Antibiotics were first discovered when Alexander Fleming noticed mold (Penicillium notatum) inhibiting the growth of bacteria. Pharmaceutical antibiotics were later developed but some have side effects. Most importantly, the overprescription and misuse of antibiotics have led to many bacteria developing antibiotic resistance. Read on to learn about natural substances with antibiotic properties.
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 some of these illnesses .
In addition, some pharmaceutical antibiotics are 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 antibacterial, antifungal, and antiviral properties, suggesting their potential as an add-on to antibiotic treatments .
You may discuss with your doctor if any of these herbs may help as a complementary approach in your case. Most important, however, is to carefully follow your treatment plan. This means you should take your antibiotic medication exactly as prescribed by your doctor and never replace it with any of these herbs.
Types of 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. For instance, Escherichia coli can help maintain a healthy digestive tract but a different strain of this species can cause food poisoning and diarrhea. Some of the most common bacterial infections are :
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 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 .
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) .
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 buildup, 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].
A lot of common diseases are actually due to fungal infections. Like with bacteria, fungi normally found in the body can sometimes become overgrown and cause health issues [3, 24].
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 .
Dandruff is a very common condition in which scalp skin flakes 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].
Although eczema has many causes, it is aggravated by Malassezia yeast (also associated with dandruff) .
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].
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 .
Garlic has been widely used throughout history for the treatment and prevention of diseases. Recent studies have evaluated the potential benefits of garlic, including its antibacterial, antifungal, and antiviral activity .
Mechanism of Action
Allicin is the main active compound in garlic, responsible for most of its 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 maintaining cell structure [33, 34, 35].
Allicin prevents bacterial and fungal growth by blocking the formation of biofilms. Biofilm infections, such as in case of pneumonia, cystic fibrosis, and persistent wounds, are chronic infections that affect millions of people each year [36, 37, 38, 39].
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. However, garlic (and jalapeño peppers) was ineffective against this infection in 2 trials on 17 people [40, 41, 42].
Additionally, a garlic extract mouthwash decreased levels of oral Streptococcus mutans in clinical trials on 75 healthy people [43, 44].
Garlic extracts might be helpful in treating swollen gums and preventing cavities since they killed oral pathogens such as Porphyromonas gingivalis, Prevotella intermedia, and Aggregatibacter actinomycetemcomitans in test tubes [45, 46].
It also increased the effectiveness of other antibiotics against Pseudomonas aeruginosa in test tubes. However, it failed to prevent this microbe from forming biofilms in lung tissue scars in a clinical trial on 34 people [47, 48, 49].
Besides killing Staphylococcus aureus and Streptococcus pyogenes, garlic extract may also protect the body from bacterial toxins (such as α-toxins and streptolysin O) by reducing their production [50, 51].
Allicin in garlic extracts blocked the germination of spores and fungal growth (Candida albicans, Cryptococcus, Aspergillus, and Saccharomyces cerevisiae) in test tubes [52, 53].
Candida may infect the mouth lining and cause an inflammatory disease called denture stomatitis or oral candidiasis. In 2 clinical trials on 96 people with this condition, garlic extract (applied as mouthwash or paste) showed similar effectiveness to the antifungal medications nystatin and clotrimazole [54, 55].
Commercial tablets with garlic extract (Garcin) improved the symptoms of vaginal candidiasis as effectively as fluconazole in a clinical trial on 110 women. However, another commercial formulation (Garlicin) was ineffective in a trial on 63 infected but asymptomatic women [56, 57].
Ajoene (0.4-1% cream), another component found in garlic, killed the fungus that causes athlete’s foot (tinea pedis) in 2 clinical trials on 81 people [58, 59].
Garlic extract was also effective against the influenza virus and herpes viruses (simplex type 1, 2, and 3) in test tubes .
A garlic supplement with allicin (1 capsule/day for 12 weeks) prevented the common cold and diminished duration of the symptoms in 2 clinical trials on 146 healthy adults and 172 children [61, 62].
Garlic can cause nausea, stomach burn, and bad breath .
