# Antibacterial and Antiproliferative Potential of Green, Roasted, and Spent Coffee Extracts
## 2 Results and Discussion
### Antibacterial Activity  
The search for antimicrobial effects in plant extracts has gained in importance recently, due to an increase in bacterial resistance to conventional drugs [29]. Several studies have demonstrated that coffee extracts exhibit antibacterial activities against pathogens such as _Escherichia coli_, _Staphylococcus aureus_, _Listeria monocytogenes_, and _Enterococcus faecalis_[8; 23; 30; 31]. The activities of bioactive compounds extracted from coffee against pathogenic bacteria have been widely studied [32; 33]; however, the effects of coffee extracts on drug-resistant bacteria, such as methicillin-resistant bacteria, have scarcely been considered in the literature. Table 2 shows the minimal inhibitory concentration (MIC)values for the GB, RC, and SCG extracts. The results demonstrate that SCG (ethanolic and aqueous) extracts exhibited an ability to inhibit the growth of clinically isolated methicillin-resistant strains at the concentration range of 2-8 mg\(\cdot\)mL\({}^{-1}\), where the most effective extract against these strains was ethanolic SCG extract (2 mg\(\cdot\)mL\({}^{-1}\)). Regarding the ATCC strains, RC (ethanolic) and SCG (aqueous) extracts inhibited the growth of _Sa1_ (MIC of 2 and 4 mg\(\cdot\)mL\({}^{-1}\), respectively), while ethanolic (GB, RC, and SCG) and aqueous (SCG) extracts exhibited MIC values of 8 mg\(\cdot\)mL\({}^{-1}\) against EC1, EClo, Sd, and Ef strains. Finally, GB (ethanolic), and GB and RC (aqueous) extracts did not demonstrate any antibacterial activity (MIC \(>\) 8 mg\(\cdot\)mL\({}^{-1}\)) against the tested bacterial strains. The results obtained in this study were similar to those reported by [PERSON] et al. [8], who found that the growth inhibition of common food-borne pathogens and food spoilage microorganisms was higher in spent coffee than coffee brews. In the same context, [PERSON] et al. [31] and [PERSON] et al. [34] exposed the noteworthy antibacterial activities of SCG against both Gram-positive and Gram-negative bacteria. This effect has been attributed to the content of phenolic acids, caffeine, and Maillard reaction products (e.g., melanoidins) quantified in spent coffee extracts [23]. [PERSON] et al. [10] stated that coffee melanoidins exert intense antimicrobial activity that could be used to avoid the growth of pathogenic bacteria in food products. These compounds possess the ability to alter the structure and function of the cytoplasmic membrane and to inhibit DNA repair mechanisms, favoring the inhibition of bacterial growth [35]. Our results demonstrate that SCG (ethanolic and aqueous extracts) possess an ability to inhibit the growth of clinically isolated methicillin-resistant strains. Antibacterial activity against clinical isolates of methicillin-resistant bacteria and methicillin-resistant _Staphylococcus aureus_ (MRSA) remains a great challenge; although some synthetic antibacterial drugs have been developed, they are not effective against these bacteria. However, several studies have shown that natural compounds, fractions, and extracts exhibit antibacterial activity against clinical isolates of methicillin-resistant bacteria and MRSA, showing MIC values similar to those for sensitive _Staphylococcus aureus_ strains (MSSA); the difference in the activity could possibly be due to different mechanisms of action of natural compounds at the cellular level, as well as the possibility that these compounds may use different pathways to exert their antibacterial activities (i.e., pathways modified and regulated by gene expression patterns, ABC transporters, fatty acid and peptidoglycan biosynthesis, aminoacyl-tRNA synthetase, and \(\beta\)-lactam resistance), as well as the increased presence of reactive oxygen species (ROS) and decreased antioxidant enzymes [36; 37]