Medicinal Herbs as Novel Therapies against Antibiotic-Resistant Bacteria

 

ABSTRACT:

Antibiotic development in the previous century resulted in a decrease in mortality and morbidity associated with infectious diseases, however their indiscriminate and irrational application resulted in the proliferation of resistant microbial populations. Pathogenic bacteria gain intrinsic resistance to antibiotics through a variety of techniques, including alteration of target sites, active efflux of drugs, and enzymatic degradation. This has resulted in an increased interest in medicinal plants, as 25–50% of existing pharmaceuticals are extracted from plants. Due to the diversity of secondary metabolites found in medicinal herbs, crude extracts can serve as an alternative source of resistance modifying agents. These metabolites (alkaloids, tannins, and polyphenols, for example) may have antimicrobial and resistance-modifying properties. Herb extracts can bind to protein domains, modifying or inhibiting protein–protein interactions. This enables herbals to act as potent modulators of host-related cellular processes, including immune response, mitosis, apoptosis, and signal transduction. Thus, they can exert their activity not only by destroying the microorganism but also by interfering with key events in the pathogenic process, reducing the ability of bacteria, fungi, and viruses to develop resistance to botanicals. The present review is intended to encourage research in which the extract's cidal activity is not the only factor considered, but also other mechanisms of action by which plants can fight drug-resistant microbes are investigated.

 

 

 

INTRODUCTION: 

Antibiotic resistance is not a problem unique to the world subcontinent; it is a global issue¹. There is currently no known mechanism for reversing antibiotic resistance in bacteria. The discovery and development of the antibiotic penicillin in the early 1900s provided medical science with a measure of optimism, but the antibiotic quickly became ineffective against the majority of susceptible bacteria². Antibiotic tolerance occurs naturally in bacteria as a result of adaptation to antimicrobial agents. Once bacteria develop resistance to an antibiotic, they pass this trait on horizontally or vertically to their progeny³.

 

 

Antibiotics are being used indiscriminately and irrationally these days, which has resulted in the evolution of new resistant strains of bacteria that are slightly more dangerous than the parent strain⁴. Cases of widespread occurrence of resistant bacteria are becoming increasingly frequent, resulting in a slew of health problems⁵.

 

Antibiotics, the 20th century's miracle drugs, are important in the treatment of bacterial infections⁶. The synthesis of Salvarsan, an arsenic-based syphilis drug, in 1910, as well as the invention of Prontosil, a sulpha drug, in 1935, and the purification and production of penicillin in the early 1940s, established the paradigms for future drug discovery research⁷. The period from the 1950s to the 1970s was regarded as the "golden age" of antibiotic discovery⁸. However, as the decades passed, bacteria that were resistant to several antibiotics became more prevalent, increasing morbidity, mortality, and health care costs. Numerous factors contributed to the rise of drug-resistant species. Inappropriate antibiotic use in patients aided in the development of drug resistance⁹. Additionally, widespread antibiotic use in the animal industry has generated significant selective pressure for the emergence of antibiotic-resistant bacteria¹⁰. With increased patient movement and travel around the world, the spread of drug-resistant species increased as well¹¹.

 

Nowadays, researchers are searching for certain novel antimicrobial molecules that have a wide range of action against Gram-negative and Gram-positive bacteria without much if any side effects. They explore the variety of medicinal plants mentioned in Ayurveda, Charak Samhita, Sushrut Samhita and other literatures in their respective countries. In this scenario, certain pathogens are emerging that are difficult to monitor by available antimicrobial agents such as Mycobacterium tuberculosis strains XDR, HIV, Hepatitis B, Hepatitis C, Swine flu, Dengue and Japanese encephalitis¹². Some antimicrobial drugs may be used to cure these diseases; however, they are associated with some permanent side effects such as liver damage, kidney failure, strokes, etc. In recent years, plant-based drug development has grown tremendously, and there is some hope seen in some medicinal plants that can be used to treat these incurable diseases. Bhumiamla's aqueous leaf extract (Phyllanthus niruri) confirmed anti-hepatitis B activity. It binds to HbSAg (surface antigen) and inhibits DNA polymerase needed to multiply hepatitis virus¹³. Allium sativum, Acalypha indica, Adhatoda vasica, Aloe vera and Allium cepa are reported to have antituberculosis activity

 

This current review focuses on antibiotic resistance, the antibiotic resistance mechanism in bacteria, and the function of plant-active secondary metabolites against microorganisms, which may be useful as an alternative and successful strategy to break resistance among microbes.

