Antibiotics were first discovered when Alexander Fleming noticed mould (Penicillium notatum) inhibiting the growth of bacteria. Pharmaceutical antibiotics were later developed but most have harmful side effects such as vomiting, diarrhoea, allergic reactions, and rashes. Infectious illnesses caused by bacteria, fungi, or viruses are extremely common. The over prescription and misuse of pharmaceutical antibiotics have led to many bacteria developing antibiotic resistance. Fortunately, there are many naturally occurring antibiotics with few side effects.
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.
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. 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. Allicin kills bacteria by blocking enzymes important for energy production and cell structure. 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.
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.
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Antifungal Activity - Allicin in garlic extracts blocked the germination of spores and fungal growth (Candida albicans, Cryptococcus, Aspergillus, and Saccharomyces cerevisiae). 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)
Antiviral Activity - Garlic extract is also effective against the influenza virus and herpes viruses (simplex type 1, 2, and 3).
Side Effects
Garlic can cause nausea, stomach burn, and bad breath.
2) 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. Thymol and carvacrol damage the cell exterior (membrane) of bacteria, killing the cell.
Antibacterial Activity - Oregano is effective against bacteria that cause food poisoning, urinary tract infections, diarrhoea, pneumonia, staph infections, and more. Thymol and carvacrol blocked the growth of cavity-causing bacteria (Streptococcus mutans), protecting rats against gum disease.
Mexican oregano oil together with thyme and mustard oils were effective against three different strains of bacteria (Listeria monocytogenes, Staphylococcus aureus, and Salmonella enteritis). 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.
Antifungal Activity - Thymol and carvacrol were effective and stopping the growth of three different infection-causing fungi (yeast, Aspergillus, and dermatophyte).
Antiviral Activity - Carvacrol and thymol have antiviral activity against:
Herpes virus (simplex type 1), Human respiratory syncytial virus, Human rotavirus, Mouse norovirus.
Side Effects
Although rare, oregano oil can cause allergic reactions, especially in people with allergies to other members of the Lamiaceae family, like thyme.
3) Echinacea
Echinacea has been used as an herbal drug since the 18th century. Echinacea extracts are known for their antibacterial and immunoprotective properties.
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 the antibacterial, antifungal, and antiviral properties.
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.
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.
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.
Antiviral Activity - Echinacea has antiviral activity against these viruses: Rhinovirus, Herpes viruses (simplex type 1 and 2), Influenza A and B, Respiratory syncytial virus.
Side Effects
Side effects from echinacea consumption are rare and include rash and mild stomach problems such as nausea and stomach aches.
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.
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.
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.
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.
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).
Weekly honey consumption was associated with a decreased risk of Helicobacter pylori infection in 150 patients with digestion problems.
Antiviral Activity - 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.
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.
5) Red Pepper
Multiple variations of the red pepper (Capsicum annuum), such as the cayenne pepper, chilli peppers, and jalapeño peppers, have antibacterial properties.
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.
A compound (CAY-1) in cayenne peppers kills fungi by disrupting the outer layer of the cells (increased cell membrane permeability).
Antibacterial Activity - Capsaicin restricted the production of α-toxins from Staphylococcus aureus and prevented pneumonia in mice.
Capsaicin blocked production of bacterial (Vibrio cholerae) toxins and prevented cell invasion by the bacteria (Streptococcus pyogenes and Staphylococcus aureus).
Antifungal Activity - CAY-1 is effective against several species like Candida albicans, Aspergillus, Microsporum and more. Some of these fungi cause skin diseases such as athlete’s foot and ringworm.
Side Effects
Capsaicin in moderate amounts is considered safe but may cause stomach irritation.
Drug Interactions
The use of capsaicin may increase the risk of developing a cough in patients using drugs for high blood pressure (ACE inhibitors).
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.
Mechanism of Action - Several 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.
Monoterpenes block energy production (cellular respiration) and disrupt the outer layer (membrane) of bacterial and fungal cells.
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.
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).
A 0.2% tea tree oil solution reduced Streptococcus mutans and other microorganisms in the saliva of 30 subjects (5-week RCT).14
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.
