**2. Antibacterial activities of curcumin**

The majority of bacteria are not harmful to humans, and some strains even assist in the digestion of food or compete against opportunistic pathogens, but infection by bacteria is one of the most common ailments among humans [40]. Many diseases are connected to bacterial infections, such as inflammatory bowel diseases [41], obesity [42], diabetes [43], liver diseases [44], heart diseases [45], cancers [46], HIV-AIDS [47], and autism [48]. Infections caused by bacteria are largely treated with antibiotics, but the struggle to defeat bacteria continues because bacteria are evolving and manifesting new resistance mechanisms [49]. Curcumin has shown the potential to solve drug resistance issues by inducing antibacterial effect through membrane disruption [30], inducing increased expression of ROS which can promote apoptosislike response in bacteria [31, 50], and interrupting cell division [32].


### **Table 2.**

*Mechanisms of curcumin on gram-negative and gram-positive bacteria.*

*Germicidal and Antineoplastic Activities of Curcumin and Curcumin-Derived Nanoparticles DOI: http://dx.doi.org/10.5772/intechopen.103076*

Researchers are documenting more evidence about the antibacterial activities of curcumin against a wide range of bacteria [30, 51, 52]. Curcumin has been demonstrated to be potent against both gram-positive and gram-negative bacteria [30, 53]. An example of a gram-positive bacteria, *Staphylococcus aureus* (*S. aureus*), has been demonstrated to be vulnerable to curcumin-mediated inhibition. *Staphylococcus aureus* is a human pathogen that can cause a variety of diseases including infective endocarditis, a feared disease that affect young to middle-aged adults with heart disease [54, 55].

The antibacterial activity of curcumin against *S. aureus* has been thoroughly reviewed by Teow et al. [56]. The *S. aureus* bacteria have developed several mechanisms for evading the human immune system and to resist antibiotic treatment. To salvage *S. aureus* drug resistance, it has been shown that curcumin binds to FtsZ proteins, inhibiting protofilaments assembly, which then inhibits the formation of Z-rings, eliciting the suppression of cytokinesis and bacterial proliferation [32]. Furthermore, the binding of curcumin to peptidoglycans on *S. aureus* cell walls, could cause damage to the cell wall and membrane, hence triggering cell lysis [30, 56]. Mechanisms of curcumin on gram-negative bacteria and gram-positive bacteria are summarized in **Table 2**. In addition to showing its effectiveness as a standalone antibacterial agent, curcumin has also shown marked antibacterial activity when combined with various antibiotics at subinhibitory doses (12.5 and 25 μg/mL) [68, 69]. The collective antibacterial activity of curcumin with antibiotics against methicillin-sensitive *S. aureus* (MSSA) and methicillin-resistant *S. aureus* (MRSA) is well demonstrated by many researchers [68–71]. In tests of *Helicobacter pylori* infection that were done *in-vivo*, mice infected with this bacteria were eradicated by curcumin [72]. In order for curcumin to exert its bactericidal effects, it appears to cause cell membrane damage [30], thus inhibiting bacterial cell division through the improper assembly of the bacterial protofilament, which provides the framework for bacterial cell division apparatus [62, 73].
