Inoculum preparation Table 1. Recommended media, inoculum and To obtain reproducible MICs from a gradient based Use the inoculum guide in TABLE 1. Emulsify several incubation1). system, the stability of the gradient must be maintai- well-isolated colonies from an overnight in lêÖ~åáëã= ^Ö~ê= fåçÅìäìã fåÅìÄ~íáçå ned throughout the critical period when the position a suitable suspension medium to achieve the specifi ed Öêçìé ãÉÇá~ of the growth/inhibition edge for a particular bac- inoculum turbidity by comparing to a McFarland pìëéÉåëáçå qìêÄáÇáíó= qÉãéÉê~íìêÉ= ^íãçëéÜÉêÉ qáãÉ= Antimicrobial Susceptibility Testing terium/ combination is determined. Due turbidity standard. For fastidious organisms such as EjÅc~êä~åÇF Eœ=O=ø`F EÜçìêëF For In Vitro Diagnostic Use to the stability and precision of the Etest predefi ned pneumococci, streptococci, gonococci, anaerobes and gradient, MIC values have been shown to be repro- Haemophilus spp., use the suspension prepared in INTENDED USE ducible and equivalent to those of the CLSI reference broth within 15 minutes. ^ÉêçÄÉë jìÉääÉê= MKURB=k~`ä MKR======PR=ø` ~ãÄáÉåí NSJOM Etest is a quantitative technique for determining dilution procedures. eáåíçå EN=áÑ=ãìÅçáÇF the antimicrobial susceptibility of Gram negative Inoculation and Gram positive aerobic such as En- REAGENTS Soak a sterile, non-toxic swab in the inoculum terobacteriaceae, , and Etest is supplied in a package of 100 or 30 (some suspension and remove excess fl uid by pressing it lop^L=lopb jìÉääÉê= MKURB=k~`ä MKR PR=ø` ~ãÄáÉåí OQ=lop^==== species and fastidious bacteria, such as reagents) test strips of one antimicrobial agent. against the inside wall of the test tube. Remove more anaerobes, N. gonorrhoeae, S. pneumoniae, Streptococ- eáåíçå=H=OB= QU=lopb fl uid when a 90 mm plate and less for a k~`ä cus and Haemophilus species. Th e system comprises STORAGE 150 mm plate. Carefully streak the entire agar surface a predefi ned antibiotic gradient which is used to All packages must be stored either at controlled room three times, rotating the plate 60 degrees each time determine the Minimum Inhibitory Concentration temperature (18-22 °C), in a refrigerator to evenly distribute the inoculum. Alternatively, use ^å~ÉêçÄÉë _êìÅÉää~= _êìÅÉää~=çê= N PR=ø` UMJURB= OQJQUJTO= (MIC), in μg/mL, of diff erent antimicrobial agents (4-8 °C) or freezer (-18- -22 °C) as specifi ed on the Retro C80 (rota-plater) to effi ciently streak the ino- _äççÇ jìÉääÉê= kOLRJNMB= ÇÉéÉåÇáåÖ= against microorganisms as tested on agar media using product label, until the given expiry date. culum over the agar surface. Allow excess moisture eáåíçå=ÄêçíÜ çå=íÜÉ= overnight incubation. `lOLNMB=eO to be absorbed for approximately 15 to 20 minutes ëéÉÅáÉë Etest gradient strips left over from an opened package so that the surface is completely dry before applying SUMMARY AND EXPLANATION must be kept dry. Th e opened package should be the Etest gradient strips. e~ÉãçéÜáäìë= eqj jìÉääÉê= MKR======PR=ø` RB=`lO OMJOQ Current Antimicrobial Susceptibility Testing (AST) either re-sealed with a sealing clamp or placed in áåÑäìÉåò~É eáåíçå=çê= EN=áÑ=ãìÅçáÇF methods are based either on quantitative dilution an airtight storage container with colour indicating Notes: eqj=ÄêçíÜ techniques or qualitative diff usion procedures. Dilu- desiccant, and stored at the temperature stated on 1. When the inoculum and inoculation are optimal, tion methods are based on two-fold serial dilutions the label or at -20 °C. Left-over strips in storage con- an even confl uent growth will be obtained. jìÉääÉê= jìÉääÉê= MKR======PR=ø` RB=`l OMJOQ of in broth or agar media. Th ese methods tainers can be used until the expiry date if correctly 2. McFarland turbidity standards do not guarantee píêÉéíçÅçÅÅìë= O generate the MIC value i.e. Minimum Inhibitory stored and handled. Ensure that the batch number correct number of viable cells in the suspension. éåÉìãçåá~É= eáåíçå=H=RB= eáåíçå=ÄêçíÜ EN=áÑ=ãìÅçáÇF Concentration