Quantifying the expression levels of mexA and mexB genes in response to the efflux pump inhibitor PAβN in ciprofloxacin-resistant Pseudomonas aeruginosa isolated from urinary tract infections

Abstract

Urinary tract infections (UTIs) are among the most prevalent bacterial infections worldwide, occurring in both community and healthcare settings. Pseudomonas aeruginosa, a Gram-negative opportunistic pathogen, is one of the five most significant nosocomial bacteria and a major contributor to UTIs. This study aimed to quantify the expression levels of efflux pump genes mexA and mexB in response to the efflux pump inhibitor phenylalanine-arginine β-naphthylamide (PAβN) in ciprofloxacin-resistant P. aeruginosa isolates.

Methods. Fifty urine specimens were collected from UTI patients at various hospitals in Baghdad. Specimens were directly cultured by streaking on differential media. Five ciprofloxacin-resistant P. aeruginosa isolates were identified, with resistance confirmed using the disk diffusion method for antibiotic susceptibility. The broth microdilution method was employed to determine the minimum inhibitory concentration (MIC) of ciprofloxacin (CIP) alone and in combination with PAβN to assess PAβN’s inhibitory activity. RNA was extracted and purified from the bacterial isolates, followed by reverse transcription and quantitative PCR to evaluate the expression of efflux pump-related genes. The expression levels of mexA and mexB were measured in the presence of the tested compounds using quantitative PCR.

Results. Antibiotic susceptibility testing revealed that the isolates were resistant to nearly all antibiotics tested, except piperacillin-tazobactam, which was effective against 64% of the isolates. None of the five selected isolates showed sensitivity to ciprofloxacin. The MIC for ciprofloxacin ranged from 31.25 to 62.5 mg/L, while the sub-MIC in the presence of PAβN was significantly reduced, ranging from 7.81 to 15.62 mg/L. The expression levels of mexA and mexB genes decreased significantly in three of the five isolates when exposed to PAβN and ciprofloxacin compared to ciprofloxacin alone, with expression levels reduced from 1.319 to 0.574, 0.159 to 0.008, and 194.0 to 4.9, respectively. However, two isolates exhibited overexpression of these genes.

Conclusions. The presence of PAβN significantly reduced ciprofloxacin MICs in most ciprofloxacin-resistant P. aeruginosa isolates in vitro. The expression levels of mexA and mexB genes decreased in most isolates when PAβN was used in combination with ciprofloxacin, suggesting that PAβN could enhance the efficacy of ciprofloxacin. These findings indicate that PAβN may be a promising adjunctive antimicrobial agent for treating UTIs caused by resistant P. aeruginosa.