Post-antibiotic effect (PAE) of moxifloxacin in multidrug-resistant Stenotrophomonas maltophilia

Small Molecule IITR08367 Potentiates Antibacterial Efficacy of Fosfomycin against Acinetobacter baumannii by Efflux Pump Inhibition

Fosfomycin is a broad-spectrum single-dose therapy approved for treating lower urinary tract infections. Acinetobacter baumannii, one of the five major UTI-causing pathogens, is intrinsically resistant to fosfomycin. Reduced uptake and active efflux are major reasons for this intrinsic resistance. AbaF, a major facilitator superfamily class of transporter in A. baumannii, is responsible for fosfomycin efflux and biofilm formation. This study describes the identification and validation of a novel small-molecule efflux pump inhibitor that potentiates fosfomycin efficacy against A. baumannii. An AbaF inhibitor screening was performed against Escherichia coli KAM32/pUC18_abaF, using the noninhibitory concentration of 24 putative efflux pump inhibitors. The inhibitory activity of IITR08367 [bis(4-methylbenzyl) disufide] against fosfomycin/H+ antiport was validated using ethidium bromide efflux, quinacrine-based proton-sensitive fluorescence, and membrane depolarization assays. IITR08367 inhibits fosfomycin/H+ antiport activity by perturbing the transmembrane proton gradient. IITR08367 is a nontoxic molecule that potentiates fosfomycin activity against clinical strains of A. baumannii and prevents biofilm formation by inhibiting efflux pump (AbaF). The IITR08367-fosfomycin combination reduced bacterial burden by > 3 log10 in kidney and bladder tissue in the murine UTI model. Overall, fosfomycin, in combination with IITR08367, holds the potential to treat urinary tract infections caused by A. baumannii.

Clinical factors associated with acquisition of resistance to levofloxacin in Stenotrophomonas maltophilia

PURPOSE

Fluoroquinolones, rapidly gaining prominence in treatment of Stenotrophomonas maltophilia (SMP), are noted for their potency and tolerability. However, SMP may rapidly acquire resistance to fluoroquinolones. We evaluated associations of clinical factors with acquisition of levofloxacin resistance (LFr) in SMP.

MATERIALS AND METHODS

Our retrospective cohort study was based on patient data collected between January 2008 and June 2010. Through screening of 1275 patients, we identified 122 patients with data for SMP antibiotic susceptibility testing in ≥3 serial SMP isolates.

RESULTS

We assigned the 122 patients to either the SS group (n=54) in which levofloxacin susceptibility was maintained or the SR group (n=31) in which susceptible SMP acquired resistance. In multivariate regression analysis, exposure to levofloxacin for more than 3 weeks [odds ratio (OR) 15.39, 95% confidential interval (CI) 3.08-76.93, p=0.001] and co-infection or co-colonization with Klebsiella pneumoniae resistant to levofloxacin (OR 4.85, 95% CI 1.16-20.24, p=0.030) were independently associated with LFr acquisition in SMP.

CONCLUSION

Acquisition of LFr during serial sampling of SMP was related to the levofloxacin exposure.

Stenotrophomonas maltophilia: an emerging global opportunistic pathogen

Stenotrophomonas maltophilia is an emerging multidrug-resistant global opportunistic pathogen. The increasing incidence of nosocomial and community-acquired S. maltophilia infections is of particular concern for immunocompromised individuals, as this bacterial pathogen is associated with a significant fatality/case ratio. S. maltophilia is an environmental bacterium found in aqueous habitats, including plant rhizospheres, animals, foods, and water sources. Infections of S. maltophilia can occur in a range of organs and tissues; the organism is commonly found in respiratory tract infections. This review summarizes the current literature and presents S. maltophilia as an organism with various molecular mechanisms used for colonization and infection. S. maltophilia can be recovered from polymicrobial infections, most notably from the respiratory tract of cystic fibrosis patients, as a cocolonizer with Pseudomonas aeruginosa. Recent evidence of cell-cell communication between these pathogens has implications for the development of novel pharmacological therapies. Animal models of S. maltophilia infection have provided useful information about the type of host immune response induced by this opportunistic pathogen. Current and emerging treatments for patients infected with S. maltophilia are discussed.

Stenotrophomonas maltophilia: emerging disease patterns and challenges for treatment

Stenotrophomonas maltophilia is a ubiquitous organism associated with opportunistic infections. In the immunocompromised host, increasing prevalence and severity of illness is observed, particularly opportunistic bloodstream infections and pneumonia syndromes. In this article, the classification and microbiology are outlined, together with clinical presentation, outcomes and management of infections due to S. maltophilia. Although virulence mechanisms and the genetic basis of antibiotic resistance have been identified, a role for standardized and uniform reporting of antibiotic sensitivity is not defined. Infections due to S. maltophilia have traditionally been treated with trimethoprim-sulfamethoxazole, ticarcillin-clavulanic acid, or fluoroquinolone agents. The use of combination therapies, newer fluoroquinolone agents and tetracycline derivatives is discussed. Finally, measures to prevent transmission of S. maltophilia within healthcare facilities are reported, especially in at-risk patient populations.