*Bioactive Compounds in Nutraceutical and Functional Food for Good Human Health*

plant but are said to be present in high extent in fruits and seeds. The composition of essential oil consists of monoterpenes and sesquiterpenes paired with aromatic compounds and lightweight esters, fatty acids, alcohols, ketones and aldehydes. Some examples include *γ*-terpinene, carvacrol, *p*-cymene, thymol, linalool, *α*terpinene, limonene, eucalyptol, geranyl propionate and *α*- and *β*-pinene [27]. Owing to their high hydrophobicity, essential oil are said to impair the cell membrane of microbes, increase their membrane permeability and decrease their cytoplasmic pH [28]. The so-described abilities explained their significant activity against bacteria and fungi including resistant strains like *Staphylococcus sp*. and *Pseudomonas sp*. with MIC values approaching 0.01 μg/mL [27]. Volatile oil play also an essential role in protecting and even preventing biofilm development which is very important as presented above [29]. However, the same lipophilicity capacity of essential oil, relevant for their good antiinfective properties, constitutes also their



#### *Plant-Derived Compounds against Microbial Infections and Cancers DOI: http://dx.doi.org/10.5772/intechopen.92596*


*Methicillin-resistant Staphylococcus aureus (MRSA), vancomycin resistant Enterococcus (VRE), methicillin-sensitive Staphylococcus aureus (MSSA), vancomycin-sensitive Enterococcus (VSE), Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis), Bacillus cereus (B. cereus), Micrococcus luteus (M. luteus), Mycobacteria smegmatis (M. smegmatis), Mycobacteria tuberculosis (M. tuberculosis), Pseudomonas aeruginosa (P. aeruginosa), Escherichia coli (E. coli), Klebsiella pneumonia (K. pneumonia), Candida albicans (C. albicans), Bacillus cereus (B. cereus), Escherichia coli (E. coli), Klebsiella pneumoniae (K. pneumoniae), Providencia stuartii (P. stuartii), Pseudomonas aeruginosa (P. aeruginosa), Enterobacter cloacae (E. cloacae), Enterobacter aerogenes (E. aerogenes), Salmonella typhimurium (S. typhimurium), Staphylococcus aureus (S. aureus), Micrococcus luteus (M. luteus), Streptococcus minor (S. minor), Vancomycin resistant Enterococcus (VRE).*

#### **Table 1.**

*Examples of plant-based natural products with significant antiinfective properties.*

*Plant-Derived Compounds against Microbial Infections and Cancers DOI: http://dx.doi.org/10.5772/intechopen.92596*

**Figure 1.** *Bioactive compounds against infective bacteria and fungi.*

main bottlenecks in drug development because essential oil present a low bioavailability. But when isolated, some of their constituents are water soluble e.g. 1.25 mg/ mL at 25°C for carvacrol (https://pubchem.ncbi.nlm.nih.gov/compound/carvac rol#section=Solubility) or 1.59 mg/mL at 25°C (https://pubchem.ncbi.nlm.nih.gov/c ompound/6549) for linalool and are being studied and used as excipient in drug formulation. Essential oil are however reputed in therapies which promoted local application, inhalation or bath modes of treatment like aromatherapy [27, 56]. They are associated to numerous of ailments including depression, indigestion, headache, insomnia, muscular pain, respiratory problems, skin ailments, swollen joints or urine complications [56]. Unlike essential oil, secondary metabolites mainly found in the solid part of a plant extract can present significant activities with considerable bioavailability and hence, constitute the main research object in natural product domain.

Since 2010 at least 44 metabolites have been reported with MIC values below 10 μg/mL. Phenolic compounds (**1**–**18**, **20**–**26**, **28**–**35**, **41**) were the group of compounds mostly active among the metabolites found. Besides, benzophenanthridine (**27**), steroids (**36**–**37**, **40**), pentacyclic triterpenoids (**38**–**39**, **43**–**44**) and diterpenoids (**19**, **42**) have been found active against various infective strains (**Table 1** and **Figure 1**). Some of the strains studied are among the microbes listed by WHO as highly harmful and needed new drugs.
