Skip to main content

Table 3 Morphological analysis of B. pseudomallei strains in the presence of IPM and optical screening-based IPM susceptibility testing

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

Strain IPM MIC
(μg/ml)
Filamentation
(# Cells ≥ 15 μm)
Time (h) to determine IPM susceptibility Time (h) cell lysis begins
½ MIC 4 μg/ml 8 μg/ml MIC 2x MIC 8 μg/ml
Bp1651 32 (R) yes (8/100) ND ND 3.6 ± 0.2 not tested not tested
724644 2 (S) no 1.7 ± 0.0 1.7 ± 0.0 3.0 ± 0.0 2.9 ± 0.2 3.0 ± 0.0
MSHR1655 1 (S) yes (15/100) 2.0 ± 0.4 1.3 ± 0.9 3.9 ± 0.4 4.0 ± 0.7 3.6 ± 0.2
1026b 1 (S) no 3.5 ± 0.2 3.8 ± 0.7 5.0 ± 0.7 5.3 ± 0.6 5.7 ± 0.9
1631 0.5 (S) no 3.9 ± 0.2 3.7 ± 0.5 9.1 ± 0.5 8.2 ± 0.8 4.6 ± 0.2
6296 0.25 (S) yes (6/100) 2.7 ± 1.4 3.7 ± 0.0 9.8 ± 0.2 8.3 ± 1.4 5.3 ± 0.3
  1. The minimal inhibitory concentrations (MICs) of imipenem (IPM) determined by conventional BMD testing based on CLSI guidelines and the time (h) required to determine susceptibility of B. pseudomallei strains (4 μg/ml and 8 μg/ml IPM) by optical screening with a confidence level (CL) of 95% (p ≤ 0.05) are listed. Susceptibility interpretations are resistant (R) or susceptible (S). All susceptible strains were monitored by optical screening 18–20 h in the presence of IPM below, at and above MICs. Cell length was measured after 4 h. Detection of filamentation in sub-inhibitory concentrations and cell lysis at inhibitory concentrations was achieved by analysis of growth kinetic data and visual observation of real-time video imaging. No statistically significant differences were observed between growth values of Bp1651 in the presence (4 μg/ml and 8 μg/ml) and absence of IPM, therefore the time to susceptibility was not determined (ND)