The resistance mechanisms of bacteria against ciprofloxacin and new approaches for enhancing the efficacy of this antibiotic

For around three decades, the fluoroquinolone (FQ) antibiotic ciprofloxacin has been used to treat a range of diseases, including chronic otorrhea, endocarditis, lower respiratory tract, gastrointestinal, skin and soft tissue, and urinary tract infections. Ciprofloxacin's main mode of action is to stop DNA replication by blocking the A subunit of DNA gyrase and having an extra impact on the substances in cell walls. Available in intravenous and oral formulations, ciprofloxacin reaches therapeutic concentrations in the majority of tissues and bodily fluids with a low possibility for side effects. Despite the outstanding qualities of this antibiotic, Salmonella typhi, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa have all shown an increase in ciprofloxacin resistance over time. The rise of infections that are resistant to ciprofloxacin shows that new pharmacological synergisms and derivatives are required. To this end, ciprofloxacin may be more effective against the biofilm community of microorganisms and multi-drug resistant isolates when combined with a variety of antibacterial agents, such as antibiotics from various classes, nanoparticles, natural products, bacteriophages, and photodynamic therapy. This review focuses on the resistance mechanisms of bacteria against ciprofloxacin and new approaches for enhancing its efficacy.

Alternations in DNA gyrase genes in low-level fluoroquinolone-resistant Moraxella catarrhalis strains isolated in Poland

PURPOSE

The purpose of this study was to investigate the molecular mechanisms of fluoroquinolone resistance in Moraxella catarrhalis clinical strains isolated in Lublin, Poland.

MATERIALS AND METHODS

A total of 150 non-duplicate clinical strains of M. catarrhalis were obtained from individuals with signs of upper respiratory tract infection. Bacterial identification was corroborated on the basis of phenotypic and biochemical characteristics as well as with the use of molecular tests. The antimicrobial susceptibility of M. catarrhalis isolates was determined using the disk diffusion method and Etest. Mutations in the gyrase (gyrA and gyrB) and topoisomerase (parC and parE) genes were determined by polymerase chain reaction and sequencing.

RESULTS

It was observed that 16.7% of the studied isolates were drug resistant. Resistance to tetracycline was detected for 12% of the strains. Resistance to nalidixic acid, moxifloxacin, and levofloxacin was exhibited by 2.7% of the strains; 1.3% of the strains were resistant to trimethoprim/sulfamethoxazole and 0.7% to erythromycin. Minimum inhibitory concentration values of the four strains demonstrating fluoroquinolone resistance were: 6-12 mg/L for nalidixic acid, 1-1.5 mg/L for levofloxacin, 1 mg/L for moxifloxacin, and 0.25-0.5 mg/L for ciprofloxacin. The research resulted in the detection of mutations in 4 strains, in gyrase gyrA and gyrB genes. In gyrA gene, there occurred mutation G412C as well as four silent transition mutations. Within gyrB gene, there occurred mutation, substitution A1481G, as well as two identical silent mutations.

CONCLUSION

Our findings reveal that resistance to fluoroquinolones in M. catarrhalis is connected with amino acid substitutions in gyrA and gyrB genes. To our knowledge, this work is the first description of fluoroquinolone-resistant clinical strains of M. catarrhalis with described mutations in gyrA and gyrB genes isolated in Poland and in Europe.

Antimicrobial Resistance and Respiratory Infections

Since their introduction into health care and clinical practice in the early 20th century, antibiotics have revolutionized medicine. Alarmingly, these drugs are increasingly threatened by bacteria that have developed a broad diversity of resistance mechanisms. Antibiotic resistance can be transferred between bacteria, often on mobile genetic elements; be acquired from the environment; or arise through mutation because of selective pressures of the drugs themselves. There are various strategies to resistance, including active efflux of the drug from the bacterial cell, reduced permeability of the cell envelope, alteration of the drug's target within the bacterial cell, and modification or destruction of the antibiotic. Streptococcus pneumoniae, Haemophilus influenzae, Pseudomonas aeruginosa, and Mycobacterium tuberculosis frequently are implicated in respiratory infections, often manifesting with reduced susceptibility to multiple classes of antibiotics. Some mechanisms of resistance, such as the β-lactamases that confer resistance to penicillins and related drugs, have been well characterized and are widespread in clinical isolates. Other newly identified determinants, including the colistin resistance gene mcr-1, are spreading rapidly worldwide and threaten last-resort treatments of multidrug-resistant organisms. Various approaches to detecting antibiotic resistance provide surveys of the determinants that are available for transfer into pathogenic bacteria. Together with molecular characterization of newly identified mechanisms, this surveillance can target drug discovery efforts and increase antibiotic stewardship. A greater understanding of the mechanisms of antibiotic resistance in respiratory pathogens combined with rapid diagnostics ultimately will reduce treatment failure due to inappropriate antibiotic use and prevent further spread of resistance.

Mutant selection window of four quinolone antibiotics against clinical isolates of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis

Community-acquired pneumonia and otitis media are caused by several bacterial species, including Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. For the treatment of these diseases, various quinolones are frequently used. We determined the mutant prevention concentration (MPC) of four quinolones, levofloxacin, sitafloxacin, tosufloxacin, and garenoxacin, using 92 clinical isolates and evaluated each mutant selection window (MSW). Furthermore, the DNA sequence of the quinolone resistance-determining region (QRDR) for the resistant mutant selected based on the MSW was determined. The MIC₉₀ and MPC₉₀ of levofloxacin were 0.781 μg/mL and 6.250 μg/mL for S. pneumoniae and 0.049 μg/mL and 1.563 μg/mL for M. catarrhalis and were higher than those for the other three quinolones. In addition, 5 strains of 30 S. pneumoniae (16.7%) selected based on the MSW of levofloxacin acquired resistance to only levofloxacin. In these 5 strains, a mutation of gyrA and/or parC was detected. In this study, no resistant mutant was selected in the MSW of any of the other three quinolones. On the other hand, clinical isolates of H. influenzae showed no resistance by all quinolone exposure. Finally, The MIC value and the mutation status in the QRDR did not change after 14 passages in antibiotic-free medium. In conclusion, our findings suggest that the increased use of levofloxacin may contribute to the increased quinolone-resistance of S. pneumoniae and M. catarrhalis.

Molecular Characterization of Fluoroquinolone-Resistant Moraxella catarrhalis Variants Generated In Vitro by Stepwise Selection

Moraxella catarrhalis causes respiratory infections. In this study, fluoroquinolone-resistant strains were selected in vitro to evaluate the mechanism of fluoroquinolone resistance. Strains with reduced fluoroquinolone susceptibility were obtained by stepwise selection in levofloxacin, and fluoroquinolone targets gyr and par were sequenced. Six novel mutations in GyrA (D84Y, T594dup, and A722dup), GyrB (E479K and D439N), and ParE (Q395R) involved in M. catarrhalis resistance to fluoroquinolones were revealed.

Antimicrobial susceptibility to β-lactam antibiotics and production of BRO β-lactamase in clinical isolates of Moraxella catarrhalis from a Japanese hospital

We investigated BRO-β-lactamase production of Moraxella catarrhalis isolates and its antimicrobial susceptibility to β-lactams. Of the 233 isolates, 232 were BRO producers and 224 were BRO-1 producers. Four isolates exhibited elevated ceftriaxone minimum inhibitory concentration (2 μg/mL) and different pulsed-field gel electrophoresis patterns and we expect this number to increase in the near future.