As with standard diffusion methods, dilution procedures require the use of laboratory control organisms. Standard cephalothin powder should give MIC values in the range of 0.12 µg/mL and 0.5 µg/mL for Staphylococcus aureus ATCC 29213. Vox Escherichia coli ATCC 25922, the MIC range should be between 4.0 µg/mL and 16.0 µg/mL. For Streptococcus faecalis ATCC 29212, the MIC range should be between 8.0 and 32.0 µg/mL.

REFERENCES

1. National Committee for Clinical Laboratory Standards, Approved Standard, Performance Standards for Antimicrobial Disk Susceptibility Test, 4th Edition, Vol. 10 (7): M2-A4, Villanova, PA, April, 1990.

2. National Committee for Clinical Laboratory Standards, Approved Standard: Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically, 2nd Edition, Vol. 10 (8): M7-A2, Villanova, PA, April, 1990.

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