Biofilm Formation Caused by Clinical Acinetobacter baumannii Isolates Is Associated with Overexpression of the AdeFGH Efflux Pump

Abstract

cChronic wound infections are associated with biofilm formation, which in turn has been correlated with drug resistance. However, the mechanism by which bacteria form biofilms in clinical environments is not clearly understood. This study was designed to investigate the biofilm formation potency of Acinetobacter baumannii and the potential association of biofilm formation with genes encoding efflux pumps, quorum-sensing regulators, and outer membrane proteins. A total of 48 clinically isolated A. baumannii strains, identified by enterobacterial repetitive intergenic consensus (ERIC)-PCR as types A-II, A-III, and A-IV, were analyzed. Three representative strains, which were designated A. baumannii ABR2, ABR11, and ABS17, were used to evaluate antimicrobial susceptibility, biofilm inducibility, and gene transcription (abaI, adeB, adeG, adeJ, carO, and ompA). A significant increase in the MICs of different classes of antibiotics was observed in the biofilm cells. The formation of a biofilm was significantly induced in all the representative strains exposed to levofloxacin. The levels of gene transcription varied between bacterial genotypes, antibiotics, and antibiotic concentrations. The upregulation of adeG correlated with biofilm induction. The consistent upregulation of adeG and abaI was detected in A-III-type A. baumannii in response to levofloxacin and meropenem (1/8 to 1/2؋ the MIC), conditions which resulted in the greatest extent of biofilm induction. This study demonstrates a potential role of the AdeFGH efflux pump in the synthesis and transport of autoinducer molecules during biofilm formation, suggesting a link between low-dose antimicrobial therapy and a high risk of biofilm infections caused by A. baumannii. This study provides useful information for the development of antibiofilm strategies.

Subinhibitory Concentrations of Trimethoprim and Sulfamethoxazole Prevent Biofilm Formation by Acinetobacter baumannii through Inhibition of Csu Pilus Expression

“…This has led to the hypothesis that antibiotics may act as signaling molecules rather than outright antibacterial agents, especially in the natural environment (31). Numerous studies have provided support for this hypothesis, finding a wide variety of phenotypic changes caused by subinhibitory antibiotic concentrations (28,(32)(33)(34)(35). In certain species, up to 5% of the promoters appear to be affected (36).…”

“…In certain species, up to 5% of the promoters appear to be affected (36). In general, most of these responses tend to increase biofilm production, with concomitant increases in resistance to the signaling antibiotic (28,(32)(33)(34)(35)37). In A. baumannii, subinhibitory concentrations of imipenem or levofloxacinmeropenem have been shown to increase biofilm, type IV pili, and surface motility, which are associated with overexpression of the AdeFGH efflux pump (33,35,37).…”

“…In general, most of these responses tend to increase biofilm production, with concomitant increases in resistance to the signaling antibiotic (28,(32)(33)(34)(35)37). In A. baumannii, subinhibitory concentrations of imipenem or levofloxacinmeropenem have been shown to increase biofilm, type IV pili, and surface motility, which are associated with overexpression of the AdeFGH efflux pump (33,35,37). In agreement with our results, previous reports have shown that subinhibitory concentrations of Tmp inhibit P fimbria expression on uropathogenic E. coli (28), quinolones inhibit type 1 fimbria expression on E. coli (32), and azithromycin inhibits piliation of Neisseria gonorrhoeae (34).…”

Biofilm Formation Restrained by Subinhibitory Concentrations of Tigecyclin in <b><i>Acinetobacter baumannii</i></b> Is Associated with Downregulation of Efflux Pumps

“…Expression of the adeM and carO genes seemed to be positively associated with adeJ expression. Reportedly, an increase in biofilm formation during the transition from a planktonic to a biofilm pattern in A. baumannii was accompanied by upregulation of the abaI gene [29]. Thus, we presume that tigecycline exerts antibiofilm activity via downregulation of the adeG gene to inhibit biofilm formation directly.…”

The Relationship Between Antibiotic Resistance Phenotypes and Biofilm Formation Capacity in Clinical Isolates of Acinetobacter baumannii

“…The high emergence rates of multidrug resistance (MDR) and extensively drug resistance (XDR) among A. baumannii isolates have led them to be considered as one of the top seven pathogens posing threats to medical and health systems (1,2). In addition to antibiotic resistance, biofilm formation is another characteristic leading to the survival of A. baumannii in the presence of antibiotics and high stresses (1)(2)(3). It was revealed that the difference in biofilm formation capacity among international clonal (IC) types of A. baumannii could affect the spreading of this microorganism (4).…”