Small Changes in Environmental Parameters Lead to Alterations in Antibiotic Resistance, Cell Morphology and Membrane Fatty Acid Composition in Staphylococcus lugdunensis
Figure 2
Integrated summary of the cellular responses to the changes in combinations of environmental parameters including temperature, osmotic pressure and pH.
The central three coloured contour plots show the influences of the combined stresses of NaCl and pH on the MIC for Gentamicin. The coloured contour plot on the left represents the effect of pH and NaCl concentration on the MIC at 35°C. pH had little effect on changing MIC, whereas higher concentrations of NaCl increased MIC as shown by the change in colour from blue to orange/red. Elevating the temperature as shown in the central plot to 37°C, and then to the plot on the right to 39°C, resulted in some enhanced responses of MIC as NaCl concentrations were increased. The fatty acid profiles measured for the cells grown at 39°C, pH 6 and 5% salt, which generated the highest MIC (circled), displayed substantial differences when compared with the corresponding profiles of the control cells shown in the difference chart on the top right-hand side of the figure. SEM evaluations for these same cells (far right (c)) revealed smaller cell sizes compared with the reference control cells (a). The fatty acid profiles measured for the cells grown at 39°C, pH 6 and 0% salt, which generated low MIC responses (circled), displayed a different pattern of alterations when compared with the corresponding profiles of the control cells shown in the difference chart on the top left-hand side of the figure. SEM evaluations for these same cells with 0% salt (far left (b)) revealed smaller cell sizes compared with the reference control cells (a). At 39°C, cells incubated at pH 8 and 0% NaCl produced the lowest MIC (circled) and had the smallest sized cells of any treatments in the study (d).