Here is a list of thirteen main antimicrobial foods.
1. Amla (Phyllanthus Emblica syn. Emblica Officinalis/Phyllanthus Niruri):
Saeed and Tariq (2007) demonstrated in vitro anti-viral and antimicrobial properties of Amla against E. coli, K. pneumoniae, K. ozaenae, P. mirabilis, P. aeruginosa, S. typhi, S. paratyphi A, S. paratyphi B and S. marcescens but did not show any antibacterial activity against Gram-negative urinary pathogens. This may be due to higher sensitivity of Gram-positive bacteria to the oils than Gram-negative bacteria.
Similarly, Liu et al. (2009) found the essential oil of amla to show a broad spectrum of antimicrobial activity against all the tested micro-organisms. The essential oil obtained by supercritical fluid extraction exhibited a higher anti-fungal activity compared to the one obtained by hydro-distillation.
But Rahman et al. (2009) observed the chloroform soluble fraction of the methanolic extract of amla to exhibit significant antimicrobial activity against some Gram-positive and Gram-negative pathogenic bacteria with strong cytotoxicity (LC50 of 10.257 ± 0.770 mcg/ml (-1)). It is thus shown that the chloroform soluble fraction of the ripe fruits of Amla containing alkaloids is biologically more active.
Aqueous extract of amla exhibited potent antimicrobial activity against E. cloacae followed by E. coli. The minimum inhibitory concentration of aqueous extract of amla was most active against K. pneumonia, whereas that of methanol extract showed maximum activity against E. coli.
Srikumar et al. (2007) reported that both individual and combined aqueous and ethanol extracts of Triphala which also contains amala, have anti-bacterial activity against the bacterial isolates (P. aeruginosa, K. pneumoniae, S. sonnei, S. flexneri, S. aureus, V. cholerae, S. paratyphi-B, E. coli, E. faecalis, S. typhi) tested.
Besides being antibacterial, amla also showed antiviral properties. Coxsackie virus B3 (CVB3) is believed to be a major contributor to viral myocarditis since virus- associated apoptosis plays a role in the pathogenesis of experimental myocarditis. Wang et al. (2009b) showed that Phyllaemblicin B exerts significant antiviral activities against CVB3 and thus is proved to be a potential therapeutic agent for viral myocarditis.
2. Berries:
Phenolic compounds present in berries selectively inhibit the growth of human gastro-intestinal pathogens. Especially cranberry (Vaccinium macrocarpon), cloudberry, raspberry, strawberry and bilberry possess clear antimicrobial effects against Salmonella and Staphylococcus. Complex phenolic polymers, such as ellagitannins, are strong anti-bacterial agents present in cloudberry, raspberry and strawberry.
Berry phenolic seem to affect the growth of different bacterial species with different mechanisms. The most sensitive bacteria on berry phenolic were found to be H. pylori and B. cereus while C. jejuni and C. albicans were inhibited only with phenolic extracts of cloudberry, raspberry, and strawberry, (rich in ellagitannins). Cloudberry extract gave strong microbicide effects on the basis of plate count with all the strains tested.
Antimicrobial activity of berries may also be related to their anti-adherence activity. Utilization of enzymes in berry processing increases the amount of phenolics and thereby the antimicrobial activity of berry products. Phenolic compounds, especially ellagitannins, were strong inhibitory compounds against Staphylococcus bacteria. Salmonella bacteria were only partly inhibited by the berry phenolics, and most of the inhibition seemed to originate from other compounds, such as organic acids.
Listeria strains were not affected by berry compounds, with the exception of cranberry. Antimicrobial activity of berries and other anthocyanin-containing fruits is likely to be caused by multiple mechanisms and synergies because they contain various compounds including anthocyanins, weak organic acids, phenolic acids, and their mixtures of different chemical forms.
Proanthocyanidins with unique molecular structures have been isolated from cranberry fruit that exhibited potent bacterial anti-adhesion activity which in turn is responsible for bacteriostatic effect of cranberries. In elderly patients, cranberry consumption reduces the incidence of bacteriuria, although this is often not treated with antibiotics.
