**4. Antipathogenic efficacy of medicinal plants**

 A natural question about the use of medicinal plants for treating gastrointestinal disorders is: how effective are the uses of plants in controlling or preventing infections by pathogenic agents? Several in vitro studies have been conducted that aimed to evaluate the biological activity of plant extracts against enteropathogenic bacteria (*Escherichia coli, Shigella sonnei, Shigella flexneri, Salmonella*, *and Campylobacter*) and parasites (*Giardia lamblia and Entamoeba histolytica*) responsible for diarrhea, dysentery and/or gastric disorders [59–61]. Several chemical compounds (alkaloids, tannins, flavonoids, and terpenes) responsible for the pharmacological effects of these plants have been identified and isolated [62, 63]. Examples of biological activity of native plants of Oaxaca, Mexico, used for the prevention and control of gastrointestinal disorders are listed in **Table 3**.

The experiences in the communities of Oaxaca indicate that the roots and aerial parts of *Geranium mexicanum* Kunth and the flowers of *Chiranthodendron pentadactylon* are effective to treat diarrhea, dysentery, and stomach pain (**Table 3**). The methanolic or aqueous extracts of these plants showed high antibacterial activity against *Shigella flexneri* and *Shigella sonnei* at minimum inhibitory concentrations of 8 mg/mL. Both extracts can be considered an alternative strategy to treat enteric pathogens resistant to common drugs [60]. In biological experiments using mice, it was demonstrated that the molecule (−)-epicatechin, which is isolated from *Geranium mexicanum*, has high antiprotozoal activity (*Giardia lamblia*) in concentrations of 0.072 μmol/kg, which is the dose required to kill 50% of microorganisms [59].

Calzada et al. [69], found that (−)-epicatechin and tiliroside, isolated from extracts of *C. pentadactylon* flowers*,* were effective against *E. histolytica, G. lamblia*, *E. coli, S. sonnei, S. flexneri, Salmonella* sp., and *Vibrio cholerae*. In another work, Calzada et al. [11] determined that root extracts of *G. mexicanum*  had a greater hyperperistaltic effect than the extracts of *Lygodium venustum*, *Chenopodium ambrosoides*, and *C. pentadactylon*, which was similar to the effect of the drug loperamide, which is used to control acute and constant diarrhea associated with intestinal inflammation. In experiments with mice, the methanolic extracts of *G. mexicanum*, *Bocconia frutescens*, and *C. pentadactylon* in a concentration of 300 mg/kg of body weight had high inhibitory or intestinal antisecretory activity against *V. cholerae*. The activity of these extracts exceeds the effect of the drug loperamide [72]. A similar effect was determined with extracts of *C. pentadactylon* flowers [73]. *B. frutescens* also showed inhibitory activity against *S. aureus*  and *E. coli* [60]. These results show that *G. mexicanum, C. pentadactylon*, and *B. frutescens* have medicinal properties and are effective for the treatment of diarrhea, among other gastrointestinal problems (**Table 3**).

The methanolic extracts *Ocimum basilicum* and *Artemisia ludoviciana* have inhibitory effects against *V. cholerae*, and the minimum bactericidal concentration varies from 0.5 to 3.0 mg/mL. The extracts have a degradative effect on the cellular membranes of *V. cholerae*, which increases membrane permeability, decreases cytoplasmic pH, hyperpolarizes the membrane, decreases the cellular ATP concentration, and consequently causes cell death [65]. This result indicates a chemical modification of the growth medium and induction of the death of the pathogen. For example, Hussain et al*.* [62] reported that basil contains essential oils (linalool, epi-α-cadinol, α-bergamotene, and γ-cadinene) that exert antimicrobial activity against *S. aureus* and *B. subtilis*. Similarly, the essential oil of *A. ludoviciana* contains camphor, 1,8-cineole, and camphene, which were effective against *Acanthamoeba castellanii*, *Leishmania infantum,* and *Trichomonas vaginalis* [66].


#### **Table 3.**

*Antimicrobial activity of native medicinal plants of Oaxaca, Mexico.* 

Aqueous extracts of *A. ludoviciana ssp. Mexicana* and methanolic extracts of *Guaiacum coulteri* showed high growth inhibitory activity against *Helicobacter pylori*  at minimum inhibitory concentrations of 125 and < 15.6 μg/mL, respectively [57].

