# Recent Advances in the Antibacterial Activities of _Citrullus_ _Ianatus_ (Watermelon) By-Products
## 4 Antibacterial Activities of _Citrullus Ianatus_ By-Products
### Rind and Peel
In fact, at this concentration, the watermelon peel extract presents the same antibacterial activity as the positive control against _S. epidermidis_. Almost a year later, [PERSON] et al. [95] came up with a different study on the antibacterial activity of watermelon peel, where the peel itself rather than the peel extract was studied. Inorder to examine the antibacterial activity, the conventional disc diffusion test was followed, using cultures of two Gram-positive bacteria, _Lactobacillus_ spp. and _Staphylococcus aureus_, and two Gram-negative bacteria, _E. coli_ and _Proteus vulgaris_. The determination of activity was performed by measuring the inhibition zone. The results showed that both _Lactobacillus_ spp. and _S. aureus_ had a zone of inhibition at 10 mm, whereas _E. coli_ had an inhibition zone of 11 mm and _P. vulgaris_ had an inhibition zone of 26 mm. In the results, it is indicated that watermelon peel can show strong antibacterial activity without being extracted. However, going deeper into the above-mentioned study, the formation of the inhibition zone for _S. aureus_ was 12, 15, and 20 mm, showing a significant difference. The same conclusions were drawn for the activity against _E. coli_, where (as in the previous research) the zone of inhibition was up to 20 mm. However, the activity against _P. vulgaris_ is noteworthy because, besides being detected as very effective, it also shows strong differences with previous research where the extract did not show any inhibitory effect against its growth. Therefore, it is concluded that the peel can also show bacterial resistance and can be used against some bacteria, especially _P. vulgaris_. In the study of [PERSON] et al. [96], the effect of drying methods on the antibacterial properties of both the seeds and mind of watermelon was examined. Samples were dried using three similar drying methods: air, oven, and sun. Air drying at RT was carried out in a well-ventilated room for a period of four weeks; oven drying was carried out in a hot air oven at 50 \({}^{\circ}\)C for 120 h; and sun drying was carried out by exposure to sunlight for three weeks. Following drying, all samples were powdered and soaked in methanol in a solid-to-liquid ratio of 1:10 for 48 h at RT. The active culture for the experiment was prepared by transferring a loop of cells from the stock cultures into a Mueller-Hinton broth test tube and incubated without agitation at 25 \({}^{\circ}\)C for 24 h. The well was filled with 0.2 mL of the test sample at different concentrations (5, 10, 15, 20, and 25 mg/mL) and allowed to diffuse at RT for 30 min. Gentamicin at a concentration of 10 mg/mL was used as a positive control. The antibacterial activity of the samples was tested against six bacteria: two Gram-positive, _S. aureus_, _Bacillus cereus_, and four Gram-negative, _Pseudomonas aeruginosa_, _Pseudomonas forescens_, _E. coli_, and _Salmonella typhimurium_. As far as the results are concerned, the extracts from the oven-dried sample showed better activity compared with those dried in a well-ventilated room or under the sun. At the optimum concentration (25 mg/mL), it showed an inhibition zone of 5.81 mm against _S. aureus_, 4.81 mm against _B. cereus_, 4.90 mm against _P. aeruginosa_, 6.40 mm against _P. forescens_, 6.81 mm against _E. coli_, and 6.41 mm against _S. typhimurium_. Concerning gentamycin and the concentration examined (10 mg/mL), it exhibited a minimal degree of inhibition for all bacteria. Moreover, it showed not over a 3 mm zone of inhibition on any bacteria, and when compared with the extracts, it presented less resistance even when the lower extract concentration of 5 mg/mL was tested. The aim of further research by [PERSON] and [PERSON] [97] was to test two different extraction methods (Soxhlet extraction and cold filtration method) using ethanol as a solvent with regard to the antibacterial activity of watermelon peel.