*3.2. Salmonella*

*Salmonella* is a rod-shaped, Gram-negative, motile, non-spore-forming bacteria belonging to family Enterobacteriaceae. Members of this genus are facultative anaerobes, oxidase negative and catalase-positive bacteria [65]. *Salmonella* species exist everywhere in nature, however, the gastrointestinal tracts of mammals, reptiles, birds and insects and environment polluted with humans or animals' excreta are the main reservoirs [66]. Their characteristic to survive and grow over a wide range of temperature (2–54 ◦C) and pH (3.6–9.6) makes them difficult to control [67]. Salmonellosis, which is an infection caused by *Salmonella* species is one of the leading causes of foodborne diseases [68]. Transmission to humans occurs via consumption of contaminated food, mostly of animal origins such as milk, eggs and meat. The antibiotics ampicillin, chloramphenicol and co-trimoxazole were once considered as the mainstay treatments for *Salmonella* infection but are largely replaced by fluoroquinolones due to bacterial resistance to antibiotics. Recently, resistance to fluoroquinolones has also emerged [69], thus necessitating the use of traditional medicines for *Salmonella* infections.

Extracts of *Acacia nilotica* L. have been tested against *Salmonella* species in which the extract disrupted the cell wall of bacteria with consequent release of electrolytes and cellular constituents [70]. Another study conducted by Khan et al. in India has also confirmed the potential use of *A. nilotica* against *Salmonella*. They recorded MIC as 9.75 μg/mL in their study [71]. Sugarcane bagasse has also been tested for anti-*Salmonella* activity. It was found to be bacteriostatic and caused leakage of electrolytes [72]. In South Africa, herbs are used as traditional medicine for the treatment of GIT disorders, e.g., stomach pain, diarrhea, etc. Bisi-Johnson et al. conducted a comprehensive study to scientifically prove the effectiveness of traditional plants for treating Salmonella infection. These plants include *Aloe arborescens* Mill., *Acacia mearnsii* De Wild., *Aloe striata* Haw., *Eucomis autumnalis* (Mill.) Chitt., *E. comosa* (Houtt.) Wehrh., *Cyathula uncinulata* (Schrad.) Schinz, *Hydnora africana* Thunb., *Hermbstaedtia odorata* (Bur ch. ex Moq.) T. Cooke, *Hypoxis latifolia* Wight, *Psidium guajava* L., *Pelargonium sidoides* DC., *Schizocarphus nervosus* (Burch.) van der Merwe. Although most of the studied plants

were active in the study, but *A. arborescens*, *A. striata, C. uncinulata, E. autumnalis, E. comosa* and *P. guajava* were particularly potent. The *Salmonella* species used in this study was extended spectrum beta-lactamase positive (ESBL) [73]. In another study from South Africa, the potent antibacterial activity of medicinal was been reported which include *Hypericum roeperianum* Schimp. ex A.Rich., *Cremaspora triflora* (Thonn.) K.Schum., *Heteromorpha arborescens* (Spreng.) Cham. & Schltdl., *Pittosporum viridiflorum* Sims, *Bolusanthus speciosus* (Bolus) Harms, *Calpurnia aurea* (Aiton) Benth., *Maesa lanceolata* Forssk., *Elaeodendron croceum* (Thunb.) DC. and *Morus mesozygia* Stapf. All the plant extracts used were active against *Salmonella* isolates, but *Cremaspora triflora* and *Maesa lanceolata* were very potent having MIC of 0.12 and 0.13 mg/mL, respectively [74]. *Entada abyssinica* A.Rich. is traditionally used in bacterial infections of the gastrointestinal tract (GIT). A total of 8 compounds were isolated from this plant including flavonoids and terpenoids and tested for anti-Salmonella activity. Entadanin was found to be the most potent compound having a MIC of 1.56 μg/mL [75]. *Leea indica* (Burm. f.) Merr. from Saudi Arabia [76], *Leea indica, Sclerocarya birrea* (A.Rich.) Hochst. from South Africa [77,78], *Lawsonia inermis* L. from Pakistan [79], *Rhus succedanea* L. from India [80], *Achillea clavennae* L., *Achillea holosericea* Sm., *Achillea lingulata* Waldst. & Kit. and *Achillea millefolium* L. from Japan [81], *Butomus umbellatus* L., *Polygonum amphibium* L. and two species of the genus *Sparganium* (*S. erectum* L. and *S. emersum* Rehmann) from Turkey [82], *Spathodea campanulata* P.Beauv., *Ficus bubu* Warb., *Carica papaya* L., *Cissus aralioides* (Welw. ex Baker) Planch., *Piptadeniastrum africana* (Hook.f.) Brenan, *Hilleria latifolia* (Lam.) H.Walter, *Gladiolus gregarious* Welw. ex Baker and *Phyllanthus muellerianus* (Kuntze) Exell from Cameroon [83,84], persimmon (*Diospyros lotus* L.), guava (*Psidium guajava* L.), sweetsop (*Annona squamosal* Linn.) and *Cichorium intybus* L. from China [85,86], *Anisophyllea laurina* R. Br ex Sabine from Guinea [87], *Sambucus australis* Cham. & Schltdl. from Brazil [88], *Terminalia avicennioides* Guill. & Perr., *Momordica balsamina*, *Combretum paniculatum* Vent., *Trema guineensis* (Schum. & Thonn.) Ficalho, *Morinda lucida* Benth. and *Ocimum gratissimum* L. from Nigeria [89] were reported to have strong antibacterial activity against *Salmonella* species. It has been observed that EO disrupt and increase the permeability of bacterial cell walls, therefore causing the release of intracellular organelles and proteins. The end result is inactivation and death of the microbes as reviewed by Franklyne et al. [90]. Most of the spices contain EO and consumption of spices has additional health benefits. The common spice ingredients like black pepper, fennel, coriander, cardamom are rich in EO [91].

