Fig. 3: SERS-DIP spectral profiles for phenotypic examination of susceptible and resistant bacterial strains.
Determination of the MIC and AST for (A, B) TMP-susceptible and (C, D) TMP-resistant E. coli strains cultivated in LB nutrient broth containing varying TMP levels with (A, C) or without (B, D) 50% D2O. Metabolically active susceptible cells grown in low TMP levels (0–0.5 µg/mL) and resistant bacteria exposed to TMP in D2O exhibited an apparent spectral peak at 2180 cm-1 assigned to the C–D vibrations in lipids and proteins (A, C). For the susceptible bacterial strain, the C–D band disappeared completely after bacterial exposure to 2 µg/mL TMP within 2 h of cell cultivation (A), which was determined as the MIC using our nanofibre sensor-based SERS-DIP approach. The impact of TMP on active susceptible bacteria was further characterised by the reduction in the intensity of several spectral bands above the MIC ( ≥ 2 µg/mL) with increasing TMP (B). In contrast, SERS intensities for resistant cells did not significantly change across TMP concentrations (D). The corresponding intensity regression plots are computed in Supplementary Figs. 5 and 7.
