The present study aimed to evaluate the effect of seasonal variation of the antibacterial activity of some seaweed. A pathogenic bacterial isolates were collected from adult patients of Tanta University Educational Hospitals, Microbiology Labs, including Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis (Gram-negative bacteria) which were the main cause of urinary tract infection (UTI). Three seaweeds (macroalgae) belonging to different divisions viz. Ulva lactuca (Chlorophyta), Sargassum vulgare (Phaeophyta) and Jania rubens (Rhodophyta) were collected seasonally during 2015-2016 from Abu-Qir Bay, Alexandria, Egypt. Different solvents (85% each of ethanol, methanol and acetone) were used to extract the antimicrobial material. The antibacterial activity was more observed during winter and spring seasons for green algae while it was higher in summer and autumn seasons for red algae. The most effective seaweeds extract against the tested UTI bacterial isolates was the ethanol extract of Ulva lactuca collected in spring season. The gas chromatography mass spectrometry (GC-MS) was determined to Ulva lactuca antibacterial extract and revealed its high content of phenolic compounds. The toxicity test revealed that Ulva lactuca antibacterial extract caused no hemolysis to red blood cells implying its safety as a proposed drug for UTI bacterial disease.
Key words: Seaweeds, UTI bacteria, Antimicrobial activity, Seasonal variation, Hemolysis, GC-MS, MIC.