Heinonen (2007) opines that tannin-containing berries exhibit antimicrobial properties against pathogenic bacteria, thus offering many new applications for food industry. The phenolics in cranberries as well as cultivated and wild blueberries have gained attention. Cranberries contain 2 compounds with anti-adherence properties that prevent fimbriated E. coli from adhering to uroepithelial cells in the urinary tract.
Among cranberry compounds, a group of proanthocyanidins (PACs) with A-type linkages were isolated which exhibit bacterial anti-adhesion activity against uropathogenic E. coli strains. These PAC inhibit P-fimbriae synthesis and induce a bacterial deformation and on both antibiotic susceptible and resistant bacteria as well.
Kylli et al (2010) found both wild and cultivated rowanberry phenolic exhibited a bacteriostatic effect toward Staphylococcus aureus and the amount of phenolic compounds decreased in all berries stored frozen for a year, but their antimicrobial activity was not influenced accordingly. Cloudberry, in particular, showed constantly strong antimicrobial activity during the storage.
Blueberries can eradicate micro-organisms for the prevention of symptomatic urinary tract infections in women. In pre-menopausal women, of trimethoprim-sulfamethoxazole 480 mg once daily, is more effective than cranberry capsules, 500 mg twice daily, to prevent recurrent urinary tract infections, at the expense of emerging antibiotic resistance.
3. Guava (Psidium Guajava):
Guava extract contain compounds that possess anti-bacterial properties suggesting that guava could be useful in controlling food borne pathogens (L. monocytogenes, S. aureus, E. coli, S. enteritidis, V. parahaemolyticus, and B. cereus), and spoilage organisms P. aeruginosa, P. putida, A. faecalis, and Aeromonas hydrophila.
4. Jamun (Syzygium Jambolanum):
Jamun fruit pulp as well as seeds have been found to possess several health benefits and suggested as remedy for various clinical conditions. The water and methanolic extracts of S. jambolanum seeds showed activity against Gram positive bacteria (B. subtilis, S. aureus), Gram negative bacteria (S. typhimurium, P. aeruginosa, K. pneumoniae and E. coli) and fungal strains – C. albicans, C. neoformans, A. flavus, A. fumigatus, A. niger, Rhizopus sp., T. rubrum, T. mentagrophytes and M. gypseum.
5. Broccoli (Brassica Oleracea):
Oral consumption of broccoli sprouts was associated with eradication of H. pylori infection in three of nine patients, the effect has been confirmed by many researchers later and the active components responsible for the same have been identified.
In vitro and in vivo experiments have shown that sulforaphane (SFN), an isothiocyanate compound found abundantly in broccoli and other cruciferous vegetables, inhibits the growth of the bacterial pathogen H. pylori. Among 18 sulforaphane and related compounds synthesized (6 amines, 6 isothiocyanates, and 6 nitriles) in brocolli, 2 amines, 6 isothiocyanates, and 1 nitrile exhibited > 5 cm inhibitory zones for H. pylori strain.
The results strongly indicated that broccoli sprouts can be an excellent food source for medicinal substances and confirmed the previous findings. The anti H. pylori property of brocolli sprouts was further strengthened through reduction of certain metabolic markers such as urease measured by the urea breath test and H. pylori stool antigen (both biomarkers of H. pylori colonization); and serum pepsinogens I and II (biomarkers of gastric inflammation). Intervention with broccoli sprouts decreased the levels of these markers. Values reached normal levels 2 months after treatment was discontinued.
Daily intake of sulforaphane-rich broccoli sprouts for 2 months reduces H. pylori colonization in mice and improves the sequelae of infection in infected mice and in humans. The treatment also seems to enhance chemo protection of the gastric mucosa against H. pylori-induced oxidative stress.
In addition H. pylori, SFN was found to inhibit 23 out of 28 different microbial species with a minimal inhibitory concentration ranging from 1-4 µg/mL. However, five pathogens – P. aeruginosa, 3 methicillin-resistant S. aureus (MRSA) isolates and C. albicans were found to be resistant to SEN, having MICs e”16- 32 µg/mL.