Biosynthesized nanoparticles of metals (metals + natural materials) are frequently reported to have enhanced pharmacological activities. A newly emerged concept is nano-antibiotics [92], which use plants mediated biogenic nanoparticles with improved antimicrobial, chemotherapeutic and biologic properties [93,94]. Using this approach, several metals are reduced using aqueous extracts of medicinal plants [95] and then used as antimicrobial agents with advanced drug delivery and therapeutic outcomes [96]. Silver (Ag) nanoparticles of aqueous leaf extract of *Eupatorium odoratum* L. were shown to have high anti-*Salmonella* activities than the aqueous leaf extract of *E. odoratum* and also AgNO3 [97]. Silver nanoparticles using the aqueous leaf extracts of *Lippia citriodora* (Palau) Kunth have also been proved to be active against *Salmonella* species [98]. Other authors have also applied nanoparticles of phytoconstituents against *Salmonella* and obtained potent antibacterial activity [99–101].

### *3.3. Escherichia coli*

*Escherichia coli* (*E. coli*), Gram-negative rods, belongs to *Enterobacteriaceae* family. They represent a vital part of human intestinal normal flora [102]. Enterohemorrhagic *E. coli* (EHEC) produces verotoxin which causes gastrointestinal cramps and diarrhea [103]. The most prevalent serotype O157:H7 which can lead to HUS followed by neurological disorders and kidney failure. Consumption of unhygienic foods including meat, unprocessed milk, fruits, vegetables can transmit the microbes [104]. This important pathogen involved in foodborne diseases was once highly responsive to fluoroquinolones and beta-lactams, but now is resistant to these antibiotics [105]. Therefore, alternative strategies, e.g., traditional medicines as such and compounds derived from such sources are used to treat foodborne diseases caused by *E. coli*. *Acacia nilotica* (L.) Del has been found to disintegrate the cell wall of *E. coli* and

release nucleic acids, proteins with a reduction in viable cell growth [70]. In an in vitro study by Elisha et al., nine plants (*Hypericum roeperianum* Schimp. ex A.Rich., *Cremaspora triflora* (Thonn.) K.Schum., *Heteromorpha arborescens* (Spreng.) Cham. & Schltdl., *Pittosporum viridiflorum* Sims, *Bolusanthus speciosus* (Bolus) Harms, *Calpurnia aurea* (Aiton) Benth., *Maesa lanceolata* Forssk., *Elaeodendron croceum* (Thunb.) DC. and *Morus mesozygia* Stapf) were selected for antibacterial activity against *E. coli*. All were found to be active against *E. coli* and thus could be used in the therapeutic managemen<sup>t</sup> of *E. coli* infection. The lowest MIC was observed for *Maesa lanceolata* as 0.04 mg/mL [74]. *Wasabia japonica* (Miq.) Matsum. is an edible plant that grows at shady, humid and cool places in Japan, China, New Zealand and Korea, and possesses many medicinal properties. This plant inhibits *E. coli* strain O157:H7 which is widely responsible for diarrhea in foodborne diseases [106]. *Punica granatum* L. (pomegranate) is a well-known fruit and is abundantly used throughout the world. It is widely used in traditional medicine for a variety of indications including anti-angiogenic, anti-cancer and antimicrobial [107,108]. Pomegranate contains a variety of phytochemicals (ellagitannins and gallotannins, catechins, procyanidins, flavonoids, anthocyanins and anthocyanidins) [109]. Its antimicrobial activity against *E. coli* has been reported by several researchers [110–112]. Traditional healers of the Limpopo province of South Africa use a variety of medicinal plants for treating diarrhea [113]. Mathabe et al. performed antibacterial experiments to scientifically validate the traditional use of plants against diarrhea/foodborne disease-causing bacteria, i.e; *E. coli*. Their findings confirmed the potential action of *Gymnosporia senegalensis* (Lam.) Loes., *Indigofera daleoides* Harv., *Ozoroa insignis* Delile, *Punica granatum* L., *Spirostachys africana* Sond. and *Syzygium cordatum* Hochst. ex Krauss in limiting *E. coli* infection [114]. Similarly, in Puerto Rico, traditional medicines are used as an alternative therapy for GIT infections. *Tamarindus indica* L., *Phyllanthus acidus* (L.), *Punica granatum* L., *Citrus aurantifolia* (Chrism.) Swingle, *Citrus aurantium* L. were active against *E. coli* [115].

