Synergism between outer membrane proteins and antimicrobials

An Outer Membrane Vesicle-Based Permeation Assay (OMPA) for Assessing Bacterial Bioavailability

When searching for new antibiotics against Gram-negative bacterial infections, a better understanding of the permeability across the cell envelope and tools to discriminate high from low bacterial bioavailability compounds are urgently needed. Inspired by the phospholipid vesicle-based permeation assay (PVPA), which is designed to predict non-facilitated permeation across phospholipid membranes, outer membrane vesicles (OMVs) of Escherichia coli either enriched or deficient of porins are employed to coat filter supports for predicting drug uptake across the complex cell envelope. OMVs and the obtained in vitro model are structurally and functionally characterized using cryo-TEM, SEM, CLSM, SAXS, and light scattering techniques. In vitro permeability, obtained from the membrane model for a set of nine antibiotics, correlates with reported in bacterio accumulation data and allows to discriminate high from low accumulating antibiotics. In contrast, the correlation of the same data set generated by liposome-based comparator membranes is poor. This better correlation of the OMV-derived membranes points to the importance of hydrophilic membrane components, such as lipopolysaccharides and porins, since those features are lacking in liposomal comparator membranes. This approach can offer in the future a high throughput screening tool with high predictive capacity or can help to identify compound- and bacteria-specific passive uptake pathways.

Vitamin D Pretreatment Attenuates Ciprofloxacin-Induced Antibacterial Activity

Background

Ciprofloxacin is an antimicrobial that is commonly used to treat several types of infections. It exerts its antimicrobial activity through interfering with bacterial DNA replication and transcription, leading to increase oxidative stress and eventually bacterial death. Vitamin D, on the other hand, has been found to have DNA protective and antioxidant effects. In the current study, the possible interactive effect of vitamin D on ciprofloxacin-induced cytotoxicity was investigated in various standard bacterial strains.

Methods

The bacterial strains that were used include Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Staphylococcus epidermidis, Acinetobacter baumannii, Proteus mirabilis, and Klebsiella pneumoniae. The antibacterial effect of ciprofloxacin with and without vitamin D treatment of the bacteria was assessed using disc diffusion method and by measuring the minimum inhibitory concentration (MIC) and zones of inhibition of bacterial growth. Moreover, reactive oxygen species (ROS) generation after pretreatment of E. Coli cells with ciprofloxacin and/or vitamin D was measured as a function of as a function of hydrogen peroxide generation.

Results

Ciprofloxacin demonstrated a potent antibacterial effect against the tested strains of bacteria. Moreover, pretreatment with vitamin D resulted in protecting the bacteria from the cytotoxicity of ciprofloxacin, this was indicated by the significantly smaller zones of inhibition and higher MIC values compared to ciprofloxacin alone as well as reduced ciprofloxacin-induced ROS generation after treatment with vitamin D.

Conclusion

Results revealed the possible reduction in the activity of ciprofloxacin when used in combination with vitamin D. This could be explained by the ability of vitamin D to reduce oxidative stress in the bacterial cells.

Antibacterial mode of action of the hydroethanolic extract of Leonotis nepetifolia (L.) R. Br. involves bacterial membrane perturbations

ETHNOPHARMACOLOGICAL RELEVANCE

Leonotis nepetifolia (L) R. Br., Lamiaceae, a pantropical shrub, popularly known in Brazil as "cordão-de-frade", "rubim", is reportedly used in Brazilian ethnomedicine as well as in different countries in the treatments of ailments such as infections, inflammations, wounds, stomach disorders, among others.

AIM OF THE STUDY

To evaluate its potential cytotoxicity and antibacterial mode of action of the hydroethanolic extract of L. nepetifolia (HELn) leaves, including phytochemical analysis.

MATERIALS AND METHODS

The cytotoxicity of HELn was investigated by Alamar blue assay, using CHO-K1 cells. Antibacterial activity of HELn was tested by broth microdilution methods against a panel of bacteria of clinical interest. The mode of action of L. nepetifolia was studied by targeting bacterial membranes. Phytochemical analysis was performed by determining total secondary metabolites with spectrophotometric assays and HPLC.

RESULTS

HELn is not cytotoxic in the in vitro evaluation (IC50>200 μg/mL). It demonstrated a good spectrum of antibacterial activity with major activity against Shigella flexneri, Enterococcus faecalis, Staphylococcus aureus and Bacillus subtilis with MIC=6.25 µg/mL, Helicobacter pylori with MIC of 25 µg/mL and Streptococcus pyogenes with MIC of 50 µg/mL. Its mode of action is associated, at least partly, with changes in the permeability of bacterial membranes, as evidenced by the increased entry of hydrophobic antibiotics in Shigella flexneri and intense efflux of K(+) and nucleotide leakage in E. faecalis and Shigella flexneri. In addition, the presence of phenols, flavonoids and carotenoids, described in the literature to possess antibacterial effects, were detected in the composition of HELn, with high phenol content (11.55%), especially the flavonoids (6.47%).

CONCLUSION

The results indicate that HELn has low cytotoxicity and potent antibacterial activity. It is bacteriostatic in nature, possibly acting at the level of bacterial membranes, especially on the cytoplasmic membrane and outer membrane, thus supporting its popular use in infectious processes. In addition, the presence of phenols, flavonoids, carotenoids, fatty acids and steroids, described in the literature as possessing antimicrobial activity, were detected in the composition of HELn.

Carbapenem-resistance mechanisms of multidrug-resistant Pseudomonas aeruginosa

Clonal dissemination of multidrug-resistant Pseudomonas aeruginosa (MDRPA) is a major concern worldwide. The aim of this study was to explore the mechanisms leading to the carbapenem resistance of an MDRPA clone. Isolates were obtained from a surgical wound, sputum, urine and a blood culture. Pulsed-field gel electrophoresis (PFGE) showed high genomic homogeneity of these isolates and confirmed the circulation of an endemic clone belonging to serotype O4. Outer membrane protein (OMP) bands were visualized by SDS-PAGE, meropenem accumulation was measured in a bioassay and integrons were detected by PCR. Efflux pumps were studied for several antimicrobial agents and synergic combinations thereof in the presence or absence of both carbonyl cyanide m-chlorophenylhydrazone (CCCP) and Phe-Arg-β-naphthylamide (PAβN) at final concentrations of 10 and 40 mg l(-1), respectively. On OMP electrophoretic profiles, MDRPA showed a reduction of outer membrane porin D (OprD) and PCR demonstrated the presence of a class 1 integron with a cassette encoding aminoglycoside adenyltransferase B (aadB). Meropenem accumulation was slightly higher in bacilli than in the filamentous cells that formed in the presence of antibiotics. Overexpression of the efflux pump MexAB-OprM and a functional MexXY-OprM were detected in all isolates.