6. Red Cabbage (Brassica Oleracea):
Red cabbage is a rich source of phenolic compounds, anthocyanin’s being the most abundant class, which might explain its potent antimicrobial action. The methanolic crude extract of red cabbage showed remarkable, antibacterial activity that was evident particularly against highly infectious micro-organisms such as Methicillin-resistant S.aureus, E. coli, P. aeruginosa, K. pneumoniae, S. aureus, and Salmonella enterica subspecies 1 serovar Typhimurium as well as against human fungal pathogens, Trichophyton rubrum and Aspergillus terreus.
7. Drumstick (Moringa Oleifera):
Drumstick leaves as well as seeds are considered very nutritious. In addition, drumstick seeds and root possess antimicrobial activity due to its principle component pterygospermin. The fresh leaf juice was found to inhibit the growth of human pathogens as S. aureus and P. aeruginosa.
8. Yogurt:
Probiotics, which include L. acidophilus and bifidobacteria, have an indirect antiobiotic effect. They help increase the number of good bacteria in the gastrointestinal tract, which in turn, helps fight against invasive microorganisms. Bifidobacteria are the primary organisms found in mothers’ milk and are effective inhibitors against many disease-causing organisms.
Besides being a probiotic, the fermented dairy product yogurt has been well known as an inhibitor of S. Mutans. A study at Hiroshima University, School of Dentistry, Japan, and at the University of Hong Kong, showed that the L. reuteri strain in fermented yogurt was effective in combating the dental bacteria.
However, the effect has been shown only by L. reuteri but no other lactobaccilli species. The results of clinical trial also demonstrated that eating yogurt with L. reuteri significantly reduced the oral carriage of Mutans streptococci, compared with the placebo yogurt.
Neutralized extracellular culture filtrate obtained from isolates of Lactobacillus acidophilus, Lactobacillus delbruecki ssp. bulgaricus, Lactobacillus salivarius and Lactococcus lactis ssp. lactis from ‘dahi’ showed weak to moderate inhibition of Staphylococcus aureus, Bacillus cereus, Escherichia coli, Bacillus brevis, Bacillus circidans, Bacillus coagulans, Bacillus laterosporus, Bacillus subtilis and Pseudomonas aeruginosa when tested by the diffusion agar well assay method. Thus Varadaraj et al. (1993) reported the antimicrobial activity of dahi and the potential of using neutralized extracellular culture filtrate of lactic acid bacteria in the bio-preservation of foods.
9. Mayan Mool (Decalepis Hamiltonii Roots):
Mayanmool as it is known in Maharashtra, exhibited strong antimicrobial activity against B. cereus, B. megaterium, C. albicans, E. coli, M. luteus, M. roseus, and S. aureus at a concentration range of 1:0 with inhibitory activities of 27,23,16,19,22,19, and 23 mm, respectively, which are comparable to those of the standards. The extract was found to contain a flavor compound 2-hydroxy-4-methoxybenzaldehyde (2H4MB) responsible for the effect.
Isolated HMBA was also found to inhibit the growth of H. pylori, a potential ulcerogen in a dose dependent manner with MIC of <“39 µg/ml as opposed to that of amoxicillin (MIC – 26 µg/ml) to which H. pylori is susceptible.
10. Flaxseeds (Linum Usitatissimum):
Fungi-static activity of flaxseed flour was investigated using the test microorganisms of strains of P. chrysogenum, A. flavus, F. graminearum, and a Penicillium sp. isolated from molded noodles. Though there were differences in the degree of mold inhibition among flaxseeds obtained from different sources and cultivars. Xu et al. (2008) suggested that flaxseed could be used as a multifunctional food ingredient as it possesses fungi-static activity.
11. Sesame Seeds (Sesamum Indicum):
A novel antimicrobial protein -SiAMP2 belonging to the 2S albumin family was isolated from sesame seeds and evaluated its effect against several bacteria and fungi. SiAMP2 specifically inhibited Klebsiella sp. reinforcing the hypothesis that plant storage proteins might also play as pathogen protection providing an insight into the mechanism of action for this novel 2S albumin antimicrobial proteins and evolutionary relations between the two.
12. Asafoetida:
β-pinene (47.1 per cent), α-pinene (21.36 per cent), and 1,2-dithiolane (18.6 per cent) were the main components of asafoetida oil which has shown anitimicrobial activity against S. typhi, E. coli, S. aureus, B. subtilis, A. niger, and C. albicans. Ferula oils could be used as safe and effective natural antioxidants to improve the oxidative stability of fatty foods during storage and to preserve foods against food burn pathogens.
