Polyamines inhibit porin-mediated fluoroquinolone uptake in mycobacteria

Polyamines decrease the permeability of the outer membrane of Escherichia coli to fluoroquinolones and β-lactams. In this study, we tested the effect of four polyamines (spermidine, spermine, cadaverine and putrescine) on fluoroquinolone uptake in Mycobacterium bovis BCG. Our results show that polyamines are also capable of reducing the permeability of the mycobacterial outer membrane to fluoroquinolones. Spermidine was most effective and demonstrated reversible dose- and pH-dependent inhibition of ciprofloxacin accumulation. The extent of this inhibition was demonstrated across the fluoroquinolone compound class to varying degrees. Furthermore, we have shown that the addition of spermidine increases the survival of M. bovis BCG after a 5-day exposure to ciprofloxacin by up to 25 times. The treatment of actively-replicating Mycobacterium tuberculosis with spermidine reduced ciprofloxacin accumulation by half while non-replicating nutrient-starved M. tuberculosis cultures lacked similar sensitivity to polyamines. Gene expression studies showed that several outer membrane proteins are significantly down-regulated during the shift to non-replication. Collectively, these characteristics of fluoroquinolone uptake in M. bovis BCG are consistent with facilitated transport by porin-like proteins and suggest that a reduction in intracellular uptake contributes to the phenotypic drug resistance demonstrated by M. tuberculosis in the non-replicating state.

Pentapeptide repeat proteins

The pentapeptide repeat protein (PRP) family has more than 500 members in the prokaryotic and eukaryotic kingdoms. These proteins are composed of, or contain domains composed of, tandemly repeated amino acid sequences with a consensus sequence of [S,T,A,V][D,N][L,F][S,T,R][G]. The biochemical function of the vast majority of PRP family members is unknown. The three-dimensional structure of the first member of the PRP family was determined for the fluoroquinolone resistance protein (MfpA) from Mycobacterium tuberculosis. The structure revealed that the pentapeptide repeats encode the folding of a novel right-handed quadrilateral beta-helix. MfpA binds to DNA gyrase and inhibits its activity. The rod-shaped, dimeric protein exhibits remarkable similarity in size, shape, and electrostatics to DNA.

A fluoroquinolone resistance protein from Mycobacterium tuberculosis that mimics DNA

Fluoroquinolones are gaining increasing importance in the treatment of tuberculosis. The expression of MfpA, a member of the pentapeptide repeat family of proteins from Mycobacterium tuberculosis, causes resistance to ciprofloxacin and sparfloxacin. This protein binds to DNA gyrase and inhibits its activity. Its three-dimensional structure reveals a fold, which we have named the right-handed quadrilateral beta helix, that exhibits size, shape, and electrostatic similarity to B-form DNA. This represents a form of DNA mimicry and explains both its inhibitory effect on DNA gyrase and fluoroquinolone resistance resulting from the protein's expression in vivo.

In vitro anti-inflammatory effects and immunomodulation by gemifloxacin in stimulated human THP-1 monocytes

Cultured human THP-1 monocytes were exposed to serial concentrations of gemifloxacin over 4 h after pre-stimulation with zymogen A for 1 h or Staphylococcus aureus for 2 h. The following parameters were assessed: pH, phagocytosis, c-AMP, NO, TNFalpha, IL-1, IL-6, IL-8 and H2O2 levels, enzyme activities of protein kinase C, NADPH oxidase, SOD, gluthathion reductase, NAG and cathepsin D as well as lipid peroxidation. The reversiblity of these changes was determined in the presence of known blockers of the phagocytic process. The effects of gemifloxacin on DNA synthesis and killing of S. aureus was assessed in bacteria alone and in those bacteria phagocytosed by THP-1 monocytes over 24 h. Gemifloxacin in stimulated THP-1 monocytes over the first 30 min caused an increase in c-AMP, NO, H2O2 and TNFalpha levels and protein kinase C, NADPH oxidase, glutathione reductase, NAG and cathepsin D activities. The pH became more acidic and phagocytosis was stimulated. These parameters were reversed at 1 h and continued to decline until 4 h. Lipid peroxidation was at the highest levels at 1 h and IL-8 levels at 2 h. DNA synthesis and bacterial growth were suppressed at 2 h in both S. aureus alone and bacteria phagocytosed by THP-1 monocytes. These effects were at a higher magnitude at 24 h. Gemifloxacin initiates a phagocyticidal effect of THP-1 monocytes at an early time of 30 min which plays a role in killing bacteria but a higher magnitude of killing of bacteria occurs later by a standard static mechanism. This early action of gemifloxacin should decrease the spread of infection and the inflammatory response since the tissue destruction process was attenuated at 4 h.

