However, our findings suggest: 1) Ng co-culture elicits an anti-chlamydial effect; 2) this anti-chlamydial effect can be associated with, or independent of, reduced chlamydial inclusion size; 3) Ng co-infection does not need to occur prior to chlamydial infection to elicit the observed anti-chlamydial effects; 4) the anti-chlamydial effect(s) appear to depend largely on Ng viability but are not mediated by media depletion of selected nutrients nor by Ng-dependent pH reduction; and 5) the factor(s) responsible for the Ng anti-chlamydial effect may be present in the conditioned culture medium. This evidence concerns the gene NRGN and coinfection.