Exclusion zones form in co-cultures of A. graevenitziiand S. aureus.
Formation of exclusion zones appeared to exhibit species specificity within the Streptococcus genus. To test whether this phenomenon might also occur for different major Firmicutes genera we co-culturedA. graevenitzii with the GFP-expressing strain ofStaphylococcus aureus (SH1000-GFP ) that had previously been shown to grow in our device. We observed formation of exclusion zones around A. graevenitzii colonies in co-culture with S. aureus (Fig. 3A,B), demonstrating that this effect is not specific to streptococcal species. Exclusion zones did not form in co-cultures ofS. aureus and A. naeslundii , suggesting that this phenomenon is not common to all actinomyces (Fig. 3C). Importantly, the ability to use a GFP-labelled strain in our studies provided considerable benefits with respect to automated image analysis.