of a given antibiotic in μg/mL that and expiry date are marked on the storage container. Perform colony counts regularly to verify that the ~åÇ= ëÜÉÉé=ÄäççÇ will inhibit the growth of a particular bacterium inoculum procedure gives the correct number of píêÉéíçÅçÅÅá=OF under defi ned experimental conditions. Prevent moisture from penetrating into or forming viable cells in CFU/mL. Please refer to the QUA- kÉáëëÉêá~= d`J~Ö~ê= jìÉääÉê= MKR PR=ø` RB=`l OMJOQ within the package or storage container. Etest strips LITY CONTROL section. O Th e MIC value is not an exact entity and the “true” must be kept dry. ÖçåçêêÜçÉ~É Ä~ëÉ=H= eáåíçå=ÄêçíÜ MIC is between the lowest concentration that Application ÇÉÑáåÉÇ= inhibits the organism’s growth and the next lower HANDLING Check that the inoculated agar surface is completely ëìééäÉãÉåíë concentration. Even under the best of controlled Before using the Etest gradient strips from an unope- dry before applying Etest gradient strips. conditions, a dilution test may not give the same ned package, visually inspect to ensure the package Open the package and handle the Etest strips as de- Notes: endpoint each time it is performed. Th e reproduci- is intact. Do not use the Etest gradient strips if the scribed under HANDLING. A template can be used 1. Please consult Etest Technical Manual for further highest value on the MIC scale. When the inhi- bility of the conventional dilution test is within ± 1 package has been damaged. to optimally position Etest strips in an equidistant information on specifi c applications. bition ellipse is below the strip (does not intersect two-fold dilution of the endpoint. Th e MIC value pattern on an agar plate. Four to six (maximum) 2. Includes ß-haemolytic Streptococci groups A, B, the strip), report the MIC < the lowest value on obtained from a standardised CLSI procedure can be Allow the original package or storage container to Etest strips can be placed on a 150 mm agar plate C and G and viridans group S. mutans, S. mitis, S. the MIC scale. regarded as the reference criterium for defi ning the reach room temperature before opening (+4 °C/ (Figure 2a). For single MICs, one or two strips can sanguis and S .bovis. • Organisms such as staphylococci, Acinetobacter susceptibility of a microorganism. approx. 30 minutes, -20 °C/ approx. 60 minutes). be used on a 90 mm agar plate (Figure 2b). Strip 3. Use well defi ned and high quality medium that spp., anaerobes and gonococci may be susceptible Ensure that moisture condensing on the outer placement is automatically optimised when using supports good growth. Th e brand chosen should to sulbactam, tazobactam or clavulanic acid per PRINCIPLES OF USE surface has evaporated completely before opening the Simplex C76 (Figure 6). For organisms expected to have good batch-to-batch reproducibility to se. For Etest PTc and TLc, this may result in an Th e Etest gradient technology is based on a com- package. Packages stored at room temperature can be be highly susceptible, use fewer strips per 150 mm ensure that accurate and reliable MIC values are inhibition ellipse with an extended parallel band bination of the concepts of dilution and diff usion used immediately. plate and only one on a 90 mm plate. obtained. of inhibition alongside the strip. Extrapolate the principles for susceptibility testing. As with other 4. For trimethoprim and trimethoprim/sulfamet- upper elliptical curvature towards the strip to ob- dilution methods, Etest directly quantifi es antimicro- Open the package by carefully cutting off the top hoxazole, ensure that the brand and batch of agar tain the MIC (consult ETEST READING GUIDE, bial susceptibility in terms of discrete MIC values. of one blister compartment, or across the top of the has a low thymine/thymidine content to minimise Figure 9). However, in using a predefi ned, stable and conti- foil pouch. When handling Etest strips manually, antagonism of the activity of trimethoprim and • If inhibition ellipses for clindamycin, erythromy- nuous antibiotic concentration gradient, Etest MIC grip only the handle of the strip i.e. the area labelled sulphonamides. cin or chloramphenicol "dip" at the endpoint, values can be more precise and reproducible than E. Do not touch the surface of the strip with the 5. Th e inherent calcium content in Mueller Hinton extrapolate the MIC at the initial indentation, i.e. results obtained from conventional procedures based antibiotic gradient, i.e. the side opposite the MIC agar may vary between brands and batch to batch. 