Insights into collateral susceptibility and collateral resistance in Acinetobacter baumannii during antimicrobial adaptation

Assessment of the potential of phage-antibiotic synergy to induce collateral sensitivity in Salmonella Typhimurium

This study was designed to evaluate the synergistic effect of phage and antibiotic on the induction of collateral sensitivity in Salmonella Typhimurium. The synergistic effects of Salmonella phage PBST32 combined with ciprofloxacin (CIP) against S. Typhimurium KCCM 40253 (ST^KCCM) were evaluated using a fractional inhibitory concentration (FIC) assay. The CIP susceptibility of ST^KCCM was increased when combined with PBST32, showing 16-fold decrease at 7 log PFU/mL. The combination of 1/2 × MIC of CIP and PBST32 (CIP[1/2]+PBST32) effectively inhibited the growth of ST^KCCM up to below the detection limit (1.3 log CFU/mL) after 12 h of incubation at 37 °C. The significant reduction in bacterial swimming motility was observed for PBST32 and CIP[1/4]+PBST32. The CIP[1/4]+PBST32 increased the fitness cost (relative fitness = 0.57) and decreased the cross-resistance to different classes of antibiotics. ST^KCCM treated with PBST32 alone treatment exhibited the highest coefficient of variation (90%), followed by CIP[1/4]+PBST32 (75%). These results suggest that the combination of PBST32 and CIP can be used to control bacterial pathogens.

Collateral sensitivity between tetracyclines and aminoglycosides constrains resistance evolution in carbapenem-resistant Klebsiella pneumoniae

AIMS

The acquisition of resistance to one antibiotic may confer an increased sensitivity to another antibiotic in bacteria, which is an evolutionary trade-off between different resistance mechanisms, defined as collateral sensitivity (CS). Exploiting the role of CS in treatment design could be an effective method to suppress or even reverse resistance evolution.

METHODS

Using experimental evolution, we systematically studied the CS between aminoglycosides and tetracyclines in carbapenem-resistant Klebsiella pneumoniae (CRKP) and explored the underlying mechanisms through genomic and transcriptome analyses. The application of CS-based therapies for resistance suppression, including combination therapy and alternating antibiotic therapy, was further evaluated in vitro and in vivo.

RESULTS

Reciprocal CS existed between tetracyclines and aminoglycosides in CRKP. The increased sensitivity of aminoglycoside-resistant strains to tetracyclines was associated with the alteration of bacterial membrane potential, whereas the unbalanced oxidation-reduction process of tetracycline-resistant strains may lead to an increased bacterial sensitivity to aminoglycosides. CS-based combination therapy could efficiently constrain the evolution of CRKP resistance in vitro and in vivo. In addition, alternating antibiotic therapy can re-sensitize CRKP to previously resistant drugs, thereby maintaining the trade-off.

CONCLUSIONS

These results provide new insights into constraining the evolution of CRKP resistance through CS-based therapies.

Drug Combination of Ciprofloxacin and Polymyxin B for the Treatment of Multidrug–Resistant Acinetobacter baumannii Infections: A Drug Pair Limiting the Development of Resistance

Polymyxins are considered as last–resort antibiotics to treat infections caused by Acinetobacter baumannii. However, there are increasing reports of resistance in A. baumannii to polymyxins. In this study, inhalable combinational dry powders consisting of ciprofloxacin (CIP) and polymyxin B (PMB) were prepared by spray–drying. The obtained powders were characterized with respect to the particle properties, solid state, in vitro dissolution and in vitro aerosol performance. The antibacterial effect of the combination dry powders against multidrug–resistant A. baumannii was assessed in a time–kill study. Mutants from the time–kill study were further investigated by population analysis profiling, minimum inhibitory concentration testing, and genomic comparisons. Inhalable dry powders consisting of CIP, PMB and their combination showed a fine particle fraction above 30%, an index of robust aerosol performance of inhaled dry powder formulations in the literature. The combination of CIP and PMB exhibited a synergistic antibacterial effect against A. baumannii and suppressed the development of CIP and PMB resistance. Genome analyses revealed only a few genetic differences of 3–6 SNPs between mutants and the progenitor isolate. This study suggests that inhalable spray–dried powders composed of the combination of CIP and PMB is promising for the treatment of respiratory infections caused by A. baumannii, and this combination can enhance the killing efficiency and suppress the development of drug resistance.