Influence of albendazole on the disposition kinetics and milk antimicrobial equivalent activity of enrofloxacin in lactating goats

The pharmacokinetics of single intravenous and intramuscular administrations and milk antimicrobial equivalent activity of enrofloxacin at a dose of 5 mg per kilogram body weight were studied in clinically healthy lactating goats which were either not treated or had received 7.5 mg per kilogram body weight of albendazole orally. The concentrations of enrofloxacin in serum and milk were determined using microbiological assay. Following intravenous injection, enrofloxacin antimicrobial equivalent activity versus time data in serum was described by a two-compartmental open model. Albendazole treatment significantly decreased the elimination half-life (t(1/2beta)) (P>or=0.05) and the mean residence time (MRT) (P>or=0.05), whereas, the rate of enrofloxacin return to central compartment from peripheral tissue (K(21)) was significantly increased (P>or=0.01). In contrast, the volumes of distribution V(d(area)) and V(d(SS)) were significantly decreased (P>or=0.01 and P>or=0.05, respectively) in albendazole-treated goats. After intramuscular injection, enrofloxacin was rapidly absorbed in control and albendazole-treated lactating goats with absorption half-lives (t(1/2ab)) 0.43 and 0.39 h, respectively. The mean peaks of serum concentration (C(max)) were 0.68 and 0.65 mcg ml(-1) attained at (t(max)) 1.08 and 1.12 h, before and after albendazole dosing, respectively. The elimination half-life (t(1/2el)) and (MRT) following intramuscular injections were also shorter in the albendazole-treated lactating goats. The systemic bioavailability of enrofloxacin was significantly decreased from 110.16 to 84.38% in albendazole-treated lactating goats. Concomitant administration of albendazole with enrofloxacin resulted in significant alterations in the disposition kinetic of enrofloxacin and significant decrease in enrofloxacin concentrations in milk. Consequently, the interaction between albendazole and enrofloxacin could be of clinical significance and may require monitoring and adjustment of enrofloxacin dosage.

[Study on the activities of fluoroquinolones against Staphylococcus aureus and the effect of reserpine on these activities]

OBJECTIVE

To investigate the activities of fluoroquinolones and the effects of reserpine on the activities of fluoroquinolones against S. aureus.

METHODS

The minimal inhibitory concentration (MICs) and the effects of reserpine on MICs of fluoroquinolones against S. Aureus were determined using standard agar dilution method.

RESULTS

Cross resistance to fluoroquinolones was found existing in S. aureus, but there was no remarkable multidrug resistance. The MICs of fluoroquinolones against many of S. aureus could be decreased by reserpine; Obvious decrease in MICs of fluoroquinolones against SA2-16 was observed; The decreasing percentage of MICs of fluoroquinolones against resistant strains was shown not significantly higher than that of sensitive strains. The decreasing percentage of MICs of hydrophilic fluoroquinolones against the strains studied was significantly higher than that of hydrophobic fluoroquinolones.

CONCLUSIONS

Cross resistance to fluoroquinolones has been found existing in S. aureus, whereas multidrug resistance is not seen in existence. The efflux of fluoroquinolones is normal in S. aureus; the amount of fluoroquinolones effluxed is related with the resistance of fluoroquinolones in S. aureus.