BACTERIAL SURVIVABILITY AND TRANSFERABILITYON BIOMETRIC DEVICES

Christine R. BlomekeResearcherBiometrics Standards,Performance, & AssuranceLaboratoryPurdue University401 N. Grant StreetWest Lafayette, IN 47906USA

Stephen J. ElliottAssociate ProfessorBiometric StandardsPerformance, & AssuranceLaboratoryPurdue University401 N. Grant StreetWest Lafayette, IN 47906USA

Thomas M. WalterContinuing LecturerDepartment. OfBiological Sciences

Purdue University915 W. State StreetWest Lafayette, IN 47906USA

Abstract - The purpose of this study was toinvestigate bacterial recovery and transfer from threebiometric sensors and the survivability of bacteria onthe devices. The modalities tested were fingerprint,hand geometry and hand vein recognition, all of whichrequire sensor contact with the hand or fingers tocollect the biometric. Each sensor was testedseparately with two species of bacteria,Staphylococcus aureus and Escherichia coli.Survivability was investigated by sterilizing the

sensor surface, applying a known volume of dilutedbacterial culture to the sensor and allowing it to dry.Bacteria were recovered at 5, 20, 40 and 60 minutesafter drying by touching the contaminated device witha sterile finger cot. The finger cot was re-suspendedin 5 mL of saline solution, and plated dilutions toobtain live cells counts from the bacterial recovery.The transferability of bacteria from each devicesurface was investigated by touching thecontaminated device and then touching a plate totransfer the bacteria to growth medium to obtain livecell counts. The time lapse between consecutivetouches was one minute, with the number of toucheswas n = 50. Again, S. aureus and E. coli were usedseparately as detection organisms. This paper willdescrbe the results of the study in terms of survivalcurves and transfer curves of each bacterial strain foreach device.

Index Terms - biometrics, hygiene, bacterialtransmission

1. IntroductionAs the concerns over infectious diseases grow, sodo the concems over the hygiene of surfaces in publicareas. This is of interest to the biometric communityas efforts are made to implement the use of biometrictechnologies in the public arena, specifically inairports, retail stores, and various financialinstitutions.The motivation to conduct the current study arises

from antidotal evidence from previous studying in theBiometrics Standards, Performance and AssuranceLaboratory. During previous studies, specifically with

fingerpfint and hand geometry, subjects would askquestons about the cleanliness of the sensor. Latentprints left on the platen glass of a device by thedeposition of finger moisture, sweat, or oils, can makeit appear to be unclean [1]. In 2006, s survey yieldedresponses about the perception of the cleanliness ofbiometric devices. Seventy-five percent of surveyedsubjects responded that they felt that biometricdevices were somewhat sanitary, neutral, orsomewhat unsanitary. This indicates that the subjectpopulation does not view biometric devices as beingoverwhelmingly sanitary nor unsanitary [2].In addition, the development of touchless sensors

has prompted the question whether or not bacteriaand other disease causing organisms are a potentialhazard that can be transferred from person to personthrough touching a common device. Studies haveshown that human pathogens can be transmittedbetween nonliving objects by direct hand contact [31.Contactless sensors eliminate the possibility of latentprints and decrease the hygiene concerns becausethe fingertip never comes into contact with the device[4. Although this lessens concems with thecleanliness of using common devices, there is a needto investigate whether using a common biometricdevice is any different that touching common surfacesin public areas. For instance, in many workplaces,individuals touch common items without a secondthought. Doorknobs, elevator buttons, pens on acountertop, are a few items that are touchedthroughout the day by various people. However,recent media attention regarding the implementationof biometric devices in the work place has cited thatemployees have concerns about the hygiene oftouching the devices, and has prompted theinstallation of hand sanitizer stations next to thebiometric devices [51.

It is important to note that the skin surface serves asthe habitat of a flora of microorganisms,predominately consisting of gram-positive bacteria.These are naturally occurring organisms living on theskin, and normally do not cause disease or infection.Temperature, humidity, and skin physiology all play arole in maintaining the skin microflora [6].

