*5.4. Cryptosporidium*

*Cryptosporidium* spp. belongs to the family, *Cryptosporidiidae*. The most common species that cause human infection are the *Cryptosporidium parvum* and *Cryptosporidium hominis*. They can be transmitted from animals, human-to-human, water, food, and tend to cause waterborne outbreaks. The clinical manifestation in immunocompetent patients is self-limiting when compared to immunocompromised individuals where it causes chronic diarrhea not responding to treatment [262]. *Cryptosporidium* spp. are well recognized as causes of diarrheal disease and is increasingly identified as an important cause of morbidity and mortality worldwide [263]. The ethanolic extract from olive (*Olea europaea*) pomace, after oil pressing and phenol recovery, reproducibly inhibited *Cryptosporidium parvum* development (MIC = 250–500 μg/mL, IC50 = 361 (279–438) μg/mL, IC90 = 467 (398–615) μg/mL) [264]. In an in vivo study, the extract of *Curcuma longa* L. had the highest e ffect on *Cryptosporidium* oocysts shedding. The inhibitory e ffect was observed at a rate of 100% on the 7th day of treatment at 750 mg/kg and on the 5th day at 1000 mg/kg in the watery extracts. At a rate of 100% on the 4th day at 1000 mg/kg in alcoholic extracts [265]. Potential cryptosporicidal effects have been observed for blueberry with its polyphenolic compounds, cinnamon with its phenolic compounds and onion with its flavonoids and sulfide compounds, garlic with its allicin, mango with its mangiferin, olive pomace with its oleuropein, pomegranate with its polyphenols and tannins and oregano with its carvacrol especially against *Cryptosporidium parvum* and *Cryptosporidium hominis* [266]. The anti-*Cryptosporidium* efficacies of various plant extracts were evaluated in four groups of age-matched neonatal Swiss albino mice. There was a 100% reduction in *Cryptosporidium* oocys<sup>t</sup> excretion in stool and copro-DNA of *O. europaea*-treated infected mice after 2 weeks. Thus, the plant of *O. europaea* is a promising natural therapeutic for cryptosporidiosis [267].

A detailed list of antiprotozoal activity of important medicinal plant extract and phytochemicals against foodborne parasites is provided in Table 1. Chemical structures of some of the plants derived bioactive compounds are given in Figure 1.


**Table 1.** Summary of effects of plant extracts and phytochemicals against foodborne parasites.


### **Table 1.** *Cont.*


### **Table 1.** *Cont.*


**Table 1.** *Cont.*


**Table 1.** *Cont.*

**NT:** not tested, **NA:** not active, ↑**:** Increase/activate, ↓**:** decrease/inhibit, ↔**:** no effect/not modulate, **CDT:** cytolethal distending toxin, **EO:** essential oils.