The evidence suggests that garlic may be effective against cavities/gum disease, oral candidiasis, athlete’s foot, and the common cold. You may discuss with your doctor if it may help as an add-on to your treatment regime. However, never use it in place of what your doctor recommends or prescribes.
2) 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 .
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 [64, 65].
Monoterpenes block energy production (cellular respiration) and disrupt the outer layer (membrane) of bacterial and fungal cells [66, 67, 68, 69].
Tea tree oil was effective against bacteria causing skin infections, acne, pneumonia, food poisoning, and more in test tubes. Some of the bacterial strains include Staphylococcus (aureus and epidermidis), Propionibacterium acnes, Pseudomonas aeruginosa, Staphylococcus, Salmonella, and Escherichia coli [64, 70, 71, 72].
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 in a clinical trial on 236 hospitalized patients .
A 0.2% tea tree oil solution reduced Streptococcus mutans and other microorganisms in the saliva of 30 subjects .
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 [68, 74, 24].
In a study of 117 patients (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 (100% tea tree oil) with 137 patients when used twice a day for 4 weeks [75, 76].
Topical tea tree oil cured a vaginal Candida infection in rats .
Tea tree oil inhibited the growth of herpesviruses (simplex type 1 and 2) [78, 79].
Tea tree oil is toxic if ingested. When used on the skin, tea tree oil may cause dryness, burning, itching, inflammation, and allergic reactions [80, 81, 82].
All in all, the evidence suggests that tea tree oil may help with bacterial and fungal skin infections, as well as possibly helping prevent cavities and gum disease. You may use it as a complementary approach if your doctor determines that it may be helpful in your case. Carefully follow your doctor’s recommendations and never use tea tree oil as a replacement for proven therapies.
1) Oregano Oil
Oregano oil has been used for centuries as a food additive. It is known for its antimicrobial, antifungal, and antioxidant properties .
Mechanism of Action
The antibiotic and antifungal activity of oregano comes from two compounds, carvacrol and thymol [84, 85, 86].
Thymol and carvacrol damage the cell exterior (membrane) of bacteria, killing the cell [87, 88, 89, 90].
In a clinical trial on 40 people recovering from surgical wounds, an ointment with oregano oil reduced the contamination of the wounds with Staphylococcus aureus, thus helping the healing process .
Thymol and carvacrol blocked the growth of cavity-causing bacteria (Streptococcus mutans), protecting rats against gum disease [92, 93].
In test tubes, oregano inhibited and killed the 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 [94, 95, 96, 87, 92, 97, 98, 99].
Mexican oregano oil together with thyme and mustard oils were effective against three different strains of bacteria (Listeria monocytogenes, Staphylococcus aureus, and Salmonella enteritidis) in test tubes .
Oregano oil together with clove and cinnamon oil inhibited the growth of Acinetobacter baumannii, Acinetobacter baumannii RCH, Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa in test tubes .
Thymol and carvacrol were effective at stopping the growth of three different infection-causing fungi (yeast, Aspergillus, and dermatophyte) in test tubes .
Carvacrol and thymol had antiviral activity against the following virus in cell-based studies:
- Herpes virus (simplex type 1) [102, 103]
- Human respiratory syncytial virus 
- Human rotavirus 
- Mouse norovirus 
In a small trial on 14 people infected with three parasites that cause digestive issues (Blastocystis hominis, Entamoeba hartmanni and Endolimax nana), supplementation with oregano oil caused the parasites to disappear completely in most cases and improved the symptoms in the rest .
Although rare, oregano oil can cause allergic reactions, especially in people with allergies to other members of the Lamiaceae family, like thyme .
Oregano blocks liver enzymes (cytochrome p450) that clear toxic substances in the blood. This may increase the effects of some drugs .
Only a couple of small clinical trials suggest that oregano may help with bacterial and parasitic infections. More clinical trials on larger populations are needed to determine its potential against infectious diseases.
Echinacea has been used as an herbal drug since the 18th century. Echinacea extracts are known for their potential antibacterial and immunoprotective properties [108, 109].
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 [110, 111].
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 [112, 110].
Echinacea is effective for reducing the growth of multiple bacterial strains such as Streptococcus pyogenes, Haemophilus influenzae, Legionella pneumophila, Clostridium difficile, and Propionibacterium acnes [111, 110].