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Each bacterial species has a different infectivitylevel. As a result, different numbers of eachbacterium must enter the body for that particularspecies to cause an infection or disease. They canenter the body through the thin tissues in the eyes,nose, and mouth, or at injury sites where the skin isbroken.The literature focuses on studies conducted on thesurvivability of bacteria on non-porous inanimatesurfaces are limited to health care and domesticenvironments, but do not consider public surfaces.Thus, this paper examines bacterial survival andtransfer on biometric devices that could be used inpublic environments.

II. Methodology

The three biometric devices tested in this study werethe Recognition Systems HandKey Ill, CrossmatchVenfier 300 LC, and TechSphere VP-Il S. Eachdevice was tested separately with two strains ofbacteria. Each bacterial strain was testedindependently of the other. The test organismsutilized were Staphylococcus aureus and Escherichiacoli. The two organisms were common teachinglaboratory strains of bacteria that contain geneticmutations so not to cause infection, but were used astracer organisms. Staphylococcus aureus is arepresentafive of gram positive bacteria, and incontrast, Eschenchia coli represent gram negativespecies.

A. Survivability of Bacteria on a Biometric Device

The survivability of the bacteria on the device wasdetermined by contaminating each device with aknown concentration of bacteria and recoveringorganisms over a period of time. Just prior tocontamination, the device was sterilized with a 70percent ethanol solution and control samples werecollected. The control samples ensured that thesterilization was complete, and only bacteria on thedevice surface were the intentional contaminates.Sterile finger cots were worn over sterilized laboratorylatex gloves. This ensured that the inside of the fingercot remained sterile, and prevented the naturallyoccurring bacteria on the skin's surface from beingintroduced into the experiment.After the collection of the control samples, 50

microliters of the bacterial suspension were applied tothe device surface. The solution was allowed to dry.Bacteria were recovered by a single touch to thedevice surface with a sterile finger cot after five,twenty, forty and sixty minutes of dry time. The fingercots were resuspended in 5 milliliters of salinesolution. Systematic dilutions of the solution wereplated onto Tryptic Soy Agar (TSA) agar plates andallowed to grow for 24 hours at 37 degrees Celsius.Tryptic soy agar is a growth medium that contains allessential nutrents for bacterial growth. The colonygrowth on the plate allowed for the quantification of

the number of surviving cells recovered at each timepoint.

B. Transfer of Bacteria from Biometric Device

The transferability of bacteria over tme frombiometric devices was investigated by intentionallycontaminating the device surface with one species ofbacteria at a time. Prior to contamination, the devicesurface was sterilized with a 70 percent ethanolsolution. Sterilized gloves were worn, and thedevice surface was touched by a sterile finger, andthen touched to a TSA agar plate. The sterilizedsurface was touched ten times with a different sterileglove fingertip, and touched to the TSA agar plate asthe control samples. The agar plates were labeledto indicate the touch number, with an averagenumber of touches to a plate being 12, see Figure 1below. Bacterial colonies will only grow where theyhave been placed, and do not migrate over thesurface; therefore the touches to the plate were non-overlapping to ensure that the colonies could bequantified for each touch. Immediately pror to touch11 on the device, the device surface wascontaminated with one species of bacteria, andallowed to dry. The remaining 40 touches werecollected after contamination of the device. A sterileglove fingertip was used to collect each successivetouch to the device. Successive touches lasted for10 seconds were collected and plated at 20 secondintervals. Touches 20, 30, 40, and 50 were collectedwith a sterile fingercot worn over the sterile glove,and was placed into 5 milliliters of saline solution.Serial dilutions of the saline solution were plated andgrown over night to quantify the number of live cellsthat were recovered from touching the contaminateddevice.

Figure 1: Transferability collection of bacteria on theTechsphere VP-Il S Vein Reader.

111. Conclusions

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The survivals of S. aureus and E. coli over timewere measured by quantifying the number of cellsrecovered from the biometric devices over time.Below in Figure 2, the survival of S. aureus isgraphically represented in terms of the percentageof cells surviving over time for all three of thebiometric devices. At five minutes past the drytime, the survival of the bacteria on the devices haddecreased to 40 percent, 20 percent, and 15percent for the hand geometry reader, vein reader,and fingerprint sensor respectively. After 20minutes, the survival rate had approached zero forall three devices, yet even at 60 minutes a smallquantity of bacteria were still recoverable.