**Figure 1.** Chemical structures of some of the phytochemicals discussed in this manuscript.

### **6. Mechanisms of Antimicrobial Activity**

Various mechanisms have been reported for the antimicrobial activities of medicinal plants and isolated natural antimicrobials. These natural products affect those pathways of macromolecular metabolism which are proven targets for antibiotic intervention. Among the existing antibacterial agents, it is clear that protein and cell wall biosynthesis are the targets of the widest variety of natural products [34]. The pathways of macromolecular metabolism as antimicrobial targets of natural products include inhibition of protein synthesis, inhibition of cell wall synthesis, disruption of membrane integrity, inhibition of RNA synthesis, inhibition of DNA synthesis, dysfunction of microtubules, inhibition of lipid synthesis, inhibition of cell division, dysfunction in ion uptake, reduction in protein secretion, dysfunction of RNA processing and inhibition of DNA methylation. These mechanisms have been investigated for the antimicrobial properties of medicinal plants and natural products including *Hemidesmus indicus* (L.) R. Br. ex Schult., *Leucas aspera* (Willd.) Link, *Plumbago zeylanica* L., *Tridax procumbens* (L.) L. [268], *Syzygium cumini* (L.) Skeels [269], *Combretum albidum* G.Don, *Hibiscus acetosella* Welw. ex Hiern, *Hibiscus cannabinus* L., *Hibiscus furcatus* Willd., *Punica granatum* L. and *Tamarindus indica* L. [270], 5,6,7-trihydroxyflavone (baicalein) [271], flavones [272], *Hibiscus sabdari*ff*<sup>a</sup>*, *Rosmarinus <sup>o</sup>*ffi*cinalis*, *Syzygium aromaticum*, *Thymus vulgaris* [273], linalyl acetate, (+)menthol, thymol [274], *Origanum vulgare* [275], essential oils [276], caffeine [277], allspice oil, lemongrass oil, citral [278], alkaloids [279], *Boerhaavia di*ff*usa* [280], paeonol (PA) and 1,2,3,4,6-penta-*O*-galloyl-β-D-glucopyranose (PGG) from *Paeonia lactiflora* Pall. [281], *Aristolochia bracteolata* Lam. [282], *Rhizophora apiculate* Blume, *Phyllanthus niruri* L., *Scutellaria baicalensis* Georgi, *Geum japonicum* L. and *Momordica charantia* L. [283]. Plants being mixture of numerous compounds can act on several targets like, inhibition of bacterial cell wall synthesis, protein synthesis and interference with microbial metabolic pathways. Hence, as a whole, the activity of crude extracts may be due to more than one antibacterial mechanism. Further, different compounds in the extract can act synergistically as well as can antagonize the effect of each other depending upon their respective concentrations. Considering the presence of large number of chemical compounds present in the extracts of medicinal plants, it is most likely that their antimicrobial activity can be attributed to more than a single specific antimicrobial mechanism.

### **7. Persisting Challenges**

However, many plant extracts and their isolated phytochemicals have been reported to show potent activity against foodborne illness causing agents, there have not been detailed studies about their mechanism using in vivo studies. As the systematic treatment, use of oral rehydration salts and antibiotics are also of grea<sup>t</sup> concern for their use in foodborne illness in children and their efficacies [17], alternative therapies like herbal extracts and compounds should be used with proper caution and with the support of scientific evidence regarding the other dosage forms of these herbal products. Human gu<sup>t</sup> microbiota plays a vital role in sustaining gastrointestinal health via inhibition of pathogenic microbes. The use of broad-spectrum antibiotics causes inhibition of normal flora beside pathogenic bacteria, thus provide the opportunity to other pathogens and secondary infections emerge [284,285]. On the other hand, herbal products like tea and many herbs and vegetables are also reported to be the source of foodborne microorganisms [286,287]. Herbal products contaminated with mycotoxins, bacterial toxins, as well as bacterial strains are reported to cause foodborne infections. For instance, herbs contaminated with *Salmonella* is a major cause of foodborne infections in North America and Europe [286]. Subsequently, several approaches were adopted to decontaminate these products including irradiation which effectively eradicate *Salmonella, S. aureus, Comphylobacter* sp., *Listeria and E. coli* without affecting nutritional properties of these products [288].

Natural product research has broadly emerged into two major fields including ethnopharmacology and toxicology. However, both strategies were successful regarding the discovery of numerous drugs against several diseases, ye<sup>t</sup> the development of antimicrobial agents from these sources is limited [289]. To augmen<sup>t</sup> the development of antimicrobial agents from the herbal source it is important to elucidate exact molecular antimicrobial mechanisms of these products. This information will enable researchers

not only to have better control of these microbes but will use modern technologies to synthesize more potent and e ffective derivatives. Moreover, studies regarding the e fficacy of these agents in combination with other herbs and drugs is limited. For instance, a combination of several EOs in combined form does not produce the synergistic antimicrobial e ffect and subsequently their use as a food preservative is limited. These agents can also interact with food ingredients which significantly a ffect their quality. Like, EOs beside their grea<sup>t</sup> beneficial e ffects has limited e fficacy as a food preservative due to the intense aroma and toxicity issues. EOs used as preservatives in food are reported to change organoleptic properties of foodstu ff and their higher doses can produce severe toxicological responses [290,291].
