15 Amazing Natural Antibiotics + Side Effects

Antibiotics were first discovered when Alexander Fleming noticed mold (Penicillium notatum) inhibiting the growth of bacteria. Pharmaceutical antibiotics were later developed but most have harmful side effects. The overprescription and misuse of pharmaceutical antibiotics have led to many bacteria developing antibiotic resistance. Fortunately, there are many naturally occurring antibiotics with few side effects.

What are Natural Antibiotics?

Infectious illnesses caused by bacteria, fungi, or viruses are extremely common. Due to their overprescription and misuse, pharmaceutical antibiotics are becoming more and more ineffective at treating these illnesses [1].

Pharmaceutical antibiotics are often accompanied by harmful side effects, such as vomiting, diarrhea, allergic reactions, and rashes. They can also cause microbiota dysfunction, which increases the risk of developing obesity, diabetes, and recurring bacterial and fungal infections [2, 1, 3].

Many spices and herbs, such as garlic, oregano, thyme, and turmeric exhibit impressive antibacterial, antifungal, and antiviral properties and can be used as natural alternatives [4].

Types of Bacterial Infections

Bacterial infections are extremely common and are caused by many different types of bacteria. Sometimes, a different strain of a bacterium normally found in the body can cause illness. While Escherichia coli can help maintain a healthy digestive tract, a different strain of Escherichia coli can cause food poisoning and diarrhea. Some common bacterial infections [5]:

Hospital-Acquired Bacterial Infections

There are several antibiotic-resistant bacteria that can cause potentially life-threatening illnesses in hospitalized patients. Clostridium difficile infections commonly cause diarrhea while Pseudomonas aeruginosa and fluorescens cause opportunistic infections (in people with low immune function). The most common hospital-acquired pneumonia is due to Klebsiella, which can also cause urinary tract infections and blood infections. Although Staphylococcus aureus is normally found on the skin, it can cause a life-threatening heart infection (infective endocarditis) [6, 7, 8, 9].

Food Poisoning and Gut Issues

Food poisoning and diarrhea are often caused by Salmonella, Escherichia coli, and Campylobacter jejuni [10, 5, 11].

Helicobacter pylori infection increases stomach acidity, resulting in heartburn and stomach ulcers [12].

Pneumonia

Haemophilus influenzae is the root of a variety of infections, including pneumonia, bronchitis, blood poisoning (septicemia), and more. Legionella pneumophila causes a type of pneumonia called Legionnaires’ disease [13, 14].

Bacterial Infections of the Skin

Streptococcus pyogenes can cause flesh-eating disease (necrotizing fasciitis) while acne is commonly caused by Propionibacterium acnes [15, 16].

Vibrio vulnificus causes skin and tissue infections, which are usually indicative of an underlying disease like liver damage (cirrhosis) [17].

Urinary Tract Infections

The main causes of urinary tract infections are Escherichia coli and Enterococcus but it can also be caused by Serratia marcescens or Proteus mirabilis [5, 18, 19, 20].

Gum Disease and Cavities

Aggregatibacter actinomycetemcomitans causes aggressive gum disease (periodontitis) while Streptococcus mutans causes dental plaque, which damages tooth enamel, and can result in gum disease and cavities [21, 22].

Toxic Shock Syndrome

Toxic shock syndrome, a rare but potentially fatal infection, is caused by toxins produced by Streptococcus pyogenes and Staphylococcus aureus bacteria [16, 23].

Types of Fungal Infections

A lot of common issues are actually due to fungal infections. Like with bacteria, fungi normally found in the body can sometimes become overgrown and cause issues [3, 24].

Athlete’s Foot

Athlete’s foot (tinea pedis) is a fungal infection of the foot that typically develops as an itchy rash between the toes. It is usually caused by Trichophyton rubrum, Trichophyton mentagrophytes, and Candida species [25].

Dandruff

Dandruff is a very common condition, in which scalp skin flake off. Although there are various factors that contribute to dandruff (such as excess oil production), dandruff severity has been linked to high amounts of a type of yeast (Malassezia) normally found on the skin [26, 27].