 

1      ANTIBIOTIC RESISTANCE  TO ANTIBACTERIA AGENT:

The origins of antibiotic resistance genes are caused by a natural process. The trigger may be genes encoding the resistance of antibiotic bacteria to their own defenses or to spontaneous mutations of the bacterial chromosome. Spontaneous antibiotic resistance mutation level is around 10⁸-10⁹. Although mutation is a rare occurrence, it takes no longer for bacterial resistance to evolve because of the rapid growth rate of bacteria and the absolute number of cells achieved⁵. Antibiotic usage that is indiscriminate and irrational has provided an unparalleled threat for human society in the form of microbes developing antimicrobial resistance. Bacterial infections are difficult to treat due to bacteria's ability to establish resistance to antimicrobial agents. Antimicrobial agents are classified according to their mode of action, which may include interference with cell wall synthesis, DNA and RNA synthesis, bacterial membrane lysis, protein synthesis inhibition, and inhibition of metabolic pathways.

 

1.     Plasmids:

While the acquirement of resistance is responsible for both chromosomal mutations and genetic transition, the transferable resistance presents a greater challenge, as it can reach wider dimensions due to rapid diffusion. R plasmids play an important role in this transferable resistance. A single plasmid may contain multiple genes for multiple drug resistance coding. The evolution of antibiotic resistance through the transfer of so-called mobile genetic elements is the responsibility of horizontal gene transfer (HGT) (MGEs)⁵.

 

2.     Antibiotic Inactivation:

Bacteria may develop enzymes that chemically alter or degrade antibiotics, rendering them inactive. For example, S. aureus is resistant to penicillin due to the development of the enzyme -lactamase, which inactivates the antibiotic by hydrolyzing the β-lactam ring⁵.

 

3.     Modification of the Target Site:

Molecules usually bound by an antibiotic are normally altered or substituted, eliminating the targets of the drug in bacterial cells. An example of this mechanism is methicillin resistance in Staphylococci due to mec A gene encoding for PBP 2A. It has low affinity for β-lactams, giving resistance to both β-lactam antibiotics and combinations of β-lactamase inhibitors (ampicillin/sulbactam), cephalosporins and carbapenems¹⁴.

 

4.     Prevent Drug Uptake:

By modifying the permeability of bacteria, the entry ports for drugs can be removed. It has been stated that P. aeruginosa can establish resistance to imipenem through mutational loss of porin proteins, thereby altering the permeability of the outer membrane¹⁵.

 

5.     Efflux Pump:

There are five main families of microbial efflux systems: NorM, multi-antimicrobial extrusion protein family (MATE), QacA major facilitators (MFS), LmrA, ATP-binding cassettes (ABC), MexAB, QacC small multidrug resistance family (SMR), and resistance-nodulation cell division (RND)¹⁶. These EPs are responsible for antibiotics being exported prior to reaching their intracellular targets. Kaplan¹⁶ established that an active pharmaceutical ingredient (EP) is a viable mechanism of macrolide resistance in Streptococcus pyogenes. The mefA gene encodes the resistance, which is unique for macrolides with 14 or 15 members.

 

6.     Biofilm Formation:

Biofilm consists of a complex microbial aggregation in which cells are embedded as an extracellular polymer material (EPS) matrix (self-produced). Biofilm development by adhering bacteria to human tissues and medical devices is a significant virulence factor associated with increased antibiotic resistance, phagocytes reduction and overall persistence of microorganisms. These biofilms are also a source of numerous insistent infections, as they are difficult to remove. Antibiotics resistance inherents from biofilms to penetration and low growth rates of species due to slower metabolism can be linked to failure of antibiotics ¹⁶.

