McFARLAND LATEX STANDARDS
|Cat. no. ML05||McFarland Latex Standard #0.5, 16x100mm Tube, 8ml||One tube/box|
|Cat. no. ML1||McFarland Latex Standard #1, 16x100mm Tube, 8ml||One tube/box|
|Cat. no. ML2||McFarland Latex Standard #2, 16x100mm Tube, 8ml||One tube/box|
|Cat. no. ML3||McFarland Latex Standard #3, 16x100mm Tube, 8ml||One tube/box|
|Cat. no. ML4||McFarland Latex Standard #4, 16x100mm Tube, 8ml||One tube/box|
|Cat. no. ML5||McFarland Latex Standard #5, 16x100mm Tube, 8ml||One tube/box|
|Cat. no. ML6||McFarland Latex Standard #6, 16x100mm Tube, 8ml||One tube/box|
|Cat. no. ML7||McFarland Latex Standard #7, 16x100mm Tube, 8ml||One tube/box|
|Cat. no. ML8||McFarland Latex Standard #8, 16x100mm Tube, 8ml||One tube/box|
McFarland Latex Standards are used as turbidity standards for adjusting densities of bacterial suspensions.
McFarland Standards provide a reference for standardization of bacterial suspensions used for susceptibility testing and other procedures that require a standardized inoculum. Original McFarland Standards were prepared by adding barium chloride to sulfuric acid resulting in a barium sulfate precipitation.(4) CLSI now accepts the use of latex particle suspension turbidity standards for the preparation of standardized bacterial suspensions.(8)
The McFarland Latex Standards (Cat. no. ML05-ML8) are prepared from suspensions of uniform latex particles with similar absorbance values as the original barium sulfate standards. The latex standards are prepared by suspending latex particles in a buffer solution. Sodium azide is added as a preservative. The standards are adjusted to an acceptable absorbance range with a one centimeter light path set at 625nm. Adjusting the bacterial suspension turbidity to a McFarland Standard produces bacterial counts in an expected range. As with the barium sulfate standards, a 0.5 McFarland Latex Standard is comparable to a bacterial suspension of 1.5 X 108 CFU/ml.
The stability of McFarland Latex Standards allows for a significantly longer shelf-life than the original barium sulfate standards due to reduced light sensitivity.
|Approximate Cell Density x 10 8 /ml||1.5||3||6||9||12||15||18||21||24|
|Absorbance Specification at 625nm (ABS)||0.08 to 0.10||0.14 to 0.17||
STORAGE AND SHELF LIFE
Storage: Upon receipt store at 2-30ºC. These products are ready for use and no further preparation is necessary. These products should be stored in their original container. Do not freeze or overheat. Do not incubate prior to use. Standards should not be used if there are any signs of deterioration, contamination, color change or if the expiration date has passed.
Specimen Collection: Not applicable since these standards are used for the standardization of inoculum for susceptibility testing. Isolation techniques and tests for purity are necessary. Information on specimen collection may be found in standard reference texts.
Method of Use:
1. Mix the standard to fully suspend the particles. Gently mix the McFarland Latex Standards (ML05-ML8) by inverting - Do not vortex the latex standards.
2. Adjust the turbidity of an actively growing broth culture or bacterial suspension of colonies selected from an 18-24 hour agar plate to obtain a turbidity visually comparable to that of the desired standard. The tubes for the suspension should be the same diameter as the McFarland Latex Standard tube.
3. For visual comparison, use adequate light and read the tubes against a white card with contrasting black lines (Wickerham Card, Cat. no. Z08).(3)
INTERPRETATION OF RESULTS
Equal obliteration or distortion of contrasting black lines on the white background indicates a turbidity match.
Do not use a mechanical mixer (vortex) with latex standards.
Broth media that is dark yellow, orange or brown will not provide the proper contrast with McFarland Latex Standards, possibly resulting in bacterial suspensions of incorrect densities. Trial comparisons should be performed.(5) Use adequate light and read the standard and test broth against a white card with contrasting black lines (Wickerham Card, Cat. no. Z08).(3)
The tubes for the suspension should be the same diameter as the McFarland Latex Standard tube.
Bacterial densities may be too heavy when colonies of Haemophilus influenzae < 24 hours old are used to prepare suspensions.(6)
McFarland Standards are recommended when performing visual comparisons or when using a spectrophotometer adjusted to the proper setting.(5,7) Use with instruments which use alternative light sources, such as scattered light, have not been established.
MATERIALS REQUIRED BUT NOT PROVIDED
Standard microbiological supplies and equipment such as loops, broth media, vortex mixer and Wickerham Card (Cat. no. Z08), etc., are not provided.
All lot numbers of McFarland Latex Standards are tested spectrophotometrically and have been found to be acceptable.
McFarland Latex Standards appear white with a bluish tinge.
McFarland Latex Standards
1. Versalovic, J., et al. Manual of Clinical Microbiology. American Society for Microbiology, Washington, D.C.
2. Tille, P., et al. Bailey and Scott's Diagnostic Microbiology, C.V. Mosby Company, St. Louis, MO.
3. Clinical and Laboratory Standards Institute (CLSI - formerly NCCLS). 2009. Performance Standards for Antimicrobial Disk Susceptibility Tests; Approved Standard - Tenth Edition. M02-A10. CLSI, Wayne, PA.
4. McFarland, J. 1907. Nephelometer: An Instrument for Estimating the Number of Bacteria in Suspension Used for Calculating the Opsonic Index for Vaccines. Journ. American Med. Assoc.;14: 1176-1178.
5. Perry, J.L. and G.R. Miller. 1992. Abstract, ASM.
6. Doern, G.V. and R.N. Jones. 1988. Antimicrobial Susceptibility Testing of Haemophilus influenzae, Branhamella catarrhalis and Neisseria gonorrhoeae. Antimicrob. Agents and Chemothr.; 32: 1747-1753.
7. Carlberg, D.M. Determining the Effect of Antibiotics on Bacterial Growth by Optical and Electrical Methods in Antibiotics in Laboratory Medicine, 2nd ed. V. Lorian, editor, Chapter 3, p. 64-92, Williams & Wilkins.
8. Clinical and Laboratory Standards Institute (CLSI - formerly NCCLS). Performance Standards for Antimicrobial Disk Susceptibility Tests, 10th ed., M02-03, Section 8.1. CLSI, Wayne, PA.