Eczema/Rashes

Although eczema has many causes, it is aggravated by Malassezia yeast (also associated with dandruff) [27].

Nail Infections

Nail infections are commonly caused by a group of fungi called dermatophytes, which includes Trichophyton, Microsporum, and Epidermophyton fungi. These infections are difficult to treat and the pharmaceutical antibiotics used can be very toxic to the liver [27, 28].

Yeast Infections

Vaginal yeast infection, which is characterized by unusual discharge and itching, is due to the overgrowth of Candida yeast normally found in the vagina. This overgrowth is thought to be caused by pharmaceutical antibiotic usage [29].

Natural Antibiotics

1) Garlic

Garlic has been widely used throughout history for the treatment and prevention of diseases. Recent studies have evaluated the many benefits of garlic, including antibacterial, antifungal, and antiviral activity [30].

Mechanism of Action

Allicin is the main active compound in garlic, responsible for most of the antimicrobial activity. It is effective against many strains of bacteria, including multidrug resistance strains [31, 32].

Allicin kills bacteria by blocking enzymes important for energy production (alcohol dehydrogenase, acetyl-CoA synthetase, and acetate kinase) and cell structure (membrane) [33, 34, 35].

Allicin prevents bacterial and fungal growth by blocking the formation of biofilms. Biofilm infections, such as in pneumonia in cystic fibrosis patients and persistent wounds, are chronic infections that affect millions of people a year [36, 37, 38, 39].

Antibacterial Activity

Allicin alone (1,200 mg/day) or in combination with standard antibiotics (4,200 mg/day) helped eradicate H. pylori infection in 34 out of 60 patients treated for 14 days (RCT) [40].

Additionally, a 2.5% garlic extract decreased levels of oral Streptococcus mutans a 5-week study (TB-RCT of 30 healthy subjects) [41].

Garlic extracts might be helpful in treating swollen gums and preventing cavities since it kills oral pathogens such as Porphyromonas gingivalis, Prevotella intermedia, and Aggregatibacter actinomycetemcomitans [42, 43].

It also increased the effectiveness of other antibiotics against Pseudomonas aeruginosa [44, 45].

Besides killing Staphylococcus aureus and Streptococcus pyogenes, garlic extract also protects the body from bacterial toxins (such as α-toxins and streptolysin O) [46, 47].

Antifungal Activity

Allicin in garlic extracts blocked the germination of spores and fungal growth (Candida albicans, Cryptococcus, Aspergillus, and Saccharomyces cerevisiae) [48, 49].

Ajoene, another component found in garlic, killed the fungus which causes athlete’s foot (tinea pedis) (0.4% cream, 14 day trial of 34 patients) [50].

Antiviral Activity

Garlic extract is also effective against the influenza virus and herpes viruses (simplex type 1, 2, and 3) [51].

A garlic supplement with allicin (1 capsule/day) prevented the common cold and diminished duration of symptoms (DB-RCT with 146 healthy subjects for 12 weeks) [52].

Side Effects

Garlic can cause nausea, stomach burn, and bad breath [41].

2) Oregano Oil

Oregano oil has been used for centuries as a food additive. It is known for its antimicrobial, antifungal, and antioxidant properties [53].

Mechanism of Action

The antibiotic and antifungal activity of oregano comes from two compounds, carvacrol and thymol [54, 55, 56].

Thymol and carvacrol damage the cell exterior (membrane) of bacteria, killing the cell [57, 58, 59, 60].

Antibacterial Activity

Oregano is effective against bacteria that cause: food poisoning, urinary tract infections, diarrhea, pneumonia, staph infections, and more. These include: Escherichia coli, Salmonella, Klebsiella pneumoniae, Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Pseudomonas fluorescens, Serratia liquefaciens, Streptococcus mutans, Enterococcus faecalis, Clostridium, Mycobacterium avium, and Shewanella putrefaciens [61, 62, 63, 57, 64, 65, 66, 67].

