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Table 2 Morphological analysis of B. pseudomallei strains in the presence of AMC and CAZ

From: Optical microscopy reveals the dynamic nature of B. pseudomallei morphology during β-lactam antimicrobial susceptibility testing

Strain AMC MIC
(μg/ml)
Filamentation (4 h) Time (h) cell lysis begins
½ MIC MIC MIC 2x MIC 4x MIC
# Cells ≥ 15 μm Median CL (μm) # Cells ≥ 15 μm Median CL (μm)
Bp1651 64/32 (R) 6/100 5 0/100 4 3.7 ± 0.0 not tested not tested
MSHR1655 32/16 (R) 62/100 19.5 61/100 19 6.1 ± 0.2 4.0 ± 0.3 not tested
724644 16/8 (I) 93/100 59 24/100 6 4.8 ± 1.0 2.9 ± 0.2 2.9 ± 0.2
6788 8/4 (S) 86/97 43 82/100 42.5 remains filamentous filaments and spheroplasts only spheroplasts
1026b 4/2 (S) 42/100 12 80/97 44 remains filamentous remains filamentous 5.2 ± 0.4
Strain CAZ MIC
(μg/ml)
Filamentation (4 h) Time (h) cell lysis begins
½ MIC MIC MIC 2x MIC 4x MIC
# Cells ≥ 15 μm Median CL (μm) # Cells ≥ 15 μm Median CL (μm)
 Bp1651 > 128 (R) 49/100* 14* 39/100* 10.5* filaments and spheroplasts* not tested not tested
 724644 8 (S) 93/100 56.5 95/100 59.5 remains filamentous remains filamentous remains filamentous
 MSHR1655 4 (S) 48/100 13 61/100 22 8.2 ± 0.4 8.0 ± 0.0 8.0 ± 0.3
 1026b 2 (S) 28/100 8 94/100 36 remains filamentous remains filamentous remains filamentous
  1. The minimal inhibitory concentrations (MICs) of amoxicillin-clavulanic acid (AMC) and ceftazidime (CAZ) were determined by conventional BMD testing based on CLSI guidelines. Susceptibility interpretations are defined as resistant (R), intermediate (I), or susceptible (S). Cell length (CL) was measured at time 4 h and median cell length at MICs was calculated (n = 95 to 100 cells). Time to cell lysis is represented as the mean ± SD of triplicate samples based on growth kinetic data and visual observation of video imaging. (*) filamentation and cell lysis data in the presence of CAZ was calculated using a value of 128 μg/ml for the MIC due to concentration range in drug panel for testing. Underlined drug concentration indicates breakpoint for susceptibility