0.5-1 dilution above the intersection. on discontinuous two-fold serial dilutions. scale (Figure 1, B). Strips can be placed in an Etest Perform quality control of agar plates on a batch • For fosfomycin showing numerous (>5 ) macro- applicator tray until ready to use (Figure 3). Th e to batch basis to qualify it for use, particularly for colonies in the inhibition ellipse, read the MIC at Although processed like the disc diff usion test, i.e. vacuum pen Nema C88™ (AB BIODISK) can be Figure 2a. Template for 6 Figure 2b. Template for 2 testing of daptomcyin. complete inhibition. A few (< 5) colonies can be similar inoculum preparation, choice of agar media used to effi ciently apply Etest strips either from the strips per 150 mm plate. strips per 90 mm plate. 6. Ensure that an effi cient anaerobic system is used ignored. When zone edges are hazy, read the MIC and incubation conditions, Etest is not a diff usion applicator tray or the original foam cartridge (Figure to achieve rapid anaerobiosis to avoid false resis- at 80% inhibition. method and diff ers totally in concept from conven- 4). Th e foam cartridges carrying the Etest strips tant results with metronidazole. • For quinupristin/dalfopristin and linezolid, hazy tional disc methods. Th e Etest antimicrobial concen- Etest strips can be applied to the inoculated agar should be directly loaded onto the automatic applica- surface with forceps, a manual applicator, Nema 7. Ensure the agar plate is incubated for the recom- and trailing growth for staphylococci and entero- tration gradient is preformed, predefi ned and stable, tor instrument Simplex C76™ (AB BIODISK). mended period before reading, especially for cocci should be read 90% inhibition as judged by and is not dependent on diff usion. C88 (Figure 5) or Simplex C76 (Figure 6). Position the Etest gradient strip with the MIC scale facing delayed expression of resistance and slow growing the naked eye. Read isolated macrocolonies in the PRECAUTIONS AND WARNINGS upwards (towards the opening of the plate) and the and fastidious organisms. inhibition ellipse at complete inhibition. Etest is a thin, inert and non-porous plastic strip. • Etest is intended for in vitro diagnostic use only. • Vancomycin inhibition ellipses can be slim. Read One side of the strip (A) carries the MIC reading concentration maximum nearest the rim of the plate • Although based on a simple procedure, Etest (Figure 2a). INTERPRETATION OF RESULTS the actual intersection at the strip and not growth scale in μg/mL and a two or three-letter code on the should only be used by trained personnel. Reading the MIC "hugging" the side of the strip. handle to designate the identity of the antibiotic. A • Etest should be used strictly according to the After the required incubation period (Table 1), predefi ned exponential gradient of antibiotic, dried procedures described herein. and only when an even lawn of growth is distinctly Interpretation and stabilised, is immobilised on the other surface • Aseptic procedures and precautions against visible, read the MIC value where the edge of the MIC breakpoints for defi ning interpretive categories of the strip (B) with the concentration maximum at microbiological hazards should be used when inhibition ellipse intersects the side of the strip. Do as published by the CLSI, USA and/or your national a, and the minimum at b (Figure 1). Th e gradient handling bacterial specimens. not