Thymol and carvacrol blocked the growth of cavity-causing bacteria (Streptococcus mutans), protecting rats against gum disease [64, 68].

Mexican oregano oil together with thyme and mustard oils were effective against three different strains of bacteria (Listeria monocytogenes, Staphylococcus aureus, and Salmonella enteritidis) [69].

Oregano oil together with clove and cinnamon oil inhibits the growth of the Acinetobacter baumannii, Acinetobacter baumannii RCH, Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa [70].

Antifungal Activity

Thymol and carvacrol were effective and stopping the growth of three different infection-causing fungi (yeast, Aspergillus, and dermatophyte) [58].

Antiviral Activity

Carvacrol and thymol have antiviral activity against:

• Herpes virus (simplex type 1) [71, 72]
• Human respiratory syncytial virus [72]
• Human rotavirus [72]
• Mouse norovirus [73]

Side Effects

Although rare, oregano oil can cause allergic reactions, especially in people with allergies to other members of the Lamiaceae family, like thyme [74].

Drug Interactions

Oregano blocks liver enzymes (cytochrome p450) that clear toxic substances in the blood. This may increase the effects of some drugs [75].

3) Echinacea

Echinacea has been used as a herbal drug since the 18th century. Echinacea extracts are known for their antibacterial and immunoprotective properties [76, 77].

Mechanism of Action

While the exact components of echinacea differ based on the species, the major ones are carbohydrates, caffeic acid, and proteins (glycoproteins). These are the active components that may have antibacterial, antifungal, and antiviral properties [78, 79].

Echinacea reduces symptoms of bacterial infections by blocking the release of inflammatory markers like cytokines. The mechanism for the antibacterial activity has not been clearly elucidated yet [80, 78].

Antibacterial Activity

Echinacea is effective for reducing the growth of multiple bacterial strains such as Streptococcus pyogenes, Haemophilus influenzae, Legionella pneumophila, Clostridium difficile, and Propionibacterium acnes [79, 78].

Antifungal Activity

Echinacea stops the growth of multiple strains of fungi and protected mice cells from lethal infections (Candida albicans and Listeria monocytogenes). It is also effective against Saccharomyces cerevisiae [79, 78, 81].

Antiviral Activity

Echinacea has antiviral activity against these viruses [82, 83, 78]:

• Rhinovirus
• Herpes viruses (simplex type 1 and 2)
• Influenza A and B
• Respiratory syncytial virus

An echinacea supplement (Echinilin) when taken at the first symptom of a cold, reduced the severity of the symptoms (10 doses the first day and 4 doses for the next 7 days, DB-RCT study with 282 patients) [84].

Side Effects

Side effects from echinacea consumption are rare and include rash and mild stomach problems such as nausea and stomach aches [85, 86].

Allergic reactions may occur, especially in people allergic to other plants of the Asteraceae family (such as chamomile) [85].

Drug Interactions

There are no known drug interactions with echinacea, although there are limited data on this [78].

4) Manuka Honey

Manuka honey is produced by bees that feed on the flowers of the manuka tree (Leptospermum scoparium). It is distinguished as the most medicinal honey but more data are needed [87].

Mechanism of Action

The main active antibiotic component of manuka honey is a compound called methylglyoxal. Another component of honey, propolis, has flavonoids (such as galangin and pinocembrin), phenolic acids, and esters that may contribute to boosting the immune system [88, 87, 89].

Manuka honey is also rich in glucose oxidase, an enzyme that converts glucose to hydrogen peroxide, which has antibacterial properties. Another compound, gluconolactone, reduces the pH of honey and has natural antibacterial properties. The inability of water to move through honey makes it difficult for bacteria to survive in it [87].

Antibacterial Activity

Manuka honey is a wide spectrum antibacterial and can kill the following bacteria: Escherichia coli, Staphylococcus aureus, several Enterococcus species, Pseudomonas aeruginosa, Streptococcus pyogenes, Proteus mirabilis, Salmonella typhimurium, and many more [90].

Topical application of manuka honey on a leg ulcer infected with antibiotic-resistant Staphylococcus aureus promoted effective wound healing in a patient on immunosuppressant drugs (case study) [91].

