Topoisomerase Mutations That Are Associated with High-Level Resistance to Earlier Fluoroquinolones in <i>Staphylococcus aureus</i> Have Less Effect on the Antibacterial Activity of Besifloxacin

Abstract

Background: The impact of mutations in DNA gyrase and topoisomerase IV on minimum inhibitory concentrations (MICs) was investigated to better understand why besifloxacin has a higher potency against Staphylococcus aureus when compared to other fluoroquinolones, which was especially pronounced against ciprofloxacin-resistant isolates. Methods: MICs were determined for 52 clinical isolates against besifloxacin, moxifloxacin, gatifloxacin, ciprofloxacin, and levofloxacin. The genes encoding GyrA, GyrB, ParC, and ParE were sequenced and the potential impact of mutations assessed in light of recent structural data. Results: For all fluoroquinolones tested, the MICs increased with the number of mutations in the quinolone resistance-determining regions. However, this increase was the smallest for besifloxacin and the largest for ciprofloxacin and levofloxacin. In addition to the commonly observed mutations in ParC and GyrA, more unusual mutations in ParE, such as Asp-432→His or Pro-585→Ser, were also detected. Conclusions: Compared to earlier fluoroquinolones, the higher potency of besifloxacin suggests that the drug’s unique combination of a 7-azepinyl ring and an 8-chloro-substituent results in unique interactions with DNA gyrase and topoisomerase IV.

Molecular Characterization of Fluoroquinolone Resistance of Methicillin –Resistant Clinical Staphylococcus aureus Isolates from Rawalpindi, Pakistan

“…Our study identified mutations within the QRDR that have been associated with FQ resistance in the past, such as S84L and G106D in gyrA and S80Y or E84G in grlA, and exhibited ciprofloxacin resistance with MICs ranging from 64-512 mg/L. Double mutations in grlB (E422D and E596D), previously reported by Sanfilippo et al [28] in methicillin-sensitive S. aureus (MSSA) isolates, were also detected. Additional mutations resulting in V615I, S437P, and D646Y substitutions were also observed.…”

“…FQ resistance in S. aureus has mainly been attributed to mutations in the QRDRs of the DNA gyrase and topoisomerase IV genes, gyrA, gyrB, grlA, and grlB [4,5,28,31]. These mutations decrease the affinity of FQ drugs for the target enzyme-DNA complexes, consequently resulting in high level FQ resistance.…”

Natural Hot Spots for Gain of Multiple Resistances: Arsenic and Antibiotic Resistances in Heterotrophic, Aerobic Bacteria from Marine Hydrothermal Vent Fields

“…The same analyses of the translated amino acid sequence of parE gene detected the amino acid exchange of valine (V) in position 327 for an isoleucine (I). In the parE translated protein sequence, other mutations where observed, but in this case, the amino acid exchanges did not correspond to the conferring of resistance mutations described in literature (27). In the case of determinants for specific resistance to heavy metals, those were found for only two metals: copper and chromium (Table 2).…”

“…The gyrB and parE genes are housekeeping genes, coding for DNA gyrase subunit B and topoisomerase IV subunit B, respectively. These genes were signaled as subject to mutations, coding for proteins with certain amino acid substitutions that confer resistance against fluoroquinolones to the bacteria carrying these plasmids (27). When analyzing the sequence obtained from the translated amino acid sequence of gyrB gene, a mutation was detected, i.e., the amino acid substitution at position 459 from asparagine (N) to histidine (H).…”

Antimicrobial Resistance of <b><i>Escherichia coli</i></b> Strains Causing Neonatal Sepsis between 1998 and 2008

“…Mutations in the quinolone resistance-determining region of the genes encoding the essential enzymes DNA gyrase and topoisomerase IV are the primary cause of clinically relevant levels of fluoroquinolone resistance in both gram-negative and gram-positive microorganisms [16]. Detection of these mutations and class 1 integrons were carried out by specific PCR amplification and sequencing as previously described [13].…”