ _ _ _ _ __ _ _ _ _ _ The result of this comparison between S. aureus and E. coli is that neither bacterial species survived for a long time on the device surface. Bacteria generally prefer warm, moist environments, but this study was conducted room temperature with low humidity, in an open-air environment, as would be implemented in most public environments. The result of the transfer of bacteria varies by the hardness of the device surface. As seen in Figure 4, the vein reader exhibits a more consistent level of transfer throughout the time frame, as it plateaus off before either the hand geometry reader or the fingerprint sensor. The vein reader device surface tested was the pliable plastic cup that is exposed to the back ofthe hand. This is the largest surface area that makes contact with a person's hand. The pliability of the surface being tested may have allowed bacteria to work itself into the microcrevices ofthe plastic surface, in which it could protect itself, and prolong the transfer to the gloved hand. In contrast, the fingerprint sensor and the hand geometry reader surfaces were hard surfaces, similar to that of a doorknob. The trend lines indicate a smoothing of the data to reveal the shape of the transferred bacteria over the consecutive touches to the surface. The fingerprint sensor rapidly decreased the amount of cells transferred with each successive touch. Essentially, the number of cells transferred over time decreases, as there are fewer cells on the surface to be transferred to the gloved hand and the agar plate. The hand geometry reader exhibited a similar curve to the fingerprint sensor, although not as extreme. 0 5 10 15 20 25 30 35 40 45 50 55 60 Time (minutes) Figure 3: Survival of E. coli, presented as the percentage of survival over time in minutes. 82 100 90 80- 70 - 60- 50 40- 30 20 10 O 100 I 90 80 *70 * 0 *S 14:30 20 10 0 ., k I I IIX I '2 a Ia.
  4. 4. Staph Cd Transfer 23 25 30 Touch nunter -FP.V - . V3 -Lol. (H% -LcZ (F Figure 4: Transfer of S. aureus cells is presented as the log ofthe percentage of the cells transferred over the touch number. Figure 5 represents the transfer curve for E. coli. In addition to testing the three biometric devices, a metal doorknob was also tested using the same method. The doorknob and hand geometry reader exhibited very similar transferability from the surface to the gloved hand. The majority of the bacteria were transferred from the surface for all four apparatuses within the first ten touches. It should be noted that the concentration of bacteria was not the same for each device. The concentration of E. coli on the fingerprint sensor was less than the concentration on the other three test surfaces. Therefore, there were a smaller number of bacteria to be transferred offthe device sensor. However, the fingerprint sensor and the vein reader followed the same general shape of the curve for transfer. Again, the pliable material that was tested on the vein reader may have influenced the transfer rate by providing microcrevices where bacteria could embed themselves, and thereby transferring fewer bacteria with each consecutive touch to the surface. E odco transfer 10 15 20 25 30 35 40 4p Touch rmu,r # mP* VR . HS . _ LZ (F Figure 5: Transfer of E. coli is presented as the log of the percentage of the cells transferred over the touch number. In summary, E. coli and S. aureus both exhibited a similar survival curve that drops off drastically after 20 minutes. E. coli did exhibit a slower death curve than S. aureus within the first 20 minutes, but the differences were negligible after 20 minutes. The transfer curves for S. aureus and E. coli were very similar in terms of most of the bacteria being transferred offthe device by touch 10. This initial investigaton of the survivability and transferability of bactera on biometric devices brings up several important points to remember, as well providing new questions for further study. From the bacterial survival curves, it is understood that these species could survive on an infrequently touched surface. However, a frequently touched surface, if contaminated, such as in the transfer experiments, is essentially cleaned within five to ten touches, as the bacteria are moved to the hand. As mentioned in the beginning of this paper, there are naturally occurring bacteria on the hand. The infectivity of each bacterial species is different. Some species would require hundreds if not thousands of cells to be ingested, enter the body through a cut in the skin, or mucus tissues for any sort of infection to occur. Likewise, if bacteria had been deposited on the device surface by an individual, most likely this would not be enough to infect a subsequent person using the device. The protocol in this study required the bacteria to be placed on the surface in liquid form and allowed to dry. In the event that a device is contaminated simply by hand to surface contact, the concentration of bactera on the surface would be far less than the concentration utilized in this study. In the event that hygiene is still a concern, it is best for those touching common surfaces to wash their hands with soap and warm water on a regular basis. This will remove the majority of bacteria from the surface ofthe hand. However, the naturally occurring bacteria on the hand will still be on the underlying layers of skin, and will rise to the epidermis when the oils, moisture, and sweat come to the surface. Further work is necessary to investigate and compare these results with results other species of bacteria. In particular, it is important to take a closer look at species of bacteria that only require a low infectivity number, as this may be the most important when regarding biosecurity measures. Additionally, other species of bactera that have a short survivability in dry conditions should be examined to determine how well they transfer. Additionally, further examination ofthe different surface types, hard and soft, could prove to be beneficial to alleviate concerns of bacterial transmission. 83 I1 0 6 -2- 3 25 I WS 3. -4 1
  5. 5. IV. References [1] Sano, E., Maeda, T., Nakamura, T., Shikai, M., Sakata, K., Matsushita, M., et al. (2006). Fingerprint authenticaton device based on optical characteristics inside a finger. In 2006 Conference on Computer Vision and Pattem Recognition (CVPRW06). [2] Elliott, S., Massie, S., and Sutton, M. (2007). Perspective of Biometric Technologies: A Survey. In Proceedings of IEEE Workshop on Automatic Identification Technologies, June 7 - 8 2007, (259-264). 31 Reynolds, K.A., Watt, P.M., Boone, S.A., & Gerba, C.P., (2005). Occurrence of bacteria and biochemical markers on public surfaces [Electronic version]. Intemational Journal of Environmental Health Research, 15(3), 225- 234. relate to biometric technologies, where he is responsible for the Biometrics Standards, Performance, & Assurance Laboratory as well as two classes related to biometric technologies. Dr. Elliott is also involved in educational initiatives for the American National Standards Institute, is a member of Purdue University's e-Enterprise, Learning and Center for Educational Research In Information Assurance Security (CERIAS) Centers. Dr. Thomas Walter is a Continuing Lecture in the Department of Biological Sciences at Purdue University. Dr. Walter is involved with teaching various microbiology and molecular biology lecture and laboratory courses at the undergraduate and graduate level. [4] Lee, C., Lee, S. and Kim, J.. (2006).A study of Touchless Fingerprint Recognition System. Republic of Korea: Yonsei University, Department of Electrical and Electronic Engineering. [5] Chan, S. (2007, January 23). Scanners for Tracking City Workers. New York Times, p. 1B. [6] McBrde, M., Duncan, W., and Knox J. (1977). The Environment and the Microbial Ecology of Human Skin. Applied and Environmental Microbiology, 33(3), 603-608. V. VITA Christy Blomeke is a member ofthe Biometrics, Standards, Performance, & Assurance Laboratory in the Department of Industrial Technology at Purdue University. She is currently pursuing a Ph.D. in Technology at Purdue University. Christy holds a Masters degree in Agricultural and Extension Education and a Bachelors degree in Biology with a specialization in Genetics. Christy's experience with biometric technologies has been in the area of animal biometrics. Dr. Stephen Elliott is an Associate Professor in the Department of Industrial Technology at Purdue University. Dr. Elliott is involved in a variety of activities relating to biometrics and security. He is actively involved in biometric standards, acting as Secretary on INCITS Ml Biometric Committee. Dr. Elliott has given numerous lectures on biometric technologies, the latest conference presentations being specifically aimed at the banking industry. Dr. Elliott is also involved in educational initatives as they 84

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