Weekly honey consumption was associated with a decreased risk of Helicobacter pylori infection in 150 patients with digestion problems [92].

Antiviral Activity

Manuka honey inhibited the growth of the varicella-zoster virus (the cause of chickenpox and shingles) in human skin cells [93].

It also inhibited influenza A virus growth in dog kidney cells [94].

Side Effects

Manuka honey taken for 4 weeks in 20 healthy adults caused no side effects. Although no allergic reactions were observed, caution is advised in individuals allergic to bees [95, 96].

5) Red Pepper

Multiple variations of the red pepper (Capsicum annuum), such as the cayenne pepper, chile peppers, and jalapeño peppers, have antibacterial properties [97, 98, 99, 100, 101].

Mechanism of Action

Capsaicin, the main active compound in peppers, which gives peppers their spicy taste, prevents bacterial infections by reducing stomach pH. Additionally, caffeic acid, quercetin, and kaempferol stiffen the outer layer (membrane) of bacterial cells, killing them [99, 102].

A compound (CAY-1) in cayenne peppers kills fungi by disrupting the outer layer of the cells (increased cell membrane permeability) [103, 104, 105].

Antibacterial Activity

Capsaicin restricted the production of α-toxins from Staphylococcus aureus and prevented pneumonia in mice [106].

Capsaicin blocked production of bacterial (Vibrio cholerae) toxins and prevented cell invasion by the bacteria (Streptococcus pyogenes and Staphylococcus aureus) [107, 108, 109].

Antifungal Activity

CAY-1 is effective against a number of species like Candida albicans, Aspergillus, Microsporum and more. Some of these fungi cause skin diseases such as athlete’s foot and ringworm [103, 104, 105, 24].

Side Effects

Capsaicin in moderate amounts is considered safe but may cause stomach irritation [110].

Drug Interactions

The use of capsaicin may increase the risk of developing a cough in patients using drugs for high blood pressure (ACE inhibitors) [111].

6) Tea Tree Oil

Tea tree oil is extracted from the tea tree plant (Melaleuca alternifolia) and is a wide spectrum antibiotic used on the skin. It is the active ingredient in many formulations used to treat skin infections [112].

Mechanism of Action

A number of compounds in tea tree oil, called monoterpenes (terpinen-4-ol, Linalool, alpha-pinene, and alpha-terpineol) are responsible for the antimicrobial activity in tea tree essential oils [113, 114]

Monoterpenes block energy production (cellular respiration) and disrupt the outer layer (membrane) of bacterial and fungal cells [115, 116, 117, 118].

Antibacterial Activity

Tea tree oil is effective against bacteria causing skin infections, acne, pneumonia, food poisoning, and more. Some of the bacterial strains include Staphylococcus (aureus and epidermidis), Propionibacterium acnes, Pseudomonas aeruginosa, Staphylococcus, Salmonella, and Escherichia coli [113, 119, 120, 121].

A cream and body wash containing tea tree oil (10% and 5% tea tree oil, respectively), used for 5 days, helped clear antibiotic-resistant Staphylococcus aureus skin infections (RCT with 236 hospitalized patients) [122].

A 0.2% tea tree oil solution reduced Streptococcus mutans and other microorganisms in the saliva of 30 subjects (5-week RCT) [41].

Antifungal Activity

Tea tree oil is effective against the following fungi: Candida albicans, Aspergillus, Microsporum, Epidermophyton, and more. These fungi can cause skin diseases (such as athlete’s foot and ringworm) among other issues [117, 123, 24].

In a study of 117 patients (DB-RCT, 25%, and 50% tea tree oil), tea tree oil application twice a day for 6 months treated toenail infections (onychomycosis). It also helped cure athlete’s foot (tinea pedis) in a study (DB-RCT, 100% tea tree oil) with 137 patients when used twice a day for 4 weeks [124, 125].

Topical tea tree oil cured a vaginal Candida infection in rats [126].

