Optimization of 4‐Substituted Benzenesulfonamide Scaffold To Reverse Acinetobacter baumannii Serum‐Adaptive Efflux Associated Antibiotic Tolerance

Abstract

Acinetobacter baumannii is a nosocomial pathogen of urgent concern for public health due to rising rates of multidrug and pandrug resistance. In the context of environmental cues such as growth in human serum, A. baumannii is known to display adaptive efflux, in which a multitude of efflux‐associated genes are upregulated, resulting in efflux‐mediated drug tolerance in strains that are otherwise susceptible to antibiotic therapy. Previously, we identified a sulfonamide‐containing scaffold molecule (ABEPI1) that reversed serum‐associated antibiotic tolerance in A. baumannii. Herein, we present structure‐activity relationship studies on 29 newly synthesized analogues. These molecules were characterized for their ability to potentiate multiple antibiotics in serum, reduce serum‐associated ethidium bromide efflux and depolarize bacterial cell membranes. In addition, they were assessed for toxicity to mammalian cells. Collectively, these molecules may represent promising potential adjuvants for use in combination with new and existing antibiotics to treat A. baumannii bacterial infections.

Genetic Determinants of Acinetobacter baumannii Serum-Associated Adaptive Efflux-Mediated Antibiotic Resistance

“…Approximately 2 × 10 7 cells were returned to 2 mL of fresh LB or serum-supplemented with 75 µM DMACA-Oflox in the presence or absence of 20 µg mL −1 A. baumannii efflux-pump inhibitor 4-[(4-Methoxybenzyl)oxy] benzene sulfonamide (AE0003; ref. [33]) and incubated for 30 min at 37 • C. Cells were washed and resuspended in PBS and flowed through a BD LSR II flow cytometer (BD Biosciences, Franklin Lakes, NJ, USA). Cells were excited with a violet 405 nm laser using a 450/50 bandpass filter.…”

“…Similarly, while fluorescence-labeling seemed to reduce ofloxacin's antimicrobial potency, wild-type cells displayed resistance to ≥200 µg mL −1 DMACA-Oflox during serum growth whereas serum-grown YhaK-mutant cells exhibited a loss of resistance to 200 µg mL −1 DMACA-Oflox (Figure 4B). Moreover, the YhaK-mutant phenocopied DMACA-Ofloxtreated serum-grown wild-type cells in the presence of the known A. baumannii AEMR inhibitor, AE0003 (structure provided in Supplemental Figure S1B), indicating that mutation of the strain's YhaK protein renders them AEMR-deficient (Figure 4C) [33].…”

“…Moreover, as shown in Figure 6, the reduced DMACA-Oflox accumulation of serum-grown wild-type cells could, at least in part, could be reversed by the A. baumannii efflux pump inhibitor AE0003, indicating that DMACA-Oflox allows measures of the organism's adaptive efflux-mediated resistance. treated serum-grown wild-type cells in the presence of the known A. baumannii AEMR inhibitor, AE0003 (structure provided in Supplemental Figure S1B), indicating that mutation of the strain's YhaK protein renders them AEMR-deficient (Figure 4C) [33].…”

The Phenylacetic Acid Catabolic Pathway Regulates Antibiotic and Oxidative Stress Responses in Acinetobacter

“… A. baumannii is becoming increasingly difficult to treat, and currently about 60% of clinical isolates are multidrug resistant (MDR). Additionally, A. baumannii causes particularly recalcitrant infections due to its ability to withstand antibiotic treatment without designated antibiotic resistance genes ( 3 – 5 ). This is a great concern as surviving antibiotic treatment is known to facilitate the development of true antibiotic resistance ( 6 ).…”