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 [111, 110, 113].
An echinacea supplement (Echinilin) when taken at the first symptom of a cold, reduced the severity of the symptoms in a clinical trial on 282 people. However, tablets with echinacea extract were ineffective at preventing this condition in a clinical trial on over 100 people and at treating it in another trial on over 700 people. A meta-analysis concluded that echinacea products are ineffective at treating the common cold but may help prevent it [114, 115, 116, 117].
In a clinical trial on 95 people with early symptoms of cold or flu, echinacea helped relieve the symptoms. A spray combining echinacea and sage was as effective against sore throats as one containing chlorhexidine and lidocaine in a clinical trial on 154 people. However, echinacea failed to treat upper respiratory infections in a trial on over 400 children and to prevent them in 2 trials on almost 400 adults [118, 119, 120, 121, 122].
Echinacea had antiviral activity against these viruses in cell-based studies [123, 124, 110]:
- Herpes viruses (simplex type 1 and 2)
- Influenza A and B
- Respiratory syncytial virus
Side effects of echinacea consumption are rare and include rash and mild stomach problems such as nausea and stomach aches [125, 126].
Allergic reactions may occur, especially in people allergic to other plants of the Asteraceae family (such as chamomile) .
There are no known drug interactions with echinacea, although there are limited data on this .
Although widely investigated in people with the common cold and other upper respiratory infections, the effectiveness of echinacea is inconclusive due to the mixed results. More clinical trials are needed to shed some light on its therapeutic potential.
3) Manuka Honey
Manuka honey is produced by bees that feed on the flowers of the manuka tree (Leptospermum scoparium). It is considered the most medicinal honey, but more data are needed .
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 [128, 127, 129].
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 .
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 in test tubes .
Weekly honey consumption was associated with a decreased risk of Helicobacter pylori infection in 150 patients with digestion problems .
In a clinical trial on 42 people with chronic rhinosinusitis, irrigation with manuka honey before surgery improved the outcome, including bacterial count .
Chewing gum with manuka honey reduced plaque buildup and gum bleeding in a pilot trial on 30 healthy volunteers .
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 .
Manuka honey inhibited the growth of the varicella-zoster virus (the cause of chickenpox and shingles) in human skin cells .
It also inhibited influenza A virus growth in dog kidney cells .
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 [137, 138].
Although the results are promising, very few, small clinical trials support the use of manuka honey in people with bacterial infections. Larger, more robust clinical trials are needed to validate these preliminary results.
Cinnamon (Cinnamomum zeylanicum and Cinnamomum cassia) is a widely used herb and is known for its antioxidant, anti-inflammatory, antiviral, antibacterial, and antifungal properties .
Mechanism of Action
Two compounds, cinnamaldehyde, and eugenol are responsible for the antibacterial and antiviral properties in cinnamon [140, 141].
Eugenol and cinnamaldehyde blocked the growth of Helicobacter pylori, which causes stomach ulcers and damage, in test tubes. However, a 4-week cinnamon treatment (80 mg/day) on 15 patients with Helicobacter pylori did not improve their condition [142, 143].
Cinnamon extracts also blocked the growth of Propionibacterium acnes and Staphylococcus epidermidis, two bacterial species that cause acne .
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 in test tubes .
Cinnamon extracts are effective against many strains of fungus, such as Candida, Aspergillus, Penicillium, and many more [146, 147, 148, 149, 150, 151, 152, 153].
In a 7-day pilot study, 8 cinnamon lozenges/day improved symptoms of an oral Candida infection in 3 out of 5 HIV patients .
In a clinical trial on 60 people with intestinal Candida infections, capsules with cinnamon and pogostemon oil resolved the infection in 72% and improved it in 28% .
A combination of cinnamon, rosemary, and thyme oils reduced Penicillium expansum and Botrytis cinerea fungal growth .
Cinnamaldehyde blocked the growth of the flu virus (influenza (A/PR/8)) and increased survival rates in rats .
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 .
In another cell study, cinnamon extracts blocked another type of influenza virus (H7N3) from entering the cells .
Cinnamon extracts may cause nausea, stomach pain, and constipation .