read the plate if the culture appears mixed or if reference group may be used for interpreting Etest covers a continuous concentration range across 15 the lawn of growth is too light or too heavy; repeat MIC values. two-fold dilutions of a conventional MIC method. PROCEDURES the test. Materials provided Being a fully quantitative MIC method, Etest enables A B • 100 or 30 Etest strips of one antibiotic Figure 3. Picking up a Figure 4. Etest strips can Etest MIC endpoints are usually clear-cut although the laboratory to report the exact MIC value together • 1 package insert gradient strip from the tray be used directly from the diff erent growth/inhibition patterns may be seen. with the interpretive category. Etest generates MIC Antibiotic using a manual applicator cartridge with Nema C88 Please consult the guidelines below and illustrations values from a continuous scale and can give results code a • 1 desiccant capsule 256 • Table 2 (separate enclosure) in the ETEST READING GUIDE (Figures 1 to 20 in-between conventional two-fold dilutions i.e. half 192 128 (next page). dilutions. An Etest MIC value which falls between 96 64 Materials required but not provided standard two-fold dilutions must be rounded up to 48 32 IMPORTANT READING OBSERVATIONS the next upper two-fold value before categorisation. 24 • Agar plates (90 mm or 150 mm) with the appro- 16 12 priate susceptibility test media (Table 1) • For bactericidal drugs e.g. ß-lactams, always read 8 the MIC at the point of complete inhibition of Example: Benzylpenicillin MIC (μg/mL) breakpoints MIC Reading 6 Exponential • Inoculum suspension media (Table 1) 4 scale 3 antimicrobial • Swabs (sterile, non-toxic and not too tightly all growth, including hazes, microcolonies and for Streptococcus pneumoniae are: 2 (μg/mL) 1.5 gradient spun), test tubes, and scissors isolated colonies. Tilt the plate and/ or use a S I R 1.0 .75 • Forceps, Etest manual applicator or Biotools™ magnifying glass to carefully examine endpoints, ≤ 0.06 0.12-1 ≥ 2 .50 .38 (Retro C80™, Nema C88, Simplex C76) Figure 5. Applying the Figure 6. Simplex C76 auto- especially for pneumococci, streptococci, entero- .25 gradient strip to the agar .19 • McFarland 0.5 and 1 turbidity standards matic applicator cocci, fusobacteria, Acinetobacter and Stenotrop- An Etest MIC of 1 μg/mL is reported as interme- .125 surface using Nema C88 .094 diate (I) while 1.5 is rounded up to 2 μg/mL and the .064 • (35 ± 2 °C), anaerobic jar or chamber homonas spp. .047 category reported as resistant (R). .032 or CO2 enriched chamber (Table 1) Ensure that the whole strip is in complete contact • For bacteriostatic drugs e.g. trimethoprim/sul- .023 .016 b • Quality control organisms with the agar surface. Do not place the strip upside famethoxazole, read trailing endpoints at 80% • Storage containers with colour indicating desic- down as no inhibition ellipse will form since the inhibition, i.e. the fi rst point of signifi cant MIC results for a quality control (QC) strain that fall Figure 1: Etest gradient configuration cant capsules, or pouches and/or sealing clamps antibiotic will not diff use across the non-porous inhibition as judged by the naked eye. a half dilution below the lower QC limit should be • Additional technical information from plastic strip. If air pockets are seen under the strip, • Excessively wet plates prior to inoculation, rounded up to the next upper two-fold value before When an Etest gradient strip is applied to an ino- www.abbiodisk.com/ Etest Technical Manual remove them by pressing gently on the strip (with- insuffi cient drying before applying strips and/or establishing QC compliance. Similarly, MIC results culated agar surface, there is immediate and eff ective out moving it) with the applicator tip or forceps, unevenly streaked surfaces may give non-confl u- that are a half dilution above the upper limit show transfer of the preformed antibiotic gradient on the Agar Medium working from the lowest