Microalgae produced during phycoremediation of swine wastewater contains effective bacteriostatic compounds against antibiotic-resistant bacteria.

Studies on the antimicrobial effects of microalgae extracts are commonly reported using algae biomass grown in sterile synthetic mineral medium and controlled laboratory conditions. However, variations in environmental conditions and culture medium composition are known to alter microalgae biochemical structure possibly affecting the type and concentrations of bioactive compounds with antimicrobial properties. In this work, solvent extracts of the microalgae Chlorella spp. were tested for antimicrobial effects against gram-positive and multidrug resistant pathogenic bacteria Staphylococcus hyicus, Enterococcus faecalis and Streptococcus suis. Microalgae was cultivated at field scale open pond reactor using raw swine wastewater as growth substrate. Dichloromethane or methanol were used to obtain the microalgae extracts. Characterization of the extracts by ultra-high performance liquid chromatography-quadrupole mass spectrometry revealed the presence of 23 phytochemicals with recognized antimicrobial properties. Bacteriostatic activity was observed in plating assays by formation of inhibition zones ranging from 7 to 18 mm in diameter. Only dichloromethane extracts were inhibitory to all three model bacteria. The minimum inhibitory concentration assessed for dichloromethane extracts were 0.5 mg mL for Staphylococcus hyicus and Enterococcus faecalis and 0.2 mg mL for Streptococcus suis. Bactericidal effects were not observed using solvent-extracts at 2 or 5 mg L. To the best of authors knowledge, this is the first report on the antimicrobial effects of Chlorella spp. extracts against Staphylococcus hyicus and Streptococcus suis. Overall, Chlorella spp. grown on swine wastewater contains several phytochemicals that could be further explored for the treatment of infections caused by antibiotic-resistant bacteria pathogens.