Effect of antibiotics (penicillin (P), streptomycin (S) and chloramphenicol (C)) on benthic diatom communities was evaluated using a modified extinction–dilution method. The high antibiotic combinations (2PSC and PSC) reduced diatoms by 99–100% and favoured emergence of yeast, probably due to high concentrations and synergistic effects. Changes in diatom communities in the individual antibiotic treatments were either direct (chloramphenicol and potentially streptomycin) or bacteria-mediated (penicillin). This study suggests that investigations on the fate of antibiotics in antibiotic-polluted and natural environments must consider effects across trophic levels and particularly, diatoms, the base of aquatic food webs
