Abstract
Pseudomonas aeruginosa causes chronic infections, such as cystic fibrosis, endocarditis, bacteremia, and sepsis, which are life-threatening and difficult to treat. The lack of antibiotic response in P. aeruginosa is due to adaptive resistance mechanism, which prevents the entry of antibiotics into the cytosol of the cell to achieve tolerance. Among the different groups of antibiotics, aminoglycosides are used as a parenteral antibiotic for the treatment of P. aeruginosa. This study aimed to determine the kinetics of antibiotic tolerance and gene expression changes in P. aeruginosa exposed to amikacin, gentamicin, and tobramycin. These antibiotics were exposed to P. aeruginosa at their MICs and the experimental setup was monitored for 72 h, followed by the measurement of optical density every 12 h. The growth of P. aeruginosa in the MICs of antibiotics represented the kinetics of antibiotic tolerance in amikacin, gentamicin, and tobramycin. The transcriptomic profile of antibiotic exposed P. aeruginosa PA14 was taken from the Gene Expression Omnibus (GEO), NCBI as microarray datasets. The gene expressions of two datasets were compared by test versus control. Tobramycin-exposed P. aeruginosa failed to develop tolerance in MICs of 0.5 µg/mL, 1 µg/mL, and 1.5 µg/mL, whereas amikacin- and gentamicin-treated P. aeruginosa developed tolerance. This illustrated the superior in vitro response of tobramycin over gentamicin and amikacin. Further, in silico transcriptomic analysis of tobramycin-treated P. aeruginosa resulted in differentially expressed genes (DEGs), enriched in 16s rRNA methyltransferase E, B, and L, alginate biosynthesis genes, and several proteins of the type II secretion system (T2SS) and type III secretion system (T3SS). The regulation of mucA in alginate biosynthesis, and gidB in RNA methyltransferases, suggested an increased antibiotic response and a low probability of developing resistance during tobramycin treatment. The use of tobramycin as a parenteral antibiotic with its synergistic combination might combat P. aeruginosa with increased response.
Highlights
The experimental setup of the in vitro treatment of antibiotics to P. aeruginosa reflects the antibiotic tolerance in chronic infections, where the response to antimicrobials is reduced due to the development of adaptive resistance [25]
Among the antibiotics evaluated for tolerance in P. aeruginosa, tobramycin exhibited a superior post-antibiotic effect in all the minimum inhibitory concentrations (MICs) and was found to be more effective at suppressing the bacterial sub-populations
In silico analysis of the differentially expressed genes (DEGs) in the microarray datasets mimicking our experimental condition exposed the possible effectiveness of tobramycin in antibiotic tolerance
Summary
P. aeruginosa is an opportunistic pathogen, which causes chronic infections that are difficult to treat due to its limited response to antimicrobials and the emergence of antibiotic resistance during therapy [1]. Multi-drug resistance (MDR) is increasing due to overexposure to antibiotics [2]. Drug resistance in P. aeruginosa is developed as a result of various physiological and genetic mechanisms, which include multidrug efflux pumps, beta-lactamase production, outer membrane protein (porin) loss, and target mutations. MDR P. aeruginosa are, in most cases, concurrently resistant to ciprofloxacin, imipenem, ceftazidime, and piperacillin-tazobactam, which limits treatment options [3]
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