Risk factors for gyrA and parC mutations in Pseudomonas aeruginosa

Molecular Mechanism of Drug Resistance

The treatment of microbial infections has suffered greatly in this present century of pathogen dominance. Inspite of extensive research efforts and scientific advancements, the worldwide emergence of microbial tolerance continues to plague survivability. The innate property of microbe to resist any antibiotic due to evolution is the virtue of intrinsic resistance. However, the classical genetic mutations and extrachromosomal segments causing gene exchange attribute to acquired tolerance development. Rampant use of antimicrobials causes certain selection pressure which increases the resistance frequency. Genomic duplication, enzymatic site modification, target alteration, modulation in membrane permeability, and the efflux pump mechanism are the major contributors of multidrug resistance (MDR), specifically antibiotic tolerance development. MDRs will lead to clinical failures for treatment and pose health crisis. The molecular mechanisms of antimicrobial resistance are diverse as well as complex and still are exploited for new discoveries in order to prevent the surfacing of “superbugs.” Antimicrobial chemotherapy has diminished the threat of infectious diseases to some extent. To avoid the indiscriminate use of antibiotics, the new ones licensed for use have decreased with time. Additionally, in vitro assays and genomics for anti-infectives are novel approaches used in resolving the issues of microbial resistance. Proper use of drugs can keep it under check and minimize the risk of MDR spread.

Dynamics of Mutations during Development of Resistance by Pseudomonas aeruginosa against Five Antibiotics

Pseudomonas aeruginosa is an opportunistic pathogen that causes considerable morbidity and mortality, specifically during intensive care. Antibiotic-resistant variants of this organism are more difficult to treat and cause substantial extra costs compared to susceptible strains. In the laboratory, P. aeruginosa rapidly developed resistance to five medically relevant antibiotics upon exposure to stepwise increasing concentrations. At several time points during the acquisition of resistance, samples were taken for whole-genome sequencing. The increase in the MIC of ciprofloxacin was linked to specific mutations in gyrA, parC, and gyrB, appearing sequentially. In the case of tobramycin, mutations in fusA, HP02880, rplB, and capD were induced. The MICs of the beta-lactam compounds meropenem and ceftazidime and the combination of piperacillin and tazobactam correlated linearly with beta-lactamase activity but not always with individual mutations. The genes that were mutated during the development of beta-lactam resistance differed for each antibiotic. A quantitative relationship between the frequency of mutations and the increase in resistance could not be established for any of the antibiotics. When the adapted strains are grown in the absence of the antibiotic, some mutations remained and others were reversed, but this reversal did not necessarily lower the MIC. The increased MIC came at the cost of moderately reduced cellular functions or a somewhat lower growth rate. In all cases except ciprofloxacin, the increase in resistance seems to be the result of complex interactions among several cellular systems rather than individual mutations.