concentration upwards. ent growth, jagged ellipse edges and uneven MIC non-QC compliance. plastic carrier surface into the agar matrix. A stable, Ensure that the agar plate has a depth of 4.0 ± 0.5 Small bubbles will not aff ect results. Once applied, intersections. Repeat the test if MIC endpoints continuous and exponential gradient of antibiotic mm, pH 7.3 ± 0.1 and fulfi ls quality specifi cations. the strip cannot be moved because of instantaneous are diffi cult to read. QUALITY CONTROL concentrations is formed directly underneath the Th e medium and supplements will depend on the release of antibiotic into the agar. • When macrocolonies are present within the To check the performance of Etest reagents, quality strip. After incubation, whereby bacterial growth organism groups being tested (Table 1). Additional ellipse for bactericidal agents, read all macrocolo- of media, inoculum and procedure used, test app- becomes visible, a symmetrical inhibition ellipse technical information on media can be obtained Incubation nies within 1-3 mm from the strip (consult ETEST ropriate quality control strains as outlined under centred along the strip is seen. Th e MIC value is read from www.abbiodisk.com. Incubate the agar plates in an inverted position READING GUIDE, Figure 15). PROCEDURE. Th e reagents and test procedure are from the scale in terms of μg/mL where the ellipse (lid down) in stacks no higher than 5, according to • When growth occurs along the entire strip i.e. no considered satisfactory if MIC values obtained fall edge intersects the strip. conditions outlined in TABLE 1. inhibition ellipse is seen, report the MIC as ≥ the within the quality control specifi cations provided (TABLE 2, separate enclosure). Chemotherapy. ETEST READING GUIDE 4. Jorgensen, J. H. et al. (1994). Detection of WARRANTY AND Do not report patient results when quality control penicillin and extended spectrum cephalosporin ORGANISM RELATED EFFECTS results are outside the stated QC ranges. Frequency resistance among S. pneumoniae clinical isolates DISCLAIMER of quality control testing should be established by using Etest. Journal of Clinical Microbiology EXPRESS LIMITED WARRANTY AND the individual laboratory. Guidelines are provided in 5. Citron D. M. et al. (1991). Evaluation of Etest DISCLAIMER CLSI Antimicrobial Susceptibility Testing documents for susceptibility testing of anaerobic bacteria. Journal of Clinical Microbiology . M7, M11 and M100 series. AB BIODISK expressly warrants that 6. Sanchez M. et al. (1993). Etest, an antimicrobial Etest quality control ranges may not be identical to susceptibility testing method with broad clinical Etest will determine the MIC of the CLSI specifi cations in all cases. Etest QC ranges are and epidemiological application. Th e Antimicro- X antimicrobial agent on each test strip, if based on extensive data generated from QC testing of bic Newsletter. the procedures, precautions and limitations a large number of reagent lots over several years and 7. Schulz J. E. et al. (1993). Reliability of the Etest X indicated in this package insert are strictly include data from multi-site studies. Consult TABLE for detection of ampicillin, vancomycin, and complied with. If the test strip does not do 2 for QC specifi cations. high-level aminoglycoside resistance in Enterococ- so, AB BIODISK shall refund the cost of cus spp. Journal of Clinical Microbiology. X the product or replace the defective test Perform regular colony counts to verify the density 8. Baker C. N. et al. (1994). Optimizing testing of Figure 1. Ignore swarming. Figure 2. Ignore haemolysis; Figure 3. Tilt plate or use Figure 4. Scrutinise ß-lactam strips. of the inoculum suspension in terms of CFU/mL methicillin resistant Staphylococcus spp. Diagnostic MIC 0.064 μg/mL read the inhibition of growth. a magnifying glass to see endpoints for pneumococci for of viable cells. For example, dilute the inoculum Microbiology and Infectious Disease. MIC 0.032 μg/mL. pin-point