Fig. 2

Comparison of CST-resistant and -susceptible ECC. A Comparison of CST MICs of ECC clinical isolates according to the origin of clinical specimens. Percentages indicate the prevalence of CST-resistant isolates. Numbers in parentheses indicate the number of ECC isolates. CST susceptibility did not significantly differ according to the origin of clinical isolates. B hsp60 cluster classification of CST-susceptible and -resistant ECC clinical isolates. Significant difference was observed between the groups (*p < 0.05). C Growth of CST-susceptible and -resistant (with and without the skip-well phenomenon) ECC clinical isolates in the presence of various CST concentrations. Bacterial growth was measured by assessing turbidity (OD₆₀₀) after cultivation for 20 h based on the broth microdilution method in 96-well plates. The skip-well phenomenon was defined as no growth (OD₆₀₀ < 0.1) at a certain CST concentration(s) and growth (OD₆₀₀ > 0.1) at higher CST concentrations. Representative ECC clinical isolate data are shown: CST-susceptible isolate (SMEnt52 strain; E. hormaechei subsp. steigerwaltii, hsp60 cluster VIII), CST-resistant isolate displaying the skip-well phenomenon (SMEnt513 strain; E. kobei, hsp60 cluster II), and CST-resistant isolate not displaying the skip-well phenomenon (none-skip-well) (SMEnt1102 strain; E. cloacae subsp. cloacae, hsp60 cluster XI). Bacterial growths (OD₆₀₀ values) in the presence of CST were compared with the bacterial growth in the absence of CST of the respective strains (*p < 0.05 and **p < 0.001)