13. Honey:
Honey is increasingly valued for its anti-bacterial activity as it has been known since the 19th century. According to Haffejee and Moosa (1985) honey shortens the duration of bacterial diarrhoea, does not prolong the duration of non-bacterial diarrhoea, and may safely be used as a substitute for glucose in an oral rehydration solution containing electrolytes. Klein et al. (2000) confirms that honey has proven antimicrobial activity.
Honey has also been used to treat adult and neo-natal post-operative infections, burns, boils, necrotizing fasciitis, venous ulcers and diabetic foot ulcers. Varietal differences were noticed in the antimicrobial property as well as the physicochemical characteristics, and thereby suitability for use in certain conditions. The Tualang honey has a bactericidal as well as bacteriostatic effect. It is used in the dressings as it is easier to apply and is less sticky compared to Manuka honey.
Tualang honey exhibited variable activities against different micro-organisms, but they were within the same range as those for manuka honey. Thus Tan et al. (2009) suggest that tualang honey could potentially be used as an alternative therapeutic agent against certain microorganisms, particularly A. baumannii and S. maltophilia.
Kuncic et al. (2012) found Slovenian honey to be effective against four bacterial species (E. coli, E. faecalis, P. aeruginosa and S. aureus) and against eight fungal species (A. niger, A. pullulans, C. albicans, C. parapsilosis, C. tropicalis, C. cladosporioides, P. chrysogenum and R. mucilaginosa) and thus supported the concept that Slovenian honeys can be applied for medicinal purposes.
Nasir et al. (2010) reported that Tualang honey is not as effective as other products such as silver-based dressing or medical grade honey dressing for Gram- positive bacteria. Mohapatra et al. (2011) proved that honey’s bacteriostatic and bactericidal effect are similar to antibiotics, against Gram-positive bacteria (S. aureus, B. subtilis, B. cereus, E. faecalis, and M. luteus) and Gram-negative bacteria (E. coli, P. aeruginosa, and S. typhi) organisms and provide alternative therapy against certain bacteria.
The good control of infection is attributed to the high osmolality, but honey can have additional anti-bacterial activity because of its content of hydrogen peroxide and unidentified substances acquired from certain floral sources. The non-peroxide antibacterial activity of manuka honey at a concentration of 1.8 per cent (v/v) completely inhibited the growth of S. aureus during incubation for 8 h.
The growth of all seven major wound-infecting species of bacteria was completely inhibited by both types of honey (non-peroxide antibacterial activity of manuka honey and a honey in which the antibacterial activity was primarily due to hydrogen peroxide) at concentrations below 11 per cent (v/v).
Voidarou et al. (2011) studied the antimicrobial activity of sixty samples of honey of various botanical origins against 16 clinical pathogens and their respective reference strains. All honey samples, despite their origin (coniferous, citrus, thyme or polyfloral), showed anti-bacterial activity against the pathogens and their respective reference strains at variable levels.
Coniferous and thyme honeys showed the highest activity with an average minimum dilution of 17.4 and 19.2 per cent (w/v) followed by citrus and polyfloral honeys with 20.8 and 23.8 per cent respectively. Fangio et al. (2007) found that honeys from the southeast region of Buenos Aires province are active against E. coli at 25 and 50 per cent (w/v) concentrations. A reduction of microbial growth of 96 per cent in Mueller-Hinton broth and of 90 per cent in Mac Conkey broth by honey solutions containing 50 per cent and 25 per cent (w/v) respectively was observed.
Elbagoury and Rasmy (1993) on testing two samples of natural Honey for their anti-bacterial effect on Bacteroides, mainly the pathogenic black pigmented B. melaninogenicus isolated from ten cases of dental infections (dental abscesses and chronic osteomyelitis) observed that the inhibitory effect of honey was not due to its high sugar content or to its acidic pH, when using Schaedler’s broth adjusted to the same pH as control. Badet and Quero (2011) who worked on oral bacteria found Manuka honey to be able to reduce oral pathogens within dental plaque and also to be able to control dental biofilm deposit.
