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Sporicidalactivityinliquidchemicalproductstosterilizeorhigh-leveldisinfectmedicalanddentalinstruments

ARTICLEinAMERICANJOURNALOFINFECTIONCONTROL·JULY2005

ImpactFactor:2.21·DOI:10.1016/j.ajic.2004.10.005·Source:PubMed

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EnriqueAcosta-Gío

UniversidadNacionalAutónomadeMéxico

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LeonorSanchez

MetropolitanAutonomousUniversity

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Sporicidal activity in liquid chemicalproducts to sterilize or high-leveldisinfect medical and dentalinstrumentsA. Enrique Acosta-Gıo, PhD,a Jose L. Rueda-Patino, IBQ,b and Leonor Sanchez-Perez, DOc

Mexico City and Ecatepec, Mexico

Background: Various liquid chemical products are commercially available in Mexico under sporicidal label claims. Frequently,information provided on their labels conflicts with published data on active ingredients, use concentrations, or exposure times.Objective: To evaluate sporicidal activity in 8 chemical products sold for the sterilization or high-level disinfection of medical anddental instruments.Methods: Bacillus atrophaeus ATCC 9372 spores were suspended (106 spores in 50 mL) in each of 4 glutaraldehyde solutions: asuper oxidized solution, a hydrogen peroxide formulation, a quaternary ammonium compound, and an ortho-phthalaldehydesolution. After up to a 10-hour exposure, the solutions were passed through 0.22-mm filters, which were then rinsed with 1%sodium bisulfite, washed, and incubated on tryptic soy agar for 5 days at 37�C.Results: At the use concentrations stipulated on their labels, only 2 of 6 products registered as sterilants showed sporicidal activitywhen challenged with 6 log10: a 2% glutaraldehyde in 10 hours and the hydrogen peroxide solution in 6 hours. Of 2 productsregistered as high-level disinfectants, only the ortho-phthalaldehyde showed noticeable sporicidal activity after 10-hour exposure.Conclusion: The results show that some chemical products, commercially available in Mexico as ‘‘Liquid Chemical Sterilants/High-Level Disinfectants’’ cannot be used reliably to process instruments between patients. (Am J Infect Control 2005;33:307-9.)

Heat sterilization of critical and semicritical instru-ments continues to be the safest and preferredmeans forinstrument processing between patients. Exceptionallyheat-sensitive instruments may be cold sterilized or, at aminimum, high-level disinfected by immersion in liquidchemical sterilants/high-level disinfectants (S/HLDs).1-3

However, in many countries a wide variety ofchemical products are sold with presumptive labelclaims for ‘‘sporicidal activity,’’ ‘‘sterilant,’’ or ‘‘fordisinfection of medical and dental instruments.’’ De-tailed analysis of the often limited informationprovided on active ingredients, use concentrations,and exposure time reveals discrepancies among the

From the Microbiology and Infection Control Laboratory, PostgraduateDivision, National University of Mexico, Dental School, Mexico Citya;Ecatepec’s Institute for Technologic Studies and Higher Education,Ecatepecb; and Clinical Science Research, Health Attention Depart-ment, Metropolitan Autonomous University, Xochimilco Unit, MexicoCity, Mexico.c

Reprint requests: Enrique Acosta-Gıo, PhD, Apdo. 70-421, CiudadUniversitaria, 04510 Mexico D.F. E-mail: acostag@servidor.unam.mx.

0196-6553/$30.00

Copyright ª 2005 by the Association for Professionals in InfectionControl and Epidemiology, Inc.

doi:10.1016/j.ajic.2004.10.005

label claims and the evidence accumulated in special-ized publications.2,4

Sporicidal potency tests demonstrate the potentialusefulness of a chemical product for sterilization orhigh-level disinfection (HLD) of instruments. In Europe,the standard NF T72-231 requires a 5 log10 reduction ofspores for approval of a product for HLD.5 For a liq-uid chemical sterilant, the US Food and Drug Admin-istration (FDA) standard tolerates no failures6 in theAssociation of Official Analytical Chemists (AOAC)Sporicidal Test7 and accepts no survivors in simu-lated-use testing with a challenge inoculum of 6 logs ofspores.6 The FDA defines HLDs as sterilants used underthe same contact conditions but for only the contacttime needed to reduceMycobacterium bovis in 6 log10.

6

The aim of this investigation was to evaluate thesporicidal activity, against 6 log10 spores, in 8 chemicalproducts sold for sterilization or high-level disinfectionof medical and dental instruments.

MATERIALS AND METHODS

Liquid chemical sterilants/high-leveldisinfectants

Eight chemical products registered in Mexico assporicidal solutions were evaluated. Information on

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308 Vol. 33 No. 5 Acosta-Gıo, Rueda-Patino, and Sanchez-Perez

Table 1. Sporicidal activity in products sold for sterilization or high-level disinfection of instruments

Information on respective labels

Product Active ingredient Use concentration

Recommended

contact time Label claim*

B atrophaeus growth, after 10-hour

exposurey

1 Glutaraldehyde 0.63% 1 h Sterilization 1

2 Glutaraldehyde 2.5% 1 h Sterilization 1

3 Glutaraldehyde 2% 10 h Sterilization 2

4 Glutaraldehyde 2% 10 h Sterilization 1

5 Super oxidized solution �80 ppm free chlorine 15 min Sterilization 1

6 Hydrogen peroxide 7.5% 6 h Sterilization 2

7 Benzalkonium chloride 0.048% 10 min High level disinfection 1

8 ortho-phthalaldehyde 0.55% 12 min High level disinfection 6

*For a sterilization claim, no survivors are tolerated in simulated use testing with a challenge inoculum of 106 spores. High-level disinfectants are expected to kill smaller numbers of

spores.yThe 7.5% hydrogen peroxide product was tested at 6 hours, as indicated on the label. All other products were challenged for 10 hours.

