# Recent Advances in the Antibacterial Activities of _Citrullus_ _Ianatus_ (Watermelon) By-Products
## 4 Antibacterial Activities of _Citrullus Ianatus_ By-Products
### Rind and Peel
sonnei_ were 7, 10, 11, and 12 mm, respectively, proving that the extract of watermelon peel is a more effective antibacterial agent than the corresponding extract of watermelon rind. In conclusion, the MIC of methanol extracts (mg/mL) against the tested bacteria was also recorded and proved that for bacteria such as _L. innocua_ (Gram-positive) and _S. enterica_ (Gram-negative), the MIC of methanol extracts was equal (8 mg/mL) between the two extracts. However, bacteria such as _M. luteus_ (Gram-positive) and _P. fluorescens_ (Gram-negative) required twice the amount of watermelon rind extract compared with peel. Furthermore, there were recorded results where the minimum inhibitory methanol extract concentration for watermelon rind was fourfold, eightfold, and so on. Results that are in full agreement with previous data from the same study. The only case where rind extract was required in a smaller amount than the peel extract was against _S. aureus_, where 8 mg/mL of peel extract and only 4 mg/mL of rind extract were required to show the formation of an inhibition zone. [PERSON] et al. [98] carried out the first study on the antibacterial activity of watermelon rind. The survey is focused on the rind of three types of watermelon. Specifically, the rinds of Charleston Grey watermelon (a characteristic light skin color), Summer Flavour 840 watermelon (elongated with dark green stripes), and Crimson Sweet watermelon (round with dark green stripes) were analyzed. The samples were dried and converted into fine powder in order to be extracted using the Soxhlet method. For this purpose, 30 g of each rind sample was extracted with _n_-hexane for 6 h. The extracts were then tested for their antibacterial activity against a Gram-positive bacterium, _S. aureus_, and a Gram-negative, _E. coli_. A modified Kirby-Bauer disk diffusion method was used to test the antibacterial activity using 100 \(\upmu\)L of each rind extract. Both a negative (NaCl) and a positive (Ciprofloxacinacin) control were used. Regarding _S. aureus_, the inhibition zones were 5 mm for the Crimson Sweet rind and 10 mm for the Summer Flavor 840 rind. Charleston gray rind showed no activity against this Gram-positive bacterium. For _E. coli_, the CrimsonSweet find appeared to have no resistance, while both the rind of Charleston Gray and Summer Flavor 840 had the same zone of inhibition of 5 mm. It is therefore obvious that the rind from Summer Flavor 840 had the highest antibacterial capacity on both bacteria compared with the other two categories. However, the Soxhlet method with hexane as a solvent may not be the most suitable method for developing antibacterial-rich extracts. Regarding the controls tested, Ciprofloxacinacin (the positive control) had a 20 mm zone of inhibition against _S. aureus_ and a 25 mm zone of inhibition against _E. coli_. However, the negative control did not form an inhibition zone. A subsequent survey was conducted by [PERSON] et al. [PERSON] et al. (2018), where various in vitro extracts of _C. lanatus_ rind against the Gram-positive bacterium _Streptococcus mutans_ were studied. In order to prepare the extracts, the rind was removed from the flesh of the watermelon, crushed, and mixed with 100 mL of distilled water. The mixture was then heated until boiling in a heating mantle until 25 mL of rind extract finally remained. To test the antibacterial activity, four different quantities of the extract were prepared, namely 25, 50, 100, and 150 mL, and after that, four Muller Hinton Agar (MHA) plates coated with _S. mutans_ were loaded with the different quantities of extracts, each. Finally, they were incubated for 24 h at 37 \({}^{\circ}\)C. For each quantity of 25, 50, 100, and 150 mL, the zone of inhibition exhibited by each sample was 26, 28, 31, and 35 mm, respectively. According to these results, it is evident that as the quantity of _C. lanatus_ rind extract increases, the resistance ability of the specific bacterium also increases. In addition, the rind shows high resistance to the bacterium _S. mutans_.