# Phytosterols in Seaweeds: An Overview on Biosynthesis to Biomedical Applications
## 4 Health Benefits and Biomedical Applications of Phytosterols
### Phytosterols as Antimicrobial Agents  
Phytosterols have antimicrobial activities against a wide range of human pathogens, including bacteria, fungi, viruses, and protozoa. The lipophilic extract of _Bifurcaria bifurcata_, with a considerable amount of fucosterol displayed antibacterial activities against both Gram-positive (_Staphylococcus aureus_ and _Staphylococcus epidermidis_) and Gram-negative bacteria (_Escherichia coli_ and _Pseudomonas aeruginosa_). Subsequently, the synergistic analysis of the extract with antibiotics significantly reduced the minimal inhibitory concentrations of the tested antibiotics ([PERSON], 2017). Intriguingly, a cholesterol derivative, 24-propylidene cholest-5-en-3\(\beta\)-ol, obtained from the red algae _Laurencia papillosa_ displayed antibacterial activity against _S. aureus_, _Bacillus subtilis_, _E. coli_, and _P. aeruginosa_. Furthermore, it exhibited strong antibacterial activity against the clinical isolates of _Klebsiella pneumoniae_, _Shigella flexineri_, _E. coli_, and _P. aeruginosa_([PERSON], 2017). In another study, assessment of the antimicrobial potential of seaweed extracts (_A. utricularis_, _C. nacovitzea_, and _U. intestinalis_) against _S. aureus_, _E. coli_, and _Salmonella typhimurium_ revealed noteworthy effects. Moreover, the study also revealed the promising antioxidant property of the seaweed extracts obtained from _D. confervoides_([PERSON], 2017). Correspondingly, _C. cylindracea_ (green seaweed) extract containing sterols in major proportions has been reported to showcase antibacterial and antioxidative properties ([PERSON], 2017). Apart from that, the evaluation of critical sterols such as campesterol, \(\beta\)-sitosterol, stigmasterol, epicoprostanol, etc. against a wide range of bacteria revealed notable antibacterial properties ([PERSON], 2017). The authors also reported a higher rate of growth inhibition in Gram-negative bacteria (_Vibrio_, _Pseudomonas_, and _Bacillus_ spp.) than Gram-positive bacteria. Conversely, the crude methanolic extracts of eight brown seaweeds (_Sargassum_ spp., _Turbinaria_ spp., and _Hormophysa cuneiformis_) had more promising antibacterial activity against Gram-positive bacteria (_S. pneumoniae_, _B. cereus_ and _S. aureus_) than Gram-negative bacteria. Additionally, the crude extracts displayed antifungal activity against _Trichospor mucoides_, _Candidia membranaefaciens_, and _Cryptococcus neoformans_. An exploration of chemical constituents revealed fucosterol as the abundant compound, along with 24-ketocholesterol, saringosterol, stigmasta-5,28-dien3b-ol, and (22E)-3b-hydroxycholesta-5,22-dien-24-one ([PERSON], 2017). Fucosterol, identified as one of the 10 constituents in methanolic extract of brown and green seaweeds--namely _P. parvonia_, and _U. lactuca_, respectively--exhibited antibacterial (against _S. aureus_ and methicillin-resistant _S. aureus_), antifungal (against _C. krusie_, _C. neoformans_), and mild antimalarial (against _Plasmodium falciparum_) activities ([PERSON], 2017). Intriguingly, the examination of the antitubercular activity of saringosterol and its epimers (obtained from _Lessonia nigrescens_) against _Mycobacterium tuberculosis_ revealed MIC values of 0.25, 1.0, and 0.125 \(\upmu\)g/mL ([PERSON], 2017). Assessment of fucosterol (extracted from brown seaweed _Himanthalia elongate_) against Herpes Simplex Virus Type 1 (HSV-1) revealed noteworthy antiviral effects ([PERSON], 2017). On the other side, fucosterol from _Fucus vesicolus_ (1.0% concentration) inhibited 100% of macroconidia growth and exhibited strong antifungal properties against the phytopathogens _Fusarium culmorum_ and _F. oxysporum_. Furthermore, even the lowest concentrations of fucosterol (0.05% and 0.2%) were observed to degrade the structure and lyse the macroconidia of phytopathogens to a greater extent ([PERSON], 2017). Besides, fucosterol from _S. linearifolium_ brown seaweed) displayed antiplasmodial activity against the malarial parasite 3D7 chloroquine-sensitive _P. falciparum_ by intervening at the schizont stage.