Antiviral Activity

Tea tree oil inhibited the growth of herpes viruses (simplex type 1 and 2) [127, 128].

Side Effects

Tea tree oil is toxic if ingested. When used on the skin, tea tree oil may cause dryness, burning, itching, inflammation, and allergic reactions [129, 130, 131].

7) Ginger

Ginger is a spice originating from the roots of the plant Zingiber officinale. It is commonly used in cooking in many Asian, Ayurvedic, and Middle Eastern cuisines. It is known for its many therapeutic qualities [132].

Mechanism of Action

Ginger contains gingerol, shogaol, zingerone, zerumbone, terpenoids, flavonoids, and other compounds that have antimicrobial and anti-biofilm properties [133, 134, 135].

Gingerol and gingerdiol are the main antifungal components [136].

Antibacterial Activity

Ginger is effective against many strains of bacteria, some of which are Staphylococcus, Bacillus, Salmonella, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Helicobacter pylori, and more [4, 137, 138].

Ginger extract reduced stress-induced damage in the stomach and inhibited stomach acid production, restricting H. pylori growth in mice [139].

In a cell study, ginger compounds killed Porphyromonas gingivalis, Porphyromonas endodontalis, and Prevotella intermedia, three species that cause gum disease [140].

Antifungal Activity

Ginger is effective against several strains of fungi, including those that cause skin diseases (such as athlete’s foot) and food spoilage: Fusarium, Aspergillus, Candida albicans, Saccharomyces cerevisiae, Microsporum gypseum, and many more [4, 141, 136, 24].

Antiviral Activity

Fresh ginger prevents the human respiratory syncytial virus (HRSV) from attaching itself to human cells and blocks the formation of plaques in the airway [142].

Additionally, ginger extracts are effective against herpes viruses (simplex type 1 and 2) [143, 144].

Side Effects

Ginger seems to have little to no side effects [145].

Drug Interactions

An active component in ginger (gingerol) blocks the activity of an enzyme that breaks down drugs (cytochrome p450), which may increase the effects of the drugs [146].

8) Cinnamon

Cinnamon (Cinnamomum zeylanicum and Cinnamomum cassia) is a widely used herb and is known for its antioxidant, anti-inflammatory, antiviral, antibacterial, and antifungal properties [147].

Mechanism of Action

Two compounds, cinnamaldehyde, and eugenol are responsible for the antibacterial and antiviral properties in cinnamon [148, 149].

Antibacterial Activity

Eugenol and cinnamaldehyde blocked the growth of Helicobacter pylori, which causes stomach ulcers and damage. However, a 4-week cinnamon treatment (80 mg/day) on 15 patients (pilot study) with Helicobacter pylori did not improve their condition [150, 151].

Cinnamon extracts also blocked the growth of Propionibacterium acnes and Staphylococcus epidermidis, two bacterial species that cause acne [152].

Cinnamon oil with clove oil blocked the growth of Escherichia coli, Yersinia enterocolitica, Pseudomonas aeruginosa, Salmonella choleraesuis, Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus, and Enterococcus faecalis [153].

Antifungal Activity

Cinnamon extracts are effective against many strains of fungus, such as Candida, Aspergillus, Penicillium, and many more [154, 155, 156, 157, 158, 159, 160, 161].

In a 7-day pilot study, 8 cinnamon lozenges/day improved symptoms of an oral Candida infection in 3 out of 5 HIV patients [156].

A combination of cinnamon, rosemary, and thyme oils reduced Penicillium expansum and Botrytis cinerea fungal growth [162].

Antiviral Activity

Cinnamaldehyde blocked the growth of the flu virus (influenza (A/PR/8)) and increased survival rates in rats [163].

In a cell study, IND02 (a procyanidin type A molecule) derived from cinnamon, prevented hepatitis C viral cell entry and thus, could be a potent therapy for hepatitis C and liver disease [164].

In another cell study, cinnamon extracts blocked another type of influenza virus (H7N3) from entering the cells [165].

Side Effects

Cinnamon extracts may cause nausea, stomach pain, and constipation [150].

