Effects of NorA Inhibitors on In Vitro Antibacterial Activities and Postantibiotic Effects of Levofloxacin, Ciprofloxacin, and Norfloxacin in Genetically Related Strains of Staphylococcus aureus

Abstract

NorA is a membrane-associated multidrug efflux protein that can decrease susceptibility to fluoroquinolones in Staphylococcus aureus. To determine the effect of NorA inhibition on the pharmacodynamics of fluoroquinolones, we evaluated the activities of levofloxacin, ciprofloxacin, and norfloxacin with and without various NorA inhibitors against three genetically related strains of S. aureus (SA 1199, the wild-type; SA 1199B, a NorA hyperproducer with a grlA mutation; and SA 1199-3, a strain that inducibly hyperproduces NorA) using susceptibility testing, time-kill curves, and postantibiotic effect (PAE) methods. Levofloxacin had the most potent activity against all three strains and was minimally affected by addition of NorA inhibitors. In contrast, reserpine, omeprazole, and lansoprazole produced 4-fold decreases in ciprofloxacin and norfloxacin MICs and MBCs for SA 1199 and 4-to 16-fold decreases for both SA 1199B and SA 1199-3. In time-kill experiments reserpine, omeprazole, or lansoprazole increased levofloxacin activity against SA 1199-3 alone by 2 log 10 CFU/ml and increased norfloxacin and ciprofloxacin activities against all three strains by 0.5 to 4 log 10 CFU/ml. Reserpine and omeprazole increased norfloxacin PAEs on SA 1199, SA 1199B, and SA 1199-3 from 0.9, 0.6, and 0.2 h to 2.5 to 4.5, 1.1 to 1.3, and 0.4 to 1.1 h, respectively; similar effects were observed with ciprofloxacin. Reserpine and omeprazole increased the levofloxacin PAE only on SA 1199B (from 1.6 to 5.0 and 3.1 h, respectively). In conclusion, the NorA inhibitors dramatically improved the activities of the more hydrophilic fluoroquinolones (norfloxacin and ciprofloxacin). These compounds may restore the activities of these fluoroquinolones against resistant strains of S. aureus or may potentially enhance their activities against sensitive strains.

MRSA Isolates from United States Hospitals Carry dfrG and dfrK Resistance Genes and Succumb to Propargyl-Linked Antifolates

“…NorA efflux activity in fluoroquinolone resistance was determined by MIC in the presence of reserpine, a NorA inhibitor. Minimal shifts in MIC for levofloxacin and up to 8-fold decrease in ciprofloxacin MIC indicate that NorA has minimal influence on fluoroquinolone resistance (Table S3) (Kaatz and Seo, 1995; Aeschlimann et al, 1999). mphC , a 2′-phosphotransferase which directly inactivates the macrolides via phosphorylation determines selective macrolide resistance (erythromycin) in UCH 121, UCH 127 and HH1184, all clonally distinct isolates(Matsuoka et al, 2003; Juda et al, 2016).…”

Structural Features of New Quinolones and Relationship to Antibacterial Activity Against Gram-positive Bacteria

“…Norfloxacin (5), ciprofloxacin (9) and ofloxacin (11) seem to be affected more than sparfloxacin (13), gatifloxacin (15), sitafloxacin (18), gemifloxacin (19), moxifloxacin (20), trovafloxacin (21) and garenoxacin (22), suggesting that these last quinolones may be poorer substrates for these pumps [22,85,90,[92][93][94]. Thus, efflux-mediated resistance mechanisms seem to affect quinolone agents to different extents, depending on the physicochemical properties and structural characteristics of the individual quinolones.…”

“…Previously, only hydrophilicity of the fluoroquinolones was thought to be an important factor for NorA-mediated transport. It was found that the NorA inhibitors reserpine and omeprazole dramatically improve the activities of the more hydrophilic quinolones [norfloxacin (5 ) and ciprofloxacin (9)] [93]. In addition, Hydrophilic quinolones, such as norfloxacin (5) and ciprofloxacin (9), appear more prone to efflux than more hydrophobic molecules like grepafloxacin (14) and gatifloxacin (15) in Gram-positive organisms such as S. pneumoniae [95,96].…”

Experimental Adaptation of Staphylococcus Aureus to Sulfuryl Derivatives of Benzazolides

“…The pathways of adaptogenesis can be divided roughly into the following: a) Reduction of the ability of a compound to penetrate bacterial cells. This may be a consequence of the loss or a change of specific permeases, active blockage of access of compounds to the cell, and factors that actively eliminate xenobiotics from cells [1,2]; b) Change of metabolism that inactivates the compounds. This may be the loss of an exchange cycle that is sensitive to a given toxicant, increased synthesis of enzymes capable of modifying the poison, or the assimilation of specific products that reduce the toxicity of xenobiotics [3].…”