Differential expression of antibiotic resistance-associated genes in MDR Acinetobacter baumannii CF12 under sub-MIC stress of meropenem and levofloxacin

Background: Acinetobacter baumannii is a critical nosocomial pathogen characterized by its multidrug resistance and strong ability to form biofilms. Efflux pumps, quorum-sensing systems, and porin proteins are major contributors to its virulence and antibiotic resistance. Objectives: This study aimed to evaluate the expression patterns of efflux pump genes (adeB, adeG, adeJ), the quorum-sensing gene (abaI), and porin genes (carO, ompA) in the virulent, multiple drug resistant isolate A. baumanniiCF12. Methods: The MDR isolate A. baumanniiCF12 was cultured in nutrient broth containing sub-MIC meropenem (16 µg/mL) and/or levofloxacin (8 µg/mL). Gene expression was assessed at 4, 8, and 12 hours using SYBR Green RT-qPCR. Relative quantification was computed using the 2⁻ΔΔCt method with ropB as the internal control. Statistical significance was determined using ANOVA and LSD tests, with p<0.05 considered significant. Results: Antibiotic exposure resulted in a time-dependent modulation of gene expression, with adeB showing significant downregulation under all treatments. adeG and adeJ were significantly upregulated at early exposure (4-8 h) to single antibiotics but downregulated at 12 h or with combined treatment. I was consistently downregulated across all conditions. carO and ompA were upregulated at 4 h but significantly suppressed at 8–12 h or when both antibiotics were combined. The meropenem -levofloxacin combination caused uniform downregulation of all genes studied. Conclusion: Sub-MIC meropenem and levofloxacin exert distinct and time-dependent effects on efflux pump, porin, and quorum-sensing gene expression in A. baumanniiCF12. Combined treatment produced the most pronounced inhibitory effect, suggesting a beneficial synergistic action that may reduce bacterial virulence and resistance.