Brominated Carbazole with Antibiotic Adjuvant Activity Displays Pleiotropic Effects in MRSA’s Transcriptome

Methicillin-resistant Staphylococcus aureus (MRSA) is a major threat to
human health, as the US mortality rate
outweighs those from HIV, tuberculosis, and viral hepatitis combined.
In the wake of the COVID-19 pandemic, antibiotic-resistant bacterial
infections acquired during hospital stays have increased. Antibiotic
adjuvants are a key strategy to combat these bacteria. We have evaluated
several small molecule antibiotic adjuvants that have strong potentiation
with β-lactam antibiotics and are likely inhibiting a master
regulatory kinase, Stk1. Here, we investigated how the lead adjuvant
(compound 8) exerts its effects in a more comprehensive
manner. We hypothesized that the expression levels of key resistance
genes would decrease once cotreated with oxacillin and the adjuvant.
Furthermore, bioinformatic analyses would reveal biochemical pathways
enriched in differentially expressed genes. RNA-seq analysis showed
176 and 233 genes significantly up- and downregulated, respectively,
in response to cotreatment. Gene ontology categories and biochemical
pathways that were significantly enriched with downregulated genes
involved carbohydrate utilization, such as the citrate cycle and the
phosphotransferase system. One of the most populated pathways was S. aureus infection. Results from an interaction
network constructed with affected gene products supported the hypothesis
that Stk1 is a target of compound 8. This study revealed
a dramatic impact of our lead adjuvant on the transcriptome that is
consistent with a pleiotropic effect due to Stk1 inhibition. These
results point to this antibiotic adjuvant having potential broad therapeutic
use in combatting MRSA.