title: The optimal wavelength of spectrophotometric broth microdilution antifungal susceptibility test for flucytosine and three azoles.
abstract: BACKGROUND
  There is no guideline for the appropriate wavelength at which to measure the optical density (OD) value in broth microdilution antifungal susceptibility testing, although a spectrophotometric reading method is commonly used. The present study aimed to analyze the difference in the OD values over the range of visible light and to ascertain the optimal wavelength for the spectrophotometric method of microdilution testing.
  
  
  METHODS
  We measured the OD of background blank controls of broth medium, antifungal agents, and inocula of five type strains using a Synergy HT multi-detection microplate reader at 5-nm intervals from 380 nm to 760 nm. We also estimated the OD differences between the 50% of growth control and blank control.
  
  
  RESULTS
  The OD of the blank control showed a parabola shape with two peaks and steadily decreased at longer wavelengths. The curves of the antifungal agent were similar to those of blank controls, and the influence of each antifungal agent on the OD was minimal. For the difference in OD between 50% of growth control and the blank control, the curve was the opposite of the blank control, and the OD increased steadily at the wavelengths above 600 nm.
  
  
  CONCLUSIONS
  The range between 600 nm and 700 nm was the optimal wavelength for broth microdilution antifungal susceptibility testing, although any wavelength within the visible light spectrum can be used.
authors.affiliation: Department of Laboratory Medicine, Inje University College of Medicine, Busan, Korea.
authors.forename: Ja Young
authors.initials: JY
authors.lastname: Lee
authors.forename: Eun Jung
authors.initials: EJ
authors.lastname: Lee
authors.forename: Si Hyun
authors.initials: SH
authors.lastname: Kim
authors.forename: Haeng Soon
authors.initials: HS
authors.lastname: Jeong
authors.forename: Seung Hwan
authors.initials: SH
authors.lastname: Oh
authors.forename: Hye Ran
authors.initials: HR
authors.lastname: Kim
authors.forename: Jeong Nyeo
authors.initials: JN
authors.lastname: Lee
authors.forename: Chulhun L
authors.initials: CL
authors.lastname: Chang
authors.forename: Weon-Gyu
authors.initials: WG
authors.lastname: Kho
authors.forename: Jeong Hwan
authors.initials: JH
authors.lastname: Shin
mesh_terms: D000935:Antifungal Agents / Q000737:chemistry*; D001393:Azoles / Q000737:chemistry*; D003470:Culture Media / Q000737:chemistry*; D005437:Flucytosine / Q000737:chemistry*; D008826:Microbial Sensitivity Tests; D013053:Spectrophotometry / Q000379:methods*
chemical_list: D000935:Antifungal Agents; D001393:Azoles; D003470:Culture Media; D005437:Flucytosine