I tried to treat the worms with antibiotics (ampicilin) to eleminate E.coli (OP50) but an easy test showed that E.coli survived the antibiotic treatment. Treatment and the test: The L4 worms were transferred to a new NGM plates containing 100mg/ml ampicilin, after ON incubation at RT the worms were transferred to a new NGM plate (NO antibiotic added). Testing the second plate showed that the bacteria survived the treatment, probabely in the intestine of the worms.
Short-term ampicillin treatment doesn’t kill bacterial cells but prevents growth of existing cells. Washing worms in sterile M9 buffer prior to replating might help although the only way to be sure of clean worms is to treat gravid hermaphrodites with a NaOH/bleach solution. the chitinous shell around the embryo will protect it. As a consequence everything around the embryos will be killed (including bacteria). As an added bonus this bleach treatment and subsequent hatchoff in M9 buffer synchronizes your population worms.
if you need to remove the bacteria at a particular developmental age, you might want to consider doing a liquid culture with penicillin-streptomycin-neomycin cocktail in it. it’ll be easier to wash out excess bacteria and the PSN cocktail will prevent any bacterial growth.