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. 2021 Oct 27;9(2):e01510-21. doi: 10.1128/Spectrum.01510-21

TABLE 1.

Concordance of trimethoprim-sulfamethoxazole Vitek 2 susceptibility testing with disk diffusion and broth microdilution in S. aureusa

AST resultb Vitek 2 result
S (n = 17)
R (n = 78)
n % n %
Mueller-Hinton agar 1 (MHBD)c
 Susceptible (standard dosing regime) 17 100 66 84.6
 Susceptible (with increased exposure) 0 0 9 11.5
 Resistant 0 0 3 3.9
Mueller-Hinton agar 2 (MHBM)d
 Susceptible (standard dosing regime) 17 100 76 97.4
 Susceptible (with increased exposure) 0 0 0 0
 Resistant 0 0 2 2.6
Mueller-Hinton agar with 5% horse blood (MHF)c
 Susceptible (standard dosing regime) 17 100 71 91.0
 Susceptible (with increased exposure) 0 0 5 6.4
 Resistant 0 0 2 2.6
Broth microdilution
 Susceptible (standard dosing regime) 17 100 44 56.4
 Susceptible (with increased exposure) 0 0 32 52.6
 Resistant 0 0 2 2.6
Trimethoprim susceptibility (DD)e
 Susceptible 13 76.5 1 1.3
 Resistant 4 23.5 77 98.7
a

S, susceptible; R, resistant; AST, antibiotic susceptibility testing; DD, disk diffusion.

b

AST was interpreted according to EUCAST clinical breakpoints (v11.0) using the following categories: susceptible (standard dosing regime), susceptible (increased exposure), and resistant.

c

MHBD purchased from Becton, Dickinson, Germany.

d

MHBM purchased from bioMérieux, Germany.

e

Trimethoprim susceptibility was determined by disk diffusion on MHBD, MHBM, and MHF (all results were concordant). Phenotypic trimethoprim resistance is associated with Vitex 2 SXT resistance (P < 0.001 using chi-square test).