Inhibition of Bacterial Adhesion by Sub-Inhibitory Concentrations: Brodimoprim vs Trimethoprim

Intermedilysin release byStreptococcus intermedius: effects of various antibacterial drugs at sub-MIC levels

Intermedilysin is a cytolytic toxin produced by Streptococcus intermedius, a pathogen of humans. In vitro studies showed that exposure of S. intermedius to sub-minimum inhibitory concentration (MIC) levels (1/2 MIC) of protein-inhibiting antibiotics and nucleic acid-inhibiting antibiotics decreased intermedilysin release by S. intermedius. The most potent antibiotic was clindamycin. On the other hand, exposure to cell wall-inhibiting antibiotics generally showed insignificant changes in intermedilysin release at sub-MIC concentrations. Investigations into possible mechanisms underlying this sub-MIC effect with clindamycin showed that there was selective decrease in biosynthesis and release of toxin after exposure to 1/2 MIC condition. However, no significant differences in the mRNA levels of the intermedilysin gene were observed.

Morphostructural damage and the inhibition of bacterial adhesiveness of Staphylococcus aureus and Moraxella catarrhalis induced by moxifloxacin

The aim of this study was to investigate the ability of moxifloxacin to interfere with the mechanism of bacterial adhesion and disrupt the morphological and structural integrity of bacteria. Three Staphylococcus aureus and three Moraxella catarrhalis strains were grown in the presence of 1/2-1/128 minimum inhibitory concentration (MIC) serial dilutions and incubated with human epithelial cells. A significant decrease in adhesion was observed from 1/2 MIC to 1/64 MIC for S. aureus, and from 1/2 MIC to 1/16 MIC for M. catarrhalis. The use of atomic force microscopy, a new technique capable of revealing surface structures in three-dimensional detail and at very high resolution, showed the rapid onset and time course of the sequence of disruptive morphostructural events following the incubation of both S. aureus and M. catarrhalis with sub-MICs of moxifloxacin. Our findings suggest that less than conventional MIC moxifloxacin concentrations may be effective in reducing bacterial adhesiveness and structural integrity on which the maintenance of bacterial activity depends.

Brodimoprim: effects of subminimal inhibitory concentrations on virulence traits of respiratory and urinary tract pathogens, and on plasmid transfer and stability

The effects of brodimoprim, a new trimethoprim analogue, on several virulence traits of respiratory and urinary tract pathogens exposed to sub-lethal levels of the drug was studied. Adherence to tracheal epithelial cells was inhibited by brodimoprim in Klebsiella pneumoniae (41-67% reduction), Moraxella catarrhalis (87-90%) and Haemophilus influenzae (0-53%), while in Streptococcus pneumoniae binding was unaffected. With buccal epithelial cells the comparison between treated and control bacteria indicated statistically significant reduction in adherence with both S.pneumoniae and H.influenzae, (P < 0.015). With M.catarrhalis and Streptococcus pyogenes only marginal changes were detected (P > 0.05). Exoenzyme and capsule production were assessed in at least three isolates of diverse respiratory pathogens grown in the presence of sub-lethal levels of the new agent. The drug affected protease and beta-hemolysin (alpha-toxin) production in both oxacillin-susceptible and -resistant S.aureus. On the contrary, synthesis of lipase, DNase, coagulase, and beta-lactamase (S.aureus), pneumolysin (S.pneumoniae), streptolysin S, DNase, and protease (S.pyogenes), capsule (K.pneumoniae, H.influenzae and S.pneumoniae), and beta-lactamase (K.pneumoniae, H.influenzae and M.catarrhalis) were not inhibited by subminimal inhibitory concentrations (sub-MICs) of the drug. Finally, motility was blocked in urinary pathogens E.coli, P.mirabilis and P.aeruginosa, while in this latter microorganism pigment production was also affected. High molecular weight low-copy F'lac, and low molecular weight high-copy pHSG298 plasmids were eliminated from E.coli treated with sub-MIC concentrations of brodimoprim. The incidence and cured cells ranged from 9% for F'lac to 23% for pHSG298. F'lac transfer was also inhibited by the drug. When conjugation was carried out with bacteria exposed to brodimoprim (5XMIC), a reduction (50%) in the number of recombinants was noted in comparison to the control. The fact that brodimoprim interferes with the expression of some virulence traits, in particular with adherence, at sub-MIC levels may assist the drug in eradicating respiratory pathogens from the epithelial lining, thus diminishing the probability of reinfection.