 *H. pylori* is the etiological agent of chronic active gastritis and peptic ulcer and is related to gastric carcinoma. It was also shown that *A. ludoviciana* has activity against *Campylobacter jejuni* and *C. coli* at minimum bactericidal concentrations of 0.5 mg/mL [74]. Ruiz-Cancino et al*.* [67] determined that the sesquiterpene lactones (douglanin, ludovicin A, 1α, 3α-dihydroxyarbusculin B, santamarin, arglanin, artemorin, chrysartemin B, armefolin, ridentin, eudesmanolide 3α-hydroxyreynosin, etc.) and flavonoids (eupatilin and jaceosidin) of *A. ludoviciana* spp. *mexicana* are the molecules responsible for the inhibitory properties against the nuclear transcription factor kappa B, NF-κB [14]. NF-κB is involved in critical mechanisms related to the development of cancer. The signaling cascades of NF-κB may be the main malignant gastrointestinal mediators that favor esophageal, gastric, and colon cancer [75].

The essential oils of *Lantana achyranthifolia* consist of monoterpenes and sesquiterpenes (carvacrol, isocaryophyllene, α-bisabolol, α-bisabolene, and 1,8-cineole), have antibacterial activities against Gram-positive and Gram-negative bacteria, *V. cholerae, Shigella boydii*, and *Yersinia enterocolitica* [76]. The antibacterial activity results from the compounds carvacrol, 1,8-cineole and linalool [77]. The essential oils of *L. achyranthifolia* and *Lippia graveolens* have antifungal activity [68] and contain carvacrol, α-terpinyl acetate, β-caryophyllene, geranyl acetate, terpinyl acetate, bornyl acetate, and limonene [77, 78]. More research is required on other medicinal species with similar potential.

The extracts of *Cnidoscolus aconitifolius*, *Crotalaria pumila*, and *Anoda cristata*  (**Table 3**) inhibit bacterial growth. The flavonoids acacetin and diosmetin from *A. cristata* have been shown to inhibit up to 90% of *H. pylori* growth. These data suggest that, through the use of nutraceutical food plants, *H. pylori* infections can be prevented [70]. *Ambrosia artemisiifolia* L. is used to treat stomach pain and contains isabelin, a germacranolide sesquiterpene dilactone with antimicrobial activity against *S. aureus* and *Candida albicans* [64].

#### **5. Remarks**

Medicinal plants continue to play an indispensable role in the daily life of rural and urban communities. However, their use is controversial, and they are often only used in teas or hot drinks; they are not associated with healing properties. Through interactions with the indigenous communities of Oaxaca, Mexico, it was found that all households use the inherited knowledge of medicinal plants. In the regions furthest from the urban centers where the hospitals are located, medicinal plants are part of the survival strategy.

 In the communities of Oaxaca and other regions of Mexico, healers (the generic name for traditional practitioners) are called "yerberos" (herbalists) because they only use plants. The consultation or intervention of the healers occurs when the symptoms of the disease or ethnodisease continue after the patient takes the "remedies" (teas, crushed, chewed, potions, etc.), which are prepared by the adults of the family. We define ethnodisease as a disorder that has no somatic symptoms, description of organic or metabolic dysfunction, or association with clinical symptomatology. Thus, "empacho" is often associated with indigestion, but has a broader sociocultural description than a gastroenterological disorder.

Based on our field notes and previous documentation of the indigenous communities in Oaxaca, Mexico, as well as our bibliography, a brief list of medicinal plants used for gastrointestinal disorders was compiled. This list comprises 71 botanical families, among which the most speciose were Asteraceae (29), Fabaceae (15), Euphorbiaceae (9), Solanaceae (9), Lamiaceae (9), Verbenaceae (6), Myrtaceae (5),

 Malvaceae (5), and Fagaceae (5). The families included 147 genera and 186 endemic species. The most frequently used genera were *Croton* (5), *Quercus* (4), *Piper* (4), *Psidium* (3), *Ocimum* (3), and *Tagetes* (3) (**Table 1A**). The medicinal species introduced to Mexico were excluded from this list, despite being widely used by Oaxacan indigenous groups.

The use of antibiotics for infectious gastrointestinal diseases is unconscionable among the users of pharmacological medicine and has generated collateral damage, including antibiotic resistance of pathogenic microorganisms. Cases of antibiotic resistance are increasingly frequent, and thus, medicinal plants will fill an important niche once their antibacterial, antiprotozoal, antisecretory, spasmolytic, and anti-inflammatory protective effects are demonstrated. In addition to these benefits, antiradical and antioxidant activity effective against gastroenterological disorders have been shown after the frequent consumption of teas. Advances have been made in the knowledge of antipathogenic effects of medicinal plants and their association with specific compounds. However, not all plants used by the indigenous groups of Mexico and Latin America are being studied and documented.