colonies and hazes, hazes and microcolonies. suspension 1:1000 and subculture 1 μL onto the re- 9. Tenover F. C. et al. (1996). Evaluation of com- e.g. enterococci, pneumococci, MIC 2 μg/mL. AB BIODISK makes no other fusobacteria, and Stenotropho- warranties, expressed or implied, commended agar (Table 1). An acceptable inoculum mercial methods for determining antimicrobial monas spp. MIC 1 μg/mL. should give approximately 100 to 500 colonies, i.e. 1 susceptibility of S. pneumoniae. Journal of Clinical including the implied warranty to 5 x 108 CFU/mL. Microbiology. DRUG RELATED EFFECTS of merchantability or fitness for 10. Rosenblatt J. E. et al. (1995). Evaluation of the particular purpose. McFarland turbidity standards do not guarantee the Etest for susceptibility testing of anaerobic bacte- correct number of viable cells in CFU/mL. ria. and Infectious Disease. Any change or modification of the product EXPECTED VALUES Note: instructions may affect results. AB BIODISK Antibiotic susceptibility levels for diff erent biological Extensive Etest references based on peer reviewed shall not be liable for any damages populations of bacteria are no longer predictable due literature are available from PubMed (internet). resulting from product tampering, variance to progressive development of resistance. Th us, the in transportation, stated storage, handling, laboratory should use the expected MIC values of BIBLIOGRAPHY testing procedures, precautions and other the diff erent antibiotics for the quality control strains 1. FDA Draft, Review Criteria for Assessment of instructions of the most recently revised to ensure that testing procedures are satisfactory and Antimicrobial Susceptibility Testing Devices. that clinical results obtained are reasonably accurate. Food and Drug Administration, Division of version of the package insert. Clinical Laboratory Devices, May 1991, revised PERFORMANCE CHARACTERISTICS February 2003. Etest® and the Etest gradient strip are Etest performance characteristics for diff erent anti- 2. Lorian, V. Antibiotics in Laboratory Medicine. 5th Figure 5. Bactericidal agents Figure 6. Bactericidal agents; Figure 7. Bacteriostatic agents; Figure 8. Linezolid; read at registered trademarks of AB BIODISK. biotic/organism groups have been established using Ed. 2005. Williams & Wilkins, USA. give sharp MIC endpoints. read at complete inhibition of read at 80% inhibition. 90% inhibition (ignore finer Simplex C76™ is a pending trademark comparative evaluations at external clinical sites and 3. Murray, P.R. et al. Manual of Clinical Microbio- MIC 0.064 μg/mL. hazes and microcolonies. MIC 1.5 μg/mL. hazes and pinpoint colonies). MIC 1.5 μg/mL. MIC 0.75 μg/mL. and the instrument and the foam cartridge in-house testing. Th ese studies have shown that Etest logy. 9th Ed. 2001. ASM Press. carrying Etest are patented products of AB MICs correlate with the CLSI reference agar dilution 4. CLSI, 2006. Methods for dilution antimicrobial BIODISK. and/or broth microdilution method, depending on susceptibility tests for bacteria that grow aerobically. Biotools™, Retro C80™ and Nema C88™ the organism tested. Etest is considered to be in es- Approved Standard, M7-A7. are pending trademarks of AB BIODISK. sential agreement (EA) with the CLSI method when 5. CLSI, 2007. Methods for dilution antimicrobial MIC values from both procedures show an EA of ≥ susceptibility tests of anaerobic bacteria. Approved 90% within ±1 dilution. Standard, M11-A7. Product specifi cations, performance characteristics 6. CLSI Performance standards for antimicrobial (organism groups cleared for clinical use), inter- susceptibility testing. M100 latest series. pretive criteria, quality control specifi cations, and limitations are provided in TABLE 2.

Th e Etest reference database comprises more than 3000 scientifi c references that have demonstrated substantial equivalence between Etest and reference MIC dilution methods for a wide variety of organism groups.

