# Recent Advances in the Antibacterial Activities of _Citrullus_ _Ianatus_ (Watermelon) By-Products
## 4 Antibacterial Activities of _Citrullus Ianatus_ By-Products
### Seeds
[111] aimed to investigate and compare the phytochemical compounds, antioxidant properties, and antibacterial activities of leaf extracts of _Bryophyllum pinnatum_, _Alchornea cordifoia_, and _Acalypha wilkesiana_ and seed extracts of _C. lanatus_. The extraction took place with 70% ethanol on an orbital shaker for 24 h, with the extract finally being concentrated. The ethanolic extract was subjected to analysis in order to determine its qualitative and quantitative phytochemical profile as well as its antioxidant activity using the corresponding methods, DPPH\({}^{\bullet}\) radical scavenging and FRAP. The antibacterial effects of the ethanolic extracts on _Streptococcus faecalis_ and _P. aeruginosa_ were determined using an agar dilution assay. _C. lanatus_ extracts were found to contain saponins (40.35 mg/100 g), tannins (43.91 mg/100 g), phenols (60.37 mg/100 g), flavonoids (78.36 mg/100 g), steroids (78.99 mg/100 g), cardiac glycosides (32.76 mg/100 g), and reducing sugars (43.20 mg/100 g). Notably, alkaloids were not detected in _C. lanatus_ seed extract. These extracts displayed a total antioxidant capacity of \(\sim\)35 mg/100 g, but remarkably, they were the only extract from the above plant extracts that did not exhibit any inhibitory effects on _S. faecalis_ and _P. aeruginosa_ at any concentration tested. Additionally, the organisms did not demonstrate any sensitivity to distilled water, which was utilized as the negative control. Nevertheless, conducting additional in vitro kinetic investigations and in vivo assessments of the antioxidative and antibiotic effects of _C. lanatus_ seed extracts may provide insights into the absence of antibacterial properties. The emergence of antibiotic resistance represents a significant and urgent concern within the medical community. In recent years, there has been a growing trend in the scientific community to conduct extensive examinations of plant material in order to identify and analyze pharmacologically active compounds. The objective of the study conducted by [PERSON] et al. [112] was to analyze the composition of bioactive compounds, assess the antibiotic activity, determine the MIC, and evaluate the antib biofilm activity of extracts derived from the seeds of two watermelon species originating from Croatia and Greece. Fine seed powder was mixed with either methanol as a maceration agent for 24 h at RT or with ethanol in a Soxhlet apparatus for 24 h and evaporated to dryness. Gram-positive bacteria such as _B. subtilis_, _E. faecalis_, and _S. aureus_ along with Gram-negative bacteria like _E. coli_, _P. aeruginosa_, and _S. enterica_ were investigated. The findings suggest that flavonoids were detected in all samples and showed antibacterial effects against specific bacterial strains. Hesperidin (0.06-0.30 mg/g dry extract), genistein (0.43 mg/g dry extract), kaempfer (3.55-26.42 mg/g dry extract), isorhametin (0.57 mg/g dry extract), fiseetin (65 mg/g dry extract), and luteolin (0.28-0.80 mg/g dry extract) were found in all four samples. In most cases, 250 \(\upmu\)g/mL as MIC was required. The ethanolic extract of watermelon seeds from Greece had the greatest antibacterial activity against _S. enterica_ subsp. _enterica_ serotype Abony (NCTC 6017) (11.67 mm), with a diameter of inhibition zone measuring 11.67 mm, whereas methanolic extract from Croatian watermelon seeds showed the lowest inhibition zone against _P. aeruginosa_ (ATCC 27853) (5.67 mm). The biofilm-forming capacity of all bacteria tested was predominantly characterized as non-adherent or weakly adherent for concentrations up to 250 ug/mL. The bacterial strains exhibited varying degrees of biofilm-forming capacity when exposed to extract concentrations below 250 ug/mL. It can be assumed that a decrease in extract concentration is associated with an increase in biofilm-forming capacity. Regarding extraction solvents, although the polarity of the methanol extract would suggest that it would have a greater effect, the method with ethanol in the Soxhlet apparatus produced slightly better results.