Medicinal Plants Classification Biosynthesis and ... - Index of

326
Philippe N. Okusa, Caroline Stevigny and Pierre Duez
4. Effects of Plant Compounds on Antibiotic
Resistance
Three main mechanisms of antibiotic resistance have been so far identified: (i) the ability
of microorganisms to reduce the intracellular concentration of drug (reduced permeability,
reduced uptake, active efflux); (ii) the inactivation of antibiotics; and (iii) the modification or
elimination of the target site. Microorganisms may use one or more of these strategies to
evade the inhibitory or lethal effects of a particular antibiotic and may transfer these
capabilities to other strains, notably through plasmids.
The fight against antibiotics resistance implies on one hand the research for active
compounds with a new mode of action, different of those described for existent antibiotics;
that is the case of platensimycin, a previously unknown class of antibiotics produced by
Streptomyces platensis. This antibiotic has a strong broad spectrum activity on Gram-positive
strains by inhibiting the bacterial lipid biosynthesis, through the selective targeting of -
ketoacyl-(acyl-carrier-protein (ACP)) synthase I/II (FabF/B) (Wang et al., 2006).
A second approach in this fight against antibiotic resistance is the use of compounds
without direct antimicrobial properties, but which enhance or restore the effects of antibiotics
on resistant microorganisms (Shahverdi et al., 2004). This approach compares the effects of
antibiotics by themselves to the combination of antibiotics and inactive compounds or plant
extracts against resistant microorganisms. It is also possible to evaluate the effect of active
plant extract (or compounds) in association, in sub-inhibitory concentrations, with antibiotics
(Shahverdi et al., 2003). Different mechanisms of antibiotic resistance and their inhibitors
from medicinal plants are summarized in Figure 1.
Figure 1. Mechanisms of antibiotic resistance and examples of their inhibitors from medicinal plants