IMPORTANT OBSERVATIONS Figure 9. ß-lactamase inhibitors Figure 10. Trim/sulfa; read at Figure 11. Tigecycline; read at Figure 12. Polypeptides; read 1. Indications for use (performance data) for various e.g. tazobactam; extrapolate 80% inhibition (ignore lawn 80% inhibition (ignore trailing at the bottom of the ”dip” if the upper curvature to the strip. of haze within the ellipse). microcolonies or hazes). colonies are absent. organism groups according to the specifi ed MIC 3 μg/mL. Stenotrophomonas spp. MIC 0.25 μg/mL. MIC 0.38 μg/mL. recommendations are shown in TABLE 2. MIC 0.19 μg/mL. 2. Occasionally, certain antibiotic/bacterium com- binations may give unusual results. In these cases, Antimicrobial Susceptibility Testing judgement of the MIC endpoint may be diffi cult RESISTANCE MECHANISM RELATED EFFECTS For In Vitro Diagnostic Use for inexperienced personnel. However, individuals © Copyright AB BIODISK 2007-07 (75001964-MH0277) can be trained through regular use of quality con- trol strains, Etest reading guides and comparisons with experienced personnel to correctly assess MIC endpoints. 3. Being agar based, Etest has been shown to cor- 256 relate best with the reference agar dilution. Corre- 192 128 lations have been shown with the reference broth 96 64 microdilution whenever an agar dilution reference 48 32 is absent. 24 16 4. As with all AST data, Etest results are in vitro 12 8 values only and may provide an indication of the 6 4 organism’s potential in vivo susceptibility. Th e use X 3 2 of results to guide therapy selection must be the 1.5 1.0 sole decision and responsibility of the attending Figure 13. Small colony vari- Figure 14. Isolated colonies Figure 15. Isolated colonies for Figure 16. Trailing growth (ha- .75 .50 physician who should base judgement on the ants and bactericidal agents; for oxacillin represent hetero- carbapenems may represent zes, microcolonies, macroco- .38 read at complete inhibition. resistant subpopulations i.e. resistant subpopulations e.g. lonies) represent VISA/hVISA. .25 particular medical history and knowledge of the .19 MIC 32 μg/mL. ORSA. MIC 48 μg/mL. KPC. MIC 8 μg/mL. MIC 8 μg/mL. .125 .094 patient, pharmacokinetics/pharmacodynamics of .064 .047 the antibiotic and clinical experience in treating .032 .023 infections caused by the particular bacterial TECHNICAL AND HANDLING EFFECTS .016 pathogen with the antibiotic, dose and dosing regimen being considered. 5. For details of specifi c interpretive limitations and/ or limitations on the clinical use of an antibiotic in various therapeutic situations, please refer to the tables and footnotes of MIC interpretive standards in the latest CLSI AST documents for dilution procedures (M7, M11 and M100 series).

REFERENCES 1. Bolmström, A. et al. (1988). A Novel Techni- que for Direct Quantifi cation of Antimicrobial Susceptibility of Microorganisms. ICAAC, poster 1209. Manufacturer 2. Baker, C. N. et al. (1991). Comparison of the Figure 17. Intersection in- Figure 18. Uneven intersec- Figure 19. Ignore a thin line of Figure 20. Complete growth AB BIODISK Etest to Agar Dilution, Broth Microdilution, and between markings, read the tions; read the higher value. If growth alongside the strip. around the whole strip edge. Dalvägen 10 upper value. MIC 0.19 μg/mL. >1 dilution, repeat the test. MIC 0.25 μg/mL. MIC ≥ 256 μg/mL. 169 56 Solna, Sweden Agar Diff usion Susceptibility Testing Techniques MIC 0.5 μg/mL. Tel. +46-(0)8-730 07 60 by Using a Special Challenge Set of Bacteria. Fax. +46-(0)8-83 81 58 Journal of Clinical Microbiology. [email protected] 3. Brown, D. F. J. and Brown, L. (1991). Evalua- www.abbiodisk.com tion of the Etest, a novel method of quantifying antimicrobial activity. Journal of Antimicrobial