Survival of S. aureus

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0 5 10 15 20 25 30 35 40 45 50 55 60

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Figure 2: Survival of S. aureus, presented as thepercentage of survival over time in minutes.

In contrast to S. aureus, the survival of E. coli, thedrop off in survival rate is not nearly as steep in thefirst five minutes. The percent survival at five minutesis 50, 40, and 28 percent for the vein reader, handgeometry reader, and fingerprint reader respectively.Similar to the test with S. aureus, the survival rateapproached zero for all three devices at 20 minutesfor E. coli. Figure 3 depicts the survival curves over aone hour time period.

Survival of E. coli

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The results of the survivability experiment can bereported as a rate of the log of the survival. Thesurvival rate of the bacteria decreases over tme, andhence can be considered a death curve. Table 1illustrates the rate at which the survival decreasesover time by device and bacterial species.

TABLE 1RATE OF LOG SURVIVAL OF BACTERIA

BY DEVICES. aureus E. coi l

Hand Geometry0.904Reader T 09004 ----

Fingerprint 0.10Sensor ___ 0.14_T___I

Vein Recognition 0.14 0.05Device__ _ _ _ _ _ __ _ _ _ _ _

The result of this comparison between S. aureus andE. coli is that neither bacterial species survived for along time on the device surface. Bacteria generallyprefer warm, moist environments, but this study wasconducted room temperature with low humidity, in anopen-air environment, as would be implemented inmost public environments.

The result of the transfer of bacteria varies by thehardness of the device surface. As seen in Figure 4,the vein reader exhibits a more consistent level oftransfer throughout the time frame, as it plateaus offbefore either the hand geometry reader or thefingerprint sensor. The vein reader device surfacetested was the pliable plastic cup that is exposed tothe back of the hand. This is the largest surfacearea that makes contact with a person's hand. Thepliability of the surface being tested may haveallowed bacteria to work itself into the microcrevicesof the plastic surface, in which it could protect itself,and prolong the transfer to the gloved hand. Incontrast, the fingerprint sensor and the handgeometry 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 theconsecutive touches to the surface. The fingerprintsensor rapidly decreased the amount of cellstransferred with each successive touch. Essentially,the number of cells transferred over time decreases,as there are fewer cells on the surface to betransferred to the gloved hand and the agar plate.The hand geometry reader exhibited a similar curveto the fingerprint sensor, although not as extreme.

0 5 10 15 20 25 30 35 40 45 50 55 60

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Figure 3: Survival of E. coli, presented as thepercentage of survival over time in minutes.

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Figure 4: Transfer of S. aureus cells is presented asthe log of the percentage of the cellstransferred over the touch number.

Figure 5 represents the transfer curve for E. coli. Inaddition to testing the three biometric devices, a metaldoorknob was also tested using the same method.The doorknob and hand geometry reader exhibitedvery similar transferability from the surface to thegloved hand. The majority of the bacteria weretransferred from the surface for all four apparatuseswithin the first ten touches. It should be noted thatthe concentration of bacteria was not the same foreach device. The concentration of E. coli on thefingerprint sensor was less than the concentration onthe other three test surfaces. Therefore, there were asmaller number of bacteria to be transferred off thedevice sensor. However, the fingerprint sensor andthe vein reader followed the same general shape ofthe curve for transfer. Again, the pliable material thatwas tested on the vein reader may have influencedthe transfer rate by providing microcrevices wherebacteria could embed themselves, and therebytransferring fewer bacteria with each consecutivetouch to the surface.

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Figure 5: Transfer of E. coli is presented as the logof the percentage of the cells transferredover the touch number.

In summary, E. coli and S. aureus both exhibited asimilar survival curve that drops off drastically after20 minutes. E. coli did exhibit a slower death curvethan S. aureus within the first 20 minutes, but thedifferences were negligible after 20 minutes. Thetransfer curves for S. aureus and E. coli were verysimilar in terms of most of the bacteria beingtransferred off the device by touch 1 0.

