The molecular array of the outermost surface of bacteria and their physico-chemical characteristics modulate various functions which, when expressed in terms of the human environment, are generally known as factors of bacterial virulence. The present study investigated the ability of sub-MIC concentrations of cefodizime to interfere with the virulence factors of Escherichia coli. Bacterial adhesiveness to human epithelial cells was inhibited down to 1/32 x MIC of cefodizime, an antibiotic that is also capable of inducing the widespread production of filamentous forms at levels ranging from 1/2 to 1/8 x MIC. Given that this interfered with the correct evaluation of other virulence parameters, the study was extended to consider the effects of 1/16 to 1/128 x MIC. Sub-MIC concentrations of cefodizime inhibit haemagglutination, hydrophobicity and electrophoretic mobility, which are correlated with each other and provide clues relating to the physico-chemical characteristics of the outer surface. Cefodizime also reduces swarming. Phagocytosis was not affected but killing increased significantly. Oxidative bursts investigated by a chemiluminescence procedure were not modified. The interpolation of these pharmacodynamic findings with pharmacokinetic curves indicates that the effect of sub-MIC concentrations of cefodizime can prolong antimicrobial effects on virulence determinants up to 12 h after the antibiotic concentration has fallen below the MIC value.
The release of reactive oxygen species (ROS) during neutrophil oxidative bursts is the last of a sequence of different steps leading to the neutralization of pathogen microorganisms. Using luminol-amplified chemiluminescence (LACL), the oxidative burst activity of neutrophils in elderly people (≥75 years) was compared with that in younger controls (39 years on average) after activation with both particulate (Candida albicans) and soluble (formyl-methionyl-leucyl-phenylalanine; fMLP) stimulants. After Candida stimulation, a reduction in LACL was observed in the elderly subjects in comparison with the controls, but the difference did not reach statistical significance. After fMLP stimulation, the reduction in LACL was significant, thus suggesting that the Candida pathway of chemiluminescence production seems to be less affected than the fMLP pathway. This finding raises questions concerning the complex differences in the pathways of cell killing and ROS generation, and their efficacy in the elderly. Various possible explanations are discussed, all of which need further investigation.
It has been reported that subinhibitory concentrations (sub-MICs) of some fluoroquinolones are still capable of affecting the topological characteristics of DNA (inhibition DNA-gyrase) and that this leads to a reduction in some of the factors responsible for bacterial virulence (by means of the disruption of protein synthesis and alterations in phenotype expression), even though the microorganisms themselves are not killed. The present study investigated the ability of sub-MICs of rufloxacin, an orally absorbed monofluorinated quinolone with a long half-life (28 to 30 h), to interfere with the bacterial virulence parameters of adhesiveness, hemagglutination, hydrophobicity, motility, and filamentation, as well as their interactions with host neutrophilic defenses such as phagocytosis, killing, and oxidative bursts. It was observed that Escherichia coli adhesiveness was significantly reduced at rufloxacin concentrations of 1/32 MIC, hemagglutination and hydrophobicity were significantly reduced at concentrations of, respectively, 1/4 MIC and 1/8 MIC, and motility was significantly reduced at concentrations of 1/16 MIC; filamentation was still present at concentrations of 1/4 MIC. Phagocytosis was not affected, but killing significantly increased from 1/2 MIC to 1/8 MIC; oxidative bursts measured by means of chemiluminescence were not affected. The fact that sub-MICs are still effective in interfering with the parameters of bacterial virulence is useful information that needs to be correlated with pharmacokinetic data in order to extend our knowledge of the most effective concentrations that can be used to optimize treatment schedules, for example, single administrations, particularly in noncomplicated lower urinary tract infections.
Summary Erdosteine (CAS 84611-23-4) is administered as a mucolytic drug in patients with pulmonary disorders who suffer from a thickening of bronchial mucus with altered physico-chemical characteristics. Erdosteine itself does not have a free thiol group but its metabolization produces active metabolites with a -SH group that is capable of breaking disulfide bonds of mucins and improving the mucociliary clearance of the airways, and thus reproducing the effects of the class of mucoactive drugs having a thiol group. It has also been reported that muco-active drugs with this group reduce bacterial adhesiveness to human mucosal cells. The aim of this study was to investigate whether erdosteine and its SH-metabolites are capable of interfering with bacterial adhesiveness. Metabolite I significantly reduces both S. aureus and E. coli adhesiveness to human mucosal epithelial cells at concentrations of 2.5, 5 and 10 &ml. The same concentrations of erdosteine, metabolite II, metabolite III and N-acetylcysteine (as a control drug) were devoid of such activity, whereas the results of hemagglutination and hydrophobicity assays showed that the behaviour of metabolite I overlapped that of bacterial adhesiveness, thus indicating that interference takes place at a fimbrial level. This is confirmed by the fact that the incubation of human buccal cells with drugs does not reduce the adhesiveness of untreated bacteria. The presence of this additional activity in a mucoactive drug is useful because bacteria not only adhere to epithelial cells but also to tracheobronchial secretions.
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