9) Turmeric/Curcumin

Turmeric (Curcuma longa), commonly used in Indian cuisine, is not only known for its flavor, but also for its numerous health benefits [166].

Mechanism of Action

Curcumin is the most active compound in turmeric. It blocks the biofilms of bacteria that cause urinary infections, like Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, and Serratia marcescens [167].

Curcumin also interferes with bacterial cell-to-cell communication (quorum sensing) and prevents the production of important compounds (pyocyanin and acyl homoserine lactone) [168].

Curcumin also disrupts the activity of proteins involved in survival (ATPase activity, ergosterol, and proteinase) in fungi [169].

Curcumin suppresses the replication of the hepatitis C virus (via the PI3K/Ak pathway) [170].

Antibacterial Activity

Curcumin intake (30 mg, 2x/day) cured only 3 of 25 Helicobacter pylori patients following a 7-week treatment. But after 2 months, symptoms improved in the remaining patients (clinical trial) [171].

Curcumin consumption reduced the stomach inflammation caused by Helicobacter pylori in rats and mice [172, 173, 174, 175].

Curcumin prevented blood poisoning due to the Vibrio vulnificus bacteria in mice [176].

When combined with antibiotics, curcumin decreased lung inflammation in mice with pneumonia (Klebsiella pneumoniae infection) [177].

Antifungal Activity

Curcumin kills Candida species by disrupting survival proteins [169].

Antiviral Activity

Curcumin is effective against the HIV virus, the hepatitis C virus, influenza A, and influenza pneumonia [178, 179, 180, 170, 181, 181].

10) Clove

Clove (Eugenia caryophyllata) is known for its antioxidant, antibacterial, antifungal, and antiviral properties [4].

Mechanism of Action

Clove damages cells and outer layers (membranes) of bacteria cells, limiting their growth and production of DNA and critical proteins [182, 121, 183].

Antibacterial Activity

Eugenol is the most important and active component of cloves and is effective against Campylobacter jejuni, Escherichia coli, Listeria monocytogenes, and Salmonella enterica [182, 121, 183].

Clove prevented the growth of many bacterial strains, including Staphylococcus aureus and Escherichia coli. It also killed bacteria in the saliva samples of people with gum disease [184, 185].

Additionally, clove oil with cinnamon oil inhibited the growth of Escherichia coli, Yersinia enterocolitica, Pseudomonas aeruginosa, Salmonella choleraesuis, Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus, and Enterococcus faecalis [153].

A combination of clove, oregano, and cinnamon oil inhibited growth of the Acinetobacter baumannii, Acinetobacter baumannii RCH, Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa bacteria [70].

Antifungal Activity

Oral intake of clove extracts prevented the growth of oral Candida albicans and reduced the symptoms of infection in rats [186].

Eugenol, the main component of the clove, fights several kinds of Candida species and can be used as a therapy for oral Candida infection (oral candidiasis) and inflammation and soreness from denture use (denture stomatitis) [187].

Antiviral activity

Clove oil can be effective against:

• Herpes simplex virus [182]
• Hepatitis C [182]

11) Thyme

Thyme (Thymus vulgaris) is a spice used in Mediterranean cuisine but is also known for its medicinal properties [188].

Mechanism of Action

Thyme extracts and essential oil block the quorum sensing of bacteria, such as Escherichia coli and Pseudomonas aeruginosa [189].

Antibacterial Activity

Thyme extracts and the essential oil is effective against many strains of bacteria, including Escherichia coli, Salmonella, Pseudomonas (fluorescens and aeruginosa), Enterococcus faecalis, and many more [189, 190, 191, 192].

Antifungal activity

Thyme oil together with rosemary and cinnamon oils reduced Penicillium expansum and Botrytis cinerea fungal growth [162].

Thyme, Mexican oregano, and mustard oil inhibited the growth of Listeria monocytogenes, Staphylococcus aureus, and Salmonella Enteritidis bacteria [69].

