# Recent Advances in the Antibacterial Activities of _Citrullus_ _Ianatus_ (Watermelon) By-Products
## 4 Antibacterial Activities of _Citrullus Ianatus_ By-Products
### Rind and Peel
The samples were washed three times with tap water and three more times with distilled water, allowed to dry under the absence of light for six days, and then ground to powder. Regarding the cold percolation method, the dried sample was immersed in 95% ethanol in a 1:5 solid-to-liquid ratio. The powder was extracted using a Soxhlet apparatus for 15 h at 65 \({}^{\circ}\)C using the same solvent. Antibacterial activity was studied through resistance to three Gram-positive bacteria, _Bacillus_ spp., _S. aureus_ (ATCC 6538), _Corynebacterium diphtherie_ (ATCC 13812), and three Gram-negative bacteria, _E. coli_ (ATCC 25922), _Proteus_ spp., and _P. aeruginosa_ (ATCC 27853). From each extract, 50 \(\upmu\)L were used, and antibacterial activity was determined using the inhibition zones (mm). In terms of Gram-positive bacteria _Bacillus_ spp., _S. aureus_, and _C. diphtherie_ using the Soxhlet method, the inhibition zones recorded were 13, 12, and 13 mm, respectively, while in terms of Gram-negative bacteria, the results were 14 mm in _E. coli_, while lack of inhibition was recorded against _Proteus_ spp. and _P. aeruginosa_. Regarding the cold percolation method, a growth resistance (development zone) appeared only in _Bacillus_ spp. and _E. coli_ bacteria and was 14 and 12 mm, while the rest of the bacteria showed complete resistance to the action of the extracts. Comparing the two methods, it is noticeable that the Soxhlet method is preferable compared with the cold filtration method. However, the interception is stronger in Gram-positive bacteria, and there is even a strong resistance to bacterial growth. Moreover, comparing this study's results with the ones of the study where the Soxhlet method but hexane as solvent were used, it can be observed that ethanol is a stronger solvent. So far, ethanol can be considered an ideal solvent. Regarding the study conducted by [PERSON] et al. [9], the antibacterial activity of both the peel and rind of _C. lamatus_ was evaluated. For the preparation of the extracts, a precise quantity of each sample was weighed and immersed in methanol. A hot air-dry furnace at 45 \({}^{\circ}\)C was used to concentrate the filtrates. The Minimum Inhibition Concentration (MIC) of the extracts against bacteria was carried out by the microdilution method. The bacteria were grown at 37 \({}^{\circ}\)C in Muller-Hinton broth, and the optical density was adjusted to 10\({}^{6}\) CFU/mL. Ten test tubes containing 200 \(\upmu\)L of a specific bacterial suspension and 200 \(\upmu\)L of different concentrations of peel and rind extracts (0-256.0 mg/mL) were prepared and incubated at 37 \({}^{\circ}\)C for 24 h. The bacteria tested were the Gram-positive bacteria _Staphylococcus albus_, _S. aureus_, _Enterococcus faecalis_, _Bacillus subtilis_, _Microococcus luteus_, _Listeria innocua_, and _Streptococcus thermophilus_, while the Gram-negative bacteria tested were _Pseudomonas fluorescens_, _E. coli_, _Klebsiella oxytocin_, _Salmonella enterica_, _Shigella sonnei_, and _S. typhimurium_. Regarding the watermelon peel at the concentration of 500 mg/mL, the inhibition zones (in mm) detected for the Gram-positive bacteria _S. albus_, _S. aureus_, _E. faecalis_, _B. subtilis_, _M. luteus_, _L. innocua_, and _S. thermophilus_ were 10, 20, 16, 16, 11, 9, and 13 mm, respectively. Meanwhile, the results for the Gram-negative bacteria _P. fluorescens_, _E. coli_, _K. oxytoca_, _S. enterica_, _S. sonnei_, and _S. typhimurium_ were 8, 12, 13, 11, 16, and 9, respectively. Moreover, for the same concentration in watermelon rind, the inhibition zones (in mm) for the Gram-positive bacteria _S. albus_, _S. aureus_, _B. subtilis_, _M. luteus_, _L. innocua_, and _S. thermophilus_ were 7, 13, 13, 15, 6, and 10, while no resistance capacity was developed for _E. faecalis_. For the same sample, the results for the Gram-negative bacteria _P. fluorescens_, _K. oxytoca_, _S. enterica_, and _S.