Novobiocin Inhibits the Antimicrobial Resistance Acquired through DNA Damage-Induced Mutagenesis in Acinetobacter baumannii

Abstract

Acinetobacter baumannii, a worldwide emerging nosocomial pathogen, acquires antimicrobial resistances in response to DNAdamaging agents, which increase the expression of multiple error-prone DNA polymerase components. Here we show that the aminocoumarin novobiocin, which inhibits the DNA damage response in Gram-positive bacteria, also inhibits the expression of error-prone DNA polymerases in this Gram-negative multidrug-resistant pathogen and, consequently, its potential acquisition of antimicrobial resistance through DNA damage-induced mutagenesis.A cinetobacter baumannii is a highly effective human colonizer in hospital settings worldwide. Its ability to acquire resistance to several extensively used antimicrobials has resulted in its emergence as a problematic nosocomial pathogen (1). As in other bacteria, A. baumannii achieves resistance against certain antimicrobials through single mutations in the corresponding target genes (i.e., point mutations in the rpoB gene can generate resistance to rifampin [2]). In previous works, we demonstrated that this bacterium contains multiple components of error-prone DNA polymerases, whose induction after DNA damage leads to the introduction of point mutations in the bacterial genome, including those conferring antibiotic resistance (3, 4).Topoisomerase enzymes maintain the topological state of DNA and are critical regulators of protein translation and cell replication. Specifically, DNA gyrase (a type II topoisomerase) catalyzes the removal of the torsional stress that accumulates in bacterial chromosomes at sites preceding replication forks and transcriptional complexes by forming double-stranded breaks in the DNA (5). The formation of these double-stranded breaks and, therefore, of single-stranded DNA activates the bacterial SOS response, which results in mutagenic repair through the expression of mutagenic genes, especially those encoding error-prone DNA polymerases. This response guarantees DNA repair and cell survival but also results in some mutations that are able to confer antimicrobial resistance (2, 6). In Escherichia coli and other bacteria, the DNA damage response is regulated by the LexA repressor. However, A. baumannii lacks the LexA repressor, and the errorprone DNA polymerase (UmuDAb) carries out its functional role (3, 4). Thus, the induction of this DNA repair response in A. baumannii also results in the introduction of point mutations, including those conferring antibiotic resistance.DNA gyrase inhibitors such as quinolones take advantage of the potential of topoisomerases to fragment the genome and thereby cause cell death. These drugs bind noncovalently at the enzyme-DNA interface in the cleavage-ligation active site to block ligation (5). Further, because quinolones also cause SOS induction, they ultimately promote antimicrobial resistance. Thus, one approach to combat the increasing prevalence of antimicrobialresistant infections is to prevent SOS activation. Antimicrobials such as novobiocin interfere with the ATPase activity of DNA gyrase, such t...

Biology of Acinetobacter baumannii: Pathogenesis, Antibiotic Resistance Mechanisms, and Prospective Treatment Options

“…The aminocoumarin novobiocin is a well-established antimicrobial agent that inhibits the DNA damage response in Gram-positive bacteria by interfering with ATPase activity of DNA gyrase (Schroder et al, 2013 ). One study showed that novobiocin also inhibits acquisition of antimicrobial resistance in MDR A. baumannii through DNA damage-induced mutagenesis (Jara et al, 2015 ).…”

Antibiotic-Induced Genetic Variation: How It Arises and How It Can Be Prevented

“…Novobiocin, an aminocoumarin antibiotic, blocks DNA gyrase and alters DNA supercoiling, which leads in turn to downregulation of recA expression in S. aureus (140). This downregulation reduces SOS induction and antibiotic-induced mutagenesis in S. aureus and Acinetobacter baumannii (80,141). Another example is the antiprotozoal drug suramin, which reduces the SOS response in M. tuberculosis, potentiating ciprofloxacin activity (114).…”

Ciprofloxacin-Mediated Mutagenesis Is Suppressed by Subinhibitory Concentrations of Amikacin in Pseudomonas aeruginosa

“…Examples of suppressors of the SOS response induced by fluoroquinolones were reported in Gram-positive and Gram-negative bacteria, such as the polyphenols baicalein (24), curcumin (25), and suramin (polysulphonated naphthylurea) (26), which have the ability to disassemble RecA single-stranded DNA filaments. Novobiocin blocks the ATP-binding site of the GyrB and inhibits ciprofloxacin and UV-induced SOS response (27,28). The small-molecule N6-(1-naphthyl)-ADP acts as an ATP competitor, which prevents the formation of the RecA-DNA filament that is essential for all RecAassociated functions (29).…”