Figure 4.

The kinase inhibitor ST085384 does not increase sensitivity of MRSA LAC∆stk1 to the bactericidal activity of Nafcillin (NAF). (A) The MRSA strain LAC∆stk1 was grown overnight from a single colony. The next morning, approximately 10⁴ CFU/mL of LAC∆stk1 was added to 1 mL TSB without antibiotics or 500 µL of TSB containing two-fold serial dilutions of Nafcillin from 0.0625 µg/mL to 4 µg/mL and was incubated O/N at 37 °C with shaking. The MIC of NAF for LAC∆stk1 under these conditions was determined to be 0.5 µg/mL (see loss of turbidity or lack of growth in Panel A); (B) approximately 10⁴ CFU/mL of LAC∆stk1 was added to 500 µL of either TSB or TSB containing MIC NAF (0.5 µg/mL, indicated as LAC∆stk1 + MIC NAF), TSB containing sub-MIC NAF (0.25 µg/mL, indicated as LAC∆stk1 + sub-MIC NAF), and TSB containing sub-MIC NAF (0.25 µg/mL + kinase inhibitor ST085384 (40 µg/mL), indicated as LAC∆stk1 + sub-MIC NAF + ST085384). All cultures were grown in a 37 °C shaker at 220 rpm. Aliquots of the media were removed immediately after subculture (T₀) and at 2, 4, 8, and 24 h post-inoculation, and were serially diluted and plated on TSA. Plates were incubated for 24–48 h at 37 °C and viable CFU were counted. The experiment was repeated twice. Note that ST085384 did not increase sensitivity of LACΔstk1 to NAF.