Antiviral Activity

Thyme extracts can be effective against:

• Herpes virus (simplex type 1) [143, 193]
• Herpes virus (simplex type 2) [144]

12) Rosemary

Rosemary (Rosmarinus officinalis L.) is a widely used herb and is known for its antioxidant, anti-inflammatory, antibacterial, antifungal, and antiviral properties [194].

Mechanism of Action

Rosemary contains compounds (phenolic acid derivatives and diterpenes) like 1,8-cineole, α-pinene, camphene, α-terpineol, and borneol, that have antioxidant, antimicrobial, and anticancer effects [195, 194].

Rosemary extracts and essential oil blocks the quorum sensing of bacteria, such as Escherichia coli and Pseudomonas aeruginosa.

Antibacterial Activity

Rosemary extract effectively reduces the growth of many bacterial strains like Salmonella, Staphylococcus, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, and many more [196, 189, 190].

Antifungal Activity

Rosemary oil together with cinnamon and thyme oils prevent the growth of Penicillium expansum and Botrytis cinerea fungi [162].

Antiviral Activity

A rosemary extract, carnosol (a phenolic diterpene), had antiviral properties against HIV [197].

13) Lemongrass

Lemongrass (Cymbopogon citratus) is known for its anti-inflammatory, antioxidant, antibacterial, and antifungal properties. It is used widely for therapeutic and fragrance purposes [198].

Mechanism of Action

Citral α and citral β, major components of lemongrass oil, block the growth of different kinds of bacteria (gram-positive and gram-negative) [199].

Antibacterial Activity

Lemongrass extracts have been effective at reducing the growth of Staphylococcus aureus, Salmonella enterica, Escherichia coli, Pseudomonas aeruginosa, and many other bacteria [65, 148, 200, 65, 199].

Antifungal Activity

Lemongrass extracts reduced the growth of Candida albicans, Aspergillus, Microsporum gypseum, and multiple species of Penicillium [155, 65, 198, 201, 202].

Lemongrass oil cured ringworm, a fungal skin infection, in guinea pigs in a 7-12 day period [203].

Antiviral Activity

Lemongrass essential oil reduced the function of a protein (HIV-1 Tat protein) important for HIV replication [204].

14) Myrrh

Myrrh (Commiphora molmol) was used in ancient Egypt for mummification. Nowadays, myrrh is used to treat injuries and infections as it has anticancer, antibacterial, and antifungal properties [205, 206, 207].

Mechanism of Action

Camphor, borneol, Linalool, and α-terpineol are major components of myrrh essential oil and have antibacterial properties [208].

Myrrh prevents the formation of biofilms [209].

Antibacterial Activity

Myrrh inhibits the growth of bacteria such as Staphylococcus aureus, Escherichia coli, Salmonella, Pseudomonas aeruginosa, and Klebsiella pneumoniae [209, 209, 210, 211, 212, 213].

Antifungal Activity

Myrrh extracts have been effective against Candida albicans, Aspergillus niger, and Penicillium [212, 213].

Side Effects

Allergic skin reactions to myrrh have been reported [214, 215].

Users have also reported possible side effects of diarrhea, nose irritation, and changes in their heart rate [207].

15) Olive Leaf Extract

Mechanism of Action

The antimicrobial activity of olive leaf extract is due to the polyphenols [216].

Antibacterial Activity

Olive leaf extract inhibited the growth of three foodborne pathogens (Listeria monocytogenes, Escherichia coli, and Salmonella enteritidis). It also inhibited the biofilms of L. monocytogenes and S. enteritidis and movement of L. monocytogenes (cell study) [216].

Antifungal Activity

Methanol extracts of the leaves inhibited yeast strains (Candida albicans and Saccharomyces cerevisiae) [217].

Side Effects

Olive leaf extract has been traditionally been prepared and used in many different ways in multiple cultures [218].

Toxicity of olive leaf extract was assessed on rats and deemed safe. Human studies will need to be conducted to verify this [219].

Limitations and Caveats

There is a lack of human trials to support the benefits of these natural antibiotics and also limited studies to support their safety. Further clinical trials are needed to confirm the benefits in humans.