Table 1.

Antibacterial activity of Spirulina platensis in in vitro studies.

Spirulina/ Extract	Concentration/Mass	Bacterial Isolates	Main Conclusions	References
Acne–in vitro studies
Methanol and hexane dry S. platensis extracts	100 µg in 100 µL H2O; concentrations: 25; 50, and 100 µL	Micrococcus aureus, Propionibacterium acnes, Staphylococcus aureus, and S. epidermidis, bacteria were isolated from the skin of acne patients (20 patients aged 15–20 years). Samples of bacterial isolates were prepared on nutrient agar with S. platensis extracts.	The hexane and methanol S. platensis extracts had antibacterial activity against Aerococcus spp. and Enterococcus. The following substances were involved in this activity: hexadecene, heptadecane, octadecene, 2-bromopropionic acid, methyl-1-docosene, benzenedicarboxylic acid, and tetradecanol.	[42]
Lyophilised S. platensis powder (SPP)	(i) 0.25% solution of S. platensis (SPP) in phosphate-buffered saline. (ii) S. platensis-containing creams with one of two different nonionic surfactants Tefose 63 (TFS) or sucrose ester SP 70 (SP70) incorporated in creams as emulsifying agents. (iii) Cream compositions (g): lyophilised S. platensis powder SPP (5), Transcutol HP (14.2), TFS or SP70 (3), cetostearyl alcohol (4.6), stearic acid (10), glycerol (5), IPM (5), propylene glycol (5), and purified water (ad 100).	Staphylococcus aureus, American Type Culture Collection (ATCC)® 43300™) and Cutibacterium (formerly Propionibacterium acnes (ATCC® 33169™)	S. platensis effectively reduced cell viability of S. aureus (66%) and C. acne (64%). S. platensis formulations with various surfactants, but especially the preparation containing the sucrose ester SP 70 emulsifying agent, were active against C. acnes and S. aureus comparably to Aknemycin™, and showed low toxicity on immortalized human keratinocyte Ha-CaT cells. Creams containing S. platensis can be an alternative option to treat acne with fewer side effects and without antibiotic resistance.	[57]
Anti-acne topical ointment of C-phycocyanin (C-PC) extracted from S. platensis	(i) formulation—oleaginous base (%): paraffin hard (5), wool fat (10), cetostearyl alcohol (10), white soft paraffin (50), liquid paraffin (15), extract C-PC (10), (ii) formulation—water base (%): PEG400 (12), PEG4000 (18), stearyl alcohol (28), extract C-PC (10), glycerine (17), and water q. s.	P. acnes, S. epidermidis	Spirulina has an anti-acne effect. Both of the topical C-PC ointment formulations can be employed in the treatment of acne against P. acnes and S. epidermidis. The formulation comprising the water-soluble base was superior to the oleaginous base due to the complete solubility of the extract in water.	[147]
Ethanolic S. platensis extract	Dried spirulina biomass was extracted with 96% ethanol using the reflux method and partitioned with hexane, distilled water, and ethyl acetate. The active compound fractions were analysed using thin layer chromatography and column chromatography.	P. acnes, S. epidermidis, and Enterobacter aerogenes	The highest activity was exhibited by ethyl acetate extracts against P. acnes, S. epidermidis, and E. aerogenes and ethanol extracts against P. acne and S. epidermidis. The ethyl acetate fraction of the S. platensis microalgae has the potential as a natural antibacterial agent.	[28]
Ethyl acetate and dimethyl carbonate A. platensis extracts; extract-loaded copper alginate-based nanocarriers	500 mg of S. platensis biomass, alginate-based nanocarriers (ANCs) were prepared using ultrasound oil-in-water emulsification followed by surface gelation with cupric ions.	Cutibacterium acnes ATCC® 6919	A. platensis extracts prevented the growth of C. acnes single-species biofilms (inhibition > 75% at 0.2 mg/mL). Nanovectorised extracts reduced the growth of both single-species (inhibition > 43% at 0.2 mg/mL) and preformed (55–77%) C. albicans ATCC® 28367™ biofilms	[153]

Explanation: quantum satis (q. s); minimal inhibitory concentration (MIC), registered (^®), trademark (TM).