Efflux pump genes of the resistance-nodulation-division family in Burkholderia cenocepacia genome

BACKGROUND: Burkholderia cenocepacia is recognized as opportunistic pathogen that can cause lung infections in cystic fibrosis patients. A hallmark of B. cenocepacia infections is the inability to eradicate the organism because of multiple intrinsic antibiotic resistance. As Resistance-Nodulation-Division (RND) efflux systems are responsible for much of the intrinsic multidrug resistance in Gram-negative bacteria, this study aims to identify RND genes in the B. cenocepacia genome and start to investigate their involvement into antimicrobial resistance. RESULTS: Genome analysis and homology searches revealed 14 open reading frames encoding putative drug efflux pumps belonging to RND family in B. cenocepacia J2315 strain. By reverse transcription (RT)-PCR analysis, it was found that orf3, orf9, orf11, and orf13 were expressed at detectable levels, while orf10 appeared to be weakly expressed in B. cenocepacia. Futhermore, orf3 was strongly induced by chloramphenicol. The orf2 conferred resistance to fluoroquinolones, tetraphenylphosphonium, streptomycin, and ethidium bromide when cloned and expressed in Escherichia coli KAM3, a strain lacking the multidrug efflux pump AcrAB. The orf2-overexpressing E. coli also accumulate low concentrations of ethidium bromide, which was restored to wild type level in the presence of CCCP, an energy uncoupler altering the energy of the drug efflux pump. CONCLUSION: The 14 RND pumps gene we have identified in the genome of B. cenocepacia suggest that active efflux could be a major mechanism underlying antimicrobial resistance in this microorganism. We have characterized the ORF2 pump, one of these 14 potential RND efflux systems. Its overexpression in E. coli conferred resistance to several antibiotics and to ethidium bromide but it remains to be determined if this pump play a significant role in the antimicrobial intrinsic resistance of B. cenocepacia. The characterization of antibiotic efflux pumps in B. cenocepacia is an obligatory step prior to the design of specific, potent bacterial inhibitors for the improved control of infectious diseases. Consequently, the topic deserves to be further investigated and future studies will involve systematic investigation on the function and expression of each of the RND efflux pump homologs

mmpL7 Gene of Mycobacterium tuberculosis Is Responsible for Isoniazid Efflux in Mycobacterium smegmatis

The Mycobacterium tuberculosis mmpL7 gene, encoding a hypothetical resistance nodulation division transporter, confers a high resistance level to isoniazid when overexpressed in Mycobacterium smegmatis. The resistance level decreased in the presence of the efflux pump inhibitors reserpine and CCCP (carbonyl cyanide m-chlorophenylhydrazone). Energy-dependent efflux of isoniazid from M. smegmatis cells expressing the mmpL7 gene was observed

Synthesis and anti-mycobacterial activities of triazoloquinolones

A number of quinolone derivatives have been reported to possess anti-mycobacterial activity. Generally. Mycobacterium tuberculosis isolates expressing resistance to both isoniazid and rifampin are susceptible to fluoroquinolones. Benzotriazole is a hetero-bicyclic aromatic ring endowed with interesting chemical and biological properties and pharmacological activities. In a preliminary study we have recently reported the activity of triazolo[4,5-h]quinolone-carboxylic acids, a new class of benzotriazole derivatives active against multi-drug resistant M. tuberculosis (MDR-Mtb). In this study we confirm that this novel class of quinolones is endowed with a selective anti-mycobacterial activity, coupled with absence of cytotoxicity. The SAR analysis of the new derivatives in comparison with the previous series shows that the methyl group is the most effective substituent in both N-3 and N-9 positions of the ring system

LfrR Is a Repressor That Regulates Expression of the Efflux Pump LfrA in Mycobacterium smegmatis

The lfrA gene of Mycobacterium smegmatis encodes an efflux pump which mediates resistance to different fluoroquinolones, cationic dyes, and anthracyclines. The deletion of the lfrR gene, coding for a putative repressor and localized upstream of lfrA, increased the lfrA expression. In this study, reverse transcription-PCR experiments showed that the two genes are organized as an operon, and lacZ reporter fusions were used to identify the lfrRA promoter region. The lfrRA promoter assignment was verified by mapping the transcription start site by primer extension. Furthermore, we found that some substrates of the multidrug transporter LfrA, e.g., acriflavine, ethidium bromide, and rhodamine 123, enhance lfrA expression at a detectable level of transcription. LfrR protein was purified from Escherichia coli as a fusion protein with a hexahistidine tag and found to bind specifically to a fragment 143 bp upstream of lfrR by gel shift analysis. Furthermore, acriflavine was able to cause the dissociation of the LfrR from the promoter, thus suggesting that this molecule interacts directly with LfrR, inducing lfrA expression. These results suggest that the LfrR repressor is able to bind to different compounds, which allows induction of LfrA multidrug efflux pump expression in response to these ones. Together, all data suggest that the LfrA pump is tightly regulated and that the repression and induction can be switched about a critical substrate concentration which is toxic for the cell

Identification and characterization of a new ligand-binding site in FnbB, a fibronectin-binding adhesin from Streptococcus dysgalactiae

Streptococcus dysgalactiae S2, a bovine mastitis isolate, expresses the fibronectin (Fn)-binding adhesin FnbB. Here, we describe a new fibronectin-binding domain called UFnBD, located 100 amino acid N-terminal to the primary repetitive Fn-binding domain (FnBRD-B) of FnbB. UFnBD interacted with N-terminal region of Fn (N29) and this binding was mostly mediated by type I module pair 2-3 of N29 fragment, whereas FnBRD-B mainly bound to type I module pair 4-5. Furthermore, UFnBD inhibited adherence of S. dysgalactiae to Fn but at lower level as compared to FnBRD-B. UFnBD exclusively shared antigenic properties with the Fn-binding unit Du of FnbpA from Staphylococcus aureus but not with ligand-binding domains or motifs of other adhesins, while Fn-induced determinants of FnBRD-B and other adhesins appeared to be conformationally related. Consistent with this, a monoclonal antibody 7E11 generated from a mouse immunized with FnbB, and that recognized UFnBD did not cross-react with FnBRD-B. The epitope for 7E11 was mapped to 40 amino acid long segment within UFnBD and interaction between the antibody and the epitope was specifically induced by Fn or N29. A similar antibody epitope was observed in Streptococcus pyogenes strains suggesting the presence of an adhesin bearing epitope related to FnbB

The multidrug transporters belonging to major facilitator superfamily in Mycobacterium tuberculosis.

BACKGROUND: Both intrinsic and acquired multidrug resistance play an important role in the insurgence of tuberculosis. Detailed knowledge of the molecular basis of drug recognition and transport by multidrug transport systems is required for the development of new antibiotics that are not extruded or of inhibitors that block the multidrug transporter and allow traditional antibiotics to be effective. MATERIALS AND METHODS: We have undertaken the inventory of the drug transporters subfamily, included in the major facilitator superfamily (MFS), encoded by the complete genome of Mycobacterium tuberculosis (MTB). These proteins were identified on the basis of their characteristic stretches of amino acids and transmembrane segments (TMS) number. CONCLUSIONS: Genome analysis and searches of homology between the identified transporters and proteins characterized in other organisms revealed 16 open reading frames encoding putative drug efflux pumps belonging to MFS. In the case of two of them, we also have demonstrated that they function as drug efflux proteins