This initial investigaton of the survivability andtransferability of bactera on biometric devicesbrings up several important points to remember, aswell providing new questions for further study.From the bacterial survival curves, it is understood

that these species could survive on an infrequentlytouched surface. However, a frequently touchedsurface, if contaminated, such as in the transferexperiments, is essentially cleaned within five to tentouches, as the bacteria are moved to the hand.As mentioned in the beginning of this paper, there

are naturally occurring bacteria on the hand. Theinfectivity of each bacterial species is different.Some species would require hundreds if notthousands of cells to be ingested, enter the bodythrough a cut in the skin, or mucus tissues for anysort of infection to occur. Likewise, if bacteria hadbeen deposited on the device surface by anindividual, most likely this would not be enough toinfect a subsequent person using the device. Theprotocol in this study required the bacteria to beplaced on the surface in liquid form and allowed todry. In the event that a device is contaminatedsimply by hand to surface contact, theconcentration of bactera on the surface would befar 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 washtheir hands with soap and warm water on a regularbasis. This will remove the majority of bacteriafrom the surface of the hand. However, thenaturally occurring bacteria on the hand will still beon the underlying layers of skin, and will rise to theepidermis when the oils, moisture, and sweat cometo the surface.Further work is necessary to investigate and

compare these results with results other species ofbacteria. In particular, it is important to take acloser look at species of bacteria that only require alow infectivity number, as this may be the mostimportant when regarding biosecurity measures.Additionally, other species of bactera that have ashort survivability in dry conditions should beexamined to determine how well they transfer.Additionally, further examination of the different

surface types, hard and soft, could prove to bebeneficial to alleviate concerns of bacterialtransmission.

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IV. References

[1] Sano, E., Maeda, T., Nakamura, T., Shikai,M., Sakata, K., Matsushita, M., et al. (2006).Fingerprint authenticaton device based onoptical characteristics inside a finger. In2006 Conference on Computer Vision andPattem Recognition (CVPRW06).

[2] Elliott, S., Massie, S., and Sutton, M. (2007).Perspective of Biometric Technologies: ASurvey. In Proceedings of IEEE Workshopon 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 bacteriaand biochemical markers on public surfaces[Electronic version]. Intemational Journal ofEnvironmental Health Research, 15(3), 225-234.

relate to biometric technologies, where he isresponsible for the Biometrics Standards,Performance, & Assurance Laboratory as well as twoclasses related to biometric technologies. Dr. Elliott isalso involved in educational initiatives for theAmerican National Standards Institute, is a member ofPurdue University's e-Enterprise, Learning andCenter for Educational Research In InformationAssurance Security (CERIAS) Centers.

Dr. Thomas Walter is a Continuing Lecture in theDepartment of Biological Sciences at PurdueUniversity. Dr. Walter is involved with teachingvarious microbiology and molecular biology lectureand laboratory courses at the undergraduate andgraduate level.

[4] Lee, C., Lee, S. and Kim, J.. (2006).A studyof Touchless Fingerprint RecognitionSystem. Republic of Korea: YonseiUniversity, Department of Electrical andElectronic Engineering.

[5] Chan, S. (2007, January 23). Scanners forTracking City Workers. New York Times, p.1B.

[6] McBrde, M., Duncan, W., and Knox J.(1977). The Environment and the MicrobialEcology of Human Skin. Applied andEnvironmental Microbiology, 33(3), 603-608.

V. VITA

Christy Blomeke is a member of the Biometrics,Standards, Performance, & Assurance Laboratory inthe Department of Industrial Technology at PurdueUniversity. She is currently pursuing a Ph.D. inTechnology at Purdue University. Christy holds aMasters degree in Agricultural and ExtensionEducation and a Bachelors degree in Biology with aspecialization in Genetics. Christy's experience withbiometric technologies has been in the area of animalbiometrics.

Dr. Stephen Elliott is an Associate Professor in theDepartment of Industrial Technology at PurdueUniversity. Dr. Elliott is involved in a variety ofactivities relating to biometrics and security. He isactively involved in biometric standards, acting asSecretary on INCITS Ml Biometric Committee. Dr.Elliott has given numerous lectures on biometrictechnologies, the latest conference presentationsbeing specifically aimed at the banking industry. Dr.Elliott is also involved in educational initatives as they

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