Presence of an Active Effiux System in the Fluoroquinolones Resistance of Mycoplasma Hominis

Objective: To investigate the possible presence ofan active efflux system in resistance tofluoroquinolones in Mycoplasma hominis. Methods: The resistant strains of M. hominis wereselected from one hundred and three clinical strainsof M. hominis by broth microdilution method. The ac-cumulation of ciprofloxacin in M. hominis and the in-fluence of carbonyl cyanide m-chlorophenyl-hydrazone(CCCP) and reserpine were measured by a fluores-cence method. Results: Two resistant strains and two susceptiblestrains of M. hominis were selected in vitro. The accu-mulation of ciprofloxacin for resistant strains is lowerthan that of susceptible strains. CCCP and reserpinehad different influence on clinical strains of M.hominis. Reserpine could dramatically increase theaccumulation of ciprofloxacin, however CCCP had alittle effect on it. Conclusion: These results suggest that the pres-ence of an active efflux system implicated in thefluoroquinolones-resistant in M. hominis.

Plant-derived secondary metabolites as the main source of efflux pump inhibitors and methods for identification

The upsurge of multiple drug resistance(MDR)bacteria substantially diminishes the effectiveness of antibiotic arsenal and therefore intensifies the rate of therapeutic failure.The major factor in MDR is efflux pump-mediated resistance.A unique pump can make bacteria withstand a wide range of structurally diverse compounds.Therefore,their inhibition is a promising route to eliminate resistance phenomenon in bacteria.Phytochemicals are excellent alternatives as resistance-modifying agents.They can directly kill bacteria or interact with the crucial events of pathogenicity,thereby decreasing the ability of bacteria to develop resistance.Numerous botanicals display noteworthy efflux pumps inhibitory activities.Edible plants are of growing interest.Likewise,some plant families would be excellent sources of efflux pump inhibitors(EPIs)including Apocynaceae,Berberidaceae,Convolvulaceae,Cucurbitaceae,Fabaceae,Lamiaceae,and Zingiberaceae.Easily applicable methods for screening plant-derived EPIs include checkerboard synergy test,berberine uptake assay and ethidium bromide test.In silico highthroughput virtual detection can be evaluated as a criterion of excluding compounds with efflux substrate-like characteristics,thereby improving the selection process and extending the identification of EPIs.To ascertain the efflux activity inhibition,real-time PCR and quantitative mass spectrometry can be applied.This review emphasizes on efflux pumps and their roles in transmitting bacterial resistance and an update plant-derived EPIs and strategies for identification.

Variation in soil organic matter accumulation and metabolic activity along an elevation gradient in the Santa Rosa Mountains of Southern California, USA

Variations in soil organic matter accumulation across an elevation can be used to explain the control of substrate supply and variability on soil metabolic activity. We investigated geographic changes in soil organic matter and metabolic rates along an elevation gradient（289–2,489 m） in the Santa Rosa Mountains, California, USA from subalpine and montane pine forests through chaparral to desert. From base（289 m） to summit（2,489 m）, 24 sites were established for collecting soil samples under canopies and inter-canopy spaces, at 0–5 and 5–15 cm soil depths increments. Soil organic matter（SOM） content was determined using weight loss on ignition at 550°C and soil CO2 efflux（R） was measured at day 5（R5） and day 20（R20） of incubation. Changes in SOM content along the elevation gradient showed a significant relationship（P〈0.05） but R5 and R20 were not related to either elevation or SOM content. However, the ratio of R and SOM（R5/SOM） showed a strong relationship across the mountains at both soil depths. R5/SOM, as an indicator of carbon use efficiency, may be applicable to other semi-arid transects at larger scale modeling of soil metabolic processes.

Accumulation of ciprofloxacin and lomefloxacinin fluoroquinolone-resistant strains of Escherichia coli

Objective To evaluate the role of outer membrane protein (Omp) F-deficiency and active efflux in the accumulation of hydrophilic fluoroquinolones ciprofloxacin (CPLX) and lomefloxacin (LMLX) in resistant E. coli strains. Methods Fluoroquinolone accumulation in bacteria and the effect of active efflux were measured by a fluorescence method. The outer membrane proteins of the bacteria were analysed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). E. coli strains in this study included control strains JF701 and JF703 that are OmpC- or OmpF-deficient mutants of E. coli K-12, respectively, and the fluoroquinolone susceptible strain the fluoroquinolone susceptible strain of Escherichia coli (Ecs) and its in vitroselected resistant strains R2 and R256, and the clinical resistant isolates R5 and R6. Results The steady-state accumulation concentration of each drug in Ecs appeared to be the same as in JF701, while in the OmpF- deficient strain JF703, it was 1/5 CPLX or 1/2 LMLX lower than that in JF701, but JF703 was still susceptible to fluoroquinolones. On the other hand, compared with susceptible strains, a 2- to 10-fold decrease in the accumulation of each drug was found in the resistant strains except R2, in which the accumulation was slightly higher than in JF703. After the addition of 2,4-dinitrophenol (DNP), accumulation of each drug increased, especially in resistant strains, indicating that the function of the active efflux (pump) system in these bacteria had been enhanced dramatically. Furthermore, both OmpF and OmpC in Ecs, OmpF-deficiency in R2 and R256 and OmpC-deficiency in R5 and R6 were observed.Conclusion The decreased accumulation of hydrophilic fluoroquinolones in E. coli involved OmpF-deficiency and active efflux (pump), and the latter may be an important factor.