Cinnamon has only been tested against candidiasis in clinical trials, one of them very small. More clinical trials on larger populations are needed to conclude for certain if cinnamon may be of any use against Candida infections.
Turmeric (Curcuma longa), commonly used in Indian cuisine, is not only known for its flavor, but also for its numerous health benefits .
Mechanism of Action
Curcumin is the most active compound in turmeric. In test tubes, it blocked the biofilms of bacteria that cause urinary infections, like Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, and Serratia marcescens .
Curcumin also interferes with bacterial cell-to-cell communication (quorum sensing) and prevents the production of important compounds (pyocyanin and acyl homoserine lactone) .
Curcumin also disrupts the activity of proteins involved in survival (ATPase activity, ergosterol, and proteinase) in fungi .
Curcumin suppresses the replication of the hepatitis C virus (via the PI3K/Ak pathway) .
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) .
Curcumin consumption reduced the stomach inflammation caused by Helicobacter pylori in rats and mice [164, 165, 166, 167].
Curcumin prevented blood poisoning due to the Vibrio vulnificus bacteria in mice .
When combined with antibiotics, curcumin decreased lung inflammation in mice with pneumonia (Klebsiella pneumoniae infection) .
Curcumin kills Candida species by disrupting survival proteins .
Curcumin inhibited the HIV virus, the hepatitis C virus, influenza A, and influenza pneumonia [170, 171, 172, 162, 173].
A small clinical trial with modest results is clearly insufficient to support the use of turmeric against Helicobacter pylori infections. Further clinical research is needed.
Animal and Cell Research (Lack of Evidence)
No clinical evidence supports the use of the following herbs to fight off infections. Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts. However, the studies should not be interpreted as supportive of any health benefit.
Multiple variations of the red pepper (Capsicum annuum), such as the cayenne pepper, chile peppers, and jalapeño peppers, have antibacterial properties [174, 175, 176, 177, 178].
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 [176, 179].
A compound (CAY-1) in cayenne peppers kills fungi by disrupting the outer layer of the cells (increased cell membrane permeability) [180, 181, 182].
Capsaicin restricted the production of α-toxins from Staphylococcus aureus and prevented pneumonia in mice .
Capsaicin blocked the production of bacterial (Vibrio cholerae) toxins and prevented cell invasion by the bacteria (Streptococcus pyogenes and Staphylococcus aureus) in test tubes [184, 185, 186].
CAY-1 was effective against a number of species like Candida albicans, Aspergillus, Microsporum and more in test tubes. Some of these fungi cause skin diseases such as athlete’s foot and ringworm [180, 181, 182, 24].
Capsaicin in moderate amounts is considered safe but may cause stomach irritation .
The use of capsaicin may increase the risk of developing a cough in patients using drugs for high blood pressure (ACE inhibitors) .
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 .
Mechanism of Action
Ginger contains gingerol, shogaol, zingerone, zerumbone, terpenoids, flavonoids, and other compounds that have antimicrobial and anti-biofilm properties [190, 191, 192].
Gingerol and gingerdiol are the main antifungal components .
Ginger was effective against many strains of bacteria, some of which are Staphylococcus, Bacillus, Salmonella, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Helicobacter pylori, and more, in test tubes [4, 194, 195].
Ginger extract reduced stress-induced damage in the stomach and inhibited stomach acid production, restricting H. pylori growth in mice .
In a cell study, ginger compounds killed Porphyromonas gingivalis, Porphyromonas endodontalis, and Prevotella intermedia, three species that cause gum disease .
Ginger was effective against several strains of fungi in test tubes, 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, 198, 193, 24].
Fresh ginger prevented the human respiratory syncytial virus (HRSV) from attaching itself to human cells and blocked the formation of plaques in the airway .
Additionally, ginger extracts inhibited herpes viruses (simplex type 1 and 2) [200, 201].
Ginger seems to have little to no side effects .
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 .
Clove (Eugenia caryophyllata) is known for its antioxidant, antibacterial, antifungal, and antiviral properties .
Mechanism of Action
Clove damages cells and outer layers (membranes) of bacteria cells, limiting their growth and production of DNA and critical proteins [204, 72, 205].