 

Figure 1: Different methods of antibiotic – resistant mechanism¹⁷.

 

2      ROLE OF MEDICINAL HERBS AGAINST BACTERIA:

The screening of plants as a source is now being carried out worldwide for alternative antimicrobial medicines. Active compounds such as quinones, phenols, alkaloids, flavonoids, terpenoids, essential oils, tannins, lignans and certain secondary metabolites are due to antimicrobial properties in plants, see table 1.

 

Although bacterial resistance to antibiotics usually involves the inactivation or modification of the drug, alteration of the target, and decrease in drug accumulation through decreased permeability and/or increased efflux, secondary metabolites from plants may affect the microbial cell in a variety of ways. These involve disturbances in the function and structure of the membrane (including the efflux system) , interruption of DNA/RNA synthesis and function  interference with intermediary metabolism, induction of coagulation of cytoplasmic constituents and interruption of normal cell communication (quorum sensing)¹⁸.

 

Berberine, an alkaloid found in Rhizoma coptidis, has been reported to possess a variety of antimicrobial properties. Berberine was confirmed to have anti-herpes effects, with the likely mechanism being inhibition of herpes simplex viral DNA synthesis. Berberine demonstrated antibacterial activity against Staphylococcus epidermidis and substantial inhibition of its biofilm formation at low concentrations of 30–45 g/ml¹⁹.

 

However, multiple components in a crude extract are usually noted at various locations and thus contribute to the overall operation of the extract. The plant extracts can carry out anti-microbial action not only by destroying the microorganism, but also by influencing key pathogenic events. One such example is the antidiarrhoeal behavior of the guava leaf extract. Guava leaf extract is not bactericidal, but influences important pathogenic events of colonization and diarrhoeal toxin production¹⁹. The Rajasekaran et al. study also shows that multiple antiviral components are present in plant extracts that act against different viral proteins or interfere with the various stages of viral replication²⁰. An Alpinia galanga extract analysis by Gupta et al. has shown that it is effective in combating M. tuberculosis multi drug resistant isolates. The efficacy of aerobic and anaerobial extracts suggests a variety of methods of action by plant extract-presented phytoactive components. Therefore a crude extract containing multiple active compounds is less likely than isolated active fractions to produce antimicrobial resistance²¹.

 

3.1 biofilm formation Inhibition:

Surface-associated microbial communities in a self-generated matrix of exopolysaccharides protect the microbes from anti-microbial agents are bacterial biofilms. Extensive studying of the potential for alternative mechanisms for controlling microbial biofilm has therefore been undertaken. This has led to many extracts of plants being identified to regulate the development of biofilm in major pathogenic agents. Terpenes such as carvacrol, thymol, and geraniol are found to contain an aromatic aldehyde of bark in cinnamon trees. Cymbopogon citratus and Syzygium aromaticum essential oils have shown significant antibiofilm activity against both fungal and bacterial biofilms. The lemongrass oil constituents inhibited the formation of biofilms, killed preformed biofilms and had many objectives in the bacterial cell²².

 

3.2 Inhibition of Efflux pump (IEP):

It is now widely recognized that EPs both alone and in combination with improvements in outer membrane permeability are becoming a critical resistance mechanism. The ability of medicinal plants to inhibit EPs has been documented, but cytoplate has also been disrupted by influencing membrane permeability²³.

 

Numerous phytoactive elements, including terpenecarnosic acid (Rosmarinus officinalis), alkaloid reserpine (Rauvolfia vomitoria) and diterpenetotarol (Chamaecyparis nootkatensis), have been shown to inhibit NorA-induced ethidium bromide (EtBr) efflux from a NorA over expressor²⁴. The flavonolignan 5-methoxyhydnocarpin inhibits the action of NorA (effux pump). It enhances the function of the antimicrobial alkaloid berberine found in the same plant synergistically. Recently, a study demonstrated that farnesol, a natural plant metabolite, not only increased the intrinsic susceptibility of Mycobacterium smegmatis to EtBr but also demonstrated relatively good anti-mycobacterial activity when compared to reference EP inhibitors; farnesol possesses an EP inhibitory ability that enhanced EtBr accumulation and inhibited efflux from cells preloaded with EtBr²⁵.

