Background: Persistent and recurrent Staphylococcus aureus infections can be associated with small colony variants (SCVs). SCVs are slow growing bacteria that show elevated antibiotic-resistance and capacity to form biofilms. As a result, standard medical care fails to eradicate SCVs, implicating quality of life and increasing health care costs. Alternative strategies to combat SCV’s related infections are required; one of which includes targeting aquaporin channels (AQP). Bacterial aquaporin, AQPZ, shares homology to mammalian AQPs 1 and 4 and plays a role in osmoregulation in Escherichia coli. No AQPZ blockers have been discovered, but bumetanide derived agents effective in blocking mammalian AQPs 1 and 4 have shown to inhibit AQPZ in preliminary data. We hypothesise that if S. aureus SCV expresses AQPZ, novel AQPZ modulators would block this channel, disrupting the biofilm matrix, subsequently improving antibiotic delivery and efficacy.
Methods: The minimal inhibitory concentration (MIC) of the AQPZ modulator AqB013 was determined on planktonic SCVs. Bacterial growth in the presence of AqB013 was measured over 24 h. The AlamarBlue viability assay determined anti-biofilm efficacy following 24 h treatment exposure to different concentrations of AqB013 (0.078 mM to 2 mM). To assess biofilm removal, the crystal violet assay was performed. E. coli ATCC 25922 was used as a control strain. Triplicates were normalised to vehicle control (DMSO) and plotted after statistical analysis by one-way ANOVA.
Results: The MIC of AqB013 was 1 mM. Bacterial growth of planktonic SCV was inhibited by AqB013 in a dose dependant manner. AlamarBlue assays showed a significant decrease in viability of SCV biofilms at AqB013 concentrations of 0.125 mM (58% decrease) and 0.06 mM (71% decrease) (P<0.0001). AqB013 did not remove the SCV biofilm matrix.
Conclusion: The effect of AqB013 on SCV suggest the possible presence of an aquaporin. Confirming these findings may lead to a new treatment for persistent and recurrent S. aureus SCV infections.