### *3.4. Staphylococcus aureus*

*Staphylococcus aureus* (*S. aureus*), a Gram-positive, coagulase producing facultative anaerobe is a major cause of foodborne diseases and hospitalization [104]. In addition to causing clinical infections, *S. aureus* also causes food poisoning (a foodborne disease). Individuals su ffering from *Staphylococcal* food poisoning are presented with diarrhea, abdominal cramps, nausea and profuse vomiting usually between 1–8 h after food consumption [116]. This pathogen produces exoproteins that are heat stable and are known as *Staphylococcal* enterotoxins (SEs). These toxins act as virulence factors [117] and are mostly responsible for food poisoning and are grouped into five toxin groups designated classically as SEA to SEE. Other *Staphylococcal* enterotoxins (SEG to SER and SEU) have also been described recently [118–120]. *Staphylococcal* foodborne disease outbreak without harboring enterotoxins has also been reported [121]. Traditional medicine is widely practiced in South Africa for treating GIT problems. Bisi-Johnson et al. evaluated the anti–staphylococcal activity of plants used in traditional medicine for GIT related problems including diarrhea and vomiting which are indication of food poisoning. They found that the medicinal plants including *Aloe arborescens* Mill., *Aloe striata* Haw., *Cyathula uncinulata* (Schrad.) Schinz, *Eucomis autumnalis* (Mill.) Chitt., *Eucomis comosa* (Houtt.) Wehrh., *Hypoxis latifolia* Wight, *Hermbstaedtia odorata* (Burch. ex Moq.) T.Cooke, *Scilla nervosa* (Burch.) J.P.Jessop, *Pelargonium sidoides* DC., *Psidium guajava* L. and *Hydnora africana* Thunb. possess strong antibacterial potential towards *S. aureus* and validates the scientific evidence of the use of these plants for food poisoning caused by *S. aureus* [73]. The plant extracts of *Aristolochia indica, Cuscuta pedicellata, Melilotus indicus* and *Tribulus terrestris* fruit which are traditionally used in Pakistan for various ailments including diarrhea have anti–staphylococcal activity [122]. From Togo, anti–staphylococcal activity has been reported for *Holarrhena floribunda* (G.Don) T.Durand & Schinz [123], from Cameroon, for *Vismia rubescens* Oliv., *Vismia laurentii* De Wild [124,125], from South Africa, *Chrysophyllum albidum* G. Don-Holl., *Terminalia ivorensis* A.Chev. [126,127], from Sudan, *Combretum hartmannianum* Schweinf., *Combretum pentagonum* M.A.Lawson, *Anogeissus schimperi* Hochst. ex Hutch. & Dalziel and *Terminalia arjuna* (Roxb. ex DC.) Wight & Arn. [128], from Egypt, clove (*Syzygium aromaticum*), cress (*Lepidium sativum* L.), lemongrass

(*Cymbopogon citratus* (DC.) Stapf.), Oregano (*Origanum vulgare* L.), rosemary (*Rosmarinus o*ffi*cinalis* L.), sage (*Salvia o*ffi*cinalis* L.) [129], from Algeria, *Stachys guyoniana* Noë ex Batt. and *Mentha aquatic* L., *Centaurea diluta* Ait. subsp. *algeriensis*, *Ferula vesceritensis* Coss. & Durieu ex Trab., *Genista saharae* Coss. & Durieu and *Zilla macroptera* Coss. [130–132] and *Clerodendrum myricoides* (Hochst.) R. Br. ex Vatke from Kenya, [133].

Juglone is a natural compound occurring in plants such as black walnut (*Juglans nigra* L.). This compound has antibacterial property and inhibits *S. aureus* by binding to DNA and disrupts cell wall synthesis, thus stressing the bacterial cells to increasing peroxidative environment [134]. Tetrandrine is an alkaloid isolated from the radix of *Stephania tetrandra* S. Moore. It inhibits *S. aureus* by binding to the peptidoglycan [135]. *Fraxinus rhynchophylla* Hance and its active constituent fraxetin is antibacterial to *S. aureus* via inhibition of essential proteins synthesis. It also decreases the activity of topoisomerase I and topoisomerase II [136]. Several researchers have reported active compounds from medicinal plants that are active against staphylococcal bacteria [137–139]. Essential oils are also utilized against *S. aureus* and studies have shown potential benefits of essential oils derived from *Petroselinum crispum* (Mill.) Fuss, *Cuminum cyminum* L, white mustard (*Sinapis alba* L.), *Chamaecyparis obtusa* (Siebold & Zucc.) Endl. [140–143].