In a study of 117 patients, 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 with 137 patients when used twice a day for 4 weeks.
Topical tea tree oil cured a vaginal Candida infection in rats.
Antiviral Activity - Tea tree oil inhibited the growth of herpes viruses (type 1 and 2).
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.
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.
Mechanism of Action- Ginger contains gingerol, shogaol, zingerone, zerumbone, terpenoids, flavonoids, and other compounds that have antimicrobial and anti-biofilm properties. Gingerol and gingerdiol are the main antifungal components.
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.
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.
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.
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. Additionally, ginger extracts are effective against herpes viruses (simplex type 1 and 2).
Side Effects
Ginger seems to have little to no side effects.
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.
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.
Mechanism of Action - Two compounds, cinnamaldehyde, and eugenol are responsible for the antibacterial and antiviral properties in cinnamon.
Antibacterial Activity - Eugenol and cinnamaldehyde blocked the growth of Helicobacter pylori, which causes stomach ulcers and damage.
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.
Antifungal Activity - Cinnamon extracts are effective against many strains of fungus, such as Candida, Aspergillus, Penicillium, and many more.
In a 7-day pilot study, 8 cinnamon lozenges/day improved symptoms of an oral Candida infection in 3 out of 5 HIV patients.
A combination of cinnamon, rosemary, and thyme oils reduced Penicillium expansum and Botrytis cinerea fungal growth.
Antiviral Activity - 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.
Side Effects
Cinnamon extracts may cause nausea, stomach pain, and constipation.
Turmeric (Curcuma longa), commonly used in Indian cuisine, is not only known for its flavour, but also for its numerous health benefits.
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
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).
Antibacterial Activity - Curcumin consumption reduced the stomach inflammation caused by Helicobacter pylori in rats and mice.
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).
Antifungal Activity - Curcumin kills Candida species by disrupting survival proteins.
Antiviral Activity - Curcumin is effective against the HIV virus, the hepatitis C virus, influenza A, and influenza.
10) Clove
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.
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.
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.
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.
Antifungal Activity - 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).
Antiviral activity - Clove oil can be effective against: Herpes simplex virus, Hepatitis C.
11) Thyme
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.
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.
Antifungal activity - 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.
Antiviral Activity - Thyme extracts can be effective against: Herpes virus (type 1 and 2).
12) Rosemary
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.
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.
Antifungal Activity - Rosemary oil together with cinnamon and thyme oils prevent the growth of Penicillium expansum and Botrytis cinerea fungi.
Antiviral Activity - A rosemary extract, carnosol (a phenolic diterpene), had antiviral properties against HIV.
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.
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.
Antibacterial Activity - Lemongrass extracts have been effective at reducing the growth of Staphylococcus aureus, Salmonella enterica, Escherichia coli, Pseudomonas aeruginosa, and many other bacteria.
Antifungal Activity - Lemongrass extracts reduced the growth of Candida albicans, Aspergillus, Microsporum gypseum, and multiple species of Penicillium.
Lemongrass oil cured ringworm, a fungal skin infection, in guinea pigs in a 7-12-day period.
Antiviral Activity - Lemongrass essential oil reduced the function of a protein (HIV-1 Tat protein) important for HIV replication.
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.
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.
Antibacterial Activity - Myrrh inhibits the growth of bacteria such as Staphylococcus aureus, Escherichia coli, Salmonella, Pseudomonas aeruginosa, and Klebsiella pneumoniae.
Antifungal Activity - Myrrh extracts have been effective against Candida albicans, Aspergillus niger, and Penicillium.
Side Effects
Allergic skin reactions to myrrh have been reported. Users have also reported possible side effects of diarrhoea, nose irritation, and changes in their heart rate.
15) Olive Leaf Extract
Mechanism of Action - The antimicrobial activity of olive leaf extract is due to the polyphenols.
Antibacterial Activity - Olive leaf extract inhibited 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).
Antifungal Activity - Methanol extracts of the leaves inhibited yeast strains (Candida albicans and Saccharomyces cerevisiae).
Side Effects
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 limited studies to support their safety. Further clinical trials are needed to confirm the benefits in humans.
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