<p>Effects of sub-inhibitory concentrations of meropenem and tigecycline on the expression of genes regulating pili, efflux pumps and virulence factors involved in biofilm formation by<em> Acinetobacter baumannii</em></p>

Abstract

Background: Sub-minimal inhibitory concentrations of antibiotics have been indicated to affect the biofilm formation in pathogens of nosocomial infections. This study aimed to investigate the effects of meropenem and tigecycline at their sub-minimum inhibitory concentrations (MICs) on the biofilm formation capacity of Acinetobacter baumannii ( A. baumannii) , as well as the expression levels of genes involved in biofilm formation, quorum sensing, pili assembly and efflux pumps. Materials and methods: In this study, four non-clonal strains (AB10, AB13, AB32 and AB55), which were different from the aspects of antibiotic susceptibility and biofilm formation from each other were selected for the evaluation of antimicrobial susceptibility, biofilm inducibility at sub-MICs of meropenem and tigecycline and the gene expression levels (the abaI, abaR, bap, pgaA, csuE, bfmS, bfmR, ompA, adeB, adeJ and adeG genes). Result: A significant increase in the MICs of all antibiotics was demonstrated in the biofilm cells in each four strains. The biofilm formation was significantly decreased in all the representative strains exposed to tigecycline. However, the biofilm inducibility at sub-MICs of meropenem was dependent on strain genotype. In concordance with these results, Pearson correlation analysis indicated a positive significant correlation between the biofilm formation capacity and the mRNA levels of genes encoding efflux pumps except adeJ , the genes involved in biofilm formation, pili assembly and quorum sensing following exposure to meropenem and tigecycline at their sub-MICs. Conclusion: These results revealed valuable data into the correlation between the gene transcription levels and biofilm formation, as well as quorum sensing and their regulation at sub-MICs of meropenem and tigecycline.

<p>Association Between Biofilm Formation, Structure, and the Expression Levels of Genes Related to biofilm formation and Biofilm-Specific Resistance of <em>Acinetobacter baumannii</em> Strains Isolated from Burn Infection in Ahvaz, Iran</p>

“…On the other hand, the efflux pumps especially the resistance-nodulation-cell division (RND) family confer low-level multidrug resistance and have several roles during the process of biofilm formation in A. baumannii . Moreover, these pumps have extruded actively the autoinducers associated with quorum sensing, and harmful molecules such as antibiotics and metabolic intermediates 24. In this present study, there was a significant association between the overexpression of adeJ and the capacity of biofilm formation, so that all strong biofilm producers and 81.5% of intermediate producers showed the overexpression of the adeJ .…”

“…The genomic DNA of these isolates were extracted using the boiling method, as previously described 17. The uniplex PCR assays were performed for the molecular identifications of the bap, pgaA, abaI, ompA and csuE genes and efflux pumps, including adeB, adeJ and adeG in a final volume of 25 μL 15,24. The sequences and sizes of the primers used in this study are shown in Table 1.…”

“…Real-time PCR amplification reaction was prepared in a final volume 20 µL, with 400 ng cDNA, 10 µL RealQ Plus Master Mix Green (Amliqon, Denmark), 0.5 µL each of forward and reverse primers (10 nM each) and RNase- and DNase-free water up to the final volume 20 µL. The Primer sequences used for the genes related to the biofilm formation, including bap, abaI ompA, csuE and pgaA gene and efflux pumps, including adeB, adeJ and adeG are shown in Table 1 24. The 16rRNA gene was used as an internal control for the normalization of gene expression levels.…”

Outer membrane protein A (OmpA) as a potential therapeutic target for Acinetobacter baumannii infection

“…The same results were observed in R3 clinical isolates in the presence of PMB [70]. Meropenem at the concentration of 64 μg/mL and 128 μg/mL increased AbOmpA expression by 1.81 and 1.63 folds, respectively [71].…”

Developing new therapeutic approaches for treating infections caused by multi-drug resistant Acinetobacter baumannii

“…35 , 38 It has been found that there is differential expression of genes controlling biofilm formation, including genes regulating pili, efflux pumps, and virulence factors when A. baumannii is exposed to sub-inhibitory concentrations of antimicrobials, specifically Meropenem and Tigecycline. 39 This promotion of biofilm formation due to sub-inhibitory concentrations of antimicrobials leads to an increase in minimum inhibitory concentrations (MIC) and the minimum biofilm eradication concentration of these antimicrobials. This was thought to be due the exopolysaccharide matrix or the overexpression of efflux pumps.…”