Eugenol is the most important and active component of cloves and is effective against Campylobacter jejuni, Escherichia coli, Listeria monocytogenes, and Salmonella enterica in test tubes [204, 72, 205].
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 [206, 207].
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 .
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 .
Oral intake of clove extracts prevented the growth of oral Candida albicans and reduced the symptoms of infection in rats .
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) .
Inhibition studies suggest that clove oil may be effective against:
Thyme (Thymus vulgaris) is a spice used in Mediterranean cuisine but is also known for its medicinal properties .
Mechanism of Action
Thyme extracts and essential oil block the quorum sensing of bacteria, such as Escherichia coli and Pseudomonas aeruginosa .
Thyme extracts and the essential oil inhibited many strains of bacteria, including Escherichia coli, Salmonella, Pseudomonas (fluorescens and aeruginosa), Enterococcus faecalis, and many more [211, 212, 213, 214].
Thyme oil together with rosemary and cinnamon oils reduced Penicillium expansum and Botrytis cinerea fungal growth .
Thyme, Mexican oregano, and mustard oil inhibited the growth of Listeria monocytogenes, Staphylococcus aureus, and Salmonella Enteritidis bacteria .
Thyme inhibited the following viruses:
Rosemary (Rosmarinus officinalis L.) is a widely used herb and is known for its antioxidant, anti-inflammatory, antibacterial, antifungal, and antiviral properties .
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 [217, 216].
Rosemary extracts and essential oil blocks the quorum sensing of bacteria, such as Escherichia coli and Pseudomonas aeruginosa.
Rosemary extract effectively reduced the growth of many bacterial strains like Salmonella, Staphylococcus, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, and many more in test tubes [218, 211, 212].
Rosemary oil together with cinnamon and thyme oils prevented the growth of Penicillium expansum and Botrytis cinerea fungi .
A rosemary extract, carnosol (a phenolic diterpene), had antiviral properties against HIV .
Lemongrass (Cymbopogon citratus) is known for its anti-inflammatory, antioxidant, antibacterial, and antifungal properties. It is used widely for therapeutic and fragrance purposes .
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) .
Lemongrass extracts have been effective at reducing the growth of Staphylococcus aureus, Salmonella enterica, Escherichia coli, Pseudomonas aeruginosa, and many other bacteria in test tubes [97, 140, 222, 97, 221].
Lemongrass extracts reduced the growth of Candida albicans, Aspergillus, Microsporum gypseum, and multiple species of Penicillium [147, 97, 220, 223, 224].
Lemongrass oil cured ringworm, a fungal skin infection, in guinea pigs in a 7-12 day period .
Lemongrass essential oil reduced the function of a protein (HIV-1 Tat protein) important for HIV replication .
Myrrh (Commiphora molmol) was used in ancient Egypt for mummification. Nowadays, myrrh is used to treat injuries and infections as it has antibacterial and antifungal properties [227, 228, 229].
Mechanism of Action
Camphor, borneol, Linalool, and α-terpineol are major components of myrrh essential oil and have antibacterial properties .
Myrrh prevents the formation of biofilms .
Myrrh inhibited the growth of bacteria such as Staphylococcus aureus, Escherichia coli, Salmonella, Pseudomonas aeruginosa, and Klebsiella pneumoniae in test tubes [231, 231, 232, 233, 234, 235].
Myrrh extracts have been effective against Candida albicans, Aspergillus niger, and Penicillium [234, 235].
Allergic skin reactions to myrrh have been reported [236, 237].
Users have also reported possible side effects of diarrhea, nose irritation, and changes in their heart rate .
Olive Leaf Extract
Mechanism of Action
The antimicrobial activity of olive leaf extract is due to its polyphenols .
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) .
Methanol extracts of the leaves inhibited yeast strains (Candida albicans and Saccharomyces cerevisiae) .
Olive leaf extract has been traditionally been prepared and used in many different ways in multiple cultures .
Toxicity of olive leaf extract was assessed on rats and deemed safe. Human studies will need to be conducted to verify this .
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. In some cases, the clinical trials had mixed results. Further clinical trials are needed to confirm the benefits in humans.