Malaysian honeys, namely gelam, kelulut and tualang, have high anti-bacterial potency derived from total and non-peroxide activities, which implies that both peroxide and other constituents are mutually important as contributing factors to the anti-bacterial property of honey. Kwakman et al. (2011) reported the differences between two medical honeys. Revamil source (RS) honey killed B. subtilis, E. coli and P. aeruginosa within 2 hours, whereas manuka honey had such rapid activity only against B. subtilis.
After 24 hours of incubation, both honeys killed all tested bacteria, including methicillin-resistant S. aureus, but manuka honey retained activity up to higher dilutions than RS honey. Methylglyoxal was a major bactericidal factor in manuka honey, but after neutralization of this compound manuka honey retained bactericidal activity due to several unknown factors. RS and manuka honey have highly distinct compositions of bactericidal factors, resulting in large differences in bactericidal activity.
Australia has unique native flora and produces honey with a wide range of different physic-chemical properties. Irish et al. (2011) analysed 477 honey samples and found potentially therapeutically useful antibacterial activity level in 57 per cent of the honey samples, with exceptional activity in samples derived from marri (Corymbia calophylla), jarrah (Eucalyptus marginata) and jelly bush (Leptospermum polygalifolium).
They attributed the anti-bacterial activity to hydrogen peroxide produced by the bee-derived enzyme glucose oxidase. Non-hydrogen peroxide activity was detected in 80 (16.8 per cent) samples, and was most consistently seen in honey produced from Leptospermum spp.
The anti-bacterial effect of honey was found to be more pronounced on E. coli than on S. typhimurium in vitro, by Badawy et al. (2004). Water content, pH value, HMF and the presence of H2O, all played an important role in the potency of honey as an anti-bacterial agent. The anti-bacterial activity of honey decreased on storage and high concentrations of honey proved more effective as anti-bacterial agents. Badawy et al. (2004) also reported lower mortality due to infections among mice treated with honey.
Chronically infected wounds are a costly source of suffering. An important factor in the failure of a sore to heal is the presence of multiple species of bacteria, living cooperatively in highly organized biofilms. The biofilm protects the bacteria from antibiotic therapy and the patient’s immune response. Honey has been used as a wound treatment for millennia.
Alandejani et al. (2009) used a previously established biofilm model to assess antibacterial activity of honey against 11 methicillin- susceptible SA (MSSA), 11 methicillin-resistant SA (MRSA), and 11 PA isolates. Honeys were tested against both planktonic and biofilm-grown bacteria and were found to be effective in killing 100 per cent of the isolates in the planktonic form.
The bactericidal rates for the Sidr and Manuka honeys against MSSA, MRSA, and P. aeruginosa biofilms were 63-82 per cent, 73-63 per cent, and 91 per cent, respectively. These rates were significantly higher (P < 0.001) than those seen with single antibiotics commonly used against and Staphylococcus aureus.
The anti-bacterial activity of honey is highly complex due to the involvement of multiple active constituents and due to the large variation in the concentrations of these compounds among honey varieties. All bacteria tested, including B. subtilis, methicillin-resistant S. aureus, extended-spectrum beta-lactamase producing E. coli, ciprofloxacin-resistant P. aeruginosa, and vancomycin-resistant E. faecium, were killed by 10-20 per cent (v/v) honey.
Kwakman et al. (2011) found the bactericidal activity differed between the Manuka honey and Revamil source (RS) honey due to their highly distinct compositions of bactericidal factors. Methyl glyoxal and antimicrobial peptide bee defensin-1 were identified as important anti-bacterial compounds in honey. Besides the chemical constituents, the high sugar concentration, hydrogen peroxide and low pH are well known anti-bacterial factors in honey.
Several scientists tried to elucidate the mechanism of antimicrobial action of honey. Jenkins et al (2011) observed enlarged cells containing septa in methicillin- resistant S. aureus exposed to inhibitory concentrations of manuka honey, suggesting that interruption of cell division was responsible for the effect.
The authors believed that these changes were not caused either by the sugars or methylglyoxal in honey but indicated the presence of additional anti-bacterial components in manuka honey. Boukraa and Amara (2008) speculated that the amylase present in honey hydrolyzed the starch chains of the media to dextrin and maltose which increased the osmotic effect of the media and consequently increased the anti-bacterial effects.