# Halophytes as Medicinal Plants against Human Infectious Diseases
## 3 Halophytes as a Source of Antimicrobial Compounds  
Plants accumulate bioactive compounds as a consequence of both phylogeny and the functional response to different environmental conditions [12]. Along with the abiotic conditions, plant species, genotype, physiology and the developmental stage also influence the type and concentration of these molecules produced by a plant [54; 55]. The concentration and diversity of bioactive compounds in halophytes are higher compared to salt-sensitive species, and some compounds are exclusive to halophytes [14]. Moreover, there seems to exist a positive correlation between salt content in the medium and the production of secondary metabolites [56]. Primary metabolites of halophytes, such as carbohydrates and lipids, are regarded with interest as supplements or nutraceuticals. Secondary metabolites, such as terpen and phenols, have antioxidant and anti-inflammatory antimuromal and antimicrobial activities [35] and underlie many of the applications of halophytes in traditional medicine [57]. Some compounds modulate and stimulate the immune system, lower the risk of heart diseases, control body weight and blood sugar levels, and can even act as antiaging agents [58; 59; 60; 61; 62; 63]. Antimicrobial activity is most commonly associated with phenolic acids, flavonoids and tannins (Figure 3). Terpenoids are the second most abundant group of bioactive molecules, followed by alkaloids, essential oils, glycosides and steroids. In spite of the accumulation of evidence on the pharmacological potential of halophytes, only a few species have been subjected to systematic phytochemical characterization and screening for biological activities. Sixty-three species are reported in TM in Rwanda to treat diarrkel-like symptoms [64]. In fact, the same plants are used to treat different diseases with similar symptomatology, such as diarrhea, dysentery, cholera and gastroenteritis in general, but different aetiology (helmiths, bacteria and viruses). Some studies have found that only some plants have antimicrobial properties in in vitro and in vivo studies. Additionally, only a few studies have researched the bioactive phytocompounds of some of these plants [64]. This situation is not exclusive to plants with antimicrobial effects. A pharmacological investigation conducted over a pool of plants used in TM to treat cancer patients found only 30% had a significant cytotoxic effect. Additionally, only 6 out of 77 bioactive compounds isolated from those plants exhibited beneficial effects with few side effects in clinical trials [65]. Ethnopharmaceutical and phytochemistry studies are essential for the pharmacological industry to look for and produce new antimicrobial drugs [66]. Even though some tests may be inconclusive or even show adverse effects, the ethnopharmaceutical approach is desirable as a selection method for screening potential new drugs. However, the phytochemistry of the plants, in vitro tests to determine the potential effect on the targeted microorganisms and clinical trials to determine toxicity and possible side effects are inherent parts of the process. The development of new antimicrobial, anticancer or anti-inflammatory drugs has been the subject of rising interest. The emergence of various drug-resistant microbes has directed attention to the need for new drugs and evaluating methods [67]. A wide variety of methods are available to evaluate and detect in vitro antimicrobial activity of plant extracts and purified compounds. Diffusion methods (disk-diffusion, well diffusion or agar plug diffusion) are commonly used bioassay methods that are officially used as routine antimicrobial susceptibility tests. These are simple, standardized and low-cost methods and allow multiple testing. However, some of these techniques are not quantifiable and  
Figure 3: Diversity of bioactive compounds (secondary metabolites) with antimicrobial activity produced by halophyte plants. do not allow for determining the minimum inhibitory concentration. Dilution methods can overcome this difficulty.