tests used for regulatory purposes was not available.According to their respective labels, the use concen-trations/immersion times to accomplish sterilizationwere as follows: Alkacyde 0.63% glutaraldehyde/1 hour(Alkapharm, Marly-le-Roi, France); Deconex 2.5% glu-taraldehyde/1 hour (Borer Chemie, Zuchwil, Switzer-land); Gafidex2%glutaraldehyde/10 hours (Altamirano,Mexico City, Mexico); Sterilex 2% glutaraldehyde/10hours (Petrocarbono, Mexico City, Mexico); Microcyn�80 ppm free chlorine/15 minutes (Oculus, Morelia,Mexico); Sporox 7.5% hydrogen peroxide/6 hours(Sultan Chemists, Englewood, NJ). Two products areoffered as HLDs without sterilization claims; Bactium0.048% benzalkonium chloride/10 minutes (Prode-quim, Mexico City, Mexico); Cidex-OPA 0.55% ortho-phthalaldehyde/12 minutes (Advanced SterilizationProducts, Irvine, CA).

The sealed product samples were voluntarily pro-vided by the manufacturers or their distributors toMexico City’s Health Authorities (Secretarıa de Saluddel Distrito Federal). Products requiring activation ordilution were prepared immediately before evaluationfollowing the indications on their respective labels,using distilled, deionized sterile water.

Sporicidal activity

The potency test for each product was done intriplicate at the use concentrations stipulated on theirrespective labels against 106 Bacillus atrophaeus sporesATCC 9372 (SPS Medical, Rush, NY) as described byCollins.8 Following strict aseptic technique, the sporeswere suspended in the chemical product to be evalu-ated (20 spores 3 mL) and maintained at roomtemperature. When the exposure time was completed(either 10 or 6 hours), the suspension was placed in afiltration funnel (Millipore, Bedford, MA), and thechemical product was removed by suction through a

0.22-mm polyvinylidene filter (Millipore). The filtersand any spores retained on the membrane were rinsedwith 100 mL 1% sodium bisulfite (Sigma Chemicals, St.Louis, MO) and washed with 200 mL sterile distilledwater. To culture the surviving spores, we placed thefilters face down onto tryptic soy agar (DIFCO; BectonDickinson, Franklin Lakes, NJ) and incubated them for5 days at 37�C. Viable spores suspended in distilledwater served as a positive control. Survival and growthof B atrophaeus was confirmed by colony morphologyand light microscopy on stained smears.

RESULTS

At the use concentrations stipulated on their labels,only 2 of 6 presumptive sterilants showed sporicidalactivity against 6 log10 spores of Bacillus atrophaeus(no growth; Table 1). One of the 2% glutaraldehydesolutions in 10 hours and the hydrogen peroxidesolution in 6 hours, as stated on their labels. Of 2products labeled as HLDs, only the ortho-phthalalde-hyde showed noticeable sporicidal activity after 10-hour exposure.

DISCUSSION

S/HLDs are the same sporicidal chemicals used atdifferent contact times.6 In simulated-use testing, attheir respective recommended contact times, sterilantsmust eliminate 6 logs of bacterial spores, whereasHLDs are expected to kill smaller numbers of spores.

We used an adaptation of Collin’s suspension test.8

Using a membrane filter avoids false-negative results(absence of growth) caused by the loss of viable spores.Rinsing the membranes is critical to avoid the possiblepersistence of disinfectant activity on the spores, whichmay cause false-negative results that will wrongly beinterpreted as sporicidal activity. Some products, other

Acosta-Gıo, Rueda-Patino, and Sanchez-Perez June 2005 309

than glutaraldehyde, may have not been optimallyinactivated by sodium bisulfite and still showed little orno sporicidal activity, even in the absence of organicand inorganic contamination.

The results of this study are consistent with reportsindicating that 7.5% hydrogen peroxide for 6 hoursand glutaraldehyde $2% for 10 hours are able to kill6 log10 bacterial spores.

9 The hydrogen peroxide-basedsterilant evaluated is FDA cleared for interstate com-merce in the United States. Of the 4 glutaraldehydeformulations evaluated (none of them FDA cleared), 3failed to destroy 6 log10 spores in 10 hours at theirrecommended use concentrations.

The super oxidation solution evaluated showedsporicidal activity but did not kill 106 spores in 10hours. No electrochemical solution has been FDAcleared as a sterilant. Apparently, not all super oxida-tion solutions are equally effective10; these productsmust be used freshly generated on rigorously pre-cleaned instruments11 because their activity is reducedby organic contamination.12 There are reports on thenosocomial contamination of super oxidation solu-tions with mycobacteria.13

The ortho-phthalaldehyde evaluated is a FDA-cleared, high-level disinfectant without a sterilizationclaim. Benzalkonium chloride (n-alkyl dimethyl benzylammonium chloride) is a low-level disinfectant notdocumented to be sporicidal.4,14

Health care workers in the United States must useFDA-cleared products (list available at www.fda.gov/cdrh/ode/germlab.html). During humanitarian mis-sions abroad, they may also want to carry theseproducts, if not locally available.

The international infection control community mustbe aware that many nations need scientifically soundstandards for the registration, sale, and use of disin-fectants. In particular, more stringent, evidence-basedvalidation for S/HLDs used on medical and dental in-struments must be introduced and enforced to avoid themarketing of ineffective products that may endangerhuman lives.

The authors thank the Director General for Medical Supplies, Mexico City’s Ministryof Health, for providing them with samples of the chemical products.

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