 

M. tuberculosis has the highest number of putative drug efflux pumps, the majority of which belong to the MFS or ABC superfamilies. Piperine has been shown to modulate Rv1258c, an efflux protein belonging to the MFS superfamily of efflux systems, increasing bioavailability and thus sensitivity of Mycobacterium tuberculosis to rifampicin. Thus, piperine increases sensitivity to rifampicin in M. tuberculosis strains that are drug resistant due to Rv1258c. Piperine had no effect on other resistant strains, which may be due to resistance being mediated by efflux pumps other than Rv1258c²⁶.

 

3.3 Attenuating bacterial virulence:

A increasing body of evidence indicates that plant extracts, while not bactericidal, are capable of attenuating bacteria's virulence factors, thus affecting pathogen survival. Extracts from a variety of plants have an effect on P. aeruginosa virulence factors, including QS gene expression and autoinducer development²⁷. Thakur et al. , reported that extracts of Berberis aristata and Camellia sinensis show noteworthy antibacterial potential by targeting hemolysin and bacterial hemagglutination on the bacterial membrane²⁷. Brijesh et al. demonstrated that Aegle marmelos' antidiarrheal activity is not due to its bactericidal activity, but rather to its ability to prevent bacterial toxin binding and colonization of intestinal epithelial cells. Omega 3 and oleic acids are well-known for their antimicrobial properties against Gram-negative bacteria. They are inserted into the outer membrane of the cell in order to increase its permeability. Thus, the concentration gradient required between the organism and its environment may be dissipated, resulting in the organism's death²⁸.

 

Table 1: some of examples anbout medicinal herbs.

Name of Plants	Antimicrobials	Target Microbes
(Acacia nilotica)	(Terpenoids, Flavanoid, Sapo nims, Tanins)	S. viridians, s. Aureus, E. coli, B. subtilis, Shigella sonnei, MD R E. coli, C. albican, K pneunoniae
Allium cepa	Flavanoid, Polyphenol	MDR Pseudomonas aruginosa, S. Typhi, E. coli
(Allium sativum)	Organosulphur compounds (Phenolic compounds), Allicin	Camphylobacter jejuni, MDR E. coli, C. albican, Entamoeba histolytica, Giardia lamblia
Amge, oca, icoda L.	Coumarins	S. viridians, S. mutans
(Chelidonian majus)	Glycoprotein	B. cereus, Staphylococcus spp.
(Cinnamomum spp.)	Cinnamaldehyde (essential oil)	Legionella pneunophila, MDR E. coli, C. albican, K pneumoniae
(Cirsium hypoleucum)	Flavones	MSR K. pneumoniae
(Curcuma longa)	Curcuminoid (A phenolic compound), turmerone, curlone, Essintial oil, curcumins, turmeric oil	S. typhi, E. coil, S.aireis, B. cereus, B. subtills, Ps. Aeruginosa, B. coagulans, A niger, P. digitatum, Antifungal and antiviral activity

 

 

4. CONCLUSION:

Traditional medicinal products, like herbs, have come to the fore as they are readily available and have almost no side effects. Plant derivatives have been shown, but only to some degree, to cure HIV infection. In most countries rich in plant diversity, the identifying and isolating of active compounds from plants remains a problem. Plants have forever been a catalyst for our healing. In order to halt the trend of increased emerging and resistant infectious disease, it will require a multi-pronged approach that includes the development of new drugs. Using plants as the inspiration for new drugs provides an infusion of novel compounds or substances for healing disease.

 

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Accepted on 08.08.2022           © RJPT All right reserved

Research J. Pharm. and Tech 2023; 16(1):62-66.